Extract Serializer Attributes into its own file

lib/active_model/serializer/attributes.rb

@@ -0,0 +1,107 @@
+module ActiveModel
+  class Serializer
+    module Attributes
+      class Attribute
+        delegate :call, to: :reader
+        attr_reader :name, :reader
+        def initialize(name)
+          @name = name
+          @reader = nil
+        end
+
+        def self.build(name, block)
+          if block
+            AttributeBlock.new(name, block)
+          else
+            AttributeReader.new(name)
+          end
+        end
+      end
+      class AttributeReader < Attribute
+        def initialize(name)
+          super(name)
+          @reader = ->(instance) { instance.read_attribute_for_serialization(name) }
+        end
+      end
+      class AttributeBlock < Attribute
+        def initialize(name, block)
+          super(name)
+          @reader = ->(instance) { instance.instance_eval(&block) }
+        end
+      end
+
+      extend ActiveSupport::Concern
+
+      included do
+        with_options instance_writer: false, instance_reader: false do |serializer|
+          serializer.class_attribute :_attribute_mappings # @api private : maps attribute key names to names to names of implementing methods, @see #attribute
+          self._attribute_mappings ||= {}
+        end
+
+        # Return the +attributes+ of +object+ as presented
+        # by the serializer.
+        def attributes(requested_attrs = nil)
+          self.class._attribute_mappings.each_with_object({}) do |(key, attribute_mapping), hash|
+            next unless requested_attrs.nil? || requested_attrs.include?(key)
+            hash[key] = attribute_mapping.call(self)
+          end
+        end
+      end
+
+      module ClassMethods
+        def inherited(base)
+          super
+          base._attribute_mappings = _attribute_mappings.dup
+        end
+
+        # @example
+        #   class AdminAuthorSerializer < ActiveModel::Serializer
+        #     attributes :id, :name, :recent_edits
+        def attributes(*attrs)
+          attrs = attrs.first if attrs.first.class == Array
+
+          attrs.each do |attr|
+            attribute(attr)
+          end
+        end
+
+        # TODO: remove the dynamic method definition
+        # @example
+        #   class AdminAuthorSerializer < ActiveModel::Serializer
+        #     attributes :id, :recent_edits
+        #     attribute :name, key: :title
+        #
+        #     attribute :full_name do
+        #       "#{object.first_name} #{object.last_name}"
+        #     end
+        #
+        #     def recent_edits
+        #       object.edits.last(5)
+        #     end
+        def attribute(attr, options = {}, &block)
+          key = options.fetch(:key, attr)
+          _attribute_mappings[key] = Attribute.build(attr, block)
+        end
+
+        # @api private
+        # names of attribute methods
+        # @see Serializer::attribute
+        def _attributes
+          _attribute_mappings.keys
+        end
+
+        # @api private
+        # maps attribute value to explict key name
+        # @see Serializer::attribute
+        # @see Adapter::FragmentCache#fragment_serializer
+        def _attributes_keys
+          _attribute_mappings
+            .each_with_object({}) do |(key, attribute_mapping), hash|
+              next if key == attribute_mapping.name
+              hash[attribute_mapping.name] = { key: key }
+            end
+        end
+      end
+    end
+  end
+end