module Scrivito

class WidgetGarbageCollection

  # @param [BasicObj] obj the Obj that the update applies to
  # @param [Hash] update the keys are content objects (Obj or Widget)
  #   and the values are their update params.
  #   update params are accepted in the same format as accepted by Obj.create or Obj#update.
  #   each content object must either be the obj itself or a widget that lives inside the obj.
  def initialize(obj, update)
    if update.blank?
      raise ScrivitoError, "blank update!"
    end

    update.keys.each do |content|
      if content.is_a?(BasicObj)
        raise "invalid obj given" unless content == obj
      elsif content.is_a?(BasicWidget)
        raise "invalid widget given" unless content.obj == obj
      else
        raise "invalid key"
      end
    end

    @update = update
    @obj = obj
  end

  # @return [Array] list containing the widgets that are no longer needed after the update.
  def widgets_to_delete
    dereferenced = []
    newreferenced = []

    @update.each do |content, params|
      (deref, newref) = changed_references_from(content, params)
      dereferenced += deref
      newreferenced += newref
    end

    deleted_by_dereference = dereferenced - newreferenced

    recursively_deleted = []
    deleted_by_dereference.each do |widget|
      recursively_deleted += all_widgets_contained_in_except(widget, newreferenced)
    end

    # we dont want to slow down every request by scanning for orphans, so
    # we only do this when widgets are being deleted
    if deleted_by_dereference.present?
      orphans = @obj.all_widgets_from_pool - @obj.contained_widgets - newreferenced
    else
      orphans = []
    end

    deleted_by_dereference + recursively_deleted + orphans
  end

  private

  def all_widgets_contained_in_except(widget, exceptions)
    widget_children = widget.referenced_widgets - exceptions

    widget_descendants = widget_children.map do |child|
      all_widgets_contained_in_except(child, exceptions)
    end.flatten

    widget_children + widget_descendants
  end

  def changed_references_from(content, params)
    dereferenced_ids = []
    newreferenced_ids = []

    if content.kind_of?(BasicWidget) && !content.persisted?
      params.each_value do |value|
        if value.kind_of?(Array)
          newreferenced_ids += value.select { |v| v.kind_of?(BasicWidget) }
        end
      end
    else
      params.each do |key, value|
        if content.type_of_attribute(key) == 'widgetlist'
          current = content[key] || []
          new = value || []

          dereferenced_ids += current - new
          newreferenced_ids += new - current
        end
      end
    end

    [dereferenced_ids, newreferenced_ids]
  end

end

end