observable

function Observer(onNext, onError = () => {}, onComplete = () => {}) {
  const def = () => {};
  if (typeof onNext === 'object') {
    onError = onNext.error || def;
    onComplete = onNext.complete || def;
    onNext = onNext.next || def;
  }
  this.completed = false;
  this.withError = false;
  this.next = (val) => {
    if (!this.completed) onNext(val);
  };
  this.error = (err) => {
    if (!this.completed) {
      this.completed = true;
      this.withError = true;
      onError(err);
    }
  };
  this.complete = () => {
    if (!this.completed) {
      this.completed = true;
      onComplete();
    }
  };
}

function Observable(observer) {
  this.subscribe = (...fns) => {
    if(observer) {
      const obs = new Observer(...fns);
      observer(obs);
    }
  };
  
  this.unsubscribe = () => {
    observer = null;
  }
}