- Added Exchange integration.

- Added Sequencer.
- Prepared migration of LDAP integration to Sequencer.
- Added and improved RSpec support helpers.

Gemfile

@@ -80,6 +80,9 @@ gem 'browser'
 gem 'slack-notifier'
 gem 'clearbit'
 gem 'zendesk_api'
+gem 'viewpoint'
+gem 'rubyntlm', git: 'https://github.com/wimm/rubyntlm.git'
+gem 'autodiscover', git: 'https://github.com/thorsteneckel/autodiscover.git'
 
 # event machine
 gem 'eventmachine'

Gemfile.lock

@@ -1,3 +1,19 @@
+GIT
+  remote: https://github.com/thorsteneckel/autodiscover.git
+  revision: 29d713ee0c8c25fcf74c4292ff13fe1fa4d0d827
+  specs:
+    autodiscover (1.0.2)
+      httpclient
+      logging
+      nokogiri
+      nori
+
+GIT
+  remote: https://github.com/wimm/rubyntlm.git
+  revision: 53969639b87b9e5d5fef560f19cf0d977259591c
+  specs:
+    rubyntlm (0.1.2)
+
 GEM
   remote: https://rubygems.org/
   specs:
@@ -166,6 +182,7 @@ GEM
       domain_name (~> 0.5)
     http-form_data (1.0.3)
     http_parser.rb (0.6.0)
+    httpclient (2.8.3)
     i18n (0.8.6)
     icalendar (2.4.1)
     inflection (1.0.0)
@@ -181,6 +198,10 @@ GEM
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
       ruby_dep (~> 1.2)
+    little-plugger (1.1.4)
+    logging (2.2.2)
+      little-plugger (~> 1.1)
+      multi_json (~> 1.10)
     loofah (2.0.3)
       nokogiri (>= 1.5.9)
     lumberjack (1.0.10)
@@ -205,6 +226,7 @@ GEM
     netrc (0.11.0)
     nokogiri (1.8.0)
       mini_portile2 (~> 2.2.0)
+    nori (2.6.0)
     notiffany (0.1.1)
       nenv (~> 0.1)
       shellany (~> 0.0)
@@ -408,6 +430,11 @@ GEM
     valid_email2 (2.0.0)
       activemodel (>= 3.2)
       mail (~> 2.5)
+    viewpoint (1.1.0)
+      httpclient
+      logging
+      nokogiri
+      rubyntlm
     webmock (3.0.1)
       addressable (>= 2.3.6)
       crack (>= 0.3.2)
@@ -428,6 +455,7 @@ DEPENDENCIES
   activerecord-nulldb-adapter
   activerecord-session_store
   argon2
+  autodiscover!
   autoprefixer-rails
   biz
   browser
@@ -479,6 +507,7 @@ DEPENDENCIES
   rb-fsevent
   rspec-rails
   rubocop
+  rubyntlm!
   sass-rails
   selenium-webdriver
   simple-rss
@@ -496,6 +525,7 @@ DEPENDENCIES
   uglifier
   unicorn
   valid_email2
+  viewpoint
   webmock
   writeexcel
   zendesk_api

app/assets/javascripts/app/controllers/_integration/exchange.coffee

@@ -0,0 +1,522 @@
+class Index extends App.ControllerIntegrationBase
+  featureIntegration: 'exchange_integration'
+  featureName: 'Exchange'
+  featureConfig: 'exchange_config'
+  description: [
+    ['This service enables Zammad to connect with your Exchange server.']
+  ]
+  events:
+    'change .js-switch input': 'switch'
+
+  render: =>
+    super
+    new Form(
+      el: @$('.js-form')
+    )
+
+    #new App.ImportJob(
+    #  el: @$('.js-importJob')
+    #  facility: 'exchange'
+    #)
+
+    new App.HttpLog(
+      el: @$('.js-log')
+      facility: 'exchange'
+    )
+
+  switch: =>
+    super
+    active = @$('.js-switch input').prop('checked')
+    if active
+      job_start = =>
+        @ajax(
+          id:   'jobs_config'
+          type: 'POST'
+          url:  "#{@apiPath}/integration/exchange/job_start"
+          processData: true
+          success: (data, status, xhr) =>
+            @render(true)
+        )
+
+      App.Delay.set(
+        job_start,
+        600,
+        'job_start',
+      )
+
+class Form extends App.Controller
+  elements:
+    '.js-lastImport': 'lastImport'
+    '.js-wizard': 'wizardButton'
+  events:
+    'click .js-wizard': 'startWizard'
+    'click .js-start-sync': 'startSync'
+
+  constructor: ->
+    super
+    @render()
+    @lastResult()
+    @activeDryRun()
+
+  currentConfig: ->
+    App.Setting.get('exchange_config') || {}
+
+  setConfig: (value) =>
+    App.Setting.set('exchange_config', value, {notify: true})
+    @startSync()
+
+  render: (top = false) =>
+    @config = @currentConfig()
+
+    folders = []
+    if !_.isEmpty(@config.folders)
+      for folder_id in @config.folders
+        folders.push @config.wizardData.backend_folders[folder_id]
+
+    @html App.view('integration/exchange')(
+      config: @config,
+      folders: folders
+    )
+    if _.isEmpty(@config)
+      @$('.js-notConfigured').removeClass('hide')
+      @$('.js-summary').addClass('hide')
+    else
+      @$('.js-notConfigured').addClass('hide')
+      @$('.js-summary').removeClass('hide')
+
+    if top
+      a = =>
+        @scrollToIfNeeded($('.content.active .page-header'))
+      @delay(a, 500)
+
+  startSync: =>
+    @ajax(
+      id:   'jobs_config'
+      type: 'POST'
+      url:  "#{@apiPath}/integration/exchange/job_start"
+      processData: true
+      success: (data, status, xhr) =>
+        @render(true)
+        @lastResult()
+    )
+
+  startWizard: (e) =>
+    e.preventDefault()
+    new ConnectionWizard(
+      container: @el.closest('.content')
+      config: @config
+      callback: (config) =>
+        @setConfig(config)
+    )
+
+  lastResult: =>
+    @ajax(
+      id:   'jobs_start_index'
+      type: 'GET'
+      url:  "#{@apiPath}/integration/exchange/job_start"
+      processData: true
+      success: (job, status, xhr) =>
+        if !_.isEmpty(job)
+          if !@lastResultShowJob || @lastResultShowJob.updated_at != job.updated_at
+            @lastResultShowJob = job
+            @lastResultShow(job)
+            if job.finished_at
+              @wizardButton.attr('disabled', false)
+            else
+              @wizardButton.attr('disabled', true)
+        @delay(@lastResult, 5000)
+    )
+
+  lastResultShow: (job) =>
+    if _.isEmpty(job)
+      @lastImport.html('')
+      return
+    countDone = job.result.created + job.result.updated + job.result.unchanged + job.result.skipped + job.result.failed
+    if !job.result.roles
+      job.result.roles = {}
+    for role_id, statistic of job.result.role_ids
+      role = App.Role.find(role_id)
+      job.result.roles[role.displayName()] = statistic
+    el = $(App.view('integration/exchange_last_import')(job: job, countDone: countDone))
+    @lastImport.html(el)
+
+  activeDryRun: =>
+    @ajax(
+      id:   'jobs_try_index'
+      type: 'GET'
+      url:  "#{@apiPath}/integration/exchange/job_try"
+      data:
+        finished: false
+      processData: true
+      success: (job, status, xhr) =>
+        return if _.isEmpty(job)
+
+        # show analyzing
+        new ConnectionWizard(
+          container: @el.closest('.content')
+          config: job.payload
+          start: 'tryLoop'
+          callback: (config) =>
+            @wizardButton.attr('disabled', false)
+            @setConfig(config)
+        )
+        @wizardButton.attr('disabled', true)
+    )
+
+class State
+  @current: ->
+    App.Setting.get('exchange_integration')
+
+class ConnectionWizard extends App.WizardModal
+  wizardConfig: {}
+  slideMethod:
+    'js-folders': 'foldersShow'
+    'js-mapping': 'mappingShow'
+
+  events:
+    'submit form.js-discover':           'discover'
+    'submit form.js-bind':               'folders'
+    'submit form.js-folders':            'mapping'
+    'click .js-mapping .js-submitTry':   'mappingChange'
+    'click .js-try .js-submitSave':      'save'
+    'click .js-close':                   'hide'
+    'click .js-remove':                  'removeRow'
+    'click .js-userMappingForm .js-add': 'addUserMapping'
+    'click .js-goToSlide':               'goToSlide'
+
+  elements:
+    '.modal-body': 'body'
+    '.js-foldersSelect': 'foldersSelect'
+    '.js-userMappingForm': 'userMappingForm'
+    '.js-expertForm': 'expertForm'
+
+  constructor: ->
+    super
+
+    if !_.isEmpty(@config)
+      @wizardConfig = @config
+
+    if @container
+      @el.addClass('modal--local')
+
+    @render()
+
+    @el.modal
+      keyboard:  true
+      show:      true
+      backdrop:  true
+      container: @container
+    .on
+      'show.bs.modal':   @onShow
+      'shown.bs.modal':  @onShown
+      'hidden.bs.modal': =>
+        @el.remove()
+
+    if @slide
+      @showSlide(@slide)
+    else
+      @showDiscoverDetails()
+
+    if @start
+      @[@start]()
+
+  render: =>
+    @html App.view('integration/exchange_wizard')()
+
+  save: (e) =>
+    e.preventDefault()
+    @callback(@wizardConfig)
+    @hide(e)
+
+  showSlide: (slide) =>
+    method = @slideMethod[slide]
+    if method && @[method]
+      @[method](true)
+    super
+
+  showDiscoverDetails: =>
+    @$('.js-discover input[name="user"]').val(@wizardConfig.user)
+    @$('.js-discover input[name="password"]').val(@wizardConfig.password)
+
+  showBindDetails: =>
+    @$('.js-bind input[name="endpoint"]').val(@wizardConfig.endpoint)
+    @$('.js-bind input[name="user"]').val(@wizardConfig.user)
+    @$('.js-bind input[name="password"]').val(@wizardConfig.password)
+
+  discover: (e) =>
+    e.preventDefault()
+    @showSlide('js-connect')
+    params = @formParam(e.target)
+    @ajax(
+      id:   'exchange_discover'
+      type: 'POST'
+      url:  "#{@apiPath}/integration/exchange/autodiscover"
+      data: JSON.stringify(params)
+      processData: true
+      success: (data, status, xhr) =>
+        if data.result isnt 'ok'
+          @showSlide('js-discover')
+          @showAlert('js-discover', data.message)
+          return
+
+        @wizardConfig.endpoint = data.endpoint
+        @wizardConfig.user     = params.user
+        @wizardConfig.password = params.password
+
+        @showSlide('js-bind')
+        @showBindDetails()
+
+      error: (xhr, statusText, error) =>
+        detailsRaw = xhr.responseText
+        details = {}
+        if !_.isEmpty(detailsRaw)
+          details = JSON.parse(detailsRaw)
+        @showSlide('js-discover')
+        @showAlert('js-discover', details.error || 'Unable to perform backend.')
+    )
+
+  folders: (e) =>
+    e.preventDefault()
+    @showSlide('js-analyze')
+    params = @formParam(e.target)
+    @ajax(
+      id:   'exchange_folders'
+      type: 'POST'
+      url:  "#{@apiPath}/integration/exchange/folders"
+      data: JSON.stringify(params)
+      processData: true
+      success: (data, status, xhr) =>
+        if data.result isnt 'ok'
+          @showSlide('js-bind')
+          @showAlert('js-bind', data.message)
+          return
+
+        @wizardConfig.endpoint = params.endpoint
+        @wizardConfig.user     = params.user
+        @wizardConfig.password = params.password
+
+        # update wizard data
+        @wizardConfig.wizardData = {}
+        @wizardConfig.wizardData.backend_folders = data.folders
+
+        @foldersShow()
+
+      error: (xhr, statusText, error) =>
+        detailsRaw = xhr.responseText
+        details = {}
+        if !_.isEmpty(detailsRaw)
+          details = JSON.parse(detailsRaw)
+        @showSlide('js-bind')
+        @showAlert('js-bind', details.error || 'Unable to perform backend.')
+    )
+
+  foldersShow: (alreadyShown) =>
+    @showSlide('js-folders') if !alreadyShown
+    @foldersSelect.html(@createColumnSelection('folders', @wizardConfig.wizardData.backend_folders, @wizardConfig.folders))
+
+  createColumnSelection: (name, options, selected) ->
+    return App.UiElement.column_select.render(
+      name: name
+      null: false
+      nulloption: false
+      options: options
+      value: selected
+    )
+
+  mapping: (e) =>
+    e.preventDefault()
+    @showSlide('js-analyze')
+    params = @formParam(e.target)
+
+    # folders might be a single selection so we
+    # have to ensure that is an Array so the
+    # backend and frontend can handle it properly
+    if typeof params.folders is 'string'
+      params.folders = [ params.folders ]
+
+    # add login params
+    params.endpoint = @wizardConfig.endpoint
+    params.user     = @wizardConfig.user
+    params.password = @wizardConfig.password
+
+    @ajax(
+      id:   'exchange_mapping'
+      type: 'POST'
+      url:  "#{@apiPath}/integration/exchange/mapping"
+      data: JSON.stringify(params)
+      processData: true
+      success: (data, status, xhr) =>
+        if data.result isnt 'ok'
+          @showSlide('js-folders')
+          @showAlert('js-folders', data.message)
+          return
+
+        attributes = {}
+        for key, value of App.User.attributesGet()
+          continue if key == 'login'
+          if (value.tag is 'input' || value.tag is 'richtext' || value.tag is 'textarea')  && value.type isnt 'password'
+            attributes[key] = value.display || key
+
+        @wizardConfig.wizardData.attributes         = attributes
+        @wizardConfig.folders                       = params.folders
+        @wizardConfig.wizardData.backend_attributes = data.attributes
+
+        @mappingShow()
+
+      error: (xhr, statusText, error) =>
+        detailsRaw = xhr.responseText
+        details = {}
+        if !_.isEmpty(detailsRaw)
+          details = JSON.parse(detailsRaw)
+        @showSlide('js-folders')
+        @showAlert('js-folders', details.error || 'Unable to perform backend.')
+    )
+
+  mappingShow: (alreadyShown) =>
+    @showSlide('js-mapping') if !alreadyShown
+    user_attribute_map = @wizardConfig.attributes
+
+    if _.isEmpty(user_attribute_map)
+      user_attribute_map =
+        given_name: 'firstname'
+        surname: 'lastname'
+        'email_addresses.emailaddress1': 'email'
+        'phone_numbers.businessphone': 'phone'
+
+    @userMappingForm.find('tbody tr.js-entry').remove()
+    @userMappingForm.find('tbody tr').before(@buildRowsUserMap(user_attribute_map))
+
+  mappingChange: (e) =>
+    e.preventDefault()
+
+    # user map
+    attributes = @formParam(@userMappingForm)
+    for key in ['source', 'dest']
+      if !_.isArray(attributes[key])
+        attributes[key] = [attributes[key]]
+    attributes_local =
+      item_id: 'login'
+    length = attributes.source.length-1
+    for count in [0..length]
+      if attributes.source[count] && attributes.dest[count]
+        attributes_local[attributes.source[count]] = attributes.dest[count]
+    @wizardConfig.attributes = attributes_local
+
+    @tryShow()
+
+  buildRowsUserMap: (user_attribute_map) =>
+
+    # show static login row
+    userUidDisplayValue = @wizardConfig.wizardData.backend_attributes['item_id']
+    el = [
+      $(App.view('integration/ldap_user_attribute_row_read_only')(
+        key:   userUidDisplayValue,
+        value: 'Login'
+      ))
+    ]
+
+    for source, dest of user_attribute_map
+      continue if source == 'item_id'
+      continue if !(source of @wizardConfig.wizardData.backend_attributes)
+      el.push @buildRowUserAttribute(source, dest)
+    el
+
+  buildRowUserAttribute: (source, dest) =>
+    el = $(App.view('integration/exchange_user_attribute_row')())
+    el.find('.js-exchangeAttribute').html(@createSelection('source', @wizardConfig.wizardData.backend_attributes, source))
+    el.find('.js-userAttribute').html(@createSelection('dest', @wizardConfig.wizardData.attributes, dest))
+    el
+
+  createSelection: (name, options, selected, unknown) ->
+    return App.UiElement.searchable_select.render(
+      name: name
+      multiple: false
+      limit: 100
+      null: false
+      nulloption: false
+      options: options
+      value: selected
+      unknown: unknown
+      class: 'form-control--small'
+    )
+
+  removeRow: (e) ->
+    e.preventDefault()
+    $(e.target).closest('tr').remove()
+
+  addUserMapping: (e) =>
+    e.preventDefault()
+    @userMappingForm.find('tbody tr').last().before(@buildRowUserAttribute())
+
+  tryShow: (e) =>
+    if e
+      e.preventDefault()
+    @showSlide('js-analyze')
+
+    # create import job
+    @ajax(
+      id:   'exchange_try'
+      type: 'POST'
+      url:  "#{@apiPath}/integration/exchange/job_try"
+      data: JSON.stringify(@wizardConfig)
+      processData: true
+      success: (data, status, xhr) =>
+        @tryLoop()
+    )
+
+  tryLoop: =>
+    @showSlide('js-dry')
+    @ajax(
+      id:   'jobs_try_index'
+      type: 'GET'
+      url:  "#{@apiPath}/integration/exchange/job_try"
+      data:
+        finished: true
+      processData: true
+      success: (job, status, xhr) =>
+        if job.result && (job.result.error || job.result.info)
+          @showSlide('js-error')
+          @showAlert('js-error', (job.result.error || job.result.info))
+          return
+
+        total = 0
+        if job.result && _.keys(job.result).length > 0
+          @$('.js-preprogress').addClass('hide')
+          @$('.js-analyzing').removeClass('hide')
+
+          analized = 0
+          total    = job.result.sum
+          for action, sum of job.result
+            continue if action == 'folders'
+            continue if action == 'sum'
+            analized += sum
+
+          @$('.js-progress progress').attr('value', analized)
+          @$('.js-progress progress').attr('max', total)
+
+        if job.finished_at
+          # reset initial state in case the back button is used
+          @$('.js-preprogress').removeClass('hide')
+          @$('.js-analyzing').addClass('hide')
+
+          @tryResult(job, total)
+        else
+          @delay(@tryLoop, 4000)
+    )
+
+  tryResult: (job, total) =>
+    @showSlide('js-try')
+    el = $(App.view('integration/exchange_summary')(job: job, countDone: total))
+    @el.find('.js-summary').html(el)
+
+App.Config.set(
+  'IntegrationExchange'
+  {
+    name: 'Exchange'
+    target: '#system/integration/exchange'
+    description: 'Exchange integration for contacts management.'
+    controller: Index
+    state: State
+  }
+  'NavBarIntegrations'
+)

app/assets/javascripts/app/controllers/_integration/ldap.coffee

@@ -28,6 +28,7 @@ class Index extends App.ControllerIntegrationBase
     super
     active = @$('.js-switch input').prop('checked')
     if active
+      job_start = =>
         @ajax(
           id:   'jobs_config'
           type: 'POST'
@@ -37,6 +38,12 @@ class Index extends App.ControllerIntegrationBase
             @render(true)
         )
 
+      App.Delay.set(
+        job_start,
+        600,
+        'job_start',
+      )
+
 class Form extends App.Controller
   elements:
     '.js-lastImport': 'lastImport'
@@ -91,6 +98,7 @@ class Form extends App.Controller
       processData: true
       success: (data, status, xhr) =>
         @render(true)
+        @lastResult()
     )
 
   startWizard: (e) =>

app/assets/javascripts/app/views/integration/exchange.jst.eco

@@ -0,0 +1,71 @@
+<div class="js-lastImport"></div>
+<div class="js-notConfigured">
+  <p><%- @T('No %s configured.', 'Exchange') %></p>
+  <button type="submit" class="btn btn--primary js-wizard"><%- @T('Configure') %></button>
+</div>
+<div class="js-summary hide">
+  <h2><%- @T('Settings') %></h2>
+  <table class="settings-list" style="width: 100%;">
+    <thead>
+      <tr>
+        <th width="30%"><%- @T('Name') %>
+        <th width="70%"><%- @T('Value') %>
+    </thead>
+    <tbody>
+      <tr>
+        <td class="settings-list-row-control"><%- @T('Endpoint') %>
+        <td class="settings-list-row-control"><%= @config.endpoint %>
+      <tbody>
+        <tr>
+          <td class="settings-list-row-control"><%- @T('User') %>
+          <td class="settings-list-row-control"><%= @config.user %>
+        <tr>
+          <td class="settings-list-row-control"><%- @T('Password') %>
+          <td class="settings-list-row-control"><%= @M(@config.password) %>
+    </tbody>
+  </table>
+
+  <h2><%- @T('Mapping') %></h2>
+
+  <h3><%- @T('Folders') %></h3>
+  <% if _.isEmpty(@folders): %>
+    <table class="settings-list settings-list--stretch settings-list--placeholder">
+      <thead><tr><th><%- @T('No Entries') %>
+    </table>
+  <% else: %>
+    <table class="settings-list" style="width: 100%;">
+      <thead>
+        <tr>
+          <th><%- @T('Folder') %>
+        <% for folder_name in @folders: %>
+          <tr>
+            <td class="settings-list-row-control"><%= folder_name %>
+        <% end %>
+      </thead>
+      <tbody>
+    </table>
+  <% end %>
+
+  <h3><%- @T('User') %></h3>
+  <% if _.isEmpty(@config.attributes): %>
+    <table class="settings-list settings-list--stretch settings-list--placeholder">
+      <thead><tr><th><%- @T('No Entries') %>
+    </table>
+  <% else: %>
+    <table class="settings-list" style="width: 100%;">
+      <thead>
+        <tr>
+          <th width="40%"><%- @T('Exchange') %>
+          <th width="60%"><%- @T('Zammad') %>
+        <% for key, value of @config.attributes: %>
+          <tr>
+            <td class="settings-list-row-control"><%= key %>
+            <td class="settings-list-row-control"><%= value %>
+        <% end %>
+      </thead>
+      <tbody>
+    </table>
+  <% end %>
+
+  <button type="submit" class="btn btn--primary js-wizard"><%- @T('Change') %></button>
+</div>

app/assets/javascripts/app/views/integration/exchange_last_import.jst.eco

@@ -0,0 +1,54 @@
+<div class="box box--message">
+  <h2><%- @T('Last sync') %></h2>
+  <% if _.isEmpty(@job.started_at): %>
+    <% if @job.result && @job.result.error: %>
+        <div class="alert alert--danger" role="alert"><%- @T('An error occurred: %s', @job.result.error) %></div>
+    <% else if @job.result && @job.result.info: %>
+        <div class="alert alert--info" role="alert"><%- @T('Info: %s', @job.result.info) %></div>
+    <% else: %>
+      <p><%- @T('Job is waiting to get started...') %></p>
+    <% end %>
+  <% else: %>
+    <% if @job.finished_at: %>
+      <p><%- @Ttimestamp(@job.started_at) %> - <%- @Ttimestamp(@job.finished_at) %></p>
+      <% if @job.result && @job.result.error: %>
+        <div class="alert alert--danger" role="alert"><%- @T('An error occurred: %s', @job.result.error) %></div>
+      <% else if @job.result && @job.result.info: %>
+        <div class="alert alert--info" role="alert"><%- @T('Info: %s', @job.result.info) %></div>
+      <% end %>
+    <% else: %>
+      <% if @job.result && @job.result.error: %>
+        <p><%- @Ttimestamp(@job.started_at) %></p>
+        <div class="alert alert--danger" role="alert"><%- @T('An error occurred: %s', @job.result.error) %></div>
+      <% else if !@countDone: %>
+        <p><%- @Ttimestamp(@job.started_at) %> - <%- @T('Counting entries. This may take a while.') %></p>
+      <% else: %>
+        <p><%- @Ttimestamp(@job.started_at) %> - <%- @T('Running...') %></p>
+        <div class="flex">
+          <progress max="<%= @job.result.sum %>" value="<%= @countDone %>"></progress>
+        </div>
+      <% end %>
+    <% end %>
+    <% if !_.isEmpty(@job.result) && @countDone: %>
+      <ul>
+        <li><%- @T('%s user to %s user', 'Exchange', 'Zammad') %> (<%= @countDone %>/<%= @job.result.sum %>):
+          <ul>
+            <li><%- @T('Users') %>: <%= @job.result.created %> <%- @T('created') %>, <%= @job.result.updated %> <%- @T('updated') %>, <%= @job.result.unchanged %> <%- @T('untouched') %>, <%= @job.result.skipped %> <%- @T('skipped') %>, <%= @job.result.failed %> <%- @T('failed') %>
+          </ul>
+          </li>
+          <% if !_.isEmpty(@job.result.folders): %>
+            <li><%- @T('%s folders', 'Exchange') %>:
+              <ul>
+                <% for folder, result of @job.result.folders: %>
+                  <li><%- folder %>: <%= result.created %> <%- @T('created') %>, <%= result.updated %> <%- @T('updated') %>, <%= result.unchanged %> <%- @T('untouched') %>, <%= result.failed %> <%- @T('failed') %>
+                <% end %>
+              </ul>
+            </li>
+          <% end %>
+      </ul>
+    <% end %>
+    <% if @job.finished_at: %>
+      <button type="submit" class="btn btn--primary js-start-sync"><%- @T('Start new') %></button>
+    <% end %>
+  <% end %>
+</div>

app/assets/javascripts/app/views/integration/exchange_summary.jst.eco

@@ -0,0 +1,16 @@
+<ul>
+  <li><%- @T('%s user to %s user', 'Exchange', 'Zammad') %> (<%= @countDone %>):
+    <ul>
+      <li><%- @T('Users') %>: <%= @job.result.created %> <%- @T('created') %>, <%= @job.result.updated %> <%- @T('updated') %>, <%= @job.result.unchanged %> <%- @T('untouched') %>, <%= @job.result.skipped %> <%- @T('skipped') %>, <%= @job.result.failed %> <%- @T('failed') %>
+    </ul>
+  </li>
+  <% if !_.isEmpty(@job.result.folders): %>
+    <li><%- @T('%s folders', 'Exchange') %>:
+      <ul>
+        <% for folder, result of @job.result.folders: %>
+          <li><%- folder %>: <%= result.created %> <%- @T('created') %>, <%= result.updated %> <%- @T('updated') %>, <%= result.unchanged %> <%- @T('untouched') %>, <%= result.failed %> <%- @T('failed') %>
+        <% end %>
+      </ul>
+    </li>
+  <% end %>
+</ul>

app/assets/javascripts/app/views/integration/exchange_user_attribute_row.jst.eco

@@ -0,0 +1,7 @@
+<tr class="js-entry">
+  <td style="max-width: 240px" class="settings-list-control-cell js-exchangeAttribute">
+  <td class="settings-list-control-cell js-userAttribute">
+  <td class="settings-list-row-control">
+    <div class="btn btn--text js-remove">
+      <%- @Icon('trash') %> <%- @T('Remove') %>
+    </div>

app/assets/javascripts/app/views/integration/exchange_wizard.jst.eco

@@ -0,0 +1,258 @@
+<div class="modal-dialog">
+
+  <form class="modal-content setup wizard js-discover">
+    <div class="modal-header">
+      <div class="modal-close js-close">
+        <%- @Icon('diagonal-cross') %>
+      </div>
+      <h1 class="modal-title"><%- @T('Exchange') %> <%- @T('Configuration') %></h1>
+    </div>
+    <div class="modal-body">
+      <div class="wizard-body vertical justified">
+        <div class="alert alert--danger hide" role="alert"></div>
+        <table class="settings-list" style="width: 100%;">
+          <thead>
+            <tr>
+              <th width="30%"><%- @T('Name') %>
+              <th width="70%"><%- @T('Value') %>
+          </thead>
+          <tbody>
+            <tr>
+              <td class="settings-list-row-control"><%- @T('User') %>
+              <td class="settings-list-control-cell"><input type="text" name="user" class="form-control form-control--small js-user" value="" placeholder="" autocomplete="off" required>
+            <tr>
+              <td class="settings-list-row-control"><%- @T('Password') %>
+              <td class="settings-list-control-cell"><input type="password" name="password" class="form-control form-control--small js-password" value="" placeholder="" autocomplete="new-password" required>
+          </tbody>
+        </table>
+      </div>
+    </div>
+    <div class="modal-footer">
+      <div class="modal-rightFooter">
+        <button class="btn btn--primary align-right js-submit"><%- @T('Connect') %></button>
+      </div>
+    </div>
+  </form>
+
+  <form class="modal-content setup wizard hide js-connect">
+    <div class="modal-header">
+      <div class="modal-close js-close">
+        <%- @Icon('diagonal-cross') %>
+      </div>
+      <h1 class="modal-title"><%- @T('Exchange') %> <%- @T('Configuration') %></h1>
+    </div>
+    <div class="modal-body">
+      <div class="wizard-body vertical justified">
+        <p class="wizard-loadingText">
+          <span class="loading icon"></span> <%- @T('Connecting ...') %>
+        </p>
+      </div>
+    </div>
+    <div class="modal-footer"></div>
+  </form>
+
+  <form class="modal-content setup wizard hide js-bind">
+    <div class="modal-header">
+      <div class="modal-close js-close">
+        <%- @Icon('diagonal-cross') %>
+      </div>
+      <h1 class="modal-title"><%- @T('Exchange') %> <%- @T('Configuration') %></h1>
+    </div>
+    <div class="modal-body">
+      <div class="wizard-body vertical justified">
+        <div class="alert alert--danger hide" role="alert"></div>
+        <table class="settings-list" style="width: 100%;">
+          <thead>
+            <tr>
+              <th width="30%"><%- @T('Name') %>
+              <th width="70%"><%- @T('Value') %>
+          </thead>
+          <tbody>
+            <tr>
+              <td class="settings-list-row-control"><%- @T('Endpoint') %>
+              <td class="settings-list-control-cell"><input type="text" name="endpoint" class="form-control form-control--small" value="" placeholder="https://outlook.office365.com/EWS/Exchange.asmx" autocomplete="off" required>
+
+            <tr>
+              <td class="settings-list-row-control"><%- @T('User') %>
+              <td class="settings-list-control-cell"><input type="text" name="user" class="form-control form-control--small js-user" value="" placeholder="" autocomplete="off" required>
+            <tr>
+              <td class="settings-list-row-control"><%- @T('Password') %>
+              <td class="settings-list-control-cell"><input type="password" name="password" class="form-control form-control--small js-password" value="" placeholder="" autocomplete="new-password" required>
+          </tbody>
+        </table>
+      </div>
+    </div>
+    <div class="modal-footer">
+      <div class="modal-rightFooter">
+        <button class="btn btn--primary align-right js-submit"><%- @T('Connect') %></button>
+      </div>
+    </div>
+  </form>
+
+  <form class="modal-content setup wizard hide js-folders">
+    <div class="modal-header">
+      <div class="modal-close js-close">
+        <%- @Icon('diagonal-cross') %>
+      </div>
+      <h1 class="modal-title"><%- @T('Exchange') %> <%- @T('Folders') %></h1>
+    </div>
+    <div class="modal-body">
+      <div class="wizard-body vertical justified">
+        <div class="alert alert--danger hide" role="alert"></div>
+
+        <div class="column_select form-group">
+            <div class="formGroup-label">
+                <label for="folders"><%- @T('Import %s', 'Folders') %></label>
+            </div>
+            <div class="controls js-foldersSelect">
+            </div>
+        </div>
+
+      </div>
+    </div>
+    <div class="modal-footer">
+      <div class="modal-rightFooter">
+        <a class="btn btn--text btn--secondary js-goToSlide align-left" data-slide="js-bind"><%- @T('Go Back') %></a>
+      </div>
+      <div class="modal-rightFooter">
+        <button class="btn btn--primary align-right js-submitTry"><%- @T('Continue') %></button>
+      </div>
+    </div>
+  </form>
+
+  <form class="modal-content setup wizard hide js-analyze">
+    <div class="modal-header">
+      <div class="modal-close js-close">
+        <%- @Icon('diagonal-cross') %>
+      </div>
+      <h1 class="modal-title"><%- @T('Exchange') %> <%- @T('Configuration') %></h1>
+    </div>
+    <div class="modal-body">
+      <div class="wizard-body vertical justified">
+        <p class="wizard-loadingText">
+          <span class="loading icon"></span> <%- @T('Analyzing structure...') %>
+        </p>
+      </div>
+    </div>
+    <div class="modal-footer"></div>
+  </form>
+
+  <div class="modal-content setup wizard hide js-mapping">
+    <div class="modal-header">
+      <div class="modal-close js-close">
+        <%- @Icon('diagonal-cross') %>
+      </div>
+      <h1 class="modal-title"><%- @T('Exchange') %> <%- @T('Mapping') %></h1>
+    </div>
+    <div class="modal-body">
+      <div class="wizard-body vertical justified">
+        <div class="alert alert--danger hide" role="alert"></div>
+
+        <h2><%- @T('User') %></h2>
+        <form class="js-userMappingForm">
+          <table class="settings-list js-userAttributeMap" style="width: 100%;">
+            <colgroup>
+              <col width="240">
+              <col>
+              <col>
+            </colgroup>
+            <thead>
+              <tr>
+                <th><%- @T('%s Attribute', 'Exchange') %>
+                <th><%- @T('%s Attribute', 'Zammad') %>
+                <th><%- @T('Action') %>
+            </thead>
+            <tbody>
+              <tr>
+                <td class="settings-list-row-control" colspan="3">
+                  <div class="btn btn--text btn--create js-add">
+                    <%- @Icon('plus-small') %> <%- @T('Add') %>
+                  </div>
+            </tbody>
+          </table>
+        </form>
+
+      </div>
+    </div>
+    <div class="modal-footer">
+      <div class="modal-rightFooter">
+        <a class="btn btn--text btn--secondary js-goToSlide align-left" data-slide="js-bind"><%- @T('Go Back') %></a>
+      </div>
+      <div class="modal-rightFooter">
+        <button class="btn btn--primary align-right js-submitTry"><%- @T('Continue') %></button>
+      </div>
+    </div>
+  </div>
+
+  <form class="modal-content setup wizard hide js-dry">
+    <div class="modal-header">
+      <div class="modal-close js-close">
+        <%- @Icon('diagonal-cross') %>
+      </div>
+      <h1 class="modal-title"><%- @T('Exchange') %> <%- @T('Configuration') %></h1>
+    </div>
+    <div class="modal-body">
+      <div class="wizard-body vertical justified">
+        <div class="js-preprogress">
+          <p class="wizard-loadingText">
+            <span class="loading icon"></span>
+            <%- @T('Counting entries. This may take a while.') %>
+          </p>
+        </div>
+        <div class="js-analyzing hide">
+          <p class="wizard-loadingText">
+            <%- @T('Analyzing entries with given configuration...') %>
+          </p>
+          <div class="centered js-progress">
+            <progress max="" value=""></progress>
+          </div>
+        </div>
+      </div>
+    </div>
+    <div class="modal-footer"></div>
+  </form>
+
+  <div class="modal-content setup wizard hide js-try">
+    <div class="modal-header">
+      <div class="modal-close js-close">
+        <%- @Icon('diagonal-cross') %>
+      </div>
+      <h1 class="modal-title"><%- @T('Exchange') %> <%- @T('Configuration') %></h1>
+    </div>
+    <div class="modal-body">
+      <div class="wizard-body vertical justified">
+        <div class="alert alert--danger hide" role="alert"></div>
+        <p><%- @T('With your current configuration the following will happen') %>:</p>
+        <div class="js-summary"></div>
+      </div>
+    </div>
+    <div class="modal-footer">
+      <div class="modal-rightFooter">
+        <a class="btn btn--text btn--secondary js-goToSlide align-left" data-slide="js-mapping"><%- @T('Go Back') %></a>
+      </div>
+      <div class="modal-rightFooter">
+        <button class="btn btn--primary align-right js-submitSave"><%- @T('Save configuration') %></button>
+      </div>
+    </div>
+  </div>
+
+  <form class="modal-content setup wizard hide js-error">
+    <div class="modal-header">
+      <div class="modal-close js-close">
+        <%- @Icon('diagonal-cross') %>
+      </div>
+      <h1 class="modal-title"><%- @T('Exchange') %></h1>
+    </div>
+    <div class="modal-body">
+      <div class="wizard-body vertical justified">
+        <div class="alert alert--danger hide" role="alert"></div>
+      </div>
+    </div>
+    <div class="modal-footer">
+      <div class="modal-rightFooter">
+        <button class="btn btn--primary align-right"><%- @T('Cancel') %></button>
+      </div>
+    </div>
+  </form>
+
+</div>

app/controllers/concerns/integration/import_job_base.rb

@@ -0,0 +1,89 @@
+module Integration::ImportJobBase
+  extend ActiveSupport::Concern
+
+  def job_try_index
+    job_index(
+      dry_run:       true,
+      take_finished: params[:finished] == 'true'
+    )
+  end
+
+  def job_try_create
+    ImportJob.dry_run(name: import_backend_namespace, payload: payload_dry_run)
+    render json: {
+      result: 'ok',
+    }
+  end
+
+  def job_start_index
+    job_index(dry_run: false)
+  end
+
+  def job_start_create
+    if !ImportJob.exists?(name: import_backend_namespace, finished_at: nil)
+      job = ImportJob.create(name: import_backend_namespace, payload: payload_import)
+      job.delay.start
+    end
+    render json: {
+      result: 'ok',
+    }
+  end
+
+  def payload_dry_run
+    params
+  end
+
+  def payload_import
+    import_setting
+  end
+
+  private
+
+  def answer_with
+    result = yield
+    render json: result.merge(result: 'ok')
+  rescue => e
+    logger.error(e)
+    render json: {
+      result:  'failed',
+      message: e.message,
+    }
+  end
+
+  def import_setting
+    Setting.get(import_setting_name)
+  end
+
+  def import_setting_name
+    "#{import_backend_name.downcase}_config"
+  end
+
+  def import_backend_namespace
+    "Import::#{import_backend_name}"
+  end
+
+  def import_backend_name
+    self.class.name.split('::').last.sub('Controller', '')
+  end
+
+  def job_index(dry_run:, take_finished: true)
+    job = ImportJob.find_by(
+      name:        import_backend_namespace,
+      dry_run:     dry_run,
+      finished_at: nil
+    )
+    if !job && take_finished
+      job = ImportJob.where(
+        name:    import_backend_namespace,
+        dry_run: dry_run
+      ).order(created_at: :desc).limit(1).first
+    end
+
+    if job
+      model_show_render_item(job)
+    else
+      render json: {}
+    end
+  end
+
+end

app/controllers/integration/exchange_controller.rb

@@ -0,0 +1,66 @@
+# Copyright (C) 2012-2016 Zammad Foundation, http://zammad-foundation.org/
+
+class Integration::ExchangeController < ApplicationController
+  include Integration::ImportJobBase
+
+  prepend_before_action { authentication_check(permission: 'admin.integration.exchange') }
+
+  def autodiscover
+    answer_with do
+      client = Autodiscover::Client.new(
+        email:    params[:user],
+        password: params[:password],
+      )
+
+      {
+        endpoint: client.autodiscover.ews_url,
+      }
+    end
+  end
+
+  def folders
+    answer_with do
+      Sequencer.process('Import::Exchange::AvailableFolders',
+                        parameters: {
+                          ews_config: {
+                            endpoint: params[:endpoint],
+                            user:     params[:user],
+                            password: params[:password],
+                          }
+                        })
+    end
+  end
+
+  def mapping
+    answer_with do
+      Sequencer.process('Import::Exchange::AttributesExamples',
+                        parameters: {
+                          ews_folder_ids: params[:folders],
+                          ews_config:     {
+                            endpoint: params[:endpoint],
+                            user:     params[:user],
+                            password: params[:password],
+                          }
+                        })
+    end
+  end
+
+  private
+
+  # currently a workaround till LDAP is migrated to Sequencer
+  def payload_dry_run
+    {
+      ews_attributes: params[:attributes],
+      ews_folder_ids: params[:folders],
+      ews_config:     {
+        endpoint: params[:endpoint],
+        user:     params[:user],
+        password: params[:password],
+      }
+    }
+  end
+
+  def payload_import
+    nil
+  end
+end

app/controllers/integration/ldap_controller.rb

@@ -4,6 +4,8 @@ require 'ldap/user'
 require 'ldap/group'
 
 class Integration::LdapController < ApplicationController
+  include Integration::ImportJobBase
+
   prepend_before_action { authentication_check(permission: 'admin.integration.ldap') }
 
   def discover
@@ -60,48 +62,4 @@ class Integration::LdapController < ApplicationController
       message: e.message,
     }
   end
-
-  def job_try_index
-    job_index(
-      dry_run:       true,
-      take_finished: params[:finished] == 'true'
-    )
-  end
-
-  def job_try_create
-    ImportJob.dry_run(name: 'Import::Ldap', payload: params)
-    render json: {
-      result: 'ok',
-    }
-  end
-
-  def job_start_index
-    job_index(dry_run: false)
-  end
-
-  def job_start_create
-    backend = 'Import::Ldap'
-    if !ImportJob.exists?(name: backend, finished_at: nil)
-      job = ImportJob.create(name: backend, payload: Setting.get('ldap_config'))
-      job.delay.start
-    end
-    render json: {
-      result: 'ok',
-    }
-  end
-
-  private
-
-  def job_index(dry_run:, take_finished: true)
-    job = ImportJob.find_by(name: 'Import::Ldap', dry_run: dry_run, finished_at: nil)
-    if !job && take_finished
-      job = ImportJob.where(name: 'Import::Ldap', dry_run: dry_run).order(created_at: :desc).limit(1).first
-    end
-
-    if job
-      model_show_render_item(job)
-    else
-      render json: {}
-    end
-  end
 end

config/routes/integration_exchange.rb

@@ -0,0 +1,11 @@
+Zammad::Application.routes.draw do
+  api_path = Rails.configuration.api_path
+
+  match api_path + '/integration/exchange/autodiscover', to: 'integration/exchange#autodiscover',      via: :post
+  match api_path + '/integration/exchange/folders',      to: 'integration/exchange#folders',           via: :post
+  match api_path + '/integration/exchange/mapping',      to: 'integration/exchange#mapping',           via: :post
+  match api_path + '/integration/exchange/job_try',      to: 'integration/exchange#job_try_index',     via: :get
+  match api_path + '/integration/exchange/job_try',      to: 'integration/exchange#job_try_create',    via: :post
+  match api_path + '/integration/exchange/job_start',    to: 'integration/exchange#job_start_index',   via: :get
+  match api_path + '/integration/exchange/job_start',    to: 'integration/exchange#job_start_create',  via: :post
+end

db/migrate/20170629000001_exchange_integration.rb

@@ -0,0 +1,51 @@
+class ExchangeIntegration < ActiveRecord::Migration
+  def up
+
+    # return if it's a new setup
+    return if !Setting.find_by(name: 'system_init_done')
+
+    Setting.set('import_backends', ['Import::Ldap', 'Import::Exchange'])
+
+    Setting.create_if_not_exists(
+      title: 'Exchange config',
+      name: 'exchange_config',
+      area: 'Integration::Exchange',
+      description: 'Defines the Exchange config.',
+      options: {},
+      state: {},
+      preferences: {
+        prio: 2,
+        permission: ['admin.integration'],
+      },
+      frontend: false,
+    )
+    Setting.create_if_not_exists(
+      title: 'Exchange integration',
+      name: 'exchange_integration',
+      area: 'Integration::Switch',
+      description: 'Defines if Exchange is enabled or not.',
+      options: {
+        form: [
+          {
+            display: '',
+            null: true,
+            name: 'exchange_integration',
+            tag: 'boolean',
+            options: {
+              true  => 'yes',
+              false => 'no',
+            },
+          },
+        ],
+      },
+      state: false,
+      preferences: {
+        prio: 1,
+        authentication: true,
+        permission: ['admin.integration'],
+      },
+      frontend: true
+    )
+  end
+
+end

db/seeds/settings.rb

@@ -2401,7 +2401,7 @@ Setting.create_if_not_exists(
   area:        'Import',
   description: 'A list of active import backends that get scheduled automatically.',
   options:     {},
-  state:       ['Import::Ldap'],
+  state:       ['Import::Ldap', 'Import::Exchange'],
   preferences: {
     permission: ['admin'],
   },
@@ -2874,6 +2874,46 @@ Setting.create_if_not_exists(
   },
   frontend: true
 )
+Setting.create_if_not_exists(
+  title: 'Exchange config',
+  name: 'exchange_config',
+  area: 'Integration::Exchange',
+  description: 'Defines the Exchange config.',
+  options: {},
+  state: {},
+  preferences: {
+    prio: 2,
+    permission: ['admin.integration'],
+  },
+  frontend: false,
+)
+Setting.create_if_not_exists(
+  title: 'Exchange integration',
+  name: 'exchange_integration',
+  area: 'Integration::Switch',
+  description: 'Defines if Exchange is enabled or not.',
+  options: {
+    form: [
+      {
+        display: '',
+        null: true,
+        name: 'exchange_integration',
+        tag: 'boolean',
+        options: {
+          true  => 'yes',
+          false => 'no',
+        },
+      },
+    ],
+  },
+  state: false,
+  preferences: {
+    prio: 1,
+    authentication: true,
+    permission: ['admin.integration'],
+  },
+  frontend: true
+)
 Setting.create_if_not_exists(
   title: 'LDAP config',
   name: 'ldap_config',

lib/import/exchange.rb

@@ -0,0 +1,13 @@
+# Copyright (C) 2012-2016 Zammad Foundation, http://zammad-foundation.org/
+
+module Import
+  class Exchange < Import::IntegrationBase
+    include Import::Mixin::Sequence
+
+    private
+
+    def sequence_name
+      'Import::Exchange::FolderContacts'
+    end
+  end
+end

lib/import/exchange/folder.rb

@@ -0,0 +1,76 @@
+require 'mixin/rails_logger'
+
+module Import
+  class Exchange
+    class Folder
+      include ::Mixin::RailsLogger
+
+      def initialize(connection)
+        @connection = connection
+        @lookup_map = {}
+      end
+
+      def id_folder_map
+        @id_folder_map ||= all.collect do |folder|
+          [folder.id, folder]
+        end.to_h
+
+        # duplicate object to avoid errors where keys get
+        # added via #get_folder while iterating over
+        # the result of this method
+        @lookup_map = @id_folder_map.dup
+        @id_folder_map
+      end
+
+      def find(id)
+        @lookup_map[id] ||= @connection.get_folder(id)
+      end
+
+      def all
+        # request folders only if neccessary and store the result
+        @all ||= children(%i(root msgfolderroot publicfoldersroot))
+      end
+
+      def children(parent_identifiers)
+        parent_identifiers.each_with_object([]) do |parent_identifier, result|
+
+          child_folders = request_children(parent_identifier)
+
+          next if child_folders.blank?
+
+          child_folder_ids = child_folders.collect(&:id)
+          child_folders   += children(child_folder_ids)
+
+          result.concat(child_folders)
+        end
+      end
+
+      def display_path(folder)
+        display_name = folder.display_name
+        return display_name if !folder.parent_folder_id
+
+        parent_folder = find(folder.parent_folder_id)
+        return display_name if !parent_folder
+
+        parent_folder = id_folder_map[folder.parent_folder_id]
+        return display_name if !parent_folder
+
+        # recursive
+        parent_folder_path = display_path(parent_folder)
+
+        "#{parent_folder_path} -> #{display_name}"
+      rescue Viewpoint::EWS::EwsError
+        folder.display_name
+      end
+
+      private
+
+      def request_children(parent_identifier)
+        @connection.folders(root: parent_identifier)
+      rescue Viewpoint::EWS::EwsFolderNotFound => e
+        logger.warn(e)
+        nil
+      end
+    end
+  end
+end

lib/import/exchange/item_attributes.rb

@@ -0,0 +1,111 @@
+module Import
+  class Exchange
+    class ItemAttributes
+
+      def self.extract(resource)
+        new(resource).extract
+      end
+
+      def initialize(resource)
+        @resource = resource
+      end
+
+      def extract
+        @attributes ||= begin
+          properties  = @resource.get_all_properties!
+          result      = normalize(properties)
+          flattened   = flatten(result)
+          booleanized = booleanize_values(flattened)
+        end
+      end
+
+      private
+
+      def booleanize_values(properties)
+        properties.each do |key, value|
+          if value.is_a?(String)
+            next if !%w(true false).include?(value)
+            properties[key] = value == 'true'
+          elsif value.is_a?(Hash)
+            properties[key] = booleanize_values(value)
+          end
+        end
+      end
+
+      def normalize(properties)
+        result = {}
+        properties.each do |key, value|
+
+          next if key == :body
+
+          if value[:text]
+            result[key] = value[:text]
+          elsif value[:attribs]
+            result[key] = value[:attribs]
+          elsif value[:elems]
+            result[key] = sub_elems(value[:elems])
+          end
+        end
+
+        result
+      end
+
+      def sub_elems(elems)
+        result = {}
+        elems.each do |elem|
+          if elem[:entry]
+            result.merge!( sub_elem_entry( elem[:entry] ) )
+          else
+            result.merge!( normalize(elem) )
+          end
+        end
+        result
+      end
+
+      def sub_elem_entry(entry)
+        entry_value = {}
+        if entry[:elems]
+          entry_value = sub_elems(entry[:elems])
+        end
+
+        if entry[:text]
+          entry_value[:text] = entry[:text]
+        end
+
+        if entry[:attribs].present?
+          entry_value.merge!(entry[:attribs])
+        end
+
+        entry_key = entry_value.delete(:key)
+        {
+          entry_key => entry_value
+        }
+      end
+
+      def flatten(properties, prefix: nil)
+
+        result = {}
+        properties.each do |key, value|
+
+          result_key = key
+          if prefix
+            result_key = if %i(text id).include?(key) && ( !result[result_key] || result[result_key] == value )
+                           prefix
+                         else
+                           "#{prefix}.#{key}".to_sym
+                         end
+          end
+          result_key = result_key.to_s.downcase
+
+          if value.is_a?(Hash)
+            sub_result = flatten(value, prefix: result_key)
+            result.merge!(sub_result)
+          else
+            result[result_key] = value.to_s
+          end
+        end
+        result
+      end
+    end
+  end
+end

lib/import/helper/attributes_examples.rb

@@ -0,0 +1,70 @@
+module Import
+  module Helper
+    class AttributesExamples
+      attr_reader :examples, :enough, :max_unkown
+
+      def initialize(&block)
+        @max_unkown     = 50
+        @no_new_counter = 1
+        @examples       = {}
+        @known          = []
+
+        # Support both builder styles:
+        #
+        #   Import::Helper::AttributesExamples.new do
+        #     extract(attributes)
+        #   end
+        #
+        # and
+        #
+        #   Import::Helper::AttributesExamples.new do |extractor|
+        #     extractor.extract(attributes)
+        #   end
+        return if !block_given?
+        if block.arity.zero?
+          instance_eval(&block)
+        else
+          yield self
+        end
+      end
+
+      def extract(attributes)
+        unknown = attributes.keys - @known
+
+        return if !unknown?(unknown)
+
+        store(attributes, unknown)
+
+        @known.concat(unknown)
+        @no_new_counter = 0
+      end
+
+      private
+
+      def unknown?(unknown)
+        return true if unknown.present?
+
+        @no_new_counter += 1
+
+        # check max 50 entries with no or no new attributes in a row
+        @enough_examples = @no_new_counter != 50
+
+        false
+      end
+
+      def store(attributes, unknown)
+        unknown.each do |attribute|
+          value = attributes[attribute]
+
+          next if value.nil?
+
+          example = value.to_s.force_encoding('UTF-8').encode('utf-8', 'binary', invalid: :replace, undef: :replace, replace: '?')
+          example.gsub!(/^(.{20,}?).*$/m, '\1...')
+
+          @examples[attribute] = "#{attribute} (e. g. #{example})"
+        end
+      end
+
+    end
+  end
+end

lib/import/integration_base.rb

@@ -0,0 +1,143 @@
+# Copyright (C) 2012-2016 Zammad Foundation, http://zammad-foundation.org/
+
+module Import
+
+  # This base class handles regular integrations.
+  # It provides generic interfaces for settings and active state.
+  # It ensures that all requirements for a regular integration are met before a import can start.
+  # It handles the case of an Scheduler interruption.
+  #
+  # It's required to implement the +start_import+ method which only has to start the import.
+  class IntegrationBase < Import::Base
+
+    def self.inherited(subclass)
+      subclass.extend(Forwardable)
+
+      # delegate instance methods to the generic class implementations
+      subclass.delegate [:identifier, :active?, :config, :display_name] => subclass
+    end
+
+    # Defines the integration identifier used for
+    # automatic config lookup and error message generation.
+    #
+    # @example
+    #  Import::Ldap.identifier
+    #  #=> "Ldap"
+    #
+    # return [String]
+    def self.identifier
+      name.split('::').last
+    end
+
+    # Provides the name that is used in texts visible to the user.
+    #
+    # @example
+    #  Import::Exchange.display_name
+    #  #=> "Exchange"
+    #
+    # return [String]
+    def self.display_name
+      identifier
+    end
+
+    # Checks if the integration is active.
+    #
+    # @example
+    #  Import::Ldap.active?
+    #  #=> true
+    #
+    # return [Boolean]
+    def self.active?
+      Setting.get("#{identifier.downcase}_integration") || false
+    end
+
+    # Provides the integration configuration.
+    #
+    # @example
+    #  Import::Ldap.config
+    #  #=> {"ssl_verify"=>true, "host_url"=>"ldaps://192...", ...}
+    #
+    # return [Hash] the configuration
+    def self.config
+      Setting.get("#{identifier.downcase}_config") || {}
+    end
+
+    # Stores the integration configuration.
+    #
+    # @example
+    #  Import::Ldap.config = {"ssl_verify"=>true, "host_url"=>"ldaps://192...", ...}
+    #
+    # return [nil]
+    def self.config=(value)
+      Setting.set("#{identifier.downcase}_config", value)
+    end
+
+    # Checks if the integration is activated and configured.
+    # Otherwise it won't get queued since it will display
+    # an error which is confusing and wrong.
+    #
+    # @example
+    #  Import::Ldap.queueable?
+    #  #=> true
+    #
+    # return [Boolean]
+    def self.queueable?
+      active? && config.present?
+    end
+
+    # Starts a live or dry run import.
+    #
+    # @example
+    #  instance = Import::Ldap.new(import_job)
+    #
+    # @raise [RuntimeError] Raised if an import should start but the integration is disabled
+    #
+    # return [nil]
+    def start
+      return if !requirements_completed?
+      start_import
+    end
+
+    # Gets called when the Scheduler gets (re-)started and an ImportJob was still
+    # in the queue. The job will always get restarted to avoid the gap till the next
+    # run triggered by the Scheduler. The result will get updated to inform the user
+    # in the agent interface result view.
+    #
+    # @example
+    #  instance = Import::Ldap.new(import_job)
+    #  instance.reschedule?(delayed_job)
+    #  #=> true
+    #
+    # return [true]
+    def reschedule?(_delayed_job)
+      inform('Restarting due to scheduler restart.')
+      true
+    end
+
+    private
+
+    def start_import
+      raise "Missing implementation of method '#{__method__}' for #{self.class.name}"
+    end
+
+    def requirements_completed?
+      return true if @import_job.dry_run
+
+      if !active?
+        message = "Sync cancelled. #{display_name} integration deactivated. Activate via the switch."
+      elsif config.blank? && @import_job.payload.blank?
+        message = "Sync cancelled. #{display_name} configration or ImportJob payload missing."
+      end
+
+      return true if !message
+      inform(message)
+      false
+    end
+
+    def inform(message)
+      @import_job.update_attribute(:result, {
+                                     info: message
+                                   })
+    end
+  end
+end

lib/import/ldap.rb

@@ -4,50 +4,17 @@ require 'ldap'
 require 'ldap/group'
 
 module Import
-  class Ldap < Import::Base
+  class Ldap < Import::IntegrationBase
 
-    # Checks if the integration is activated and configured.
+    # Provides the name that is used in texts visible to the user.
-    # Otherwise it won't get queued since it will display
-    # an error which is confusing and wrong.
     #
     # @example
-    #  Import::LDAP.queueable?
+    #  Import::Ldap.display_name
-    #  #=> true
+    #  #=> "LDAP"
     #
-    # return [Boolean]
+    # return [String]
-    def self.queueable?
+    def self.display_name
-      Setting.get('ldap_integration') && Setting.get('ldap_config').present?
+      identifier.upcase
-    end
-
-    # Starts a live or dry run LDAP import.
-    #
-    # @example
-    #  instance = Import::LDAP.new(import_job)
-    #
-    # @raise [RuntimeError] Raised if an import should start but the ldap integration is disabled
-    #
-    # return [nil]
-    def start
-      return if !requirements_completed?
-      start_import
-    end
-
-    # Gets called when the Scheduler gets (re-)started and a LDAP ImportJob was still
-    # in the queue. The job will always get restarted to avoid the gap till the next
-    # run triggered by the Scheduler. The result will get updated to inform the user
-    # in the agent interface result view.
-    #
-    # @example
-    #  instance = Import::LDAP.new(import_job)
-    #  instance.reschedule?(delayed_job)
-    #  #=> true
-    #
-    # return [true]
-    def reschedule?(_delayed_job)
-      @import_job.update_attribute(:result, {
-                                     info: 'Restarting due to scheduler restart.'
-                                   })
-      true
     end
 
     private
@@ -63,23 +30,5 @@ module Import
 
       @import_job.result = Import::Ldap::UserFactory.statistics
     end
-
-    def requirements_completed?
-      return true if @import_job.dry_run
-
-      if !Setting.get('ldap_integration')
-        message = 'Sync cancelled. LDAP integration deactivated. Activate via the switch.'
-      elsif Setting.get('ldap_config').blank? && @import_job.payload.blank?
-        message = 'Sync cancelled. LDAP configration or ImportJob payload missing.'
-      end
-
-      return true if !message
-
-      @import_job.update_attribute(:result, {
-                                     info: message
-                                   })
-
-      false
-    end
   end
 end

lib/import/mixin/sequence.rb

@@ -0,0 +1,19 @@
+module Import
+  module Mixin
+    module Sequence
+      private
+
+      def sequence_name
+        raise "Missing implementation of '#{__method__}' method for '#{self.class.name}'"
+      end
+
+      def process
+        Sequencer.process(sequence_name,
+                          parameters: {
+                            import_job: @import_job
+                          })
+      end
+      alias start_import process
+    end
+  end
+end

lib/mixin/instance_wrapper.rb

@@ -0,0 +1,43 @@
+module Mixin
+  # This modules enables to redirect all calls to methods that are
+  # not defined to the declared instance variable. This comes handy
+  # when you wan't extend a Ruby core class like Hash.
+  # To inherit directly from such classes is a bad idea and should be avoided.
+  # This way allows it indirectly.
+  module InstanceWrapper
+    module ClassMethods
+      # Creates the class macro `wrap` that activates
+      # the wrapping for the given instance variable name.
+      #
+      # @param [Symbol] variable the name of the instance variable to wrap around
+      #
+      # @example
+      #  wrap :@some_hash
+      #
+      # @return [nil]
+      def wrap(variable)
+        define_method(:instance) {
+          instance_variable_get(variable)
+        }
+      end
+    end
+
+    def self.included(base)
+      base.extend(ClassMethods)
+    end
+
+    private
+
+    def method_missing(method, *args, &block)
+      if instance.respond_to?(method)
+        instance.send(method, *args, &block)
+      else
+        super
+      end
+    end
+
+    def respond_to_missing?(method_sym, include_all)
+      instance.respond_to?(method_sym, include_all)
+    end
+  end
+end

lib/mixin/rails_logger.rb

@@ -0,0 +1,9 @@
+module Mixin
+  module RailsLogger
+    extend Forwardable
+    extend SingleForwardable
+
+    instance_delegate [:logger] => self
+    single_delegate   [:logger] => :Rails
+  end
+end

lib/mixin/required_sub_paths.rb

@@ -0,0 +1,44 @@
+module Mixin
+  module RequiredSubPaths
+
+    def self.included(_base)
+      path     = caller_locations.first.path
+      sub_path = File.join(File.dirname(path), File.basename(path, '.rb'))
+      eager_load_recursive(sub_path)
+    end
+
+    # Loads a directory recursivly.
+    # The specialty of this method is that it will first load all
+    # files in a directory and then start with the sub directories.
+    # This is needed since otherwise some parent namespaces might not
+    # be initialized yet.
+    #
+    # The cause of this is that Rails autoload doesn't work properly
+    # for same named classes or modules in different namespaces.
+    # Here is a good description how autoload works:
+    # http://urbanautomaton.com/blog/2013/08/27/rails-autoloading-hell/
+    #
+    # This avoids a) Rails autoloading issues and b) require '...' workarounds
+    def self.eager_load_recursive(path)
+
+      excluded  = ['.', '..']
+      sub_paths = []
+      Dir.entries(path).each do |entry|
+        next if excluded.include?(entry)
+
+        sub_path = File.join(path, entry)
+
+        if File.directory?(sub_path)
+          sub_paths.push(sub_path)
+        elsif sub_path =~ /\A(.*)\.rb\z/
+          require_path = $1
+          require(require_path)
+        end
+      end
+
+      sub_paths.each do |sub_path|
+        eager_load_recursive(sub_path)
+      end
+    end
+  end
+end

lib/mixin/start_finish_logger.rb

@@ -0,0 +1,11 @@
+module Mixin
+  module StartFinishLogger
+    include ::Mixin::RailsLogger
+
+    def log_start_finish(level, prefix)
+      logger.public_send(level, "#{prefix} started.")
+      yield
+      logger.public_send(level, "#{prefix} finished.")
+    end
+  end
+end

lib/sequencer.rb

@@ -0,0 +1,83 @@
+require 'mixin/rails_logger'
+require 'mixin/start_finish_logger'
+
+class Sequencer
+  include ::Mixin::RailsLogger
+  include ::Mixin::StartFinishLogger
+
+  attr_reader :sequence
+
+  # Convenience wrapper for instant processing with the given attributes.
+  #
+  # @example
+  #  Sequencer.process('Example::Sequence')
+  #
+  # @example
+  #  Sequencer.process('Example::Sequence',
+  #    parameters: {
+  #      some: 'value',
+  #    },
+  #    expecting: [:result, :answer]
+  #  )
+  #
+  # @return [Hash{Symbol => Object}] the final result state attributes and values
+  def self.process(sequence, *args)
+    new(sequence, *args).process
+  end
+
+  # Initializes a new Sequencer instance for the given Sequence with parameters and expecting result.
+  #
+  # @example
+  #  Sequencer.new('Example::Sequence')
+  #
+  # @example
+  #  Sequencer.new('Example::Sequence',
+  #    parameters: {
+  #      some: 'value',
+  #    },
+  #    expecting: [:result, :answer]
+  #  )
+  def initialize(sequence, parameters: {}, expecting: nil)
+    @sequence   = Sequencer::Sequence.constantize(sequence)
+    @parameters = parameters
+    @expecting  = expecting
+
+    # fall back to sequence default expecting if no explicit
+    # expecting was given for this sequence
+    return if !@expecting.nil?
+    @expecting = @sequence.expecting
+  end
+
+  # Processes the Sequence the instance was initialized with.
+  #
+  # @example
+  #  sequence.process
+  #
+  # @return [Hash{Symbol => Object}] the final result state attributes and values
+  def process
+    log_start_finish(:info, "Sequence '#{@sequence.name}'") do
+
+      sequence.units.each_with_index do |unit, index|
+
+        state.process do
+
+          log_start_finish(:info, "Sequence '#{sequence.name}' Unit '#{unit.name}' (index: #{index})") do
+            unit.process(state)
+          end
+        end
+      end
+    end
+
+    state.to_h.tap do |result|
+      logger.debug("Returning Sequence '#{@sequence.name}' result: #{result.inspect}")
+    end
+  end
+
+  private
+
+  def state
+    @state ||= Sequencer::State.new(sequence,
+                                    parameters: @parameters,
+                                    expecting:  @expecting)
+  end
+end

lib/sequencer/mixin/exchange/folder.rb

@@ -0,0 +1,18 @@
+class Sequencer
+  module Mixin
+    module Exchange
+      module Folder
+
+        def self.included(base)
+          base.uses :ews_connection
+        end
+
+        private
+
+        def ews_folder
+          @ews_folder ||= ::Import::Exchange::Folder.new(ews_connection)
+        end
+      end
+    end
+  end
+end

lib/sequencer/mixin/import_job/resource_loop.rb

@@ -0,0 +1,37 @@
+require 'sequencer/mixin/sub_sequence'
+
+class Sequencer
+  module Mixin
+    module ImportJob
+      module ResourceLoop
+        include ::Sequencer::Mixin::SubSequence
+
+        private
+
+        def resource_sequence(sequence_name, items)
+          default_params = {
+            dry_run:    import_job.dry_run,
+            import_job: import_job,
+          }
+
+          items.each do |item|
+            resource_params = {}
+            if block_given?
+              resource_params = yield item
+            else
+              resource_params[:resource] = item
+            end
+
+            resource_params[:resource] = resource_params[:resource].with_indifferent_access
+
+            sub_sequence(sequence_name,
+                         parameters: default_params.merge(resource_params))
+          end
+
+          # store possible unsaved values in result e.g. statistics
+          import_job.save!
+        end
+      end
+    end
+  end
+end

lib/sequencer/mixin/prefixed_constantize.rb

@@ -0,0 +1,43 @@
+class Sequencer
+  module Mixin
+    # Classes that extend this module need a PREFIX constant.
+    module PrefixedConstantize
+      # Returns the class for a given name String independend of the prefix.
+      #
+      # @param [String] sequence the name String for the requested class
+      #
+      # @example
+      #  Sequencer::Sequence.constantize('ExampleSequence')
+      #  #=> Sequencer::Sequence::ExampleSequence
+      #
+      # @example
+      #  Sequencer::Unit.constantize('Sequencer::Unit::Example::Unit')
+      #  #=> Sequencer::Unit::Example::Unit
+      #
+      # @return [Object] the class for the given String
+      def constantize(name_string)
+        namespace(name_string).constantize
+      end
+
+      # Returns the complete class namespace for a given name String
+      # independend of the prefix.
+      #
+      # @param [String] sequence the name String for the requested class namespace
+      #
+      # @example
+      #  Sequencer::Sequence.namespace('ExampleSequence')
+      #  #=> 'Sequencer::Sequence::ExampleSequence'
+      #
+      # @example
+      #  Sequencer::Unit.namespace('Sequencer::Unit::Example::Unit')
+      #  #=> 'Sequencer::Unit::Example::Unit'
+      #
+      # @return [String] the class namespace for the given String
+      def namespace(name_string)
+        prefix = const_get(:PREFIX)
+        return name_string if name_string.start_with?(prefix)
+        "#{prefix}#{name_string}"
+      end
+    end
+  end
+end

lib/sequencer/mixin/sub_sequence.rb

@@ -0,0 +1,9 @@
+class Sequencer
+  module Mixin
+    module SubSequence
+      def sub_sequence(sequence, args = {})
+        Sequencer.process(sequence, args)
+      end
+    end
+  end
+end

lib/sequencer/sequence.rb

@@ -0,0 +1,16 @@
+require 'sequencer/mixin/prefixed_constantize'
+
+class Sequencer
+  class Sequence
+    extend ::Sequencer::Mixin::PrefixedConstantize
+
+    PREFIX = 'Sequencer::Sequence::'.freeze
+
+    attr_reader :units, :expecting
+
+    def initialize(units:, expecting: [])
+      @units     = units
+      @expecting = expecting
+    end
+  end
+end

lib/sequencer/sequence/base.rb

@@ -0,0 +1,48 @@
+class Sequencer
+  class Sequence
+    class Base
+
+      # Defines the default attributes that will get returned for the sequence.
+      # These can be overwritten by giving the :expecting key to a sequence process call.
+      #
+      # @example
+      #  Sequencer::Sequence::Example.expecting
+      #  # => [:result, :list]
+      #
+      # @return [Array<Symbol>] the list of expected result keys.
+      def self.expecting
+        []
+      end
+
+      # Defines the list of Units that form the sequence. The units will get
+      # processed in the order they are defined in. The namespaces can be
+      # absolute or without the `Sequencer::Unit` prefix.
+      #
+      # @example
+      #  Sequencer::Sequence::Example.sequence
+      #  # => ['Import::Example::Resource', 'Sequencer::Unit::Import::Model::Create', ...]
+      #
+      # @return [Array<String>] the list of units forming the sequence.
+      def self.sequence
+        raise "Missing implementation of '#{__method__}' method for '#{name}'"
+      end
+
+      # This is an internally used method that converts the defined sequence to a
+      # Sequencer::Units instance which has special methods.
+      #
+      # @example
+      #  Sequencer::Sequence::Example.units
+      #  # => <Sequencer::Units @units=[....>
+      #
+      # @return [Object]
+      def self.units
+        Sequencer::Units.new(*sequence)
+      end
+
+      # @see .units
+      def units
+        self.class.units
+      end
+    end
+  end
+end

lib/sequencer/sequence/exchange/folder/attributes.rb

@@ -0,0 +1,17 @@
+class Sequencer
+  class Sequence
+    module Exchange
+      module Folder
+        class Attributes < Sequencer::Sequence::Base
+
+          def self.sequence
+            [
+              'Exchange::Connection',
+              'Exchange::Folder::Attributes',
+            ]
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/sequence/import/exchange/attributes_examples.rb

@@ -0,0 +1,23 @@
+class Sequencer
+  class Sequence
+    module Import
+      module Exchange
+        class AttributesExamples < Sequencer::Sequence::Base
+
+          def self.expecting
+            [:attributes]
+          end
+
+          def self.sequence
+            [
+              'Exchange::Connection',
+              'Exchange::Folders::ByIds',
+              'Import::Exchange::AttributeExamples',
+              'Import::Exchange::AttributeMapper::AttributeExamples',
+            ]
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/sequence/import/exchange/available_folders.rb

@@ -0,0 +1,22 @@
+class Sequencer
+  class Sequence
+    module Import
+      module Exchange
+        class AvailableFolders < Sequencer::Sequence::Base
+
+          def self.expecting
+            [:folders]
+          end
+
+          def self.sequence
+            [
+              'Exchange::Connection',
+              'Exchange::Folders::IdPathMap',
+              'Import::Exchange::AttributeMapper::AvailableFolders',
+            ]
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/sequence/import/exchange/folder_contact.rb

@@ -0,0 +1,33 @@
+class Sequencer
+  class Sequence
+    module Import
+      module Exchange
+        class FolderContact < Sequencer::Sequence::Base
+
+          def self.sequence
+            [
+              'Import::Exchange::FolderContact::RemoteId',
+              'Import::Exchange::FolderContact::Mapping',
+              'Import::Common::Model::Skip::Blank::Mapped',
+              'Import::Exchange::FolderContact::StaticAttributes',
+              'Import::Common::Model::ExternalSync::Lookup',
+              'Import::Common::Model::Associations::Extract',
+              'Import::Common::User::Attributes::Downcase',
+              'Import::Common::User::Email::CheckValidity',
+              'Import::Common::Model::Attributes::AddByIds',
+              'Import::Common::Model::Update',
+              'Import::Common::Model::Create',
+              'Import::Common::Model::Associations::Assign',
+              'Import::Common::Model::Save',
+              'Import::Common::Model::ExternalSync::Create',
+              'Import::Exchange::FolderContact::HttpLog',
+              'Import::Exchange::FolderContact::Statistics::Diff',
+              'Import::Common::ImportJob::Statistics::Update',
+              'Import::Common::ImportJob::Statistics::Store',
+            ]
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/sequence/import/exchange/folder_contacts.rb

@@ -0,0 +1,22 @@
+class Sequencer
+  class Sequence
+    module Import
+      module Exchange
+        class FolderContacts < Sequencer::Sequence::Base
+
+          def self.sequence
+            [
+              'Import::Exchange::FolderContacts::DryRunPayload',
+              'Exchange::Connection',
+              'Import::Exchange::FolderContacts::FolderIds',
+              'Import::Exchange::FolderContacts::Sum',
+              'Import::Common::ImportJob::Statistics::Update',
+              'Import::Common::ImportJob::Statistics::Store',
+              'Import::Exchange::FolderContacts::SubSequence',
+            ]
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/state.rb

@@ -0,0 +1,272 @@
+require 'mixin/rails_logger'
+require 'mixin/start_finish_logger'
+
+class Sequencer
+  class State
+    include ::Mixin::RailsLogger
+    include ::Mixin::StartFinishLogger
+
+    def initialize(sequence, parameters: {}, expecting: nil)
+      @index        = -1
+      @units        = sequence.units
+      @result_index = @units.count
+      @values       = {}
+
+      initialize_attributes(sequence.units)
+      initialize_parameters(parameters.with_indifferent_access)
+      initialize_expectations(expecting || sequence.expecting)
+    end
+
+    # Stores a value for the given attribute. Value can be a regular object
+    # or the result of a given code block.
+    # The attribute gets validated against the .provides list of attributes.
+    # In the case than an attribute gets provided that is not declared to
+    # be provided an exception will be raised.
+    #
+    # @param [Symbol] attribute the attribute for which the value gets provided.
+    # @param [Object] value the value that should get stored for the given attribute.
+    # @yield [] executes the given block and takes the result as the value.
+    # @yieldreturn [Object] the value for the given attribute.
+    #
+    # @example
+    #  state.provide(:sum, 3)
+    #
+    # @example
+    #  state.provide(:sum) do
+    #    some_value = rand(100)
+    #    some_value * 3
+    #  end
+    #
+    # @raise [RuntimeError] if the attribute is not provideable from the calling Unit
+    #
+    # @return [nil]
+    def provide(attribute, value = nil)
+      if provideable?(attribute)
+        value = yield if block_given?
+        set(attribute, value)
+      else
+        value = "UNEXECUTED BLOCK: #{caller(1..1).first}" if block_given?
+        unprovideable_setter(attribute, value)
+      end
+    end
+
+    # Returns the value of the given attribute.
+    # The attribute gets validated against the .uses list of attributes. In the
+    # case than an attribute gets used that is not declared to be used
+    # an exception will be raised.
+    #
+    # @param [Symbol] attribute the attribute for which the value is requested.
+    #
+    # @example
+    #  state.use(:answer)
+    #  #=> 42
+    #
+    # @raise [RuntimeError] if the attribute is not useable from the calling Unit
+    #
+    # @return [nil]
+    def use(attribute)
+      if useable?(attribute)
+        get(attribute)
+      else
+        unaccessable_getter(attribute)
+      end
+    end
+
+    # Returns the value of the given attribute.
+    # The attribute DOES NOT get validated against the .uses list of attributes.
+    #
+    # @param [Symbol] attribute the attribute for which the value is requested.
+    #
+    # @example
+    #  state.optional(:answer)
+    #  #=> 42
+    #
+    # @example
+    #  state.optional(:unknown)
+    #  #=> nil
+    #
+    # @return [Object, nil]
+    def optional(attribute)
+      return get(attribute) if @attributes.known?(attribute)
+      logger.debug("Access to unknown optional attribute '#{attribute}'.")
+      nil
+    end
+
+    # Checks if a value for the given attribute is provided.
+    # The attribute DOES NOT get validated against the .uses list of attributes.
+    #
+    # @param [Symbol] attribute the attribute which should get checked.
+    #
+    # @example
+    #  state.provided?(:answer)
+    #  #=> true
+    #
+    # @example
+    #  state.provided?(:unknown)
+    #  #=> false
+    #
+    # @return [Boolean]
+    def provided?(attribute)
+      optional(attribute) != nil
+    end
+
+    # Unsets the value for the given attribute.
+    # The attribute gets validated against the .uses list of attributes.
+    # In the case than an attribute gets unset that is not declared
+    # to be used an exception will be raised.
+    #
+    # @param [Symbol] attribute the attribute for which the value gets unset.
+    #
+    # @example
+    #  state.unset(:answer)
+    #
+    # @raise [RuntimeError] if the attribute is not useable from the calling Unit
+    #
+    # @return [nil]
+    def unset(attribute)
+      value = nil
+      if useable?(attribute)
+        set(attribute, value)
+      else
+        unprovideable_setter(attribute, value)
+      end
+    end
+
+    # Handles state processing of the next Unit in the Sequence while executing
+    # the given block. After the Unit is processed the state will get cleaned up
+    # and no longer needed attribute values will get discarded.
+    #
+    # @yield [] executes the given block and handles the state changes before and afterwards.
+    #
+    # @example
+    #  state.process do
+    #   unit.process
+    #  end
+    #
+    # @return [nil]
+    def process
+      @index += 1
+      yield
+      cleanup
+    end
+
+    # Handles state processing of the next Unit in the Sequence while executing
+    # the given block. After the Unit is processed the state will get cleaned up
+    # and no longer needed attribute values will get discarded.
+    #
+    # @example
+    #  state.to_h
+    #  #=> {"ssl_verify"=>true, "host_url"=>"ldaps://192...", ...}
+    #
+    # @return [Hash{Symbol => Object}]
+    def to_h
+      available.map { |identifier| [identifier, @values[identifier]] }.to_h
+    end
+
+    private
+
+    def available
+      @attributes.select do |_identifier, attribute|
+        @index.between?(attribute.from, attribute.to)
+      end.keys
+    end
+
+    def unit(index = nil)
+      @units[index || @index]
+    end
+
+    def provideable?(attribute)
+      unit.provides.include?(attribute)
+    end
+
+    def useable?(attribute)
+      unit.uses.include?(attribute)
+    end
+
+    def set(attribute, value)
+      logger.debug("Setting '#{attribute}' value (#{value.class.name}): #{value.inspect}")
+      @values[attribute] = value
+    end
+
+    def get(attribute)
+      value = @values[attribute]
+      logger.debug("Getting '#{attribute}' value (#{value.class.name}): #{value.inspect}")
+      value
+    end
+
+    def unprovideable_setter(attribute, value)
+      message = "Unprovideable attribute '#{attribute}' set with value (#{value.class.name}): '#{value}'"
+      logger.error(message)
+      raise message
+    end
+
+    def unaccessable_getter(attribute)
+      message = "Unaccessable getter used for attribute '#{attribute}'"
+      logger.error(message)
+      raise message
+    end
+
+    def initialize_attributes(units)
+      log_start_finish(:debug, 'Attributes lifespan initialization') do
+        @attributes = Sequencer::Units::Attributes.new(units.declarations)
+        logger.debug("Attributes lifespan: #{@attributes.inspect}")
+      end
+    end
+
+    def initialize_parameters(parameters)
+      logger.debug("Initializing Sequencer::State with initial parameters: #{parameters.inspect}")
+
+      log_start_finish(:debug, 'Attribute value provisioning check and initialization') do
+
+        @attributes.each do |identifier, attribute|
+
+          if !attribute.will_be_used?
+            logger.debug("Attribute '#{identifier}' is provided by Unit(s) but never used.")
+            next
+          end
+
+          init_param    = parameters.key?(identifier)
+          provided_attr = attribute.will_be_provided?
+
+          if !init_param && !provided_attr
+            message = "Attribute '#{identifier}' is used in Unit '#{unit(attribute.to).name}' (index: #{attribute.to}) but is not provided or given via initial parameters."
+            logger.error(message)
+            raise message
+          end
+
+          # skip if attribute is provided by an Unit but not
+          # an initial parameter
+          next if !init_param
+
+          # update 'from' lifespan information for attribute
+          # since it's provided via the initial parameter
+          attribute.from = @index
+
+          # set initial value
+          set(identifier, parameters[identifier])
+        end
+      end
+    end
+
+    def initialize_expectations(expected_attributes)
+      expected_attributes.each do |identifier|
+        logger.debug("Adding attribute '#{identifier}' to the list of expected result attributes.")
+        @attributes[identifier].to = @result_index
+      end
+    end
+
+    def cleanup
+      log_start_finish(:info, "State cleanup of Unit #{unit.name} (index: #{@index})") do
+
+        @attributes.delete_if do |identifier, attribute|
+          remove = !attribute.will_be_used?
+          remove ||= attribute.to <= @index
+          if remove && attribute.will_be_used?
+            logger.debug("Removing unneeded attribute '#{identifier}': #{@values[identifier]}")
+          end
+          remove
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit.rb

@@ -0,0 +1,71 @@
+require 'sequencer/mixin/prefixed_constantize'
+
+class Sequencer
+  class Unit
+    include ::Mixin::RequiredSubPaths
+    extend ::Sequencer::Mixin::PrefixedConstantize
+
+    PREFIX = 'Sequencer::Unit::'.freeze
+
+    # Convenience wrapper for processing a single Unit.
+    #
+    # ATTENTION: This should only be used for development, testing or debugging purposes.
+    # There might be a check in the future to prevent using this method in other scopes.
+    #
+    # @see #initialize
+    # @see #process
+    def self.process(unit, parameters, &block)
+      new(unit).process(parameters, &block)
+    end
+
+    # Initializes a new Sequencer::Unit for processing it.
+    #
+    # ATTENTION: This should only be used for development, testing or debugging purposes.
+    # There might be a check in the future to prevent using this method in other scopes.
+    #
+    # @param [String] unit the name String for the Unit that should get processed
+    def initialize(unit)
+      @unit = self.class.constantize(unit)
+    end
+
+    # Processes the Sequencer::Unit that the instance was initialized with.
+    #
+    # ATTENTION: This should only be used for development, testing or debugging purposes.
+    # There might be a check in the future to prevent using this method in other scopes.
+    #
+    # @param [Hash{Symbol => Object}] parameters the parameters for initializing the Sequencer::State
+    # @yield [instance] optional block to access the Unit instance
+    # @yieldparam instance [Object] the Unit instance for e.g. adding expectations
+    def process(parameters)
+      @parameters = parameters
+      instance    = @unit.new(state)
+
+      # yield instance to apply expectations
+      yield instance if block_given?
+
+      state.process do
+        instance.process
+      end
+
+      state.to_h
+    end
+
+    private
+
+    def state
+      @state ||= begin
+        units = Sequencer::Units.new(
+          @unit.name
+        )
+
+        sequence = Sequencer::Sequence.new(
+          units:     units,
+          expecting: @unit.provides,
+        )
+
+        Sequencer::State.new(sequence,
+                             parameters: @parameters)
+      end
+    end
+  end
+end

lib/sequencer/unit/base.rb

@@ -0,0 +1,212 @@
+require 'mixin/rails_logger'
+
+class Sequencer
+  class Unit
+    class Base
+      include ::Mixin::RailsLogger
+
+      attr_reader :state
+
+      # Creates the class macro `uses` that allows a Unit to
+      # declare the attributes it will use via parameter or block.
+      # On the other hand it returns the declared attributes if
+      # called without parameters.
+      #
+      # This method can be called multiple times and will add the
+      # given attributes to the list. It takes care of handling
+      # duplicates so no uniq check is required. It's safe to use
+      # for inheritance structures and modules.
+      #
+      # It additionally creates a getter instance method for each declared
+      # attribute like e.g. attr_reader does. This allows direct access
+      # to an attribute via `attribute_name`. See examples.
+      #
+      # @param [Array<Symbol>] attributes an optional list of attributes that the Unit uses
+      #
+      # @yield [] A block returning a list of attributes
+      #
+      # @example Via regular Array<Symbol> parameter
+      #  uses :instance, :action, :connection
+      #
+      # @example Via block
+      #  uses do
+      #    additional = method(parameter)
+      #    [:some, additional]
+      #  end
+      #
+      # @example Listing declared attributes
+      #  Unit::Name.uses
+      #  # => [:instance, :action, :connection, :some, :suprise]
+      #
+      # @example Using declared attribute in the Unit via state object
+      #  state.use(:instance).id
+      #
+      # @example Using declared attribute in the Unit via getter
+      #  instance.id
+      #
+      # @return [Array<Symbol>] the list of all declared uses of a Unit.
+      def self.uses(*attributes, &block)
+        declaration_accessor(
+          key:        __method__,
+          attributes: attributes(*attributes, &block)
+        ) do |attribute|
+          use_getter(attribute)
+        end
+      end
+
+      # Creates the class macro `provides` that allows a Unit to
+      # declare the attributes it will provided via parameter or block.
+      # On the other hand it returns the declared attributes if
+      # called without parameters.
+      #
+      # This method can be called multiple times and will add the
+      # given attributes to the list. It takes care of handling
+      # duplicates so no uniq check is required. It's safe to use
+      # for inheritance structures and modules.
+      #
+      # It additionally creates a setter instance method for each declared
+      # attribute like e.g. attr_writer does. This allows direct access
+      # to an attribute via `self.attribute_name = `. See examples.
+      #
+      # A Unit should usually not provide more than one or two attributes.
+      # If your Unit provides it's doing to much and should be splitted
+      # into multiple Units.
+      #
+      # @param [Array<Symbol>] attributes an optional list of attributes that the Unit provides
+      #
+      # @yield [] A block returning a list of attributes
+      #
+      # @example Via regular Array<Symbol> parameter
+      #  provides :instance, :action, :connection
+      #
+      # @example Via block
+      #  provides do
+      #    additional = method(parameter)
+      #    [:some, additional]
+      #  end
+      #
+      # @example Listing declared attributes
+      #  Unit::Name.provides
+      #  # => [:instance, :action, :connection, :some, :suprise]
+      #
+      # @example Providing declared attribute in the Unit via state object parameter
+      #  state.provide(:action, :created)
+      #
+      # @example Providing declared attribute in the Unit via state object block
+      #  state.provide(:instance) do
+      #    # ...
+      #    instance
+      #  end
+      #
+      # @example Providing declared attribute in the Unit via setter
+      #  self.action = :created
+      #
+      # @return [Array<Symbol>] the list of all declared provides of a Unit.
+      def self.provides(*attributes, &block)
+        declaration_accessor(
+          key:        __method__,
+          attributes: attributes(*attributes, &block)
+        ) do |attribute|
+          provide_setter(attribute)
+        end
+      end
+
+      def self.attributes(*attributes)
+        # exectute block if given and add
+        # the result to the (possibly empty)
+        # list of given attributes
+        attributes.concat(yield) if block_given?
+        attributes
+      end
+
+      # This method is the heart of the #uses and #provides method.
+      # It takes the declaration key and decides based on the given
+      # parameters if the given attributes should get stored or
+      # the stored values returned.
+      def self.declaration_accessor(key:, attributes:)
+
+        # if no attributes were given (storing)
+        # return the already stored list of attributes
+        return declarations(key).to_a if attributes.blank?
+
+        # loop over all given attributes and
+        # add them to the list of already stored
+        # attributes for the given declaration key
+        attributes.each do |attribute|
+          next if !declarations(key).add?(attribute)
+
+          # yield callback if given to create
+          # getter or setter or whatever
+          yield(attribute) if block_given?
+        end
+      end
+
+      # This method creates the convenience method
+      # getter for the given attribute.
+      def self.use_getter(attribute)
+        define_method(attribute) do
+          instance_variable_cached(attribute) do
+            state.use(attribute)
+          end
+        end
+      end
+
+      # This method creates the convenience method
+      # setter for the given attribute.
+      def self.provide_setter(attribute)
+        define_method("#{attribute}=") do |value|
+          state.provide(attribute, value)
+        end
+      end
+
+      # This method is the attribute store for the given declaration key.
+      def self.declarations(key)
+        instance_variable_cached("#{key}_declarations") do
+          declarations_initial(key)
+        end
+      end
+
+      # This method initializes the attribute store for the given declaration key.
+      # It checks if a parent class already has an existing store and duplicates it
+      # for independent usage. Otherwise it creates a new one.
+      def self.declarations_initial(key)
+        return Set.new([]) if !superclass.respond_to?(:declarations)
+        superclass.send(:declarations, key).dup
+      end
+
+      # This method creates an accessor to a cached instance variable for the given scope.
+      # It will create a new variable with the result of the given block as an initial value.
+      # On later calls it will return the already initialized, cached variable state.
+      # The variable will be created by default as a class variable. If a instance scope is
+      # passed it will create an instance variable instead.
+      def self.instance_variable_cached(key, scope: self)
+        cache = "@#{key}"
+        value = scope.instance_variable_get(cache)
+        return value if value
+        value = yield
+        scope.instance_variable_set(cache, value)
+      end
+
+      # This method is an instance wrapper around the class method .instance_variable_cached.
+      # It will behave the same but passed the instance scope to create an
+      # cached instance variable.
+      def instance_variable_cached(key, &block)
+        self.class.instance_variable_cached(key, scope: self, &block)
+      end
+
+      # This method is an convenience wrapper to create an instance
+      # and then directly processing it.
+      def self.process(*args)
+        new(*args).process
+      end
+
+      def initialize(state)
+        @state = state
+      end
+
+      def process
+        raise "Missing implementation of '#{__method__}' method for '#{self.class.name}'"
+      end
+    end
+  end
+end

lib/sequencer/unit/common/attribute_mapper.rb

@@ -0,0 +1,28 @@
+class Sequencer
+  class Unit
+    module Common
+      class AttributeMapper < Sequencer::Unit::Base
+
+        def self.map
+          raise "Missing implementation of '#{__method__}' method for '#{name}'"
+        end
+
+        def self.uses
+          map.keys
+        end
+
+        def self.provides
+          map.values
+        end
+
+        def process
+          self.class.map.each do |original, renamed|
+            state.provide(renamed) do
+              state.use(original)
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/exchange/connection.rb

@@ -0,0 +1,23 @@
+class Sequencer
+  class Unit
+    module Exchange
+      class Connection < Sequencer::Unit::Base
+
+        uses :ews_config
+        provides :ews_connection
+
+        def process
+          # check if EWS connection is already given (sub sequence)
+          return if state.provided?(:ews_connection)
+
+          state.provide(:ews_connection) do
+            config   = ews_config
+            config ||= ::Import::Exchange.config
+
+            Viewpoint::EWSClient.new(config[:endpoint], config[:user], config[:password])
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/exchange/folders/by_ids.rb

@@ -0,0 +1,24 @@
+require 'sequencer/mixin/exchange/folder'
+
+class Sequencer
+  class Unit
+    module Exchange
+      module Folders
+        class ByIds < Sequencer::Unit::Base
+          include ::Sequencer::Mixin::Exchange::Folder
+
+          uses :ews_folder_ids
+          provides :ews_folders
+
+          def process
+            state.provide(:ews_folders) do
+              ews_folder_ids.collect do |folder_id|
+                ews_folder.find(folder_id)
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/exchange/folders/id_path_map.rb

@@ -0,0 +1,31 @@
+require 'sequencer/mixin/exchange/folder'
+
+class Sequencer
+  class Unit
+    module Exchange
+      module Folders
+        class IdPathMap < Sequencer::Unit::Base
+          include ::Sequencer::Mixin::Exchange::Folder
+
+          provides :ews_folder_id_path_map
+
+          def process
+            state.provide(:ews_folder_id_path_map) do
+
+              ids   = state.optional(:ews_folder_ids)
+              ids ||= []
+
+              ews_folder.id_folder_map.collect do |id, folder|
+                next if ids.present? && ids.exclude?(id)
+                next if folder.total_count.blank?
+                next if folder.total_count.zero?
+
+                [id, ews_folder.display_path(folder)]
+              end.compact.to_h
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/import_job/payload/to_state.rb

@@ -0,0 +1,25 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module ImportJob
+          module Payload
+            class ToState < Sequencer::Unit::Base
+
+              uses :import_job
+
+              def process
+                provides = self.class.provides
+                raise "Can't find any provides for #{self.class.name}" if provides.blank?
+
+                provides.each do |attribute|
+                  state.provide(attribute, import_job.payload[attribute])
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/import_job/statistics/store.rb

@@ -0,0 +1,35 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module ImportJob
+          module Statistics
+            class Store < Sequencer::Unit::Base
+
+              uses :import_job, :statistics
+
+              def process
+                # update the attribute temporarily so we can update it when:
+                # - the last update is more than 10 seconds in the past
+                # - all instances are processed but the last statistics entry is not written here.
+                #    This will be done in the calling Unit of the executed sub sequence
+                import_job.result = statistics
+
+                return if !store?
+                import_job.save!
+              end
+
+              private
+
+              def store?
+                return true if import_job.updated_at.blank?
+                # update every 10 seconds to reduce DB load
+                import_job.updated_at > Time.zone.now + 10.seconds
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/import_job/statistics/update.rb

@@ -0,0 +1,50 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module ImportJob
+          module Statistics
+            class Update < Sequencer::Unit::Base
+
+              uses :statistics_diff
+              provides :statistics
+
+              def process
+                state.provide(:statistics) do
+                  sum_deeply(
+                    existing:  statistics,
+                    additions: statistics_diff
+                  )
+                end
+
+                # reset diff to avoid situations where old diff gets added multiple times
+                state.unset(:statistics_diff)
+              end
+
+              private
+
+              def statistics
+                import_job = state.optional(:import_job)
+                return {} if import_job.nil?
+                import_job.result
+              end
+
+              def sum_deeply(existing:, additions:)
+                existing.merge(additions) do |_key, oldval, newval|
+                  if oldval.is_a?(Hash) || newval.is_a?(Hash)
+                    sum_deeply(
+                      existing:  oldval,
+                      additions: newval
+                    )
+                  else
+                    oldval + newval
+                  end
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/import_job/sub_sequence/general.rb

@@ -0,0 +1,66 @@
+require 'sequencer/mixin/sub_sequence'
+
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module ImportJob
+          module SubSequence
+            class General < Sequencer::Unit::Base
+              include ::Sequencer::Mixin::SubSequence
+
+              uses :import_job
+
+              def process
+                resource_sequence
+              end
+
+              private
+
+              # INFO: Cache results via `@sequence ||= ...`, if needed
+              def sequence
+                raise "Missing implementation of '#{__method__}' method for '#{self.class.name}'"
+              end
+
+              # INFO: Cache results via `@resources ||= ...`, if needed
+              def resources
+                raise "Missing implementation of '#{__method__}' method for '#{self.class.name}'"
+              end
+
+              def default_parameters
+                {
+                  dry_run:    import_job.dry_run,
+                  import_job: import_job,
+                }
+              end
+
+              def resource_sequence
+                return if resources.blank?
+
+                defaults = default_parameters
+
+                resources.each do |resource|
+
+                  arguments = {
+                    parameters: defaults.merge(resource: resource)
+                  }
+
+                  yield resource, arguments if block_given?
+
+                  arguments[:parameters][:resource] = arguments[:parameters][:resource].with_indifferent_access
+
+                  result = sub_sequence(sequence, arguments)
+
+                  processed(result)
+                end
+              end
+
+              def processed(_result)
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/import_job/sub_sequence/resource.rb

@@ -0,0 +1,15 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module ImportJob
+          module SubSequence
+            class Resource < Sequencer::Unit::Import::Common::ImportJob::SubSequence::General
+              uses :resource
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/mapping/flat_keys.rb

@@ -0,0 +1,35 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Mapping
+          class FlatKeys < Sequencer::Unit::Base
+            include ::Sequencer::Unit::Import::Common::Mapping::Mixin::ProvideMapped
+
+            uses :resource
+            provides :mapped
+
+            def process
+              provide_mapped do
+                mapped
+              end
+            end
+
+            private
+
+            def mapped
+              resource_with_indifferent_access = resource.with_indifferent_access
+              mapping.symbolize_keys.collect do |source, local|
+                [local, resource_with_indifferent_access[source]]
+              end.to_h.with_indifferent_access
+            end
+
+            def mapping
+              raise "Missing implementation of '#{__method__}' method for '#{self.class.name}'"
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/mapping/mixin/provide_mapped.rb

@@ -0,0 +1,30 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Mapping
+          module Mixin
+            module ProvideMapped
+
+              def self.included(base)
+                base.provides :mapped
+              end
+
+              private
+
+              def existing_mapped
+                @existing_mapped ||= state.optional(:mapped) || ActiveSupport::HashWithIndifferentAccess.new
+              end
+
+              def provide_mapped
+                state.provide(:mapped) do
+                  existing_mapped.merge(yield)
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/associations/assign.rb

@@ -0,0 +1,59 @@
+require 'sequencer/unit/import/common/model/mixin/handle_failure'
+
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Associations
+            class Assign < Sequencer::Unit::Base
+              include ::Sequencer::Unit::Import::Common::Model::Mixin::HandleFailure
+
+              uses :instance, :associations, :instance_action, :dry_run
+              provides :instance_action
+
+              def process
+                return if dry_run
+                return if instance.blank?
+
+                instance.assign_attributes(associations)
+
+                # execute associations check only if needed for performance reasons
+                return if instance_action != :unchanged
+                return if !changed?
+                state.provide(:instance_action, :changed)
+              rescue => e
+                handle_failure(e)
+              end
+
+              private
+
+              def changed?
+                logger.debug("Changed instance associations: #{changes.inspect}")
+                changes.present?
+              end
+
+              def changes
+                @changes ||= begin
+                  return {} if associations.blank?
+                  associations.collect do |association, value|
+                    before = compareable(instance.send(association))
+                    after  = compareable(value)
+                    next if before == after
+                    [association, [before, after]]
+                  end.compact.to_h.with_indifferent_access
+                end
+              end
+
+              def compareable(value)
+                return nil if value.blank?
+                return value.sort if value.respond_to(:sort)
+                value
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/associations/extract.rb

@@ -0,0 +1,65 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Associations
+            class Extract < Sequencer::Unit::Base
+
+              uses :model_class, :mapped
+              provides :associations
+
+              def process
+                state.provide(:associations) do
+                  associations.collect do |association|
+                    next if !mapped.key?(association)
+
+                    # remove from the mapped values if it's an association
+                    value = mapped.delete(association)
+
+                    # skip if we don't track them
+                    next if tracked_associations.exclude?(association)
+
+                    [association, value]
+                  end.compact.to_h
+                end
+              end
+
+              private
+
+              def associations
+                @associations ||= begin
+                  associations = []
+                  # loop over all reflections
+                  model_class.reflect_on_all_associations.each do |reflection|
+
+                    # refection name is something like groups or organization (singular/plural)
+                    associations.push(reflection.name)
+
+                    # key is something like group_id or organization_id (singular)
+                    key = reflection.klass.name.foreign_key
+
+                    # add trailing 's' to get pluralized key
+                    reflection_name = reflection.name.to_s
+                    if reflection_name.singularize == reflection_name
+                      key = "#{key}s"
+                    end
+
+                    # store _id/_ids name
+                    associations.push(key.to_sym)
+                  end
+                  associations
+                end
+              end
+
+              def tracked_associations
+                # track all associations by default
+                associations
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/attributes/add_by_ids.rb

@@ -0,0 +1,24 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Attributes
+            class AddByIds < Sequencer::Unit::Base
+              include ::Sequencer::Unit::Import::Common::Mapping::Mixin::ProvideMapped
+
+              def process
+                provide_mapped do
+                  {
+                    created_by_id: 1,
+                    updated_by_id: 1,
+                  }
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/attributes/check_mandatory.rb

@@ -0,0 +1,32 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Attributes
+            class CheckMandatory < Sequencer::Unit::Base
+              prepend ::Sequencer::Unit::Import::Common::Model::Mixin::SkipOnProvidedInstanceAction
+
+              uses :mapped
+              provides :instance_action
+
+              def process
+                mandatory.each do |mapped_attribute|
+                  next if mapped[mapped_attribute].present?
+                  state.provide(:instance_action, :skipped)
+                  break
+                end
+              end
+
+              private
+
+              def mandatory
+                raise "Missing implementation of '#{__method__}' method for '#{self.class.name}'"
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/attributes/remote_id.rb

@@ -0,0 +1,32 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Attributes
+            class RemoteId < Sequencer::Unit::Base
+              include ::Sequencer::Unit::Import::Common::Model::Mixin::HandleFailure
+
+              uses :resource
+              provides :remote_id
+
+              def process
+                state.provide(:remote_id) do
+                  resource.fetch(attribute)
+                end
+              rescue KeyError => e
+                handle_failure(e)
+              end
+
+              private
+
+              def attribute
+                :id
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/create.rb

@@ -0,0 +1,25 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          class Create < Sequencer::Unit::Base
+            include ::Sequencer::Unit::Import::Common::Model::Mixin::HandleFailure
+            prepend ::Sequencer::Unit::Import::Common::Model::Mixin::SkipOnProvidedInstanceAction
+
+            uses :mapped, :model_class
+            provides :instance, :instance_action
+
+            def process
+              instance = model_class.new(mapped)
+              state.provide(:instance, instance)
+              state.provide(:instance_action, :created)
+            rescue => e
+              handle_failure(e)
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/external_sync/create.rb

@@ -0,0 +1,29 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module ExternalSync
+            class Create < Sequencer::Unit::Base
+              prepend ::Sequencer::Unit::Import::Common::Model::Mixin::SkipOnSkippedInstance
+
+              uses :instance, :instance_action, :remote_id, :dry_run, :external_sync_source, :model_class
+
+              def process
+                return if dry_run
+                return if instance_action != :created
+
+                ::ExternalSync.create(
+                  source:    external_sync_source,
+                  source_id: remote_id,
+                  object:    model_class.name,
+                  o_id:      instance.id
+                )
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/external_sync/local.rb

@@ -0,0 +1,63 @@
+require 'sequencer/unit/import/common/model/mixin/handle_failure'
+
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module ExternalSync
+            class Local < Sequencer::Unit::Base
+              include ::Sequencer::Unit::Import::Common::Model::Mixin::HandleFailure
+              prepend ::Sequencer::Unit::Import::Common::Model::Mixin::SkipOnSkippedInstance
+
+              uses :mapped, :remote_id, :model_class, :external_sync_source, :instance_action
+              provides :instance
+
+              def process
+                return if state.provided?(:instance)
+
+                return if value.blank?
+                return if instance.blank?
+
+                create_external_sync
+
+                state.provide(:instance, instance)
+              end
+
+              private
+
+              def attribute
+                raise "Missing implementation of '#{__method__}' method for '#{self.class.name}'"
+              end
+
+              def value
+                mapped[attribute]
+              end
+
+              def instance
+                @instance ||= begin
+                  model_class.where(attribute => value).find do |local|
+                    !ExternalSync.exists?(
+                      source: external_sync_source,
+                      object: model_class.name,
+                      o_id:   local.id
+                    )
+                  end
+                end
+              end
+
+              def create_external_sync
+                ExternalSync.create(
+                  source:    external_sync_source,
+                  source_id: remote_id,
+                  object:    import_class.name,
+                  o_id:      instance.id
+                )
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/external_sync/lookup.rb

@@ -0,0 +1,34 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module ExternalSync
+            class Lookup < Sequencer::Unit::Base
+              include ::Sequencer::Unit::Import::Common::Model::Mixin::HandleFailure
+              prepend ::Sequencer::Unit::Import::Common::Model::Mixin::SkipOnSkippedInstance
+
+              uses :remote_id, :model_class, :external_sync_source
+              provides :instance
+
+              def process
+                synced_instance = ::ExternalSync.find_by(
+                  source:    external_sync_source,
+                  source_id: remote_id,
+                  object:    model_class.name,
+                )
+                return if !synced_instance
+
+                state.provide(:instance) do
+                  model_class.find(synced_instance.o_id)
+                end
+              rescue => e
+                handle_failure(e)
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/http_log.rb

@@ -0,0 +1,50 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          class HttpLog < Sequencer::Unit::Base
+
+            uses :dry_run, :instance_action, :remote_id, :mapped, :exception
+
+            def process
+              return if dry_run
+              ::HttpLog.create(
+                direction: 'out',
+                facility:  facility,
+                method:    'tcp',
+                url:       "#{instance_action} -> #{remote_id}",
+                status:    status,
+                ip:        nil,
+                request:   {
+                  content: mapped,
+                },
+                response: {
+                  message: response
+                },
+                created_by_id: 1,
+                updated_by_id: 1,
+              )
+            end
+
+            private
+
+            def status
+              @status ||= begin
+                instance_action == :failed ? :failed : :success
+              end
+            end
+
+            def response
+              exception ? exception.message : status
+            end
+
+            def facility
+              raise "Missing implementation of '#{__method__}' method for '#{self.class.name}'"
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/mixin/handle_failure.rb

@@ -0,0 +1,24 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Mixin
+            module HandleFailure
+
+              def self.included(base)
+                base.provides :exception, :instance_action
+              end
+
+              def handle_failure(e)
+                logger.error(e)
+                state.provide(:exception, e)
+                state.provide(:instance_action, :failed)
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/mixin/skip_on_provided_instance_action.rb

@@ -0,0 +1,22 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Mixin
+            module SkipOnProvidedInstanceAction
+
+              def process
+                if state.provided?(:instance_action)
+                  logger.debug("Skipping. Attribute 'instance_action' already provided.")
+                else
+                  super
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/mixin/skip_on_skipped_instance.rb

@@ -0,0 +1,26 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Mixin
+            module SkipOnSkippedInstance
+
+              def self.prepended(base)
+                base.uses :instance_action
+              end
+
+              def process
+                if instance_action == :skipped
+                  logger.debug("Skipping. Attribute 'instance_action' is set to :skipped.")
+                else
+                  super
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/save.rb

@@ -0,0 +1,25 @@
+require 'sequencer/unit/import/common/model/mixin/handle_failure'
+
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          class Save < Sequencer::Unit::Base
+            include ::Sequencer::Unit::Import::Common::Model::Mixin::HandleFailure
+
+            uses :instance, :dry_run
+
+            def process
+              return if dry_run
+              return if instance.blank?
+              instance.save!
+            rescue => e
+              handle_failure(e)
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/skip/blank/base.rb

@@ -0,0 +1,43 @@
+require 'sequencer/unit/mixin/dynamic_attribute'
+
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Skip
+            module Blank
+              class Base < Sequencer::Unit::Base
+                prepend ::Sequencer::Unit::Import::Common::Model::Mixin::SkipOnProvidedInstanceAction
+                include ::Sequencer::Unit::Mixin::DynamicAttribute
+
+                provides :instance_action
+
+                def process
+                  return if !skip?
+                  logger.debug("Skipping. Blank #{attribute} found: #{attribute_value.inspect}")
+                  state.provide(:instance_action, :skipped)
+                end
+
+                private
+
+                def ignore
+                  [:id]
+                end
+
+                def skip?
+                  return true if attribute_value.blank?
+                  relevant_blank?
+                end
+
+                def relevant_blank?
+                  !attribute_value.except(*ignore).values.any?(&:present?)
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/skip/blank/mapped.rb

@@ -0,0 +1,17 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Skip
+            module Blank
+              class Mapped < Sequencer::Unit::Import::Common::Model::Skip::Blank::Base
+                uses :mapped
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/skip/blank/resource.rb

@@ -0,0 +1,17 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Skip
+            module Blank
+              class Resource < Sequencer::Unit::Import::Common::Model::Skip::Blank::Base
+                uses :resource
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/skip/missing_mandatory/base.rb

@@ -0,0 +1,46 @@
+require 'sequencer/unit/mixin/dynamic_attribute'
+
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Skip
+            module MissingMandatory
+              class Base < Sequencer::Unit::Base
+                prepend ::Sequencer::Unit::Import::Common::Model::Mixin::SkipOnProvidedInstanceAction
+                include ::Sequencer::Unit::Mixin::DynamicAttribute
+
+                provides :instance_action
+
+                def process
+                  return if !skip?
+                  logger.debug("Skipping. Missing mandatory attributes for #{attribute}: #{attribute_value.inspect}")
+                  state.provide(:instance_action, :skipped)
+                end
+
+                private
+
+                def mandatory
+                  raise "Missing implementation of '#{__method__}' method for '#{self.class.name}'"
+                end
+
+                def skip?
+                  return true if attribute_value.blank?
+                  mandatory_missing?
+                end
+
+                def mandatory_missing?
+                  values = attribute_value.fetch_values(*mandatory)
+                  !values.any?(&:present?)
+                rescue KeyError => e
+                  false
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/skip/missing_mandatory/resource.rb

@@ -0,0 +1,17 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Skip
+            module MissingMandatory
+              class Resource < Sequencer::Unit::Import::Common::Model::Skip::MissingMandatory::Base
+                uses :resource
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/statistics/diff.rb

@@ -0,0 +1,21 @@
+require 'sequencer/unit/import/common/model/statistics/mixin/diff'
+
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Statistics
+            class Diff < Sequencer::Unit::Base
+              include ::Sequencer::Unit::Import::Common::Model::Statistics::Mixin::Diff
+
+              def process
+                state.provide(:statistics_diff, diff)
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/statistics/mixin/diff.rb

@@ -0,0 +1,47 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          module Statistics
+            module Mixin
+              module Diff
+
+                def self.included(base)
+                  base.uses :instance_action
+                  base.provides :statistics_diff
+                end
+
+                private
+
+                def actions
+                  %i(skipped created updated unchanged failed deactivated)
+                end
+
+                def diff
+                  raise "Unknown action '#{instance_action}'" if !possible?
+                  defaults.merge(
+                    instance_action => 1,
+                    sum: 1,
+                  )
+                end
+
+                def possible?
+                  possible_actions.include?(instance_action)
+                end
+
+                def defaults
+                  possible_actions.collect { |key| [key, 0] }.to_h
+                end
+
+                def possible_actions
+                  @possible_actions ||= actions
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/model/update.rb

@@ -0,0 +1,56 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module Model
+          class Update < Sequencer::Unit::Base
+            include ::Sequencer::Unit::Import::Common::Model::Mixin::HandleFailure
+            prepend ::Sequencer::Unit::Import::Common::Model::Mixin::SkipOnProvidedInstanceAction
+
+            uses :instance, :mapped
+            provides :instance_action
+
+            def process
+              # check if no instance is given - so we can't update it
+              return if !instance
+
+              # lock the current instance for write access
+              instance.with_lock do
+                # delete since we have an update and
+                # the record is already created
+                mapped.delete(:created_by_id)
+
+                # assign regular attributes
+                instance.assign_attributes(mapped)
+
+                action = changed? ? :updated : :unchanged
+                state.provide(:instance_action, action)
+              end
+            rescue => e
+              handle_failure(e)
+            end
+
+            private
+
+            def changed?
+              logger.debug("Changed instance attributes: #{changes.inspect}")
+              changes.present?
+            end
+
+            def changes
+              @changes ||= begin
+                if instance.changed?
+                  # dry run
+                  instance.changes
+                else
+                  # live run
+                  instance.previous_changes
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/user/attributes/downcase.rb

@@ -0,0 +1,24 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module User
+          module Attributes
+            class Downcase < Sequencer::Unit::Base
+              prepend ::Sequencer::Unit::Import::Common::Model::Mixin::SkipOnSkippedInstance
+
+              uses :mapped
+
+              def process
+                %i(login email).each do |attribute|
+                  next if mapped[attribute].blank?
+                  mapped[attribute].downcase!
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/common/user/email/check_validity.rb

@@ -0,0 +1,45 @@
+class Sequencer
+  class Unit
+    module Import
+      module Common
+        module User
+          module Email
+            class CheckValidity < Sequencer::Unit::Base
+              prepend ::Sequencer::Unit::Import::Common::Model::Mixin::SkipOnSkippedInstance
+
+              uses :mapped
+
+              def process
+                return if mapped[:email].blank?
+
+                # TODO: This should be done totally somewhere central
+                mapped[:email] = ensure_valid_email(mapped[:email])
+              end
+
+              private
+
+              def ensure_valid_email(source)
+                # TODO: should get unified with User#check_email
+                email = extract_email(source)
+                return if !email
+                email.downcase
+              end
+
+              def extract_email(source)
+                # Support format like "Bob Smith (bob@example.com)"
+                if source =~ /\((.+@.+)\)/
+                  source = $1
+                end
+
+                Mail::Address.new(source).address
+              rescue
+                return source if source !~ /<\s*([^>]+)/
+                $1.strip
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/exchange/attribute_examples.rb

@@ -0,0 +1,32 @@
+require 'sequencer/mixin/exchange/folder'
+
+class Sequencer
+  class Unit
+    module Import
+      module Exchange
+        class AttributeExamples < Sequencer::Unit::Base
+          include ::Sequencer::Mixin::Exchange::Folder
+
+          uses :ews_folder_ids
+          provides :ews_attributes_examples
+
+          def process
+            state.provide(:ews_attributes_examples) do
+              ::Import::Helper::AttributesExamples.new do |extractor|
+
+                ews_folder_ids.collect do |folder_id|
+
+                  ews_folder.find(folder_id).items.each do |resource|
+                    attributes = ::Import::Exchange::ItemAttributes.extract(resource)
+                    extractor.extract(attributes)
+                    break if extractor.enough
+                  end
+                end
+              end.examples
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/exchange/attribute_mapper/attribute_examples.rb

@@ -0,0 +1,18 @@
+class Sequencer
+  class Unit
+    module Import
+      module Exchange
+        module AttributeMapper
+          class AttributeExamples < Sequencer::Unit::Common::AttributeMapper
+
+            def self.map
+              {
+                ews_attributes_examples: :attributes,
+              }
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/exchange/attribute_mapper/available_folders.rb

@@ -0,0 +1,18 @@
+class Sequencer
+  class Unit
+    module Import
+      module Exchange
+        module AttributeMapper
+          class AvailableFolders < Sequencer::Unit::Common::AttributeMapper
+
+            def self.map
+              {
+                ews_folder_id_path_map: :folders,
+              }
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/exchange/folder_contact/http_log.rb

@@ -0,0 +1,18 @@
+class Sequencer
+  class Unit
+    module Import
+      module Exchange
+        module FolderContact
+          class HttpLog < Import::Common::Model::HttpLog
+
+            private
+
+            def facility
+              'EWS'
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/exchange/folder_contact/mapping.rb

@@ -0,0 +1,27 @@
+class Sequencer
+  class Unit
+    module Import
+      module Exchange
+        module FolderContact
+          class Mapping < Sequencer::Unit::Import::Common::Mapping::FlatKeys
+
+            uses :import_job
+
+            private
+
+            def mapping
+              from_import_job || ::Import::Exchange.config[:attributes]
+            end
+
+            def from_import_job
+              return if !state.provided?(:import_job)
+              payload = import_job.payload
+              return if payload.blank?
+              payload[:ews_attributes]
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/exchange/folder_contact/remote_id.rb

@@ -0,0 +1,17 @@
+class Sequencer
+  class Unit
+    module Import
+      module Exchange
+        module FolderContact
+          class RemoteId < Sequencer::Unit::Import::Common::Model::Attributes::RemoteId
+            private
+
+            def attribute
+              :item_id
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/exchange/folder_contact/static_attributes.rb

@@ -0,0 +1,19 @@
+class Sequencer
+  class Unit
+    module Import
+      module Exchange
+        module FolderContact
+          class StaticAttributes < Sequencer::Unit::Base
+
+            provides :model_class, :external_sync_source
+
+            def process
+              state.provide(:model_class, ::User)
+              state.provide(:external_sync_source, 'EWS::FolderContact')
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/exchange/folder_contact/statistics/diff.rb

@@ -0,0 +1,39 @@
+class Sequencer
+  class Unit
+    module Import
+      module Exchange
+        module FolderContact
+          module Statistics
+            class Diff < Sequencer::Unit::Base
+              include ::Sequencer::Unit::Import::Common::Model::Statistics::Mixin::Diff
+
+              uses :ews_folder_name
+
+              def process
+                state.provide(:statistics_diff) do
+                  # remove :sum since it's already set via
+                  # the exchange item attribte
+                  result = diff.except(:sum)
+
+                  # build structure for a general diff
+                  # and a folder specific sub structure
+                  result.merge(
+                    folders: {
+                      ews_folder_name => result
+                    }
+                  )
+                end
+              end
+
+              private
+
+              def actions
+                %i(created updated unchanged skipped failed)
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/exchange/folder_contacts/dry_run_payload.rb

@@ -0,0 +1,14 @@
+class Sequencer
+  class Unit
+    module Import
+      module Exchange
+        module FolderContacts
+          class DryRunPayload < Sequencer::Unit::Import::Common::ImportJob::Payload::ToState
+
+            provides :ews_config, :ews_folder_ids
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/exchange/folder_contacts/folder_ids.rb

@@ -0,0 +1,27 @@
+require 'sequencer/mixin/exchange/folder'
+
+class Sequencer
+  class Unit
+    module Import
+      module Exchange
+        module FolderContacts
+          class FolderIds < Sequencer::Unit::Base
+            include ::Sequencer::Mixin::Exchange::Folder
+
+            provides :ews_folder_ids
+
+            def process
+              # check if ids are already processed
+              return if state.provided?(:ews_folder_ids)
+
+              state.provide(:ews_folder_ids) do
+                config = ::Import::Exchange.config
+                config[:folders]
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/exchange/folder_contacts/sub_sequence.rb

@@ -0,0 +1,37 @@
+require 'sequencer/mixin/exchange/folder'
+require 'sequencer/mixin/import_job/resource_loop'
+
+class Sequencer
+  class Unit
+    module Import
+      module Exchange
+        module FolderContacts
+          class SubSequence < Sequencer::Unit::Base
+            include ::Sequencer::Mixin::Exchange::Folder
+            include ::Sequencer::Mixin::ImportJob::ResourceLoop
+
+            uses :ews_folder_ids, :import_job
+
+            def process
+
+              ews_folder_ids.each do |folder_id|
+                folder       = ews_folder.find(folder_id)
+                display_path = ews_folder.display_path(folder)
+
+                resource_sequence('Import::Exchange::FolderContact', folder.items) do |item|
+
+                  logger.debug("Extracting attributes from Exchange item: #{item.get_all_properties!.inspect}")
+
+                  {
+                    resource:        ::Import::Exchange::ItemAttributes.extract(item),
+                    ews_folder_name: display_path,
+                  }
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/import/exchange/folder_contacts/sum.rb

@@ -0,0 +1,48 @@
+require 'sequencer/mixin/exchange/folder'
+
+class Sequencer
+  class Unit
+    module Import
+      module Exchange
+        module FolderContacts
+          class Sum < Sequencer::Unit::Base
+            include ::Sequencer::Mixin::Exchange::Folder
+
+            uses :ews_folder_ids
+            provides :statistics_diff
+
+            def process
+              state.provide(:statistics_diff, diff)
+            end
+
+            private
+
+            def diff
+              result = {
+                sum: 0,
+              }
+              folder_sum_map.each do |display_path, sum|
+
+                result[display_path] = {
+                  sum: sum
+                }
+
+                result[:sum] += sum
+              end
+              result
+            end
+
+            def folder_sum_map
+              ews_folder_ids.collect do |folder_id|
+                folder       = ews_folder.find(folder_id)
+                display_path = ews_folder.display_path(folder)
+
+                [display_path, folder.total_count]
+              end.to_h
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/mixin/dynamic_attribute.rb

@@ -0,0 +1,35 @@
+# rubocop:disable Lint/NestedMethodDefinition
+class Sequencer
+  class Unit
+    module Mixin
+      module DynamicAttribute
+
+        def self.included(base)
+
+          class << base
+
+            def inherited(base)
+              base.extend(Forwardable)
+              base.instance_delegate [:attribute] => base
+            end
+
+            def attribute
+              @attribute ||= begin
+                if uses.size != 1
+                  raise "DynamicAttribute classes can use exactly one attribute. Found #{uses.size}."
+                end
+                uses.first
+              end
+            end
+          end
+        end
+
+        private
+
+        def attribute_value
+          @attribute_value ||= state.use(attribute)
+        end
+      end
+    end
+  end
+end

lib/sequencer/units.rb

@@ -0,0 +1,70 @@
+require 'mixin/instance_wrapper'
+
+class Sequencer
+  class Units
+    include ::Enumerable
+    include ::Mixin::InstanceWrapper
+
+    wrap :@units
+
+    # Initializes a new Sequencer::Units instance with the given Units Array.
+    #
+    # @param [*Array<String>] *units a list of Units with or without the Sequencer::Unit prefix.
+    #
+    # @example
+    #  Sequencer::Units.new('Example::Unit', 'Sequencer::Unit::Second::Unit')
+    def initialize(*units)
+      @units = units
+    end
+
+    # Required #each implementation for ::Enumerable functionality. Constantizes
+    # the list of units given when initialized.
+    #
+    # @example
+    #  units.each do |unit|
+    #    unit.process(sequencer)
+    #  end
+    #
+    # @return [nil]
+    def each
+      @units.each do |unit|
+        yield constantize(unit)
+      end
+    end
+
+    # Provides an Array of :uses and :provides declarations for each Unit.
+    #
+    # @example
+    #  units.declarations
+    #  #=> [{uses: [:question], provides: [:answer], ...}]
+    #
+    # @return [Array<Hash{Symbol => Array<Symbol>}>] the declarations of the Units
+    def declarations
+      collect do |unit|
+        {
+          uses:     unit.uses,
+          provides: unit.provides,
+        }
+      end
+    end
+
+    # Enables the access to an Unit class via index.
+    #
+    # @param [Integer] index the index for the requested Unit class.
+    #
+    # @example
+    #  units[1]
+    #  #=> Sequencer::Unit::Example
+    #
+    # @return [Object] the Unit class for the requested index
+    def [](index)
+      constantize(@units[index])
+    end
+
+    private
+
+    def constantize(unit)
+      Sequencer::Unit.constantize(unit)
+    end
+  end
+end

lib/sequencer/units/attribute.rb

@@ -0,0 +1,30 @@
+class Sequencer
+  class Units
+    class Attribute
+
+      attr_accessor :from, :to
+
+      # Checks if the attribute will be provided by one or more Units.
+      #
+      # @example
+      #  attribute.will_be_provided?
+      #  # => true
+      #
+      # @return [Boolean]
+      def will_be_provided?
+        !from.nil?
+      end
+
+      # Checks if the attribute will be used by one or more Units.
+      #
+      # @example
+      #  attribute.will_be_used?
+      #  # => true
+      #
+      # @return [Boolean]
+      def will_be_used?
+        !to.nil?
+      end
+    end
+  end
+end

lib/sequencer/units/attributes.rb

@@ -0,0 +1,87 @@
+require 'mixin/instance_wrapper'
+
+class Sequencer
+  class Units
+    class Attributes
+      include ::Mixin::InstanceWrapper
+
+      wrap :@attributes
+
+      # Initializes the lifespan store for the attributes
+      # of the given Units declarations.
+      #
+      # @param [Array<Hash{Symbol => Array<:Symbol>}>] declarations the list of Unit declarations.
+      #
+      # @example
+      #  declarations = [{uses: [:attribute1, ...], provides: [:result], ...}]
+      #  attributes = Sequencer::Units::Attributes(declarations)
+      #
+      # @return [nil]
+      def initialize(declarations)
+        @declarations = declarations
+
+        initialize_attributes
+        initialize_lifespan
+      end
+
+      # Lists all `provides` declarations of the Units the instance was initialized with.
+      #
+      # @example
+      #  attributes.provided
+      #  # => [:result, ...]
+      #
+      # @return [Array<Symbol>] the list of all `provides` declarations
+      def provided
+        select do |_attribute, instance|
+          instance.will_be_provided?
+        end.keys
+      end
+
+      # Lists all `uses` declarations of the Units the instance was initialized with.
+      #
+      # @example
+      #  attributes.used
+      #  # => [:attribute1, ...]
+      #
+      # @return [Array<Symbol>] the list of all `uses` declarations
+      def used
+        select do |_attribute, instance|
+          instance.will_be_used?
+        end.keys
+      end
+
+      # Checks if the given attribute is known in the list of Unit declarations.
+      #
+      # @example
+      #  attributes.known?(:attribute2)
+      #  # => false
+      #
+      # @return [Boolean]
+      def known?(attribute)
+        key?(attribute)
+      end
+
+      private
+
+      def initialize_attributes
+        @attributes = Hash.new do |hash, key|
+          hash[key] = Sequencer::Units::Attribute.new
+        end
+      end
+
+      def initialize_lifespan
+        @declarations.each_with_index do |unit, index|
+
+          unit[:uses].try(:each) do |attribute|
+            self[attribute].to = index
+          end
+
+          unit[:provides].try(:each) do |attribute|
+            next if self[attribute].will_be_provided?
+            self[attribute].from = index
+          end
+        end
+      end
+    end
+  end
+end

spec/lib/import/base_resource_spec.rb

@@ -1,7 +1,5 @@
 require 'rails_helper'
 
-RSpec::Matchers.define_negated_matcher :not_change, :change
-
 RSpec.describe Import::BaseResource do
 
   it "needs an implementation of the 'import_class' method" do

spec/lib/import/ldap/user_spec.rb

@@ -1,8 +1,6 @@
 require 'rails_helper'
 require 'import/ldap/user'
 
-RSpec::Matchers.define_negated_matcher :not_change, :change
-
 RSpec.describe Import::Ldap::User do
 
   let(:uid) { 'exampleuid' }

spec/lib/import/otrs/state_factory_spec.rb

@@ -1,8 +1,6 @@
 require 'rails_helper'
 require 'lib/import/transaction_factory_examples'
 
-RSpec::Matchers.define_negated_matcher :not_change, :change
-
 RSpec.describe Import::OTRS::StateFactory do
   it_behaves_like 'Import::TransactionFactory'
 

spec/lib/sequencer/unit/common/attribute_mapper_spec.rb

@@ -0,0 +1,42 @@
+require 'rails_helper'
+
+RSpec.describe Sequencer::Unit::Common::AttributeMapper, sequencer: :unit do
+
+  let(:map) {
+    {
+      old_key: :new_key,
+      second:  :new_second,
+    }
+  }
+
+  it 'expects an implementation of the .map method' do
+    expect do
+      described_class.map
+    end.to raise_error(RuntimeError)
+  end
+
+  it 'declares uses from map keys' do
+    expect(described_class).to receive(:map).and_return(map)
+    expect(described_class.uses).to eq(map.keys)
+  end
+
+  it 'declares provides from map values' do
+    expect(described_class).to receive(:map).and_return(map)
+    expect(described_class.provides).to eq(map.values)
+  end
+
+  it 'maps as configured' do
+
+    old = {
+      old_key: :value,
+      second:  :second_value,
+    }
+
+    allow(described_class).to receive(:map).and_return(map)
+    result = process(old)
+
+    expect(result.keys.size).to eq 2
+    expect(result[:new_key]).to eq old[:old_key]
+    expect(result[:new_second]).to eq old[:second]
+  end
+end

spec/lib/sequencer/unit/import/common/mapping/flat_keys_spec.rb

@@ -0,0 +1,38 @@
+require 'rails_helper'
+
+RSpec.describe Sequencer::Unit::Import::Common::Mapping::FlatKeys, sequencer: :unit do
+
+  it 'raises an error if mapping method is not implemented' do
+    expect do
+      process(
+        resource: {
+          remote_attribute: 'value',
+        }
+      )
+    end.to raise_error(RuntimeError, /mapping/)
+  end
+
+  it 'maps flat key structures' do
+
+    parameters = {
+      resource: {
+        remote_attribute: 'value',
+      }
+    }
+
+    mapping = {
+      remote_attribute: :local_attribute
+    }
+
+    provided = process(parameters) do |instance|
+      expect(instance).to receive(:mapping).and_return(mapping)
+    end
+
+    expect(provided).to eq(
+      mapped: {
+        'local_attribute' => 'value',
+      }
+    )
+    expect(provided[:mapped]).to be_a(ActiveSupport::HashWithIndifferentAccess)
+  end
+end

spec/models/scheduler_spec.rb

@@ -1,7 +1,5 @@
 require 'rails_helper'
 
-RSpec::Matchers.define_negated_matcher :not_change, :change
-
 RSpec.describe Scheduler do
 
   before do

spec/support/negated_matchers.rb

@@ -0,0 +1 @@
+RSpec::Matchers.define_negated_matcher :not_change, :change

spec/support/sequencer.rb

@@ -0,0 +1,19 @@
+module SequencerUnit
+
+  def process(parameters, &block)
+    Sequencer::Unit.process(described_class.name, parameters, &block)
+  end
+end
+
+module SequencerSequence
+
+  def process(parameters = {})
+    Sequencer.process(described_class.name,
+                      parameters: parameters)
+  end
+end
+
+RSpec.configure do |config|
+  config.include SequencerUnit, sequencer: :unit
+  config.include SequencerSequence, sequencer: :sequence
+end