temporal-time-utils/UpdatableTimer.ts

This is a library with some reusable functions for [Temporal.io TypeScript SDK](https://docs.temporal.io/docs/typescript/introduction):

import * as wf from "@temporalio/workflow";

// // example usage
// export async function countdownWorkflow(): Promise<void> {
//   const target = Date.now() + 24 * 60 * 60 * 1000; // 1 day!!!
//   const timer = new UpdatableTimer(target);
//   console.log('timer set for: ' + new Date(target).toString());
//   wf.setListener(setDeadlineSignal, (deadline) => {
//     // send in new deadlines via Signal
//     timer.deadline = deadline;
//     console.log('timer now set for: ' + new Date(deadline).toString());
//   });
//   wf.setListener(timeLeftQuery, () => timer.deadline - Date.now());
//   await timer; // if you send in a signal with a new time, this timer will resolve earlier!
//   console.log('countdown done!');
// }

/**
 * A timer that can be updated with a new deadline.
 */
export class UpdatableTimer implements PromiseLike<void> {
  deadlineUpdated = false;
  #deadline: number;

  constructor(deadline: number) {
    this.#deadline = deadline;
  }

  private async run(): Promise<void> {
    /* eslint-disable no-constant-condition */
    while (true) {
      this.deadlineUpdated = false;
      if (
        !(await wf.condition(
          () => this.deadlineUpdated,
          this.#deadline - Date.now()
        ))
      ) {
        break;
      }
    }
  }

  then<TResult1 = void, TResult2 = never>(
    onfulfilled?: (value: void) => TResult1 | PromiseLike<TResult1>,
    onrejected?: (reason: any) => TResult2 | PromiseLike<TResult2>
  ): PromiseLike<TResult1 | TResult2> {
    return this.run().then(onfulfilled, onrejected);
  }

  set deadline(value: number) {
    this.#deadline = value;
    this.deadlineUpdated = true;
  }

  get deadline(): number {
    return this.#deadline;
  }
}