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import * as doms from '../shared/utils/dom';
const SCROLL_DELTA_X = 64;
const SCROLL_DELTA_Y = 64;
// dirty way to store scrolling state on globally
let scrolling = false;
let lastTimeoutId: number | null = null;
const isScrollableStyle = (element: Element): boolean => {
let { overflowX, overflowY } = window.getComputedStyle(element);
return !(overflowX !== 'scroll' && overflowX !== 'auto' &&
overflowY !== 'scroll' && overflowY !== 'auto');
};
const isOverflowed = (element: Element): boolean => {
return element.scrollWidth > element.clientWidth ||
element.scrollHeight > element.clientHeight;
};
// Find a visiable and scrollable element by depth-first search. Currently
// this method is called by each scrolling, and the returned value of this
// method is not cached. That does not cause performance issue because in the
// most pages, the window is root element i,e, documentElement.
const findScrollable = (element: Element): Element | null => {
if (isScrollableStyle(element) && isOverflowed(element)) {
return element;
}
let children = Array.from(element.children).filter(doms.isVisible);
for (let child of children) {
let scrollable = findScrollable(child);
if (scrollable) {
return scrollable;
}
}
return null;
};
const scrollTarget = () => {
if (isOverflowed(window.document.documentElement)) {
return window.document.documentElement;
}
if (isOverflowed(window.document.body)) {
return window.document.body;
}
let target = findScrollable(window.document.documentElement);
if (target) {
return target;
}
return window.document.documentElement;
};
const resetScrolling = () => {
scrolling = false;
};
class Scroller {
private element: Element;
private smooth: boolean;
constructor(element: Element, smooth: boolean) {
this.element = element;
this.smooth = smooth;
}
scrollTo(x: number, y: number): void {
if (!this.smooth) {
this.element.scrollTo(x, y);
return;
}
this.element.scrollTo({
left: x,
top: y,
behavior: 'smooth',
});
this.prepareReset();
}
scrollBy(x: number, y: number): void {
let left = this.element.scrollLeft + x;
let top = this.element.scrollTop + y;
this.scrollTo(left, top);
}
prepareReset(): void {
scrolling = true;
if (lastTimeoutId) {
clearTimeout(lastTimeoutId);
lastTimeoutId = null;
}
lastTimeoutId = setTimeout(resetScrolling, 100);
}
}
const getScroll = () => {
let target = scrollTarget();
return { x: target.scrollLeft, y: target.scrollTop };
};
const scrollVertically = (count: number, smooth: boolean): void => {
let target = scrollTarget();
let delta = SCROLL_DELTA_Y * count;
if (scrolling) {
delta = SCROLL_DELTA_Y * count * 4;
}
new Scroller(target, smooth).scrollBy(0, delta);
};
const scrollHorizonally = (count: number, smooth: boolean): void => {
let target = scrollTarget();
let delta = SCROLL_DELTA_X * count;
if (scrolling) {
delta = SCROLL_DELTA_X * count * 4;
}
new Scroller(target, smooth).scrollBy(delta, 0);
};
const scrollPages = (count: number, smooth: boolean): void => {
let target = scrollTarget();
let height = target.clientHeight;
let delta = height * count;
if (scrolling) {
delta = height * count;
}
new Scroller(target, smooth).scrollBy(0, delta);
};
const scrollTo = (x: number, y: number, smooth: boolean): void => {
let target = scrollTarget();
new Scroller(target, smooth).scrollTo(x, y);
};
const scrollToTop = (smooth: boolean): void => {
let target = scrollTarget();
let x = target.scrollLeft;
let y = 0;
new Scroller(target, smooth).scrollTo(x, y);
};
const scrollToBottom = (smooth: boolean): void => {
let target = scrollTarget();
let x = target.scrollLeft;
let y = target.scrollHeight;
new Scroller(target, smooth).scrollTo(x, y);
};
const scrollToHome = (smooth: boolean): void => {
let target = scrollTarget();
let x = 0;
let y = target.scrollTop;
new Scroller(target, smooth).scrollTo(x, y);
};
const scrollToEnd = (smooth: boolean): void => {
let target = scrollTarget();
let x = target.scrollWidth;
let y = target.scrollTop;
new Scroller(target, smooth).scrollTo(x, y);
};
export {
getScroll,
scrollVertically, scrollHorizonally, scrollPages,
scrollTo,
scrollToTop, scrollToBottom, scrollToHome, scrollToEnd
};
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