/** Used to compose unicode character classes. */
const rsAstralRange = '\\ud800-\\udfff'
const rsComboMarksRange = '\\u0300-\\u036f'
const reComboHalfMarksRange = '\\ufe20-\\ufe2f'
const rsComboSymbolsRange = '\\u20d0-\\u20ff'
const rsComboRange = rsComboMarksRange + reComboHalfMarksRange + rsComboSymbolsRange
const rsDingbatRange = '\\u2700-\\u27bf'
const rsLowerRange = 'a-z\\xdf-\\xf6\\xf8-\\xff'
const rsMathOpRange = '\\xac\\xb1\\xd7\\xf7'
const rsNonCharRange = '\\x00-\\x2f\\x3a-\\x40\\x5b-\\x60\\x7b-\\xbf'
const rsPunctuationRange = '\\u2000-\\u206f'
const rsSpaceRange = ' \\t\\x0b\\f\\xa0\\ufeff\\n\\r\\u2028\\u2029\\u1680\\u180e\\u2000\\u2001\\u2002\\u2003\\u2004\\u2005\\u2006\\u2007\\u2008\\u2009\\u200a\\u202f\\u205f\\u3000'
const rsUpperRange = 'A-Z\\xc0-\\xd6\\xd8-\\xde'
const rsVarRange = '\\ufe0e\\ufe0f'
const rsBreakRange = rsMathOpRange + rsNonCharRange + rsPunctuationRange + rsSpaceRange

/** Used to compose unicode capture groups. */
const rsApos = "['\u2019]"
const rsBreak = `[${ rsBreakRange }]`
const rsCombo = `[${ rsComboRange }]`
const rsDigits = '\\d+'
const rsDingbat = `[${ rsDingbatRange }]`
const rsLower = `[${ rsLowerRange }]`
const rsMisc = `[^${ rsAstralRange }${ rsBreakRange + rsDigits + rsDingbatRange + rsLowerRange + rsUpperRange }]`
const rsFitz = '\\ud83c[\\udffb-\\udfff]'
const rsModifier = `(?:${ rsCombo }|${ rsFitz })`
const rsNonAstral = `[^${ rsAstralRange }]`
const rsRegional = '(?:\\ud83c[\\udde6-\\uddff]){2}'
const rsSurrPair = '[\\ud800-\\udbff][\\udc00-\\udfff]'
const rsUpper = `[${ rsUpperRange }]`
const rsZWJ = '\\u200d'

/** Used to compose unicode regexes. */
const rsMiscLower = `(?:${ rsLower }|${ rsMisc })`
const rsMiscUpper = `(?:${ rsUpper }|${ rsMisc })`
const rsOptContrLower = `(?:${ rsApos }(?:d|ll|m|re|s|t|ve))?`
const rsOptContrUpper = `(?:${ rsApos }(?:D|LL|M|RE|S|T|VE))?`
const reOptMod = `${ rsModifier }?`
const rsOptVar = `[${ rsVarRange }]?`
const rsOptJoin = `(?:${ rsZWJ }(?:${ [rsNonAstral, rsRegional, rsSurrPair].join('|') })${ rsOptVar + reOptMod })*`
const rsOrdLower = '\\d*(?:(?:1st|2nd|3rd|(?![123])\\dth)\\b)'
const rsOrdUpper = '\\d*(?:(?:1ST|2ND|3RD|(?![123])\\dTH)\\b)'
const rsSeq = rsOptVar + reOptMod + rsOptJoin
const rsEmoji = `(?:${ [rsDingbat, rsRegional, rsSurrPair].join('|') })${ rsSeq }`

/** Used to match complex or compound words. */
const reUnicodeWord = RegExp([
  `${ rsUpper }?${ rsLower }+${ rsOptContrLower }(?=${ [rsBreak, rsUpper, '$'].join('|') })`,
  `${ rsMiscUpper }+${ rsOptContrUpper }(?=${ [rsBreak, rsUpper + rsMiscLower, '$'].join('|') })`,
  `${ rsUpper }?${ rsMiscLower}+${ rsOptContrLower }`,
  `${ rsUpper }+${ rsOptContrUpper }`,
  rsOrdUpper,
  rsOrdLower,
  rsDigits,
  rsEmoji
].join('|'), 'g')

/**
 * Splits a Unicode `string` into an array of its words.
 *
 * @private
 * @param {string} The string to inspect.
 * @returns {Array} Returns the words of `string`.
 */
function unicodeWords(string) {
  return string.match(reUnicodeWord) || []
}

export default unicodeWords