class Eco::API::UseCases::GraphQL::Helpers::Location::Command::Diff
  module Compare
    # Sorts from top to bottom (parents go first)
    # @note
    #   1. The analysis below will assume that NO `nodeId` has changed. Which is what
    #     this class helper tries to somehow ensure/emmulate.
    #   2. The below has been thought for NodesDiff::STAGES order:
    #     [:unarchive,  :id_name, :insert, :move, :archive]
    # @note
    #   - If there was a change of id involved in child or parent, the method used
    #     on each (attr vs prev_attr) could be different. We would need to know at
    #     what stage we are in the general update.
    #   - If MOVE has yet to come, `attr_prev` is alright, as we are interested
    #     in the current parent-to-child order in the locations structure.
    #     UNARCHIVE nodes have `attr_prev` and, therefore, this can be used to sort.
    #   - If MOVE has happened, then `attr_prev` is missleading (order could be different),
    #     so `attr` should be used, which refers to the final parents. However,
    #     ARCHIVE nodes only have `attr_prev`, which could refer to the previous parent. And yet
    #     as there's no current data, they have NOT been moved, which makes `prev_attr` reliable.
    # @note
    #   - One thing is still to be resolved. `unarchive?` could entail a later `move?` (same NodeDiff).
    #     Therefore, the STAGE when the comparison is done is relevant.
    #   - This has been resolved with `sort_before_move` & `sort_after_move` methods.
    def <=>(other)
      if archive? || unarchive?
        return -1 if node_id_prev   == other.parent_id_prev
        return  1 if parent_id_prev == other.node_id_prev
      elsif insert? || move?
        return -1 if node_id        == other.parent_id
        return  1 if parent_id      == other.node_id
      end
      0
    end

    def sort_before_move(other)
      self <=> other
    end

    def sort_after_move(other)
      if move?
        return -1 if node_id   == other.parent_id
        return  1 if parent_id == other.node_id
        0
      else
        self <=> other
      end
    end
  end
end