Convert Cron expression to RRule string

cronrrule.js

const parser = require('cron-parser')
const { RRule } = require('rrule')
const logger = require('tracer').colorConsole()

const maps = {
  dayofmonth: 'bymonthday',
  dayofweek: 'byweekday',
}

module.exports = {
  convert: function (expr, currentDate, endDate) {
    try {
      let interval = parser.parseExpression(expr, {
        currentDate: new Date(currentDate),
        endDate: new Date(endDate),
      })

      // Does not support yet RRule.HOURLY and RRule.MINUTELY
      let freq =
        interval.fields.month.length === 12 &&
        interval.fields.dayOfMonth.length === 31 &&
        interval.fields.dayOfWeek.length === 8
          ? 'DAILY'
          : interval.fields.month.length === 12 &&
            interval.fields.dayOfWeek.length === 8
          ? 'MONTHLY'
          : interval.fields.dayOfMonth.length === 1 &&
            interval.fields.month.length === 1
          ? 'YEARLY'
          : 'WEEKLY'

      let rule = new RRule({
        freq: RRule[freq],
        ...Object.keys(interval.fields).reduce(function (result, key) {
          result[
            key.includes('day') ? maps[key.toLowerCase()] : `by${key}`
          ] = key.includes('day')
            ? interval.fields[key] - 1
            : interval.fields[key]
          return result
        }, {}),
        dtstart: currentDate,
        until: endDate,
      })

      return rule.toString()
    } catch (err) {
      logger.error(err.message)
    }
  },
}