engine/app/models/locomotive/extensions/page/tree.rb

module Locomotive
  module Extensions
    module Page
      module Tree

        extend ActiveSupport::Concern

        included do
          include ::Mongoid::Acts::Tree

          ## fields ##
          field :position, :type => Integer

          ## indexes ##
          index :position
          index [[:depth, :asc], [:position, :asc]]

          ## behaviours ##
          acts_as_tree :order => ['position', 'asc']

          ## callbacks ##
          before_validation :reset_parent
          before_save { |p| p.send(:write_attribute, :parent_id, nil) if p.parent_id.blank? }
          before_save :change_parent
          before_create { |p| p.send(:fix_position, false) }
          before_create :add_to_list_bottom
          before_destroy :remove_from_list

          # Fixme (Didier L.): Instances methods are defined before the include itself
          alias :fix_position :hacked_fix_position
          alias :descendants :hacked_descendants
        end

        module ClassMethods

          # Warning: should be used only in read-only
          def quick_tree(site, minimal_attributes = true)
            pages = (minimal_attributes ? site.pages.minimal_attributes : site.pages).order_by([[:depth, :asc], [:position, :asc]]).to_a

            tmp = []

            while !pages.empty?
              tmp << _quick_tree(pages.delete_at(0), pages)
            end

            tmp
          end

          def _quick_tree(current_page, pages)
            i, children = 0, []

            while !pages.empty?
              page = pages[i]

              break if page.nil?

              if page.parent_id == current_page.id
                page = pages.delete_at(i)

                children << _quick_tree(page, pages)
              else
                i += 1
              end
            end

            current_page.instance_eval do
              def children=(list); @children = list; end
              def children; @children || []; end
            end

            current_page.children = children

            current_page
          end

        end

        module InstanceMethods

          def children?
            self.class.where(self.parent_id_field => self.id).count
          end

          def children_with_minimal_attributes
            self.class.where(self.parent_id_field => self.id).
              order_by(self.tree_order).
              minimal_attributes
          end

          def sort_children!(ids)
            ids.each_with_index do |id, position|
              child = self.children.detect { |p| p._id == BSON::ObjectId(id) }
              child.position = position
              child.save
            end
          end

          def parent=(owner) # missing in acts_as_tree
            @_parent = owner
            self.fix_position(false)
            self.instance_variable_set :@_will_move, true
          end

          def hacked_descendants
            return [] if new_record?
            self.class.all_in(path_field => [self._id]).order_by tree_order
         end

          protected

          def change_parent
            if self.parent_id_changed?
              self.fix_position(false)

              unless self.parent_id_was.nil?
                self.position = nil # make it move to bottom
                self.add_to_list_bottom
              end

              self.instance_variable_set :@_will_move, true
            end
          end

          def hacked_fix_position(perform_save = true)
            if parent.nil?
              self.write_attribute parent_id_field, nil
              self[path_field] = []
              self[depth_field] = 0
            else
              self.write_attribute parent_id_field, parent._id
              self[path_field] = parent[path_field] + [parent._id]
              self[depth_field] = parent[depth_field] + 1
              self.save if perform_save
            end
          end

          def reset_parent
            if self.parent_id_changed?
              @_parent = nil
            end
          end

          def add_to_list_bottom
            self.position ||= (self.class.where(:_id.ne => self._id).and(:parent_id => self.parent_id).max(:position) || 0) + 1
          end

          def remove_from_list
            return if (self.site rescue nil).nil?

            self.class.where(:parent_id => self.parent_id).and(:position.gt => self.position).each do |p|
              p.position -= 1
              p.save
            end
          end

        end
      end
    end
  end
end