import { MuxAsyncIterator } from "../util/async.ts";

export type Disposable = { dispose: () => void };

/**
 * Generates an AsyncIterable which can be awaited on for one or more signals.
 * `dispose()` can be called when you are finished waiting on the events.
 *
 * Example:
 *
 *       const sig = signal(Deno.Signal.SIGUSR1, Deno.Signal.SIGINT);
 *       setTimeout(() => {}, 5000); // Prevents exiting immediately
 *
 *       for await (const _ of sig) {
 *         console.log("interrupt or usr1 signal received");
 *       }
 *
 *       // At some other point in your code when finished listening:
 *       sig.dispose();
 *
 * @param signos - one or more `Deno.Signal`s to await on
 */
export function signal(
  ...signos: [number, ...number[]]
): AsyncIterable<void> & Disposable {
  const mux = new MuxAsyncIterator<void>();

  if (signos.length < 1) {
    throw new Error(
      "No signals are given. You need to specify at least one signal to create a signal stream."
    );
  }

  const streams = signos.map(Deno.signal);

  streams.forEach((stream) => {
    mux.add(stream);
  });

  // Create dispose method for the muxer of signal streams.
  const dispose = (): void => {
    streams.forEach((stream) => {
      stream.dispose();
    });
  };

  return Object.assign(mux, { dispose });
}

/**
 * Registers a callback function to be called on triggering of a signal event.
 *
 *       const handle = onSignal(Deno.Signal.SIGINT, () => {
 *         console.log('Received SIGINT');
 *         handle.dispose();  // de-register from receiving further events
 *       });
 *
 * @param signo One of Deno.Signal (e.g. Deno.Signal.SIGINT)
 * @param callback Callback function triggered upon signal event
 */
export function onSignal(signo: number, callback: () => void): Disposable {
  const sig = signal(signo);

  //setTimeout allows `sig` to be returned before blocking on the await
  setTimeout(async () => {
    for await (const _ of sig) {
      callback();
    }
  }, 0);

  return sig;
}