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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;
// Check if an element is scrollable by actually scrolling it.
// Only checks for vertical scrollability.
// Credit: https://github.com/philc/vimium/blob/bdf654aebe6f570f427c5f7bc9592cad86e642b5/content_scripts/scroller.js#L93
const canBeScrolled = (element: Element): boolean => {
const scrollTopBefore = element.scrollTop;
element.scrollBy(0, 1);
const scrollTopAfter = element.scrollTop;
element.scrollBy(0, -1);
return scrollTopBefore + 1 === scrollTopAfter;
};
// Check if the element's overflow and visibility permit scrolling.
// Credit: https://github.com/philc/vimium/blob/bdf654aebe6f570f427c5f7bc9592cad86e642b5/content_scripts/scroller.js#L74
const isScrollableStyle = (element: Element): boolean => {
const {
overflowX,
overflowY,
overflow,
visibility,
} = window.getComputedStyle(element);
if ([overflow, overflowX, overflowY].includes("hidden")) {
return false;
}
if (["hidden", "collapse"].includes(visibility)) {
return false;
}
return canBeScrolled(element);
};
// Find a visible 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)) {
return element;
}
const children = Array.from(element.children).filter(doms.isVisible);
for (const child of children) {
const scrollable = findScrollable(child);
if (scrollable) {
return scrollable;
}
}
return null;
};
const scrollTarget = () => {
if (
window.document.scrollingElement &&
isScrollableStyle(window.document.scrollingElement)
) {
return window.document.scrollingElement;
}
const 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 {
const left = this.element.scrollLeft + x;
const top = this.element.scrollTop + y;
this.scrollTo(left, top);
}
prepareReset(): void {
scrolling = true;
if (lastTimeoutId) {
clearTimeout(lastTimeoutId);
lastTimeoutId = null;
}
lastTimeoutId = window.setTimeout(resetScrolling, 100);
}
}
export type Point = { x: number; y: number };
export default interface ScrollPresenter {
getScroll(): Point;
scrollVertically(amount: number, smooth: boolean): void;
scrollHorizonally(amount: number, smooth: boolean): void;
scrollPages(amount: number, smooth: boolean): void;
scrollTo(x: number, y: number, smooth: boolean): void;
scrollToTop(smooth: boolean): void;
scrollToBottom(smooth: boolean): void;
scrollToHome(smooth: boolean): void;
scrollToEnd(smooth: boolean): void;
}
export class ScrollPresenterImpl {
getScroll(): Point {
const target = scrollTarget();
return { x: target.scrollLeft, y: target.scrollTop };
}
scrollVertically(count: number, smooth: boolean): void {
const target = scrollTarget();
let delta = SCROLL_DELTA_Y * count;
if (scrolling) {
delta = SCROLL_DELTA_Y * count * 4;
}
new Scroller(target, smooth).scrollBy(0, delta);
}
scrollHorizonally(count: number, smooth: boolean): void {
const target = scrollTarget();
let delta = SCROLL_DELTA_X * count;
if (scrolling) {
delta = SCROLL_DELTA_X * count * 4;
}
new Scroller(target, smooth).scrollBy(delta, 0);
}
scrollPages(count: number, smooth: boolean): void {
const target = scrollTarget();
const height = target.clientHeight;
let delta = height * count;
if (scrolling) {
delta = height * count;
}
new Scroller(target, smooth).scrollBy(0, delta);
}
scrollTo(x: number, y: number, smooth: boolean): void {
const target = scrollTarget();
new Scroller(target, smooth).scrollTo(x, y);
}
scrollToTop(smooth: boolean): void {
const target = scrollTarget();
const x = target.scrollLeft;
const y = 0;
new Scroller(target, smooth).scrollTo(x, y);
}
scrollToBottom(smooth: boolean): void {
const target = scrollTarget();
const x = target.scrollLeft;
const y = target.scrollHeight;
new Scroller(target, smooth).scrollTo(x, y);
}
scrollToHome(smooth: boolean): void {
const target = scrollTarget();
const x = 0;
const y = target.scrollTop;
new Scroller(target, smooth).scrollTo(x, y);
}
scrollToEnd(smooth: boolean): void {
const target = scrollTarget();
const x = target.scrollWidth;
const y = target.scrollTop;
new Scroller(target, smooth).scrollTo(x, y);
}
}
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