execute method

@override FutureOr<Step?> execute(FlowContextController controller, [ FutureOr<Step?> candidate()? ])

Executes the builder function until an escape prompt is received.

Increases the FlowContext's depth and runs steps.

If closed the function will return it's given candidate or null.

Implementation

@override
FutureOr<Step?> execute(
    final FlowContextController controller, [
      FutureOr<Step?> candidate()?,
    ]) async {
  controller.depth++;
  final int initialDepth = controller.depth;
  final none = () => null;

  /*
   * The [decide()] function will be the candidate for every [Step] of his
   * builder. Therefore whenever the next Step should be returned, the [Bubble]
   * will decide if it is still open and return the next [decide()] or the actual
   * next "[candidate]" ([Step] in execution order).
   */
  FutureOr<Step?> decide() async {

    /*
     * The [depth] of the controller will be able to change from the
     * [Step]s the [Bubble] includes.
     */
    if (initialDepth > controller.depth) {
      return (candidate ?? none)();
    }

    /*
     * In a derived class, leave can be set to leave the [Bubble] successfully.
     * (Just without an error message)
     */
    if (leave) {
      controller.depth--;
      return (candidate ?? none)();
    }
    return builder().execute(controller, decide);
  }
  return decide();
}