# Copyright (C) 2012-2016 Zammad Foundation, http://zammad-foundation.org/

# encoding: utf-8

class Channel::EmailParser
  EMAIL_REGEX = /.+@.+/
  RECIPIENT_FIELDS = %w[to cc delivered-to x-original-to envelope-to].freeze
  SENDER_FIELDS = %w[from reply-to return-path].freeze

=begin

  parser = Channel::EmailParser.new
  mail = parser.parse(msg_as_string)

  mail = {
    from:              'Some Name <some@example.com>',
    from_email:        'some@example.com',
    from_local:        'some',
    from_domain:       'example.com',
    from_display_name: 'Some Name',
    message_id:        'some_message_id@example.com',
    to:                'Some System <system@example.com>',
    cc:                'Somebody <somebody@example.com>',
    subject:           'some message subject',
    body:              'some message body',
    content_type:      'text/html', # text/plain
    date:              Time.zone.now,
    attachments:       [
      {
        data:        'binary of attachment',
        filename:    'file_name_of_attachment.txt',
        preferences: {
          'content-alternative' => true,
          'Mime-Type'           => 'text/plain',
          'Charset:             => 'iso-8859-1',
        },
      },
    ],

    # ignore email header
    x-zammad-ignore: 'false',

    # customer headers
    x-zammad-customer-login:     '',
    x-zammad-customer-email:     '',
    x-zammad-customer-firstname: '',
    x-zammad-customer-lastname:  '',

    # ticket headers (for new tickets)
    x-zammad-ticket-group:    'some_group',
    x-zammad-ticket-state:    'some_state',
    x-zammad-ticket-priority: 'some_priority',
    x-zammad-ticket-owner:    'some_owner_login',

    # ticket headers (for existing tickets)
    x-zammad-ticket-followup-group:    'some_group',
    x-zammad-ticket-followup-state:    'some_state',
    x-zammad-ticket-followup-priority: 'some_priority',
    x-zammad-ticket-followup-owner:    'some_owner_login',

    # article headers
    x-zammad-article-internal: false,
    x-zammad-article-type:     'agent',
    x-zammad-article-sender:   'customer',

    # all other email headers
    some-header: 'some_value',
  }

=end

  def parse(msg)
    mail = Mail.new(msg.utf8_encode(from: charset_from_headers_of(msg)))

    message_attributes = [
      { mail_instance: mail },
      message_header_hash(mail),
      message_body_hash(mail),
      self.class.sender_attributes(mail),
    ]

    message_attributes.reduce({}.with_indifferent_access, &:merge)
  end

=begin

  parser = Channel::EmailParser.new
  ticket, article, user, mail = parser.process(channel, email_raw_string)

returns

  [ticket, article, user, mail]

do not raise an exception - e. g. if used by scheduler

  parser = Channel::EmailParser.new
  ticket, article, user, mail = parser.process(channel, email_raw_string, false)

returns

  [ticket, article, user, mail] || false

=end

  def process(channel, msg, exception = true)

    _process(channel, msg)
  rescue => e
    # store unprocessable email for bug reporting
    path = Rails.root.join('tmp', 'unprocessable_mail')
    FileUtils.mkpath path
    md5 = Digest::MD5.hexdigest(msg)
    filename = "#{path}/#{md5}.eml"
    message = "ERROR: Can't process email, you will find it for bug reporting under #{filename}, please create an issue at https://github.com/zammad/zammad/issues"
    p message # rubocop:disable Rails/Output
    p 'ERROR: ' + e.inspect # rubocop:disable Rails/Output
    Rails.logger.error message
    Rails.logger.error e
    File.open(filename, 'wb') do |file|
      file.write msg
    end
    return false if exception == false
    raise e.inspect + "\n" + e.backtrace.join("\n")
  end

  def _process(channel, msg)

    # parse email
    mail = parse(msg)

    Rails.logger.info "Process email with msgid '#{mail[:message_id]}'"

    # run postmaster pre filter
    UserInfo.current_user_id = 1
    filters = {}
    Setting.where(area: 'Postmaster::PreFilter').order(:name).each do |setting|
      filters[setting.name] = Setting.get(setting.name).constantize
    end
    filters.each do |key, backend|
      Rails.logger.debug { "run postmaster pre filter #{key}: #{backend}" }
      begin
        backend.run(channel, mail)
      rescue => e
        Rails.logger.error "can't run postmaster pre filter #{key}: #{backend}"
        Rails.logger.error e.inspect
        raise e
      end
    end

    # check ignore header
    if mail['x-zammad-ignore'.to_sym] == 'true' || mail['x-zammad-ignore'.to_sym] == true
      Rails.logger.info "ignored email with msgid '#{mail[:message_id]}' from '#{mail[:from]}' because of x-zammad-ignore header"
      return
    end

    # set interface handle
    original_interface_handle = ApplicationHandleInfo.current

    ticket       = nil
    article      = nil
    session_user = nil

    # use transaction
    Transaction.execute(interface_handle: "#{original_interface_handle}.postmaster") do

      # get sender user
      session_user_id = mail['x-zammad-session-user-id'.to_sym]
      if !session_user_id
        raise 'No x-zammad-session-user-id, no sender set!'
      end
      session_user = User.lookup(id: session_user_id)
      if !session_user
        raise "No user found for x-zammad-session-user-id: #{session_user_id}!"
      end

      # set current user
      UserInfo.current_user_id = session_user.id

      # get ticket# based on email headers
      if mail['x-zammad-ticket-id'.to_sym]
        ticket = Ticket.find_by(id: mail['x-zammad-ticket-id'.to_sym])
      end
      if mail['x-zammad-ticket-number'.to_sym]
        ticket = Ticket.find_by(number: mail['x-zammad-ticket-number'.to_sym])
      end

      # set ticket state to open if not new
      if ticket
        set_attributes_by_x_headers(ticket, 'ticket', mail, 'followup')

        # save changes set by x-zammad-ticket-followup-* headers
        ticket.save! if ticket.has_changes_to_save?

        state      = Ticket::State.find(ticket.state_id)
        state_type = Ticket::StateType.find(state.state_type_id)

        # set ticket to open again or keep create state
        if !mail['x-zammad-ticket-followup-state'.to_sym] && !mail['x-zammad-ticket-followup-state_id'.to_sym]
          new_state = Ticket::State.find_by(default_create: true)
          if ticket.state_id != new_state.id && !mail['x-zammad-out-of-office'.to_sym]
            ticket.state = Ticket::State.find_by(default_follow_up: true)
            ticket.save!
          end
        end
      end

      # create new ticket
      if !ticket

        preferences = {}
        if channel[:id]
          preferences = {
            channel_id: channel[:id]
          }
        end

        # get default group where ticket is created
        group = nil
        if channel[:group_id]
          group = Group.lookup(id: channel[:group_id])
        end
        if group.blank? || group.active == false
          group = Group.where(active: true).order('id ASC').first
        end
        if group.blank?
          group = Group.first
        end
        title = mail[:subject]
        if title.blank?
          title = '-'
        end
        ticket = Ticket.new(
          group_id: group.id,
          title: title,
          preferences: preferences,
        )
        set_attributes_by_x_headers(ticket, 'ticket', mail)

        # create ticket
        ticket.save!

      end

      # apply tags to ticket
      if mail['x-zammad-ticket-tags'.to_sym].present?
        mail['x-zammad-ticket-tags'.to_sym].each do |tag|
          ticket.tag_add(tag)
        end
      end

      # set attributes
      ticket.with_lock do
        article = Ticket::Article.new(
          ticket_id: ticket.id,
          type_id: Ticket::Article::Type.find_by(name: 'email').id,
          sender_id: Ticket::Article::Sender.find_by(name: 'Customer').id,
          content_type: mail[:content_type],
          body: mail[:body],
          from: mail[:from],
          reply_to: mail[:"reply-to"],
          to: mail[:to],
          cc: mail[:cc],
          subject: mail[:subject],
          message_id: mail[:message_id],
          internal: false,
        )

        # x-headers lookup
        set_attributes_by_x_headers(article, 'article', mail)

        # create article
        article.save!

        # store mail plain
        article.save_as_raw(msg)

        # store attachments
        mail[:attachments]&.each do |attachment|
          filename = attachment[:filename].force_encoding('utf-8')
          if !filename.force_encoding('UTF-8').valid_encoding?
            filename = filename.utf8_encode(fallback: :read_as_sanitized_binary)
          end
          Store.add(
            object: 'Ticket::Article',
            o_id: article.id,
            data: attachment[:data],
            filename: filename,
            preferences: attachment[:preferences]
          )
        end
      end
    end

    ticket.reload
    article.reload
    session_user.reload

    # run postmaster post filter
    filters = {}
    Setting.where(area: 'Postmaster::PostFilter').order(:name).each do |setting|
      filters[setting.name] = Kernel.const_get(Setting.get(setting.name))
    end
    filters.each_value do |backend|
      Rails.logger.debug { "run postmaster post filter #{backend}" }
      begin
        backend.run(channel, mail, ticket, article, session_user)
      rescue => e
        Rails.logger.error "can't run postmaster post filter #{backend}"
        Rails.logger.error e.inspect
      end
    end

    # return new objects
    [ticket, article, session_user, mail]
  end

  def self.check_attributes_by_x_headers(header_name, value)
    class_name = nil
    attribute = nil
    # skip check attributes if it is tags
    return true if header_name == 'x-zammad-ticket-tags'
    if header_name =~ /^x-zammad-(.+?)-(followup-|)(.*)$/i
      class_name = $1
      attribute = $3
    end
    return true if !class_name
    if class_name.downcase == 'article'
      class_name = 'Ticket::Article'
    end
    return true if !attribute
    key_short = attribute[ attribute.length - 3, attribute.length ]
    return true if key_short != '_id'

    class_object = Object.const_get(class_name.to_classname)
    return if !class_object
    class_instance = class_object.new

    return false if !class_instance.association_id_validation(attribute, value)
    true
  end

  def self.sender_attributes(from)
    if from.is_a?(Mail::Message)
      from = SENDER_FIELDS.map { |f| from.header[f] }.compact
                          .map(&:to_utf8).reject(&:blank?)
                          .partition { |address| address.match?(EMAIL_REGEX) }
                          .flatten.first
    end

    data = {}.with_indifferent_access
    return data if from.blank?

    from = from.gsub('<>', '').strip
    mail_address = begin
                     Mail::AddressList.new(from).addresses
                                      .select { |a| a.address.present? }
                                      .partition { |a| a.address.match?(EMAIL_REGEX) }
                                      .flatten.first
                   rescue Mail::Field::ParseError => e
                     STDOUT.puts e
                   end

    if mail_address&.address.present?
      data[:from_email]        = mail_address.address
      data[:from_local]        = mail_address.local
      data[:from_domain]       = mail_address.domain
      data[:from_display_name] = mail_address.display_name || mail_address.comments&.first
    elsif from =~ /^(.+?)<((.+?)@(.+?))>/
      data[:from_email]        = $2
      data[:from_local]        = $3
      data[:from_domain]       = $4
      data[:from_display_name] = $1
    else
      data[:from_email]        = from
      data[:from_local]        = from
      data[:from_domain]       = from
      data[:from_display_name] = from
    end

    # do extra decoding because we needed to use field.value
    data[:from_display_name] =
      Mail::Field.new('X-From', data[:from_display_name].to_utf8)
                 .to_s
                 .delete('"')
                 .strip
                 .gsub(/(^'|'$)/, '')

    data
  end

  def set_attributes_by_x_headers(item_object, header_name, mail, suffix = false)

    # loop all x-zammad-header-* headers
    item_object.attributes.each_key do |key|

      # ignore read only attributes
      next if key == 'updated_by_id'
      next if key == 'created_by_id'

      # check if id exists
      key_short = key[ key.length - 3, key.length ]
      if key_short == '_id'
        key_short = key[ 0, key.length - 3 ]
        header = "x-zammad-#{header_name}-#{key_short}"
        if suffix
          header = "x-zammad-#{header_name}-#{suffix}-#{key_short}"
        end

        # only set value on _id if value/reference lookup exists
        if mail[ header.to_sym ]

          Rails.logger.info "set_attributes_by_x_headers header #{header} found #{mail[header.to_sym]}"
          item_object.class.reflect_on_all_associations.map do |assoc|

            next if assoc.name.to_s != key_short

            Rails.logger.info "set_attributes_by_x_headers found #{assoc.class_name} lookup for '#{mail[header.to_sym]}'"
            item = assoc.class_name.constantize

            assoc_object = nil
            if item.respond_to?(:name)
              assoc_object = item.lookup(name: mail[header.to_sym])
            end
            if !assoc_object && item.respond_to?(:login)
              assoc_object = item.lookup(login: mail[header.to_sym])
            end

            if assoc_object.blank?

              # no assoc exists, remove header
              mail.delete(header.to_sym)
              next
            end

            Rails.logger.info "set_attributes_by_x_headers assign #{item_object.class} #{key}=#{assoc_object.id}"

            item_object[key] = assoc_object.id

          end
        end
      end

      # check if attribute exists
      header = "x-zammad-#{header_name}-#{key}"
      if suffix
        header = "x-zammad-#{header_name}-#{suffix}-#{key}"
      end
      if mail[header.to_sym]
        Rails.logger.info "set_attributes_by_x_headers header #{header} found. Assign #{key}=#{mail[header.to_sym]}"
        item_object[key] = mail[header.to_sym]
      end
    end
  end

=begin

process unprocessable_mails (tmp/unprocessable_mail/*.eml) again

  Channel::EmailParser.process_unprocessable_mails

=end

  def self.process_unprocessable_mails(params = {})
    path = Rails.root.join('tmp', 'unprocessable_mail')
    files = []
    Dir.glob("#{path}/*.eml") do |entry|
      ticket, article, user, mail = Channel::EmailParser.new.process(params, IO.binread(entry))
      next if ticket.blank?
      files.push entry
      File.delete(entry)
    end
    files
  end

  private

  def charset_from_headers_of(msg)
    Mail.new(msg.b)
        .header['Content-Type']
        .try(:parameters)
        .try(:[], :charset)
  end

  def message_header_hash(mail)
    imported_fields = mail.header.fields.map do |f|
      value = begin
                f.to_utf8
              rescue NameError # handle bug #1238 in Mail 2.7.1.rc1
                ''             # swap out for commented line below once upgrade is available
              end

      [f.name.downcase, value]
    end.to_h

    # imported_fields = mail.header.fields.map { |f| [f.name.downcase, f.to_utf8] }.to_h
    raw_fields = mail.header.fields.map { |f| ["raw-#{f.name.downcase}", f] }.to_h
    custom_fields = {}.tap do |h|
      validated_recipients = imported_fields.slice(*RECIPIENT_FIELDS)
                                            .transform_values { |v| v.match?(EMAIL_REGEX) ? v : '' }
      h.merge!(validated_recipients)

      h['date']            = Time.zone.parse(mail.date.to_s) || imported_fields['date']
      h['message_id']      = imported_fields['message-id']
      h['subject']         = imported_fields['subject']&.sub(/^=\?us-ascii\?Q\?(.+)\?=$/, '\1')
      h['x-any-recipient'] = validated_recipients.values.select(&:present?).join(', ')
    end

    [imported_fields, raw_fields, custom_fields].reduce({}.with_indifferent_access, &:merge)
  end

  def message_body_hash(mail)
    message = [mail.html_part, mail.text_part, mail].find { |m| m&.body.present? }

    if message.present? && (message.mime_type.nil? || message.mime_type.match?(%r{^text/(plain|html)$}))
      content_type = message.mime_type || 'text/plain'
      body = body_text(message, strict_html: content_type.eql?('text/html'))
    end

    content_type = 'text/plain' if body.blank?

    {
      attachments:  collect_attachments(mail),
      content_type: content_type || 'text/plain',
      body:         body.presence || 'no visible content'
    }.with_indifferent_access
  end

  def body_text(message, **options)
    body_text = begin
                  message.body.to_s
                rescue Mail::UnknownEncodingType # see test/data/mail/mail043.box / issue #348
                  message.body.raw_source
                end

    body_text = body_text.utf8_encode(from: message.charset, fallback: :read_as_sanitized_binary)
    body_text = Mail::Utilities.to_lf(body_text)

    return body_text.html2html_strict if options[:strict_html]
    body_text
  end

  def collect_attachments(mail)
    attachments = []

    # Add non-plaintext body as an attachment
    if mail.html_part&.body.present? ||
       (!mail.multipart? && mail.mime_type.present? && mail.mime_type != 'text/plain')
      message = mail.html_part || mail

      filename = message.filename.presence ||
                 (message.mime_type.eql?('text/html') ? 'message.html' : '-no name-')

      headers_store = {
        'content-alternative' => true,
        'original-format'     => message.mime_type.eql?('text/html'),
        'Mime-Type'           => message.mime_type,
        'Charset'             => message.charset,
      }.reject { |_, v| v.blank? }

      attachments.push({ data:        body_text(message),
                         filename:    filename,
                         preferences: headers_store })
    end

    mail.parts.each do |part|
      begin
        new_attachments = get_attachments(part, attachments, mail).flatten.compact
        attachments.push(*new_attachments)
      rescue => e # Protect process to work with spam emails (see test/fixtures/mail15.box)
        raise e if (fail_count ||= 0).positive?
        (fail_count += 1) && retry
      end
    end

    attachments
  end

  def get_attachments(file, attachments, mail)
    return file.parts.map { |p| get_attachments(p, attachments, mail) } if file.parts.any?
    return [] if [mail.text_part, mail.html_part].include?(file)

    # get file preferences
    headers_store = {}
    file.header.fields.each do |field|

      # full line, encode, ready for storage
      begin
        value = field.to_utf8
        if value.blank?
          value = field.raw_value
        end
        headers_store[field.name.to_s] = value
      rescue => e
        headers_store[field.name.to_s] = field.raw_value
      end
    end

    # cleanup content id, <> will be added automatically later
    if headers_store['Content-ID']
      headers_store['Content-ID'].gsub!(/^</, '')
      headers_store['Content-ID'].gsub!(/>$/, '')
    end

    # get filename from content-disposition

    # workaround for: NoMethodError: undefined method `filename' for #<Mail::UnstructuredField:0x007ff109e80678>
    filename = file.header[:content_disposition].try(:filename)

    begin
      if file.header[:content_disposition].to_s =~ /filename="(.+?)"/i
        filename = $1
      elsif file.header[:content_disposition].to_s =~ /filename='(.+?)'/i
        filename = $1
      elsif file.header[:content_disposition].to_s =~ /filename=(.+?);/i
        filename = $1
      end
    rescue
      Rails.logger.debug { 'Unable to get filename' }
    end

    # as fallback, use raw values
    if filename.blank?
      if headers_store['Content-Disposition'].to_s =~ /filename="(.+?)"/i
        filename = $1
      elsif headers_store['Content-Disposition'].to_s =~ /filename='(.+?)'/i
        filename = $1
      elsif headers_store['Content-Disposition'].to_s =~ /filename=(.+?);/i
        filename = $1
      end
    end

    # for some broken sm mail clients (X-MimeOLE: Produced By Microsoft Exchange V6.5)
    filename ||= file.header[:content_location].to_s

    # generate file name based on content-id
    if filename.blank? && headers_store['Content-ID'].present?
      if headers_store['Content-ID'] =~ /(.+?)@.+?/i
        filename = $1
      end
    end

    # generate file name based on content type
    if filename.blank? && headers_store['Content-Type'].present?
      if headers_store['Content-Type'].match?(%r{^message/rfc822}i)
        begin
          parser = Channel::EmailParser.new
          mail_local = parser.parse(file.body.to_s)
          filename = if mail_local[:subject].present?
                       "#{mail_local[:subject]}.eml"
                     elsif headers_store['Content-Description'].present?
                       "#{headers_store['Content-Description']}.eml".to_s.force_encoding('utf-8')
                     else
                       'Mail.eml'
                     end
        rescue
          filename = 'Mail.eml'
        end
      end

      # e. g. Content-Type: video/quicktime; name="Video.MOV";
      if filename.blank?
        ['name="(.+?)"(;|$)', "name='(.+?)'(;|$)", 'name=(.+?)(;|$)'].each do |regexp|
          if headers_store['Content-Type'] =~ /#{regexp}/i
            filename = $1
            break
          end
        end
      end

      # e. g. Content-Type: video/quicktime
      if filename.blank?
        map = {
          'message/delivery-status': ['txt', 'delivery-status'],
          'text/plain': %w[txt document],
          'text/html': %w[html document],
          'video/quicktime': %w[mov video],
          'image/jpeg': %w[jpg image],
          'image/jpg': %w[jpg image],
          'image/png': %w[png image],
          'image/gif': %w[gif image],
        }
        map.each do |type, ext|
          next if headers_store['Content-Type'] !~ /^#{Regexp.quote(type)}/i
          filename = if headers_store['Content-Description'].present?
                       "#{headers_store['Content-Description']}.#{ext[0]}".to_s.force_encoding('utf-8')
                     else
                       "#{ext[1]}.#{ext[0]}"
                     end
          break
        end
      end
    end

    if filename.blank?
      filename = 'file'
    end

    local_filename = ''
    local_extention = ''
    if filename =~ /^(.*?)\.(.+?)$/
      local_filename = $1
      local_extention = $2
    end

    1.upto(1000) do |i|
      filename_exists = false
      attachments.each do |attachment|
        if attachment[:filename] == filename
          filename_exists = true
        end
      end
      break if filename_exists == false
      filename = if local_extention.present?
                   "#{local_filename}#{i}.#{local_extention}"
                 else
                   "#{local_filename}#{i}"
                 end
    end

    # get mime type
    if file.header[:content_type]&.string
      headers_store['Mime-Type'] = file.header[:content_type].string
    end

    # get charset
    if file.header&.charset
      headers_store['Charset'] = file.header.charset
    end

    # remove not needed header
    headers_store.delete('Content-Transfer-Encoding')
    headers_store.delete('Content-Disposition')

    # workaround for mail gem
    # https://github.com/zammad/zammad/issues/928
    filename = Mail::Encodings.value_decode(filename)

    attach = {
      data: file.body.to_s,
      filename: filename,
      preferences: headers_store,
    }

    [attach]
  end
end

module Mail

  # workaround to get content of no parseable headers - in most cases with non 7 bit ascii signs
  class Field
    def raw_value
      value = @raw_value.try(:utf8_encode)
      return value if value.blank?
      value.sub(/^.+?:(\s|)/, '')
    end
  end

  # workaround to parse subjects with 2 different encodings correctly (e. g. quoted-printable see test/fixtures/mail9.box)
  module Encodings
    def self.value_decode(str)
      # Optimization: If there's no encoded-words in the string, just return it
      return str if !str.index('=?')

      str = str.gsub(/\?=(\s*)=\?/, '?==?') # Remove whitespaces between 'encoded-word's

      # Split on white-space boundaries with capture, so we capture the white-space as well
      str.split(/([ \t])/).map do |text|
        if text.index('=?') .nil?
          text
        else
          # Join QP encoded-words that are adjacent to avoid decoding partial chars
          #          text.gsub!(/\?\=\=\?.+?\?[Qq]\?/m, '') if text =~ /\?==\?/

          # Search for occurences of quoted strings or plain strings
          text.scan(/(                                  # Group around entire regex to include it in matches
          \=\?[^?]+\?([QB])\?[^?]+?\?\=  # Quoted String with subgroup for encoding method
          |                                # or
          .+?(?=\=\?|$)                    # Plain String
          )/xmi).map do |matches|
            string, method = *matches
            if    method == 'b' || method == 'B' # rubocop:disable Style/MultipleComparison
              b_value_decode(string)
            elsif method == 'q' || method == 'Q' # rubocop:disable Style/MultipleComparison
              q_value_decode(string)
            else
              string
            end
          end
        end
      end.join('')
    end
  end
end