# encoding: utf-8
module Mongoid #:nodoc:
  module Dirty #:nodoc:
    extend ActiveSupport::Concern

    # Get the changed attributes for the document.
    #
    # @example Get the changed attributes.
    #   model.changed
    #
    # @return [ Array<String> ] The changed attributes.
    #
    # @since 2.4.0
    def changed
      changed_attributes.keys
    end

    # Has the document changed?
    #
    # @example Has the document changed?
    #   model.changed?
    #
    # @return [ true, false ] If the document is changed.
    #
    # @since 2.4.0
    def changed?
      changed_attributes.any?
    end

    # Get the attribute changes.
    #
    # @example Get the attribute changes.
    #   model.changed_attributes
    #
    # @return [ Hash<String, Object> ] The attribute changes.
    #
    # @since 2.4.0
    def changed_attributes
      @changed_attributes ||= {}
    end

    # Get all the changes for the document.
    #
    # @example Get all the changes.
    #   model.changes
    #
    # @return [ Hash<String, Array<Object, Object> ] The changes.
    #
    # @since 2.4.0
    def changes
      changed.inject({}.with_indifferent_access) do |changes, attr|
        changes.tap do |hash|
          hash[attr] = attribute_change(attr)
        end
      end
    end

    # Call this method after save, so the changes can be properly switched.
    #
    # This will unset the memoized children array, set new record to
    # false, set the document as validated, and move the dirty changes.
    #
    # @example Move the changes to previous.
    #   person.move_changes
    #
    # @since 2.1.0
    def move_changes
      @_children = nil
      @previous_changes = changes
      Atomic::UPDATES.each do |update|
        send(update).clear
      end
      changed_attributes.clear
    end

    # Get the previous changes on the document.
    #
    # @example Get the previous changes.
    #   model.previous_changes
    #
    # @return [ Hash<String, Array<Object, Object> ] The previous changes.
    #
    # @since 2.4.0
    def previous_changes
      @previous_changes
    end

    # Remove a change from the dirty attributes hash. Used by the single field
    # atomic updators.
    #
    # @example Remove a flagged change.
    #   model.remove_change(:field)
    #
    # @param [ Symbol, String ] name The name of the field.
    #
    # @since 2.1.0
    def remove_change(name)
      changed_attributes.delete(name.to_s)
    end

    # Gets all the new values for each of the changed fields, to be passed to
    # a MongoDB $set modifier.
    #
    # @todo: Durran: Refactor 3.0
    #
    # @example Get the setters for the atomic updates.
    #   person = Person.new(:title => "Sir")
    #   person.title = "Madam"
    #   person.setters # returns { "title" => "Madam" }
    #
    # @return [ Hash ] A +Hash+ of atomic setters.
    def setters
      {}.tap do |modifications|
        changes.each_pair do |name, changes|
          if changes
            old, new = changes
            field = fields[name]
            key = embedded? ? "#{atomic_position}.#{name}" : name
            if field && field.resizable?
              pushes, pulls = new - (old || []), (old || []) - new
              field.add_atomic_changes(self, key, modifications, pushes, pulls)
            else
              modifications[key] = new
            end
          end
        end
      end
    end

    private

    # Get the old and new value for the provided attribute.
    #
    # @example Get the attribute change.
    #   model.attribute_change("name")
    #
    # @param [ String ] attr The name of the attribute.
    #
    # @return [ Array<Object> ] The old and new values.
    #
    # @since 2.1.0
    def attribute_change(attr)
      [changed_attributes[attr], attributes[attr]] if attribute_changed?(attr)
    end

    # Determine if a specific attribute has changed.
    #
    # @example Has the attribute changed?
    #   model.attribute_changed?("name")
    #
    # @param [ String ] attr The name of the attribute.
    #
    # @return [ true, false ] Whether the attribute has changed.
    #
    # @since 2.1.6
    def attribute_changed?(attr)
      return false unless changed_attributes.has_key?(attr)
      changed_attributes[attr] != attributes[attr]
    end

    # Get the previous value for the attribute.
    #
    # @example Get the previous value.
    #   model.attribute_was("name")
    #
    # @param [ String ] attr The attribute name.
    #
    # @since 2.4.0
    def attribute_was(attr)
      attribute_changed?(attr) ? changed_attributes[attr] : attributes[attr]
    end

    # Flag an attribute as going to change.
    #
    # @example Flag the attribute.
    #   model.attribute_will_change!("name")
    #
    # @param [ String ] attr The name of the attribute.
    #
    # @return [ Object ] The old value.
    #
    # @since 2.3.0
    def attribute_will_change!(attr)
      unless changed_attributes.has_key?(attr)
        changed_attributes[attr] = read_attribute(attr)._deep_copy
      end
    end

    # Set the attribute back to it's old value.
    #
    # @example Reset the attribute.
    #   model.reset_attribute!("name")
    #
    # @param [ String ] attr The name of the attribute.
    #
    # @return [ Object ] The old value.
    #
    # @since 2.4.0
    def reset_attribute!(attr)
      attributes[attr] = changed_attributes[attr] if attribute_changed?(attr)
    end

    module ClassMethods #:nodoc:

      private

      # Generate all the dirty methods needed for the attribute.
      #
      # @example Generate the dirty methods.
      #   Model.create_dirty_methods("name")
      #
      # @param [ String ] name The name of the attribute.
      #
      # @return [ Module ] The fields module.
      #
      # @since 2.4.0
      def create_dirty_methods(name)
        generated_methods.module_eval do
          class_eval <<-EOM
            def #{name}_change
              attribute_change(#{name.inspect})
            end

            def #{name}_changed?
              attribute_changed?(#{name.inspect})
            end

            def #{name}_was
              attribute_was(#{name.inspect})
            end

            def #{name}_will_change!
              attribute_will_change!(#{name.inspect})
            end

            def reset_#{name}!
              reset_attribute!(#{name.inspect})
            end
          EOM
        end
      end
    end
  end
end