require 'active_support/core_ext/module/attribute_accessors'

module ActiveRecord
  module AttributeMethods
    module Dirty # :nodoc:
      extend ActiveSupport::Concern

      include ActiveModel::Dirty

      included do
        if self < ::ActiveRecord::Timestamp
          raise "You cannot include Dirty after Timestamp"
        end

        class_attribute :partial_writes, instance_writer: false
        self.partial_writes = true
      end

      # Attempts to +save+ the record and clears changed attributes if successful.
      def save(*)
        if status = super
          changes_applied
        end
        status
      end

      # Attempts to <tt>save!</tt> the record and clears changed attributes if successful.
      def save!(*)
        super.tap do
          changes_applied
        end
      end

      # <tt>reload</tt> the record and clears changed attributes.
      def reload(*)
        super.tap do
          clear_changes_information
        end
      end

      def initialize_dup(other) # :nodoc:
        super
        calculate_changes_from_defaults
      end

      def changes_applied
        super
        store_original_raw_attributes
      end

      def clear_changes_information
        super
        original_raw_attributes.clear
      end

      def changed_attributes
        # This should only be set by methods which will call changed_attributes
        # multiple times when it is known that the computed value cannot change.
        if defined?(@cached_changed_attributes)
          @cached_changed_attributes
        else
          super.reverse_merge(attributes_changed_in_place).freeze
        end
      end

      def changes
        cache_changed_attributes do
          super
        end
      end

      def attribute_changed_in_place?(attr_name)
        old_value = original_raw_attribute(attr_name)
        @attributes[attr_name].changed_in_place_from?(old_value)
      end

      private

      def calculate_changes_from_defaults
        @changed_attributes = nil
        self.class.column_defaults.each do |attr, orig_value|
          set_attribute_was(attr, orig_value) if _field_changed?(attr, orig_value)
        end
      end

      # Wrap write_attribute to remember original attribute value.
      def write_attribute(attr, value)
        attr = attr.to_s

        old_value = old_attribute_value(attr)

        result = super
        store_original_raw_attribute(attr)
        save_changed_attribute(attr, old_value)
        result
      end

      def raw_write_attribute(attr, value)
        attr = attr.to_s

        result = super
        original_raw_attributes[attr] = value
        result
      end

      def save_changed_attribute(attr, old_value)
        if attribute_changed?(attr)
          clear_attribute_changes(attr) unless _field_changed?(attr, old_value)
        else
          set_attribute_was(attr, old_value) if _field_changed?(attr, old_value)
        end
      end

      def old_attribute_value(attr)
        if attribute_changed?(attr)
          changed_attributes[attr]
        else
          clone_attribute_value(:_read_attribute, attr)
        end
      end

      def _update_record(*)
        partial_writes? ? super(keys_for_partial_write) : super
      end

      def _create_record(*)
        partial_writes? ? super(keys_for_partial_write) : super
      end

      # Serialized attributes should always be written in case they've been
      # changed in place.
      def keys_for_partial_write
        changed
      end

      def _field_changed?(attr, old_value)
        @attributes[attr].changed_from?(old_value)
      end

      def attributes_changed_in_place
        changed_in_place.each_with_object({}) do |attr_name, h|
          orig = @attributes[attr_name].original_value
          h[attr_name] = orig
        end
      end

      def changed_in_place
        self.class.attribute_names.select do |attr_name|
          attribute_changed_in_place?(attr_name)
        end
      end

      def original_raw_attribute(attr_name)
        original_raw_attributes.fetch(attr_name) do
          read_attribute_before_type_cast(attr_name)
        end
      end

      def original_raw_attributes
        @original_raw_attributes ||= {}
      end

      def store_original_raw_attribute(attr_name)
        original_raw_attributes[attr_name] = @attributes[attr_name].value_for_database
      end

      def store_original_raw_attributes
        attribute_names.each do |attr|
          store_original_raw_attribute(attr)
        end
      end

      def cache_changed_attributes
        @cached_changed_attributes = changed_attributes
        yield
      ensure
        remove_instance_variable(:@cached_changed_attributes)
      end
    end
  end
end