const now = Date.now;

export function debounce(func: Function, wait = 300) {
  let lastArgs;
  let lastThis;
  let maxWait;
  let result;
  let timerId;
  let lastCallTime;
  let lastInvokeTime = 0;
  const leading = false;
  const maxing = false;
  const trailing = true;

  if (typeof func !== 'function') {
    throw new TypeError('Expected a function');
  }

  function invokeFunc(time) {
    const args = lastArgs;
    const thisArg = lastThis;

    // eslint-disable-next-line no-multi-assign
    lastArgs = lastThis = undefined;
    lastInvokeTime = time;
    result = func.apply(thisArg, args);
    return result;
  }

  function shouldInvoke(time) {
    const timeSinceLastCall = time - lastCallTime;
    const timeSinceLastInvoke = time - lastInvokeTime;

    // Either this is the first call, activity has stopped and we're at the
    // trailing edge, the system time has gone backwards and we're treating
    // it as the trailing edge, or we've hit the `maxWait` limit.
    return (lastCallTime === undefined || (timeSinceLastCall >= wait) ||
      (timeSinceLastCall < 0) || (maxing && timeSinceLastInvoke >= maxWait));
  }

  function remainingWait(time) {
    const timeSinceLastCall = time - lastCallTime;
    const timeSinceLastInvoke = time - lastInvokeTime;
    const timeWaiting = wait - timeSinceLastCall;

    return maxing
      ? Math.min(timeWaiting, maxWait - timeSinceLastInvoke)
      : timeWaiting;
  }

  function trailingEdge(time) {
    timerId = undefined;

    // Only invoke if we have `lastArgs` which means `func` has been
    // debounced at least once.
    if (trailing && lastArgs) {
      return invokeFunc(time);
    }
    // eslint-disable-next-line no-multi-assign
    lastArgs = lastThis = undefined;
    return result;
  }

  function timerExpired() {
    const time = now();
    if (shouldInvoke(time)) {
      return trailingEdge(time);
    }
    // Restart the timer.
    timerId = setTimeout(timerExpired, remainingWait(time));
  }

  function leadingEdge(time) {
    // Reset any `maxWait` timer.
    lastInvokeTime = time;
    // Start the timer for the trailing edge.
    timerId = setTimeout(timerExpired, wait);
    // Invoke the leading edge.
    return leading ? invokeFunc(time) : result;
  }

  function cancel() {
    if (timerId !== undefined) {
      clearTimeout(timerId);
    }
    lastInvokeTime = 0;
    // eslint-disable-next-line no-multi-assign
    lastArgs = lastCallTime = lastThis = timerId = undefined;
  }

  function flush() {
    return timerId === undefined ? result : trailingEdge(now());
  }

  function debounced() {
    const time = now();
    const isInvoking = shouldInvoke(time);

    // eslint-disable-next-line prefer-rest-params
    lastArgs = arguments;
    // eslint-disable-next-line @typescript-eslint/no-this-alias
    lastThis = this;
    lastCallTime = time;

    if (isInvoking) {
      if (timerId === undefined) {
        return leadingEdge(lastCallTime);
      }
      if (maxing) {
        // Handle invocations in a tight loop.
        clearTimeout(timerId);
        timerId = setTimeout(timerExpired, wait);
        return invokeFunc(lastCallTime);
      }
    }
    if (timerId === undefined) {
      timerId = setTimeout(timerExpired, wait);
    }
    return result;
  }
  debounced.cancel = cancel;
  debounced.flush = flush;
  return debounced;
}