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// Basic port modification of Reacts Scheduler: https://github.com/facebook/react/tree/master/packages/schedulerexport interface Task {  id: number;  fn: ((didTimeout: boolean) => void) | null;  startTime: number;  expirationTime: number;}
// experimental new feature proposal stufftype NavigatorScheduling = Navigator & {  scheduling: { isInputPending?: () => boolean };};
let taskIdCounter = 1,  isCallbackScheduled = false,  isPerformingWork = false,  taskQueue: Task[] = [],  currentTask: Task | null = null,  shouldYieldToHost: (() => boolean) | null = null,  yieldInterval = 5,  deadline = 0,  maxYieldInterval = 300,  scheduleCallback: (() => void) | null = null,  scheduledCallback: ((hasTimeRemaining: boolean, initialTime: number) => boolean) | null = null;
const maxSigned31BitInt = 1073741823;/* istanbul ignore next */function setupScheduler() {  const channel = new MessageChannel(),    port = channel.port2;  scheduleCallback = () => port.postMessage(null);  channel.port1.onmessage = () => {    if (scheduledCallback !== null) {      const currentTime = performance.now();      deadline = currentTime + yieldInterval;      const hasTimeRemaining = true;      try {        const hasMoreWork = scheduledCallback(hasTimeRemaining, currentTime);        if (!hasMoreWork) {          scheduledCallback = null;        } else port.postMessage(null);      } catch (error) {        // If a scheduler task throws, exit the current browser task so the        // error can be observed.        port.postMessage(null);        throw error;      }    }  };
  if (    navigator &&    (navigator as NavigatorScheduling).scheduling &&    (navigator as NavigatorScheduling).scheduling.isInputPending  ) {    const scheduling = (navigator as NavigatorScheduling).scheduling;    shouldYieldToHost = () => {      const currentTime = performance.now();      if (currentTime >= deadline) {        // There's no time left. We may want to yield control of the main        // thread, so the browser can perform high priority tasks. The main ones        // are painting and user input. If there's a pending paint or a pending        // input, then we should yield. But if there's neither, then we can        // yield less often while remaining responsive. We'll eventually yield        // regardless, since there could be a pending paint that wasn't        // accompanied by a call to `requestPaint`, or other main thread tasks        // like network events.        if (scheduling.isInputPending!()) {          return true;        }        // There's no pending input. Only yield if we've reached the max        // yield interval.        return currentTime >= maxYieldInterval;      } else {        // There's still time left in the frame.        return false;      }    };  } else {    // `isInputPending` is not available. Since we have no way of knowing if    // there's pending input, always yield at the end of the frame.    shouldYieldToHost = () => performance.now() >= deadline;  }}
function enqueue(taskQueue: Task[], task: Task) {  function findIndex() {    let m = 0;    let n = taskQueue.length - 1;
    while (m <= n) {      const k = (n + m) >> 1;      const cmp = task.expirationTime - taskQueue[k].expirationTime;      if (cmp > 0) m = k + 1;      else if (cmp < 0) n = k - 1;      else return k;    }    return m;  }  taskQueue.splice(findIndex(), 0, task);}
export function requestCallback(fn: () => void, options?: { timeout: number }): Task {  if (!scheduleCallback) setupScheduler();  let startTime = performance.now(),    timeout = maxSigned31BitInt;
  if (options && options.timeout) timeout = options.timeout;
  const newTask: Task = {    id: taskIdCounter++,    fn,    startTime,    expirationTime: startTime + timeout  };
  enqueue(taskQueue, newTask);  if (!isCallbackScheduled && !isPerformingWork) {    isCallbackScheduled = true;    scheduledCallback = flushWork;    scheduleCallback!();  }
  return newTask;}
export function cancelCallback(task: Task) {  task.fn = null;}
function flushWork(hasTimeRemaining: boolean, initialTime: number) {  // We'll need a host callback the next time work is scheduled.  isCallbackScheduled = false;  isPerformingWork = true;  try {    return workLoop(hasTimeRemaining, initialTime);  } finally {    currentTask = null;    isPerformingWork = false;  }}
function workLoop(hasTimeRemaining: boolean, initialTime: number) {  let currentTime = initialTime;  currentTask = taskQueue[0] || null;  while (currentTask !== null) {    if (currentTask.expirationTime > currentTime && (!hasTimeRemaining || shouldYieldToHost!())) {      // This currentTask hasn't expired, and we've reached the deadline.      break;    }    const callback = currentTask.fn;    if (callback !== null) {      currentTask.fn = null;      const didUserCallbackTimeout = currentTask.expirationTime <= currentTime;      callback(didUserCallbackTimeout);      currentTime = performance.now();      if (currentTask === taskQueue[0]) {        taskQueue.shift();      }    } else taskQueue.shift();    currentTask = taskQueue[0] || null;  }  // Return whether there's additional work  return currentTask !== null;}