module Elasticsearch
  module Model
    module Adapter

      # An adapter for ActiveRecord-based models
      #
      module ActiveRecord

        Adapter.register self,
                         lambda { |klass| !!defined?(::ActiveRecord::Base) && klass.ancestors.include?(::ActiveRecord::Base) }

        module Records
          # Returns an `ActiveRecord::Relation` instance
          #
          def records
            sql_records = klass.where(klass.primary_key => ids)

            # Re-order records based on the order from Elasticsearch hits
            # by redefining `to_a`, unless the user has called `order()`
            #
            sql_records.instance_exec(response.response['hits']['hits']) do |hits|
              define_singleton_method :to_a do
                if defined?(::ActiveRecord) && ::ActiveRecord::VERSION::MAJOR >= 4
                  self.load
                else
                  self.__send__(:exec_queries)
                end
                @records.sort_by { |record| hits.index { |hit| hit['_id'].to_s == record.id.to_s } }
              end
            end

            sql_records
          end

          # Prevent clash with `ActiveSupport::Dependencies::Loadable`
          #
          def load
            records.load
          end

          # Intercept call to the `order` method, so we can ignore the order from Elasticsearch
          #
          def order(*args)
            sql_records = records.__send__ :order, *args

            # Redefine the `to_a` method to the original one
            #
            sql_records.instance_exec do
              define_singleton_method(:to_a) do
                if defined?(::ActiveRecord) && ::ActiveRecord::VERSION::MAJOR >= 4
                  self.load
                else
                  self.__send__(:exec_queries)
                end
                @records
              end
            end

            sql_records
          end
        end

        module Callbacks

          # Handle index updates (creating, updating or deleting documents)
          # when the model changes, by hooking into the lifecycle
          #
          # @see http://guides.rubyonrails.org/active_record_callbacks.html
          #
          def self.included(base)
            base.class_eval do
              after_commit lambda { __elasticsearch__.index_document  },  on: :create
              after_commit lambda { __elasticsearch__.update_document },  on: :update
              after_commit lambda { __elasticsearch__.delete_document },  on: :destroy
            end
          end
        end

        module Importing

          # Fetch batches of records from the database
          #
          # @see http://api.rubyonrails.org/classes/ActiveRecord/Batches.html ActiveRecord::Batches.find_in_batches
          #
          def __find_in_batches(options={}, &block)
            named_scope = options.delete(:scope)

            scope = named_scope ? self.__send__(named_scope) : self

            scope.find_in_batches(options) do |batch|
              yield batch
            end
          end

          def __transform
            lambda { |model|  { index: { _id: model.id, data: model.__elasticsearch__.as_indexed_json } } }
          end
        end
      end
    end
  end
end