module Extensions
  module Page
    module Tree

      extend ActiveSupport::Concern

      included do
        include Mongoid::Acts::Tree

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

        ## 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 ||= (::Page.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?

          ::Page.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