import { Source, Subscription, TalkbackKind, SignalKind } from './types';
import { talkbackPlaceholder } from './helpers';

export function subscribe<T>(subscriber: (value: T) => void) {
  return (source: Source<T>): Subscription => {
    let talkback = talkbackPlaceholder;
    let ended = false;
    source(signal => {
      if (signal === SignalKind.End) {
        ended = true;
      } else if (signal.tag === SignalKind.Start) {
        (talkback = signal[0])(TalkbackKind.Pull);
      } else if (!ended) {
        subscriber(signal[0]);
        talkback(TalkbackKind.Pull);
      }
    });
    return {
      unsubscribe() {
        if (!ended) {
          ended = true;
          talkback(TalkbackKind.Close);
        }
      },
    };
  };
}

export function forEach<T>(subscriber: (value: T) => void) {
  return (source: Source<T>): void => {
    subscribe(subscriber)(source);
  };
}

export function publish<T>(source: Source<T>): void {
  subscribe(_value => {
    /*noop*/
  })(source);
}

export function toArray<T>(source: Source<T>): T[] {
  const values: T[] = [];
  let talkback = talkbackPlaceholder;
  let ended = false;
  source(signal => {
    if (signal === SignalKind.End) {
      ended = true;
    } else if (signal.tag === SignalKind.Start) {
      (talkback = signal[0])(TalkbackKind.Pull);
    } else {
      values.push(signal[0]);
      talkback(TalkbackKind.Pull);
    }
  });
  if (!ended) talkback(TalkbackKind.Close);
  return values;
}

export function toPromise<T>(source: Source<T>): Promise<T> {
  return new Promise(resolve => {
    let talkback = talkbackPlaceholder;
    let value: T | void;
    source(signal => {
      if (signal === SignalKind.End) {
        resolve(value!);
      } else if (signal.tag === SignalKind.Start) {
        (talkback = signal[0])(TalkbackKind.Pull);
      } else {
        value = signal[0];
        talkback(TalkbackKind.Pull);
      }
    });
  });
}