# Copyright (C) 2012-2016 Zammad Foundation, http://zammad-foundation.org/
require 'net/ldap'
require 'net/ldap/entry'

# Class for establishing LDAP connections. A wrapper around Net::LDAP needed for Auth and Sync.
# ATTENTION: Loads custom 'net/ldap/entry' from 'lib/core_ext' which extends the Net::LDAP::Entry class.
#
# @!attribute [r] connection
#   @return [Net::LDAP] the Net::LDAP instance with the established connection
# @!attribute [r] base_dn
#   @return [String] the base dn used while initializing the connection
class Ldap

  attr_reader :connection, :base_dn, :host, :port, :ssl

  # Initializes a LDAP connection.
  #
  # @param [Hash] config the configuration for establishing a LDAP connection. Default is Setting 'ldap_config'.
  # @option config [String] :host_url The LDAP host URL in the format '*protocol*://*host*:*port*'.
  # @option config [String] :host The LDAP explicit host. May contain the port. Gets overwritten by host_url if given.
  # @option config [Number] :port The LDAP port. Default is 389 LDAP or 636 for LDAPS. Gets overwritten by host_url if given.
  # @option config [Boolean] :ssl The LDAP SSL setting. Is set automatically for 'ldaps' protocol. Sets Port to 636 if non other is given.
  # @option config [String] :base_dn The base DN searches etc. are applied to.
  # @option config [String] :bind_user The username which should be used for bind.
  # @option config [String] :bind_pw The password which should be used for bind.
  #
  # @example
  #  ldap = Ldap.new
  #
  # @return [nil]
  def initialize(config = nil)
    @config = config

    if @config.blank?
      @config = Setting.get('ldap_config')
    end

    connect
  end

  # Requests the rootDSE (the root of the directory data tree on a directory server).
  #
  # @example
  #  ldap.preferences
  #  #=> [:namingcontexts=>["DC=domain,DC=tld", "CN=Configuration,DC=domain,DC=tld"], :supportedldapversion=>["3", "2"], ...]
  #
  # @return [Hash{String => Array<String>}] The found RootDSEs.
  def preferences
    @connection.search_root_dse.to_h
  end

  # Performs a LDAP search and yields over the found LDAP entries.
  #
  # @param filter [String] The filter that should get applied to the search.
  # @param base [String] The base DN on which the search should get executed. Default is initialization parameter.
  # @param scope [Net::LDAP::SearchScope] The search scope as defined in Net::LDAP SearchScopes. Default is WholeSubtree.
  # @param attributes [Array<String>] Limits the requested entry attributes to the given list of attributes which increses the performance.
  #
  # @example
  #  ldap.search('(objectClass=group)') do |entry|
  #    p entry
  #  end
  #  #=> <Net::LDAP::Entry...>
  #
  # @return [true] Returns always true
  def search(filter, base: nil, scope: nil, attributes: nil)

    base  ||= base_dn()
    scope ||= Net::LDAP::SearchScope_WholeSubtree

    @connection.search(
      base:          base,
      filter:        filter,
      scope:         scope,
      attributes:    attributes,
      return_result: false, # improves performance
    ) do |entry|
      # needed for the #entries? method -> returns nil on break
      break if !block_given?
      yield entry
    end
  end

  # Checks if there are any entries for the given search criteria.
  #
  # @param (see Ldap#search)
  #
  # @example
  #  ldap.entries?('(objectClass=group)')
  #  #=> true
  #
  # @return [Boolean] Returns true if entries are present false if not.
  def entries?(*args)
    # since #search returns nil if entries are found (due to the break in the yield block)
    # and returns true otherwise we have to invert the result which matches the
    # expected result of a ...? method and suites our needs since it checks one entry max.
    !search(*args)
  end

  # Counts the entries for the given search criteria.
  #
  # @param (see Ldap#search)
  #
  # @example
  #  ldap.entries?('(objectClass=group)')
  #  #=> 10
  #
  # @return [Number] The count of matching entries.
  def count(*args)
    counter = 0
    search(*args) do |_entry|
      counter += 1
    end
    counter
  end

  private

  def connect
    @connection ||= begin
      attributes_from_config
      binded_connection
    end
  end

  def binded_connection
    # ldap connect
    ldap = Net::LDAP.new(connection_params)

    # set auth data if needed
    if @bind_user && @bind_pw
      ldap.auth @bind_user, @bind_pw
    end

    return ldap if ldap.bind

    result = ldap.get_operation_result
    raise Exceptions::UnprocessableEntity, "Can't bind to '#{@host}', #{result.code}, #{result.message}"
  rescue => e
    raise Exceptions::UnprocessableEntity, "Can't connect to '#{@host}' on port '#{@port}', #{e}"
  end

  def connection_params
    params = {
      host: @host,
      port: @port,
    }

    if @encryption
      params[:encryption] = @encryption
    end

    params
  end

  def attributes_from_config
    # might change below
    @host = @config[:host]
    @port = @config[:port]
    @ssl  = @config.fetch(:ssl, false)

    parse_host_url
    parse_host
    handle_ssl_config
    handle_bind_crendentials

    @base_dn = @config[:base_dn]

    # fallback to default
    # port if none given
    @port ||= 389
  end

  def parse_host_url
    @host_url = @config[:host_url]
    return if @host_url.blank?
    raise "Invalid host url '#{@host_url}'" if @host_url !~ %r{\A([^:]+)://(.+?)/?\z}
    @protocol = $1.to_sym
    @host     = $2
    @ssl      = @protocol == :ldaps
  end

  def parse_host
    return if @host !~ /\A([^:]+):(.+?)\z/
    @host = $1
    @port = $2.to_i
  end

  def handle_ssl_config
    return if !@ssl
    @port       ||= @config.fetch(:port, 636)
    @encryption   = {
      method: :simple_tls,
    }

    if !@config[:ssl_verify]
      @encryption[:tls_options] = {
        verify_mode: OpenSSL::SSL::VERIFY_NONE
      }
    end
  end

  def handle_bind_crendentials
    @bind_user = @config[:bind_user]
    @bind_pw   = @config[:bind_pw]
  end

end