Count a deadline date using a moment date as start point and a moment duration as the duration of hours, considering your work schedule and that you don't work at weekends, holidays

worktime-counter.js

const moment = require('moment')

const HOURS = {
  WORK_START: 8,
  LUNCH_START: 12,
  LUNCH_END: 13,
  WORK_END: 17
}

const INT_LUNCH_DURATION = (HOURS.LUNCH_END - HOURS.LUNCH_START)
const INT_WORK_DURATION  = (HOURS.WORK_END - HOURS.WORK_START - (INT_LUNCH_DURATION))

const DURATIONS = {
  LUNCH_DURATION: moment.duration(INT_LUNCH_DURATION, 'hour'),
  HALF_WORKTIME: moment.duration(INT_WORK_DURATION / 2, 'hour'),
  DAILY_WORKTIME: moment.duration(INT_WORK_DURATION, 'hour')
}

const WEEKEND_DAYS = [ 6, 0 ]

class WorktimeCounter {
  constructor() {
    this.holidays = []
  }

  pushHoliday(holiday) {
    if (!moment.isMoment(holiday))
      throw new Error("holiday must be a moment date.")

    this.holidays.push(holiday)

    return this.holidays
  }

  clearHolidays() {
    this.holidays = []
  }

  getDeadlineDate(initialDate, duration) {
    if (!moment.isMoment(initialDate))
      throw new Error("initialDate must be a moment date.")

    if (!moment.isDuration(duration))
      throw new Error("duration must be a moment duration object")

    return this.adjustDate(initialDate, duration)
  }

  adjustDate(date, duration) {
    var result = date.clone()
    var remainingDuration = moment.duration(duration)

    while (remainingDuration.as('hour')) {
      while (this.mustSkipDate(result)) {
        this.setNextDay(result)
      }

      var _duration = this.getDuration(result, remainingDuration)
      
      result.add(_duration)
      remainingDuration.subtract(_duration)
  
      if (this.hasLunchtimeBetween(date, result)) {
        result.add(DURATIONS.LUNCH_DURATION)
      }
    }

    return result
  }

  getDuration(result, remainingDuration) {
    var _duration = remainingDuration
    
    if (remainingDuration.as('hour') >= INT_WORK_DURATION) {
      var _durationInt = INT_WORK_DURATION
      
      if (this.isBetweenWorkSchedule(result)) {
        _durationInt = Math.abs(HOURS.WORK_END - result.hour())

        var _preResult = result.clone().add(moment.duration(_durationInt, 'hour'))
        
        if (this.hasLunchtimeBetween(result, _preResult)) {
          _durationInt--
        }
      }

      _duration = moment.duration(_durationInt, 'hour')
    }

    return _duration
  }

  isBetweenWorkSchedule(date) {
    var workStart = moment(date).hour(HOURS.WORK_START)
    var workEnd = moment(date).hour(HOURS.WORK_END)

    return date.isBetween(workStart, workEnd)
  }

  mustGoToNextDay(date) {
    return date.hour() >= HOURS.WORK_END
  }

  setNextDay(date) {
    date.add(1, 'day').hour(HOURS.WORK_START)
  }
  
  hasLunchtimeBetween(initialDate, resultDate) {
    let lunchStart = moment(resultDate).hour(HOURS.LUNCH_START)

    return (
      lunchStart.isBetween(initialDate, resultDate) ||
      lunchStart.isSame(initialDate)
    )
  }

  getCountOfDays(duration) {
    return duration / DURATIONS.DAILY_WORKTIME
  }

  mustSkipDate(date) {
    return this.isWeekend(date) || 
           this.isHoliday(date) || 
           this.mustGoToNextDay(date)
  }

  isWeekend(date) {
    for (var i = 0; i < WEEKEND_DAYS.length; i++)
      if (date.day() == WEEKEND_DAYS[i])
        return true

    return false
  }

  isHoliday(date) {
    for (var i = 0; i < this.holidays.length; i++)
      if (date.isSame(this.holidays[i], 'day'))
        return true

    return false
  }
}

module.exports = WorktimeCounter