date time range calculator

dateTimeRangeCalc.js

export const writeEnums = (n, words, { zero = false, space = ' ' } = {}) => {
  if (!zero && n === 0) return ''

  const i10 = n % 10
  const i100 = n % 100

  if (i10 === 1 && i100 !== 11) {
    return `${n}${space}${words[0]}`
  } else if (i10 !== 0 && i100 !== 0 && i100 !== 11 && (i100 > 21 || i100 < 5) && i10 < 5) {
    return `${n}${space}${words[1]}`
  } else {
    return `${n}${space}${words[2]}`
  }
}

export const calcRange = (range, { separator = ' ', space = ' ', zero = false, short = false } = {}) => {
  range = moment.range(range.start, range.end.add(1, 'd'))
  const dur = moment.duration(range.duration())

  const y = dur.years()
  const m = dur.months()
  const d = dur.days()

  if (short) {
    return [
      writeEnums(y, ['г', 'г', 'л'], { zero, space }),
      writeEnums(m, ['м', 'м', 'м'], { zero, space }),
      writeEnums(d, ['д', 'д', 'д'], { zero, space }),
    ].filter(_ => _).join(separator)
  } else {
    return [
      writeEnums(y, ['год', 'года', 'лет'], { zero, space }),
      writeEnums(m, ['месяц', 'месяца', 'месяцев'], { zero, space }),
      writeEnums(d, ['день', 'дня', 'дней'], { zero, space }),
    ].filter(_ => _).join(separator)
  }
}