@sepbit/dekajs/src/dekatrian.js

This is a simple library to convert Dekatrian and Gregorian.

/**
 * @licstart  The following is the entire license notice for the
 * JavaScript code in this page.
 *
 * Dekajs - DEKAtrian for JavaScript
 * Copyright (C) 2017-2019  Sepbit
 *
 * The JavaScript code in this page is free software: you can
 * redistribute it and/or modify it under the terms of the GNU
 * General Public License (GNU GPL) as published by the Free Software
 * Foundation, either version 3 of the License, or (at your option)
 * any later version.  The code is distributed WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU GPL for more details.
 *
 * As additional permission under GNU GPL version 3 section 7, you
 * may distribute non-source (e.g., minimized or compacted) forms of
 * that code without the copy of the GNU GPL normally required by
 * section 4, provided you include this license notice and a URL
 * through which recipients can access the Corresponding Source.
 *
 * @licend  The above is the entire license notice
 * for the JavaScript code in this page.
 *
 * @module Dekatrian
 */

/**
 * Check if a year is leap year or not
 *
 * @access private
 *
 * @param {integer} year Year
 *
 * @return {boolean} Year is leap year or not
 */
function checkLeapYear (year) {
  if (year % 4 === 0 && year % 100 !== 0) {
    return true
  }
  if (year % 400 === 0) {
    return true
  }
  return false
}

/**
 * Get Gregorian day of year
 *
 * @access private
 *
 * @param {integer} year  Gregorian year
 * @param {integer} month Gregorian month
 * @param {integer} day   Gregorian day
 *
 * @return {integer} Gregorian day of year
 */
function getGregorianYearDay (year, month, day) {
  month--
  let end = new Date()
  end = end.setFullYear(year, month, day)
  let start = new Date()
  start = start.setFullYear(year, 0, 0)
  return Math.round((end - start) / 864e5)
}

/**
 * Check if a Gregorian date is valid or not
 *
 * @access private
 *
 * @param {integer} year  Gregorian year
 * @param {integer} month Gregorian month
 * @param {integer} day   Gregorian day
 *
 * @return {boolean} Gregorian date is valid or not
 */
function checkGregorian (year, month, day) {
  if (month === 2 && checkLeapYear(year) && day > 29) {
    return false
  }
  if (month === 2 && !checkLeapYear(year) && day > 28) {
    return false
  }
  if (month === 1 || month === 3 || month === 5 || month === 7 ||
      month === 8 || month === 10 || month === 12) {
    if (day > 31) {
      return false
    }
  } else {
    if (month > 12 || day > 30) {
      return false
    }
  }
  return true
}

/**
 * Check if a Dekatrian date is valid or not
 *
 * @access private
 *
 * @param {integer} year  Dekatrian year
 * @param {integer} month Dekatrian month
 * @param {integer} day   Dekatrian day
 *
 * @return {boolean} Dekatrian date is valid or not
 */
function checkDekatrian (year, month, day) {
  if (checkLeapYear(year)) {
    if (month === 0 && day > 2) {
      return false
    }
  } else {
    if (month === 0 && day > 1) {
      return false
    }
  }
  if (month > 13 || day > 28) {
    return false
  }
  return true
}

/**
 * Convert a Dekatrian date to Gregorian date
 *
 * @param {integer} year  Dekatrian year
 * @param {integer} month Dekatrian month
 * @param {integer} day   Dekatrian day
 *
 * @throws {Error} Is not a valid Dekatrian date
 *
 * @return {string} Gregorian date e.g. 2018-12-31
 */
function dekaToGreg (year, month, day) {
  if (!checkDekatrian(year, month, day)) {
    throw new Error('The provider arguments are not a valid Dekatrian date')
  }

  /** Achronian day */
  if (month === 0 && day === 1) {
    return year + '-1-1'
  }

  /** leap year */
  if (checkLeapYear(year)) {
    /** Sinchronian day */
    if (month === 0 && day === 2) {
      return year + '-1-2'
    }

    day++
  }

  const dayYear = (month * 28) - 28 + day + 1
  let gregDate = new Date(year, 0)
  gregDate = new Date(gregDate.setDate(dayYear))
  const gregYear = gregDate.getFullYear()
  const gregMonth = gregDate.getMonth() + 1
  const gregDay = gregDate.getDate()

  return gregYear + '-' + gregMonth + '-' + gregDay
}

/**
 * Convert a Gregorian date to Dekatrian date
 *
 * @param {integer} year  Gregorian year
 * @param {integer} month Gregorian month
 * @param {integer} day   Gregorian day
 *
 * @throws {Error} Is not a valid Gregorian date
 *
 * @return {string} Dekatrian date e.g. 2018-13-28
 */
function gregToDeka (year, month, day) {
  if (!checkGregorian(year, month, day)) {
    throw new Error('The provider arguments are not a valid Gregorian date')
  }

  let yearDay = getGregorianYearDay(year, month, day) - 1

  /** leap year */
  if (checkLeapYear(year)) {
    yearDay--

    /** Sinchronian day */
    if (month === 1 && day === 2) {
      return year + '-0-2'
    }
  }

  /** Achronian day */
  if (month === 1 && day === 1) {
    return year + '-0-1'
  }

  let dekaMonth = Math.floor(yearDay / 28)
  let dekaDay = yearDay - (dekaMonth * 28)
  dekaMonth++

  if (!dekaDay) {
    dekaDay = 28
    dekaMonth--
  }

  return year + '-' + dekaMonth + '-' + dekaDay
}

/** ECMAScript module */
export { dekaToGreg, gregToDeka }