client/src/app/shared/video/infinite-scroller.directive.ts

   1 import { distinct, distinctUntilChanged, filter, map, share, startWith, throttleTime } from 'rxjs/operators'
   2 import { Directive, ElementRef, EventEmitter, Input, OnDestroy, OnInit, Output } from '@angular/core'
   3 import { fromEvent, Subscription } from 'rxjs'
   4
   5 @Directive({
   6   selector: '[myInfiniteScroller]'
   7 })
   8 export class InfiniteScrollerDirective implements OnInit, OnDestroy {
   9   @Input() percentLimit = 70
  10   @Input() autoInit = false
  11   @Input() onItself = false
  12
  13   @Output() nearOfBottom = new EventEmitter<void>()
  14
  15   private decimalLimit = 0
  16   private lastCurrentBottom = -1
  17   private scrollDownSub: Subscription
  18   private container: HTMLElement
  19
  20   constructor (private el: ElementRef) {
  21     this.decimalLimit = this.percentLimit / 100
  22   }
  23
  24   ngOnInit () {
  25     if (this.autoInit === true) return this.initialize()
  26   }
  27
  28   ngOnDestroy () {
  29     if (this.scrollDownSub) this.scrollDownSub.unsubscribe()
  30   }
  31
  32   initialize () {
  33     if (this.onItself) {
  34       this.container = this.el.nativeElement
  35     }
  36
  37     // Emit the last value
  38     const throttleOptions = { leading: true, trailing: true }
  39
  40     const scrollObservable = fromEvent(this.container || window, 'scroll')
  41       .pipe(
  42         startWith(null),
  43         throttleTime(200, undefined, throttleOptions),
  44         map(() => this.getScrollInfo()),
  45         distinctUntilChanged((o1, o2) => o1.current === o2.current),
  46         share()
  47       )
  48
  49     // Scroll Down
  50     this.scrollDownSub = scrollObservable
  51       .pipe(
  52         // Check we scroll down
  53         filter(({ current }) => {
  54           const res = this.lastCurrentBottom < current
  55
  56           this.lastCurrentBottom = current
  57           return res
  58         }),
  59         filter(({ current, maximumScroll }) => maximumScroll <= 0 || (current / maximumScroll) > this.decimalLimit)
  60       )
  61       .subscribe(() => this.nearOfBottom.emit())
  62   }
  63
  64   private getScrollInfo () {
  65     if (this.container) {
  66       return { current: this.container.scrollTop, maximumScroll: this.container.scrollHeight }
  67     }
  68
  69     return { current: window.scrollY, maximumScroll: document.body.clientHeight - window.innerHeight }
  70   }
  71 }