export const abortError = () => new DOMException("Playback stopped", "AbortError");

// Promises advance only when physics advances. No wall-clock callbacks are
// used to guess when a robot, posture transition, or recorded motion finishes.
export function createSimulationTimeline() {
  const jobs = new Set();
  function run({ duration, update = () => {}, until, maxDuration = Infinity, signal }) {
    if (signal?.aborted) return Promise.reject(abortError());
    return new Promise((resolve, reject) => {
      const job = { elapsed: 0, duration, update, until, maxDuration };
      const finish = (error) => {
        jobs.delete(job);
        signal?.removeEventListener("abort", abort);
        error ? reject(error) : resolve();
      };
      const abort = () => finish(abortError());
      job.finish = finish;
      signal?.addEventListener("abort", abort, { once: true });
      jobs.add(job);
    });
  }
  return {
    run,
    wait: (duration, signal) => run({ duration, signal }),
    until: (until, maxDuration, signal) => run({ until, maxDuration, signal }),
    tick(dt) {
      for (const job of [...jobs]) {
        try {
          job.elapsed += dt;
          const t = job.duration === undefined ? job.elapsed : Math.min(job.elapsed, job.duration);
          job.update(t);
          if (job.until ? job.until(job.elapsed) : job.elapsed + 1e-9 >= job.duration) job.finish();
          else if (job.elapsed >= job.maxDuration) job.finish(new Error("Robot did not finish its movement"));
        } catch (e) { job.finish(e); }
      }
    },
    cancel() { for (const job of [...jobs]) job.finish(abortError()); },
  };
}