index.ts

import toDate from '../toDate/index.ts'
import formatters from '../_lib/format/lightFormatters/index.ts'
import getTimezoneOffsetInMilliseconds from '../_lib/getTimezoneOffsetInMilliseconds/index.js'
import isValid from '../isValid/index.js'
import subMilliseconds from '../subMilliseconds/index.ts'
import requiredArgs from '../_lib/requiredArgs/index.ts'

// This RegExp consists of three parts separated by `|`:
// - (\w)\1* matches any sequences of the same letter
// - '' matches two quote characters in a row
// - '(''|[^'])+('|$) matches anything surrounded by two quote characters ('),
//   except a single quote symbol, which ends the sequence.
//   Two quote characters do not end the sequence.
//   If there is no matching single quote
//   then the sequence will continue until the end of the string.
// - . matches any single character unmatched by previous parts of the RegExps
const formattingTokensRegExp = /(\w)\1*|''|'(''|[^'])+('|$)|./g

const escapedStringRegExp = /^'([^]*?)'?$/
const doubleQuoteRegExp = /''/g
const unescapedLatinCharacterRegExp = /[a-zA-Z]/

/**
 * @name lightFormat
 * @category Common Helpers
 * @summary Format the date.
 *
 * @description
 * Return the formatted date string in the given format. Unlike `format`,
 * `lightFormat` doesn't use locales and outputs date using the most popular tokens.
 *
 * > ⚠️ Please note that the `lightFormat` tokens differ from Moment.js and other libraries.
 * > See: https://git.io/fxCyr
 *
 * The characters wrapped between two single quotes characters (') are escaped.
 * Two single quotes in a row, whether inside or outside a quoted sequence, represent a 'real' single quote.
 *
 * Format of the string is based on Unicode Technical Standard #35:
 * https://www.unicode.org/reports/tr35/tr35-dates.html#Date_Field_Symbol_Table
 *
 * Accepted patterns:
 * | Unit                            | Pattern | Result examples                   |
 * |---------------------------------|---------|-----------------------------------|
 * | AM, PM                          | a..aaa  | AM, PM                            |
 * |                                 | aaaa    | a.m., p.m.                        |
 * |                                 | aaaaa   | a, p                              |
 * | Calendar year                   | y       | 44, 1, 1900, 2017                 |
 * |                                 | yy      | 44, 01, 00, 17                    |
 * |                                 | yyy     | 044, 001, 000, 017                |
 * |                                 | yyyy    | 0044, 0001, 1900, 2017            |
 * | Month (formatting)              | M       | 1, 2, ..., 12                     |
 * |                                 | MM      | 01, 02, ..., 12                   |
 * | Day of month                    | d       | 1, 2, ..., 31                     |
 * |                                 | dd      | 01, 02, ..., 31                   |
 * | Hour [1-12]                     | h       | 1, 2, ..., 11, 12                 |
 * |                                 | hh      | 01, 02, ..., 11, 12               |
 * | Hour [0-23]                     | H       | 0, 1, 2, ..., 23                  |
 * |                                 | HH      | 00, 01, 02, ..., 23               |
 * | Minute                          | m       | 0, 1, ..., 59                     |
 * |                                 | mm      | 00, 01, ..., 59                   |
 * | Second                          | s       | 0, 1, ..., 59                     |
 * |                                 | ss      | 00, 01, ..., 59                   |
 * | Fraction of second              | S       | 0, 1, ..., 9                      |
 * |                                 | SS      | 00, 01, ..., 99                   |
 * |                                 | SSS     | 000, 0001, ..., 999               |
 * |                                 | SSSS    | ...                               |
 *
 * @param {Date|Number} date - the original date
 * @param {String} format - the string of tokens
 * @returns {String} the formatted date string
 * @throws {TypeError} 2 arguments required
 * @throws {RangeError} format string contains an unescaped latin alphabet character
 *
 * @example
 * const result = lightFormat(new Date(2014, 1, 11), 'yyyy-MM-dd')
 * //=> '2014-02-11'
 */

type Token = keyof typeof formatters

export default function lightFormat(
  dirtyDate: Date | number,
  formatStr: string
): string {
  requiredArgs(2, arguments)

  const originalDate = toDate(dirtyDate)

  if (!isValid(originalDate)) {
    throw new RangeError('Invalid time value')
  }

  // Convert the date in system timezone to the same date in UTC+00:00 timezone.
  // This ensures that when UTC functions will be implemented, locales will be compatible with them.
  // See an issue about UTC functions: https://github.com/date-fns/date-fns/issues/376
  const timezoneOffset = getTimezoneOffsetInMilliseconds(originalDate)
  const utcDate = subMilliseconds(originalDate, timezoneOffset)

  const tokens = formatStr.match(formattingTokensRegExp)

  // The only case when formattingTokensRegExp doesn't match the string is when it's empty
  if (!tokens) return ''

  const result = tokens
    .map((substring) => {
      // Replace two single quote characters with one single quote character
      if (substring === "''") {
        return "'"
      }

      const firstCharacter = substring[0]
      if (firstCharacter === "'") {
        return cleanEscapedString(substring)
      }

      const formatter = formatters[firstCharacter as Token]
      if (formatter) {
        return formatter(utcDate, substring)
      }

      if (firstCharacter.match(unescapedLatinCharacterRegExp)) {
        throw new RangeError(
          'Format string contains an unescaped latin alphabet character `' +
            firstCharacter +
            '`'
        )
      }

      return substring
    })
    .join('')

  return result
}

function cleanEscapedString(input: string) {
  const matches = input.match(escapedStringRegExp)

  if (!matches) {
    return input
  }

  return matches[1].replace(doubleQuoteRegExp, "'")
}