client/src/app/shared/shared-main/angular/infinite-scroller.directive.ts

   1 import { fromEvent, Observable, Subscription } from 'rxjs'
   2 import { distinctUntilChanged, filter, map, share, startWith, throttleTime } from 'rxjs/operators'
   3 import { AfterViewChecked, Directive, ElementRef, EventEmitter, Input, OnDestroy, OnInit, Output } from '@angular/core'
   4
   5 @Directive({
   6   selector: '[myInfiniteScroller]'
   7 })
   8 export class InfiniteScrollerDirective implements OnInit, OnDestroy, AfterViewChecked {
   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   ngAfterViewChecked () {
  28     if (this.checkScroll) {
  29       this.checkScroll = false
  30
  31       // Wait HTML update
  32       setTimeout(() => {
  33         if (this.hasScroll() === false) this.nearOfBottom.emit()
  34       })
  35     }
  36   }
  37
  38   ngOnInit () {
  39     if (this.autoInit === true) return this.initialize()
  40   }
  41
  42   ngOnDestroy () {
  43     if (this.scrollDownSub) this.scrollDownSub.unsubscribe()
  44   }
  45
  46   initialize () {
  47     this.container = this.onItself
  48       ? this.el.nativeElement
  49       : document.documentElement
  50
  51     // Emit the last value
  52     const throttleOptions = { leading: true, trailing: true }
  53
  54     const scrollableElement = this.onItself ? this.container : window
  55     const scrollObservable = fromEvent(scrollableElement, 'scroll')
  56       .pipe(
  57         startWith(true),
  58         throttleTime(200, undefined, throttleOptions),
  59         map(() => this.getScrollInfo()),
  60         distinctUntilChanged((o1, o2) => o1.current === o2.current),
  61         share()
  62       )
  63
  64     // Scroll Down
  65     this.scrollDownSub = scrollObservable
  66       .pipe(
  67         filter(({ current }) => this.isScrollingDown(current)),
  68         filter(({ current, maximumScroll }) => (current / maximumScroll) > this.decimalLimit)
  69       )
  70       .subscribe(() => this.nearOfBottom.emit())
  71
  72     if (this.dataObservable) {
  73       this.dataObservable
  74           .pipe(filter(d => d.length !== 0))
  75           .subscribe(() => this.checkScroll = true)
  76     }
  77   }
  78
  79   private getScrollInfo () {
  80     return { current: this.container.scrollTop, maximumScroll: this.getMaximumScroll() }
  81   }
  82
  83   private getMaximumScroll () {
  84     const elementHeight = this.onItself ? this.container.clientHeight : window.innerHeight
  85
  86     return this.container.scrollHeight - elementHeight
  87   }
  88
  89   private hasScroll () {
  90     return this.getMaximumScroll() > 0
  91   }
  92
  93   private isScrollingDown (current: number) {
  94     const result = this.lastCurrentBottom < current
  95
  96     this.lastCurrentBottom = current
  97     return result
  98   }
  99 }