module ActiveRecord
  module Associations
    module ClassMethods
      def has_many_with_deferred_save(*args)
        collection_name = args[0].to_s
        collection_singular_ids = "#{collection_name.singularize}_ids"

        return if method_defined?("#{collection_name}_with_deferred_save")

        has_many *args

        if args[1].is_a?(Hash) && args[1].keys.include?(:through)
          logger.warn "You are using the option :through on #{name}##{collection_name}. This was not tested very much with has_many_with_deferred_save. Please write many tests for your functionality!"
        end

        after_save :"hmwds_update_#{collection_name}"

        define_obj_setter    collection_name
        define_obj_getter    collection_name
        define_id_setter     collection_name, collection_singular_ids
        define_id_getter     collection_name, collection_singular_ids

        define_update_method collection_name
        define_reload_method collection_name
      end

      def define_obj_setter(collection_name)
        define_method("#{collection_name}_with_deferred_save=") do |objs|
          instance_variable_set "@hmwds_temp_#{collection_name}", objs || []
          attribute_will_change!(collection_name) if objs != send("#{collection_name}_without_deferred_save")
        end

        alias_method(:"#{collection_name}_without_deferred_save=", :"#{collection_name}=")
        alias_method(:"#{collection_name}=", :"#{collection_name}_with_deferred_save=")
      end

      def define_obj_getter(collection_name)
        define_method("#{collection_name}_with_deferred_save") do
          save_in_progress = instance_variable_get "@hmwds_#{collection_name}_save_in_progress"

          # while updating the association, rails loads the association object - this needs to be the original one
          unless save_in_progress
            elements = instance_variable_get "@hmwds_temp_#{collection_name}"
            if elements.nil?
              elements = ArrayToAssociationWrapper.new(send("#{collection_name}_without_deferred_save"))
              elements.defer_association_methods_to self, collection_name
              instance_variable_set "@hmwds_temp_#{collection_name}", elements
            end

            result = elements
          else
            result = send("#{collection_name}_without_deferred_save")
          end

          result
        end

        alias_method(:"#{collection_name}_without_deferred_save", :"#{collection_name}")
        alias_method(:"#{collection_name}", :"#{collection_name}_with_deferred_save")
      end

      def define_id_setter(collection_name, collection_singular_ids)
        # only needed for ActiveRecord >= 3.0
        if ActiveRecord::VERSION::STRING >= '3'
          define_method "#{collection_singular_ids}_with_deferred_save=" do |ids|
            ids = Array.wrap(ids).reject(&:blank?)
            new_values = send("#{collection_name}_without_deferred_save").klass.find(ids)
            send("#{collection_name}=", new_values)
          end

          alias_method(:"#{collection_singular_ids}_without_deferred_save=", :"#{collection_singular_ids}=")
          alias_method(:"#{collection_singular_ids}=", :"#{collection_singular_ids}_with_deferred_save=")
        end
      end

      def define_id_getter(collection_name, collection_singular_ids)
        define_method "#{collection_singular_ids}_with_deferred_save" do
          send(collection_name).map { |e| e[:id] }
        end
        alias_method(:"#{collection_singular_ids}_without_deferred_save", :"#{collection_singular_ids}")
        alias_method(:"#{collection_singular_ids}", :"#{collection_singular_ids}_with_deferred_save")
      end

      def define_update_method(collection_name)
        define_method "hmwds_update_#{collection_name}" do
          unless frozen?
            elements = instance_variable_get "@hmwds_temp_#{collection_name}"
            unless elements.nil? # nothing has been done with the association
              # save is done automatically, if original behaviour is restored
              instance_variable_set "@hmwds_#{collection_name}_save_in_progress", true
              send("#{collection_name}_without_deferred_save=", elements)
              instance_variable_set "@hmwds_#{collection_name}_save_in_progress", false

              instance_variable_set "@hmwds_temp_#{collection_name}", nil
            end
          end
        end
      end

      def define_reload_method(collection_name)
        define_method "reload_with_deferred_save_for_#{collection_name}" do |*args|
          # Reload from the *database*, discarding any unsaved changes.
          send("reload_without_deferred_save_for_#{collection_name}", *args).tap do
            instance_variable_set "@hmwds_temp_#{collection_name}", nil
          end
        end
        alias_method(:"reload_without_deferred_save_for_#{collection_name}", :reload)
        alias_method(:reload, :"reload_with_deferred_save_for_#{collection_name}")
      end
    end
  end
end