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import { Component, OnInit, OnChanges, Input, Output, EventEmitter,
HostListener, ElementRef } from '@angular/core';
import { throttle as _throttle, noop as _noop } from "lodash-es";
enum ScrollDirection {
UP = 'up',
DOWN = 'down'
}
enum ScrollListener {
HOST = 'scroll',
WINDOW = 'window:scroll'
}
@Component({
selector: 'rdp-scroll-container',
templateUrl: './rdp-scroll-container.component.html',
styleUrls: ['./rdp-scroll-container.component.scss']
})
export class RdpScrollContainerComponent implements OnInit, OnChanges {
private _element: Element;
private _window: Element;
public scrollTop = 0;
@Input() more = true;
@Input() scrollDelay = 500;
@Input() scrollOffset = 1000;
@Output() scrolled: EventEmitter<boolean> = new EventEmitter<boolean>();
@HostListener(ScrollListener.HOST) _scroll: Function;
@HostListener(ScrollListener.WINDOW) _windowScroll: Function;
constructor(private elRef: ElementRef) {
this._element = this.elRef.nativeElement;
this._window = document.documentElement as Element;
}
ngOnInit() {
this.setThrottle();
}
ngOnChanges(changes) {
if (changes.scrollDelay) this.setThrottle();
}
setThrottle() {
this._scroll = this._windowScroll = _throttle(this.handleScroll, this.scrollDelay);
}
getListener = () => this.elRef.nativeElement.clientHeight === this.elRef.nativeElement.scrollHeight
? ScrollListener.WINDOW
: ScrollListener.HOST
roundTo = (from: number, to: number = this.scrollOffset) => Math.floor(from / to) * to;
getScrollDirection = (st: number) => this.scrollTop <= st ? ScrollDirection.DOWN : ScrollDirection.UP;
canScroll(e: Element): boolean {
const scrolled = this.more
&& this.getScrollDirection(e.scrollTop) === ScrollDirection.DOWN
&& this.roundTo(e.clientHeight) === this.roundTo(e.scrollHeight - e.scrollTop);
this.scrollTop = e.scrollTop;
return scrolled;
}
handleScroll = () => this.getListener() === ScrollListener.HOST
? this.scrolled.emit( this.canScroll(this._element) )
: this.scrolled.emit( this.canScroll(this._window) )
}
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