const PENDING = 'pending';
const FULFILLED = 'fulfilled';
const REJECTED = 'rejected';

class Waiter {
  constructor (callback) {
    this.accept = this.accept.bind(this);
    this.reject = this.reject.bind(this);
    this.state = PENDING;
    this.successCallbacks = [];
    this.failureCallbacks = [];
    this.isWaiter = true;
    this.value = null;

    if (callback) callback(this.accept, this.reject);
  }

  accept(value) {
    setTimeout(() => {
      this.state = FULFILLED;
      this.value = value;

      for (var i = 0; i < this.successCallbacks.length; i++)
        this.successCallbacks[i](value);

      this.successCallbacks = [];
    }, 0);
  }

  reject(value) {
    setTimeout(() => {
      this.state = REJECTED;
      this.value = value;

      if (this.failureCallbacks.length === 0)
        throw new Error("Unhandled waiter rejection: " + value);

      for (var i = 0; i < this.failureCallbacks.length; i++)
        this.failureCallbacks[i](value);

      this.failureCallbacks = [];
    });
  }

  then(successCallback, failureCallback) {
    var tmpAccept, tmpReject;
    var tmpWaiter = new Waiter((accept, reject) => {
      tmpAccept = accept;
      tmpReject = reject;
    });

    if (successCallback)
      this.successCallbacks.push(
        this.createRunner(successCallback, tmpAccept, tmpReject)
      );

    if (failureCallback)
      this.failureCallbacks.push(
        this.createRunner(failureCallback, tmpAccept, tmpReject)
      );

    if (this.state === FULFILLED) this.accept(this.value);
    if (this.state === REJECTED) this.reject(this.value);

    tmpWaiter.resolve = null;
    return tmpWaiter;
  }

  catch(failureCallback) {
    return this.then(null, failureCallback);
  }

  resolve() {
    this.accept();
    return this;
  }

  createRunner(callback, tmpAccept, tmpReject) {
    return (value) => {
      try {
        let result = callback(value);

        if (result && result.isWaiter) {
          result.then(tmpAccept, tmpReject);
        } else {
          tmpAccept(result);
        }
      } catch (error) {
        tmpReject(error);
      }
    };
  }
}


// Testing Code

let testWaiter = new Waiter(function (accept, reject) {
  setTimeout(() => accept('hi'), 500);
});

testWaiter.then(function (value) {
  console.log(value + ' friend');
  return new Waiter(function (accept, reject) {
    setTimeout(() => reject('oh man'), 1000);
  });
})
.then(function (value) {
  console.log('todo bien');
},
function (error) {
  console.log('"' + error + '"');
});

testWaiter.then(function (value) {
  console.log(value);
  console.log('Robert');
  return new Waiter(function (accept, reject) {
    setTimeout(() => accept('how?'), 250);
  });
})
.then(function (value) {
  console.log(value);
})
.then(function (value) {
  console.log('what?');
  throw new Error('test');
})
.catch(function (value) {
  console.log('"' + value + '"');
})
.then(function (value) {
  console.log('After error: ' + value);
});