// runs on load
export function* main() {
  const pollingInstance = yield fork(pollingWatcher);
  // fork other watchers ...

  // if location changes, kill the watcher(s)
  yield take(LOCATION_CHANGE);
  yield cancel(pollingInstance);
  // cancel other watchers ...
}


// Listen for every START and fork off saga that will start/stop polling
export function* pollingWatcher() {
  yield fork(takeEvery, START, pollRacer);
}


export function* pollRacer(raceAction) {
  const { response, cancelPolling } = yield race({
    response: call(pollingSaga, raceAction),
    cancelPolling: take(action => (action.type.endsWith('CANCEL') && action.payload.data.id === raceAction.payload.data.id))
  });
}


// try polling every 3 seconds until the server completes or errors out
// put success or failure actions
export function* pollingSaga(action) {
  try {
    const { id } = action.payload.data;

    let status = 'p';
    let pollResponse;

    while (status !== 'complete') {
      yield call(delay, 3000);
      pollResponse = yield call(request, someUrl, id);
      status = pollResponse.data && pollResponse.data.status;
      if (status === 'error') throw new Error('Runtime error');
    }

    yield put(pollSuccess(pollResponse.data));
  } catch (error) {
    yield put(pollFailure(error));
  } finally {
    if (yield cancelled()) {
      console.log('pollingSaga cancelled');
    }
  }
}