Creating a spawn point that will enqueue a build

spawn-point.ts

import { createQueue, main, on, Operation, Resource } from 'effection';
import { daemon, exec, Process } from '@effection/process';

import { watch } from 'chokidar';

main(function*() {
  let watcher = watch('./src/**/*.ts', { ignoreInitial: true, ignored: 'dist' });
  try {
    let build = yield createSpawnPoint(start);

    build();

    yield on(watcher, 'all').forEach(build);
  } finally {
    watcher.close();
  }
});

function* start() {
  yield sh("npm run clean");

  yield sh("npm run build");

  let { stdout }: Process = yield daemon('node start.js');


  yield stdout.forEach(output => console.log(output));
}

function *sh(command: string): Operation<void> {
  let process: Process = yield exec(command);
  yield process.stdout.forEach(output => console.log(output));
}


interface SpawnPoint<T> {
  spawn(): void;
}

function createSpawnPoint<T>(operation: Operation<T>): Resource<SpawnPoint<T>> {
  return {
    *init(scope) {
      let current = false;
      let again = false;
      let queue = createQueue<undefined>();
      let enqueue = () => queue.send(undefined);

      yield scope.spawn(queue.forEach(function*() {
        try {
          current = true;
          yield operation;
        } finally {
          current = false;
          if (again) {
            again = false;
            enqueue();
          }
        }
      }));

      return {
        spawn() {
          if (!current) {
            enqueue();
          } else {
            again = true;
          }
        }
      }
    }
  }
}