/* eslint-disable no-plusplus */
import { raf, cancelRaf } from '../raf';
import { isIOS as checkIsIOS } from '../validate/system';

function isWindow(val) {
  return val === window;
}

export function getScrollTop(el) {
  var top = 'scrollTop' in el ? el.scrollTop : el.pageYOffset; // iOS scroll bounce cause minus scrollTop

  return Math.max(top, 0);
}
export function getRootScrollTop() {
  return window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop || 0;
}
export function setRootScrollTop(value) {
  setScrollTop(window, value); // setScrollTop(document.body, value);
} // get distance from element top to page top or scroller top

export function getElementTop(el, scroller) {
  if (isWindow(el)) {
    return 0;
  }

  var scrollTop = scroller ? getScrollTop(scroller) : getRootScrollTop();
  return el.getBoundingClientRect().top + scrollTop;
}
export function getVisibleHeight(el) {
  if (isWindow(el)) {
    return el.innerHeight;
  }

  return el.getBoundingClientRect().height;
}
export function getVisibleTop(el) {
  if (isWindow(el)) {
    return 0;
  }

  return el.getBoundingClientRect().top;
}
export function setScrollTop(el, value) {
  if ('scrollTop' in el) {
    el.scrollTop = value;
  } else {
    el.scrollTo(el.scrollX, value);
  }
}
var rafId;
export function scrollLeftTo(scroller, to, duration) {
  cancelRaf(rafId);
  var count = 0;
  var from = scroller.scrollLeft;
  var frames = duration === 0 ? 1 : Math.round(duration / 16);

  function animate() {
    scroller.scrollLeft += (to - from) / frames;

    if (++count < frames) {
      rafId = raf(animate);
    }
  }

  animate();
}
export function scrollTopTo(scroller, to, duration, callback) {
  var current = getScrollTop(scroller);
  var isDown = current < to;
  var frames = duration === 0 ? 1 : Math.round(duration / 16);
  var step = (to - current) / frames;

  function animate() {
    current += step;

    if (isDown && current > to || !isDown && current < to) {
      current = to;
    }

    setScrollTop(scroller, current);

    if (isDown && current < to || !isDown && current > to) {
      raf(animate);
    } else if (callback) {
      raf(callback);
    }
  }

  animate();
}
var isIOS = checkIsIOS(); // hack for iOS12 page scroll
// see: https://developers.weixin.qq.com/community/develop/doc/00044ae90742f8c82fb78fcae56800

export function resetScroll() {
  if (isIOS) {
    setRootScrollTop(getRootScrollTop());
  }
}