RFC(StepFunctions): A way to have States inside a Chain more easily exposed

[andrestone]

Maybe I'm missing something, but I couldn't find any friendly path to play with definitions programatically. All properties / methods that could be used to this purpose are inaccessible from outside the class definition scope.

I'd like to have a simple public method similar to findReachableEndStates, that could be defined like this:

  /**
   * Find the set of states reachable through transitions from the given start state
   */
  public static findReachableStates(start: State, options: FindStateOptions = {}) {
    const visited = new Set<State>();
    const ret = new Set<State>();
    const queue = [start];
    while (queue.length > 0) {
      const state = queue.splice(0, 1)[0]!;
      if (visited.has(state)) { continue; }
      visited.add(state);
      const outgoing = state.outgoingTransitions(options);
      queue.push(...outgoing);
      ret.add(state);
    }
    return Array.from(ret);
  }

[nija-at]

Hi @andrestone - thanks for updating. I'm not sure I quite follow what you've said. Can you expand or provide a concrete example?

Sure.

This method takes an original definition and adds a ResumeTo Choice state to the top of the chain, programatically adding each existing state id as a Choice condition to be matched.

private static transformToResumable(definition: sf.IChainable): sf.IChainable {
    // Building a set of States
    const states = new Set<sf.State>();

    // All states starting from a giving state (using the method of this PR)
    sf.State.findReachableStates(definition.startState).forEach(state => {
        states.add(state);
    });

    // Here we add our ResumeTo logic to the top of the chain
    const choices = new sf.Choice(scope, "ResumeTo");

    // We used Set to ensure we have only a single state, although it's redundant with
    // the method implementation
    let statesArray = Array.from(states);

    // For each pre-existing state, we add a Choice condition
    for (let i = 0; i < statesArray.length; i++) {
        choices.when(sf.Condition.stringEquals('$.resumeTo', statesArray[i].id), statesArray[i]);
    }

    // The default is the original definition
    choices.otherwise(definition);

    // This is our new State Machine definition ready to accept `resumeTo` as part of the input
    // to resume the execution starting from the referred state
    return choices
}

Should I add this to the commit message?

Thanks.

Originally posted by @andrestone in #7324 (comment)