bindcallback.ts

import { AsyncIterableX } from '../asynciterable';
import { AsyncSink } from '../asyncsink';
import { memoize } from './memoize';

export function bindCallback<TSource>(
  func: Function,
  selector: Function
): (...args: any[]) => AsyncIterableX<TSource> {
  return function(...args: any[]) {

    const sink = new AsyncSink<TSource>();

    const handler = function(...innerArgs: any[]) {
      if (selector) {
        try {
          const result = selector(...innerArgs);
          sink.write(result);
        } catch (e) {
          sink.error(e);
        }
      } else {
        sink.write(innerArgs.length <= 1 ? innerArgs[0] : innerArgs);
      }
    };

    try {
      func.apply(null, args.concat(handler));
    } catch (e) {
      sink.error(e);
    }

    return memoize(
      (async function*() {
        for (let next; !(next = await sink.next()).done; ) {
          yield next.value;
        }

        sink.end();
      })()
    );
  };
}