sclass Schedule<A extends Runnable> extends Meta {
  sclass Entry {}
  srecord Action<A>(A action) extends Entry {}
  srecord Jump (Seconds dest) extends Entry {}

  new TreeMultiMap<Seconds, Entry> entries;
  
  Timestamp start;
  TreeMultiMap<Seconds, Entry> currentEntries;

  void add(double seconds, A a) {
    entries.put(Seconds(seconds), new Action<A>(a));
  }
  
  void jumpFromTo(double from, double to) {
    entries.put(Seconds(from), new Jump(Seconds(to)));
  }
  
  void speedUp(double factor) {
    entries = (TreeMultiMap) mapMultiMapKeys(entries, seconds -> seconds.div(factor));
  }
  
  run {
    start = tsNow();
    reschedule(Seconds(0));
    while ping (nempty(currentEntries))
      fire(first(currentEntries));
  }
  
  void reschedule(Seconds startInSchedule) {
    currentEntries = (TreeMultiMap) cloneTailMultiMap(entries, startInSchedule, true);
    /*if (scaffoldActive(this))
      printStruct(this);*/
  }
  
  scaffolded void fire(Pair<Seconds, Entry> p) {
    if (p == null) ret;
    currentEntries.removePair(p);
    sleepUntil(start.plus(p.a));
    var e = p.b;
    if (e cast Action<A>)
      pcallF(e.action);
    else if (e cast Jump) {
      start = start.plus(p.a.minus(e.dest));
      reschedule(e.dest);
    } else
      fail(e);
  }
}