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

   1 import { Directive, EventEmitter, Input, OnInit, Output } from '@angular/core'
   2 import 'rxjs/add/operator/debounceTime'
   3 import 'rxjs/add/operator/distinct'
   4 import 'rxjs/add/operator/distinctUntilChanged'
   5 import 'rxjs/add/operator/filter'
   6 import 'rxjs/add/operator/map'
   7 import 'rxjs/add/operator/startWith'
   8 import 'rxjs/add/operator/throttleTime'
   9 import { fromEvent } from 'rxjs/observable/fromEvent'
  10 import 'rxjs/add/operator/share'
  11
  12 @Directive({
  13   selector: '[myInfiniteScroller]'
  14 })
  15 export class InfiniteScrollerDirective implements OnInit {
  16   private static PAGE_VIEW_TOP_MARGIN = 500
  17
  18   @Input() containerHeight: number
  19   @Input() pageHeight: number
  20   @Input() percentLimit = 70
  21   @Input() autoLoading = false
  22
  23   @Output() nearOfBottom = new EventEmitter<void>()
  24   @Output() nearOfTop = new EventEmitter<void>()
  25   @Output() pageChanged = new EventEmitter<number>()
  26
  27   private decimalLimit = 0
  28   private lastCurrentBottom = -1
  29   private lastCurrentTop = 0
  30
  31   constructor () {
  32     this.decimalLimit = this.percentLimit / 100
  33   }
  34
  35   ngOnInit () {
  36     if (this.autoLoading === true) return this.initialize()
  37   }
  38
  39   initialize () {
  40     // Emit the last value
  41     const throttleOptions = { leading: false, trailing: true }
  42
  43     const scrollObservable = fromEvent(window, 'scroll')
  44       .startWith(true)
  45       .throttleTime(200, undefined, throttleOptions)
  46       .map(() => ({ current: window.scrollY, maximumScroll: document.body.clientHeight - window.innerHeight }))
  47       .share()
  48
  49     // Scroll Down
  50     scrollObservable
  51       // Check we scroll down
  52       .filter(({ current }) => {
  53         const res = this.lastCurrentBottom < current
  54
  55         this.lastCurrentBottom = current
  56         return res
  57       })
  58       .filter(({ current, maximumScroll }) => maximumScroll <= 0 || (current / maximumScroll) > this.decimalLimit)
  59       .subscribe(() => this.nearOfBottom.emit())
  60
  61     // Scroll up
  62     scrollObservable
  63       // Check we scroll up
  64       .filter(({ current }) => {
  65         const res = this.lastCurrentTop > current
  66
  67         this.lastCurrentTop = current
  68         return res
  69       })
  70       .filter(({ current, maximumScroll }) => {
  71         return current !== 0 && (1 - (current / maximumScroll)) > this.decimalLimit
  72       })
  73       .subscribe(() => this.nearOfTop.emit())
  74
  75     // Page change
  76     scrollObservable
  77       .distinct()
  78       .map(({ current }) => this.calculateCurrentPage(current))
  79       .distinctUntilChanged()
  80       .subscribe(res => this.pageChanged.emit(res))
  81   }
  82
  83   private calculateCurrentPage (current: number) {
  84     return Math.max(1, Math.round((current + InfiniteScrollerDirective.PAGE_VIEW_TOP_MARGIN) / this.pageHeight))
  85   }
  86 }