export type ScrollListener = {

	source: Event;
	viewWidth: number;
	viewHeight: number;
	top: number;
	bottom: number;
}

export default class Scroller {

	private static instance: Scroller;

	listeners = new Map<string, Function>();

	private constructor() {

		window.addEventListener("scroll", source => {
			// 滚动距离
			const top = document.body.scrollTop || document.documentElement.scrollTop;
			// 可视高度
			const viewWidth = document.documentElement.clientWidth || document.body.clientWidth;
			// 可视高度
			const viewHeight = document.documentElement.clientHeight || document.body.clientHeight;
			// 滚动高度
			const sH = document.documentElement.scrollHeight || document.body.scrollHeight;
			// 触发事件
			const bottom = sH - top - viewHeight;
			this.listeners.forEach(listener => listener({
				source,
				viewWidth,
				viewHeight,
				top,
				bottom
			} as ScrollListener));
		}, true);
	}

	private static getInstance(): Scroller {
		if (!Scroller.instance) {
			Scroller.instance = new Scroller();
		}
		return Scroller.instance;
	}

	/**
	 * 添加监听
	 *
	 * @param name     事件名
	 * @param listener 监听事件
	 */
	public static addListener(name: string, listener: (event: ScrollListener) => void) {
		Scroller.getInstance().listeners.set(name, listener);
	}

	/**
	 * 移除监听
	 *
	 * @param name 事件名
	 */
	public static removeListener(name: string) {
		Scroller.getInstance().listeners.delete(name);
	}

	/** 滚动至顶（平滑地） */
	public static toTop() {
		document.body.scrollIntoView({behavior: "smooth"});
	}

	/** 滚动至指定节点（平滑地） */
	public static toElement(el: HTMLElement) {
		el.scrollIntoView({behavior: "smooth"});
	}
}