const callbacks = [];
let pending = false;

function flushCallbacks() {
  pending = false;
  const copiedCallbacks = callbacks.slice(0);

  callbacks.length = 0;

  copiedCallbacks.forEach(callback => callback());
}


let microTimerFunction = null;
let macroTimerFunction = null;

if (window && typeof (window as any).setImmediate  !== 'undefined') {
  macroTimerFunction = () => {
    (window as any).setImmediate(flushCallbacks);
  };
} else if (typeof MessageChannel !== 'undefined') {
  const channel = new MessageChannel();
  const port = channel.port2;
  channel.port1.onmessage = flushCallbacks;
  macroTimerFunction = () => {
    port.postMessage(1);
  };
} else {
  macroTimerFunction = () => {
    window.setTimeout(flushCallbacks, 0);
  };
}


if (typeof Promise !== 'undefined') {
  const promise = Promise.resolve();
  microTimerFunction = () => {
    promise.then(flushCallbacks);
  };
} else {
  // fallback to macro
  microTimerFunction = macroTimerFunction;
}


const nextTick = (callback: Function) => {
  callbacks.push(callback);

  if (!pending) {
    pending = true;
    microTimerFunction();
  }
};

export {
  nextTick,
};