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

    included do
      attr_accessor :_parent
    end

    # Get all child +Documents+ to this +Document+, going n levels deep if
    # necessary. This is used when calling update persistence operations from
    # the root document, where changes in the entire tree need to be
    # determined. Note that persistence from the embedded documents will
    # always be preferred, since they are optimized calls... This operation
    # can get expensive in domains with large hierarchies.
    #
    # @example Get all the document's children.
    #   person._children
    #
    # @return [ Array<Document> ] All child documents in the hierarchy.
    def _children
      @_children ||=
        [].tap do |children|
          relations.each_pair do |name, metadata|
            if metadata.embedded?
              child = send(name)
              Array.wrap(child).each do |doc|
                children.push(doc)
                children.concat(doc._children) unless metadata.versioned?
              end if child
            end
          end
        end
    end

    # Determines if the document is a subclass of another document.
    #
    # @example Check if the document is a subclass
    #   Square.new.hereditary?
    #
    # @return [ true, false ] True if hereditary, false if not.
    def hereditary?
      self.class.hereditary?
    end

    # Sets up a child/parent association. This is used for newly created
    # objects so they can be properly added to the graph.
    #
    # @example Set the parent document.
    #   document.parentize(parent)
    #
    # @param [ Document ] document The parent document.
    #
    # @return [ Document ] The parent document.
    def parentize(document)
      self._parent = document
    end

    # Remove a child document from this parent. If an embeds one then set to
    # nil, otherwise remove from the embeds many.
    #
    # This is called from the +RemoveEmbedded+ persistence command.
    #
    # @example Remove the child.
    #   document.remove_child(child)
    #
    # @param [ Document ] child The child (embedded) document to remove.
    #
    # @since 2.0.0.beta.1
    def remove_child(child)
      name = child.metadata.name
      child.embedded_one? ? remove_ivar(name) : send(name).delete_one(child)
    end

    # After children are persisted we can call this to move all their changes
    # and flag them as persisted in one call.
    #
    # @example Reset the children.
    #   document.reset_persisted_children
    #
    # @return [ Array<Document> ] The children.
    #
    # @since 2.1.0
    def reset_persisted_children
      _children.each do |child|
        child.move_changes
        child.new_record = false
      end
    end

    # Return the root document in the object graph. If the current document
    # is the root object in the graph it will return self.
    #
    # @example Get the root document in the hierarchy.
    #   document._root
    #
    # @return [ Document ] The root document in the hierarchy.
    def _root
      object = self
      while (object._parent) do object = object._parent; end
      object || self
    end

    module ClassMethods #:nodoc:

      # Determines if the document is a subclass of another document.
      #
      # @example Check if the document is a subclass.
      #   Square.hereditary?
      #
      # @return [ true, false ] True if hereditary, false if not.
      def hereditary?
        Mongoid::Document > superclass
      end
    end
  end
end