# =============================================================================
#
# class Book
#   include Mongoid::Document
#   include Mongoid::SortedRelations
#
#   field :title
#
#   has_many :chapters
#   sorted_relations_for :chapters
#
#   has_and_belongs_to_many :authors
#   sorted_relations_for :authors
# end
#
# b = Book.create('Hello')
#
# b.sorted_chapter_ids = [ Chapter.create(:title => 'The End').id,
#                          Chapter.create(:title => 'Part 3' ).id,
#                          Chapter.create(:title => 'Part 2' ).id,
#                          Chapter.create(:title => 'Part 1' ).id,
#                          Chapter.create(:title => 'Intro'  ).id ]
#
# b.sorted_chapters()
#
# book.sorted_author_ids = [ Author.create(:name => 'Sun Tzu').id,
#                            Author.create(:name => 'Sun Wu' ).id,
#                            Author.create(:name => 'Lao Zi' ).id ]
#
# book.sorted_authors()
#
# =============================================================================

module Ants
  module SortedRelations
    extend ActiveSupport::Concern

    class_methods do

      def sorted_relations_for(relation_name)
        relation = self.relations[relation_name.to_s]

        if relation.macro == :has_and_belongs_to_many
          define_has_and_belongs_to_many_sorted_methods(relation)
        end

        if relation.macro == :has_many
          define_has_many_sorted_methods(relation)
        end
      end


      #
      # HAS_AND_BELONGS_TO_MANY
      #
      def define_has_and_belongs_to_many_sorted_methods(relation)
        # sorted_#{ relation.name }
        self.send(:define_method, "sorted_#{ relation.name }") do
          related_documents   = self.send(relation.name)
          sorted_relation_ids = self.send("#{ relation.name.to_s.singularize }_ids").map { |id| id.to_s }

          sorted_documents = related_documents.sort_by do |document|
            sorted_relation_ids.index(document.id.to_s) || -1
          end

          return Mongoid::FakeCriteria.new(sorted_documents)
        end

        # sorted_#{ relation.name } = [ <array of ids> ]
        self.send(:define_method, "sorted_#{ relation.name.to_s.singularize }_ids=") do |ids|
          self.send("#{ relation.name.to_s.singularize }_ids=", ids)
        end
      end


      #
      # HAS_MANY
      #
      def define_has_many_sorted_methods(relation)
        # define field to store order for has_many related documents
        self.field "_sorted_#{ relation.name.to_s.singularize }_ids", :type => Array, default: []

        # sorted_#{ relation.name }
        self.send(:define_method, "sorted_#{ relation.name }") do
          related_documents   = self.send(relation.name)
          sorted_relation_ids = self["_sorted_#{ relation.name.to_s.singularize }_ids"].map { |id| id.to_s }

          # missing or new ids are in random order
          sorted_documents = related_documents.sort_by do |document|
            sorted_relation_ids.index(document.id.to_s) || -1
          end

          return Mongoid::FakeCriteria.new(sorted_documents)
        end

        # sorted_#{ relation.name } = [ <array of ids> ]
        self.send(:define_method, "sorted_#{ relation.name.to_s.singularize }_ids=") do |ids|
          ids = ids.map{ |id| id.to_s }

          self.update_attributes({
            "_sorted_#{ relation.name.to_s.singularize }_ids" => ids, # store order
            "#{ relation.name.to_s.singularize }_ids"         => ids  # update relations
          })
        end
      end


    end
  end
end