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

   1 import { distinctUntilChanged, filter, map, share, startWith, throttleTime } from 'rxjs/operators'
   2 import { AfterContentChecked, Directive, ElementRef, EventEmitter, Input, OnDestroy, OnInit, Output } from '@angular/core'
   3 import { fromEvent, Observable, Subscription } from 'rxjs'
   4
   5 @Directive({
   6   selector: '[myInfiniteScroller]'
   7 })
   8 export class InfiniteScrollerDirective implements OnInit, OnDestroy, AfterContentChecked {
   9   @Input() percentLimit = 70
  10   @Input() autoInit = false
  11   @Input() onItself = false
  12   @Input() dataObservable: Observable<any[]>
  13
  14   @Output() nearOfBottom = new EventEmitter<void>()
  15
  16   private decimalLimit = 0
  17   private lastCurrentBottom = -1
  18   private scrollDownSub: Subscription
  19   private container: HTMLElement
  20
  21   private checkScroll = false
  22
  23   constructor (private el: ElementRef) {
  24     this.decimalLimit = this.percentLimit / 100
  25   }
  26
  27   ngAfterContentChecked () {
  28     if (this.checkScroll) {
  29       this.checkScroll = false
  30
  31       console.log('Checking if the initial state has a scroll.')
  32
  33       if (this.hasScroll() === false) this.nearOfBottom.emit()
  34     }
  35   }
  36
  37   ngOnInit () {
  38     if (this.autoInit === true) return this.initialize()
  39   }
  40
  41   ngOnDestroy () {
  42     if (this.scrollDownSub) this.scrollDownSub.unsubscribe()
  43   }
  44
  45   initialize () {
  46     this.container = this.onItself
  47       ? this.el.nativeElement
  48       : document.documentElement
  49
  50     // Emit the last value
  51     const throttleOptions = { leading: true, trailing: true }
  52
  53     const scrollableElement = this.onItself ? this.container : window
  54     const scrollObservable = fromEvent(scrollableElement, 'scroll')
  55       .pipe(
  56         startWith(true),
  57         throttleTime(200, undefined, throttleOptions),
  58         map(() => this.getScrollInfo()),
  59         distinctUntilChanged((o1, o2) => o1.current === o2.current),
  60         share()
  61       )
  62
  63     // Scroll Down
  64     this.scrollDownSub = scrollObservable
  65       .pipe(
  66         filter(({ current }) => this.isScrollingDown(current)),
  67         filter(({ current, maximumScroll }) => (current / maximumScroll) > this.decimalLimit)
  68       )
  69       .subscribe(() => this.nearOfBottom.emit())
  70
  71     if (this.dataObservable) {
  72       this.dataObservable
  73           .pipe(filter(d => d.length !== 0))
  74           .subscribe(() => this.checkScroll = true)
  75     }
  76   }
  77
  78   private getScrollInfo () {
  79     return { current: this.container.scrollTop, maximumScroll: this.getMaximumScroll() }
  80   }
  81
  82   private getMaximumScroll () {
  83     return this.container.scrollHeight - window.innerHeight
  84   }
  85
  86   private hasScroll () {
  87     return this.getMaximumScroll() > 0
  88   }
  89
  90   private isScrollingDown (current: number) {
  91     const result = this.lastCurrentBottom < current
  92
  93     this.lastCurrentBottom = current
  94     return result
  95   }
  96 }