import { Pipe, PipeTransform, NgZone, ChangeDetectorRef, OnDestroy } from '@angular/core'

@Pipe({
  name: 'timeAgo',
  pure: false,
})
export class TimeAgoPipe implements PipeTransform, OnDestroy {
  private timer: number

  constructor(private changeDetectorRef: ChangeDetectorRef, private ngZone: NgZone) {}

  transform(value: string) {
    this.removeTimer()

    const d = new Date(value)
    const now = new Date()
    const seconds = Math.round(Math.abs((now.getTime() - d.getTime()) / 1000))
    const timeToUpdate = Number.isNaN(seconds) ? 1000 : this.getSecondsUntilUpdate(seconds) * 1000

    this.timer = this.ngZone.runOutsideAngular(() => {
      if (typeof window !== 'undefined') {
        return window.setTimeout(() => {
          this.ngZone.run(() => this.changeDetectorRef.markForCheck())
        }, timeToUpdate)
      }
      return null
    })

    const minutes = Math.round(Math.abs(seconds / 60))
    const hours = Math.round(Math.abs(minutes / 60))
    const days = Math.round(Math.abs(hours / 24))
    const months = Math.round(Math.abs(days / 30.416))
    const years = Math.round(Math.abs(days / 365))

    if (Number.isNaN(seconds)) {
      return ''
    } else if (seconds <= 45) {
      return 'a few seconds ago'
    } else if (seconds <= 90) {
      return 'a minute ago'
    } else if (minutes <= 45) {
      return minutes + ' minutes ago'
    } else if (minutes <= 90) {
      return 'an hour ago'
    } else if (hours <= 22) {
      return hours + ' hours ago'
    } else if (hours <= 36) {
      return 'a day ago'
    } else if (days <= 25) {
      return days + ' days ago'
    } else if (days <= 45) {
      return 'a month ago'
    } else if (days <= 345) {
      return months + ' months ago'
    } else if (days <= 545) {
      return 'a year ago'
    } else {
      // (days > 545)
      return years + ' years ago'
    }
  }

  ngOnDestroy(): void {
    this.removeTimer()
  }

  private removeTimer() {
    if (this.timer) {
      window.clearTimeout(this.timer)
      this.timer = null
    }
  }

  private getSecondsUntilUpdate(seconds: number) {
    const min = 60
    const hr = min * 60
    const day = hr * 24
    if (seconds < min) {
      // less than 1 min, update every 2 secs
      return 2
    } else if (seconds < hr) {
      // less than an hour, update every 30 secs
      return 30
    } else if (seconds < day) {
      // less then a day, update every 5 mins
      return 300
    } else {
      // update every hour
      return 3600
    }
  }
}