module RelativePositioning extend ActiveSupport::Concern MIN_POSITION = 0 START_POSITION = Gitlab::Database::MAX_INT_VALUE / 2 MAX_POSITION = Gitlab::Database::MAX_INT_VALUE IDEAL_DISTANCE = 500 included do after_save :save_positionable_neighbours end def max_relative_position self.class.in_projects(project.id).maximum(:relative_position) end def prev_relative_position prev_pos = nil if self.relative_position prev_pos = self.class .in_projects(project.id) .where('relative_position < ?', self.relative_position) .maximum(:relative_position) end prev_pos end def next_relative_position next_pos = nil if self.relative_position next_pos = self.class .in_projects(project.id) .where('relative_position > ?', self.relative_position) .minimum(:relative_position) end next_pos end def move_between(before, after) return move_after(before) unless after return move_before(after) unless before # If there is no place to insert an issue we need to create one by moving the before issue closer # to its predecessor. This process will recursively move all the predecessors until we have a place if (after.relative_position - before.relative_position) < 2 before.move_before @positionable_neighbours = [before] end self.relative_position = position_between(before.relative_position, after.relative_position) end def move_after(before = self) pos_before = before.relative_position pos_after = before.next_relative_position if before.shift_after? issue_to_move = self.class.in_projects(project.id).find_by!(relative_position: pos_after) issue_to_move.move_after @positionable_neighbours = [issue_to_move] pos_after = issue_to_move.relative_position end self.relative_position = position_between(pos_before, pos_after) end def move_before(after = self) pos_after = after.relative_position pos_before = after.prev_relative_position if after.shift_before? issue_to_move = self.class.in_projects(project.id).find_by!(relative_position: pos_before) issue_to_move.move_before @positionable_neighbours = [issue_to_move] pos_before = issue_to_move.relative_position end self.relative_position = position_between(pos_before, pos_after) end def move_to_end self.relative_position = position_between(max_relative_position || START_POSITION, MAX_POSITION) end # Indicates if there is an issue that should be shifted to free the place def shift_after? next_pos = next_relative_position next_pos && (next_pos - relative_position) == 1 end # Indicates if there is an issue that should be shifted to free the place def shift_before? prev_pos = prev_relative_position prev_pos && (relative_position - prev_pos) == 1 end private # This method takes two integer values (positions) and # calculates the position between them. The range is huge as # the maximum integer value is 2147483647. We are incrementing position by IDEAL_DISTANCE * 2 every time # when we have enough space. If distance is less then IDEAL_DISTANCE we are calculating an average number def position_between(pos_before, pos_after) pos_before ||= MIN_POSITION pos_after ||= MAX_POSITION pos_before, pos_after = [pos_before, pos_after].sort halfway = (pos_after + pos_before) / 2 distance_to_halfway = pos_after - halfway if distance_to_halfway < IDEAL_DISTANCE halfway else if pos_before == MIN_POSITION pos_after - IDEAL_DISTANCE elsif pos_after == MAX_POSITION pos_before + IDEAL_DISTANCE else halfway end end end def save_positionable_neighbours return unless @positionable_neighbours status = @positionable_neighbours.all?(&:save) @positionable_neighbours = nil status end end