GC_Hook::resort_active_iterations()

	private function resort_active_iterations( $new_priority = false, $priority_existed = false ) {
		$new_priorities = array_keys( $this->callbacks );

		// If there are no remaining hooks, clear out all running iterations.
		if ( ! $new_priorities ) {
			foreach ( $this->iterations as $index => $iteration ) {
				$this->iterations[ $index ] = $new_priorities;
			}

			return;
		}

		$min = min( $new_priorities );

		foreach ( $this->iterations as $index => &$iteration ) {
			$current = current( $iteration );

			// If we're already at the end of this iteration, just leave the array pointer where it is.
			if ( false === $current ) {
				continue;
			}

			$iteration = $new_priorities;

			if ( $current < $min ) {
				array_unshift( $iteration, $current );
				continue;
			}

			while ( current( $iteration ) < $current ) {
				if ( false === next( $iteration ) ) {
					break;
				}
			}

			// If we have a new priority that didn't exist, but ::apply_filters() or ::do_action() thinks it's the current priority...
			if ( $new_priority === $this->current_priority[ $index ] && ! $priority_existed ) {
				/*
				 * ...and the new priority is the same as what $this->iterations thinks is the previous
				 * priority, we need to move back to it.
				 */

				if ( false === current( $iteration ) ) {
					// If we've already moved off the end of the array, go back to the last element.
					$prev = end( $iteration );
				} else {
					// Otherwise, just go back to the previous element.
					$prev = prev( $iteration );
				}

				if ( false === $prev ) {
					// Start of the array. Reset, and go about our day.
					reset( $iteration );
				} elseif ( $new_priority !== $prev ) {
					// Previous wasn't the same. Move forward again.
					next( $iteration );
				}
			}
		}

		unset( $iteration );
	}