var toString = require('./toString');

/** Used to compose unicode character classes. */
var rsAstralRange = '\\ud800-\\udfff',
    rsComboMarksRange = '\\u0300-\\u036f\\ufe20-\\ufe23',
    rsComboSymbolsRange = '\\u20d0-\\u20f0',
    rsDingbatRange = '\\u2700-\\u27bf',
    rsLowerRange = 'a-z\\xdf-\\xf6\\xf8-\\xff',
    rsMathOpRange = '\\xac\\xb1\\xd7\\xf7',
    rsNonCharRange = '\\x00-\\x2f\\x3a-\\x40\\x5b-\\x60\\x7b-\\xbf',
    rsQuoteRange = '\\u2018\\u2019\\u201c\\u201d',
    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',
    rsUpperRange = 'A-Z\\xc0-\\xd6\\xd8-\\xde',
    rsVarRange = '\\ufe0e\\ufe0f',
    rsBreakRange = rsMathOpRange + rsNonCharRange + rsQuoteRange + rsSpaceRange;

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

/** Used to compose unicode regexes. */
var rsLowerMisc = '(?:' + rsLower + '|' + rsMisc + ')',
    rsUpperMisc = '(?:' + rsUpper + '|' + rsMisc + ')',
    reOptMod = rsModifier + '?',
    rsOptVar = '[' + rsVarRange + ']?',
    rsOptJoin = '(?:' + rsZWJ + '(?:' + [rsNonAstral, rsRegional, rsSurrPair].join('|') + ')' + rsOptVar + reOptMod + ')*',
    rsSeq = rsOptVar + reOptMod + rsOptJoin,
    rsEmoji = '(?:' + [rsDingbat, rsRegional, rsSurrPair].join('|') + ')' + rsSeq;

/** Used to match non-compound words composed of alphanumeric characters. */
var reBasicWord = /[a-zA-Z0-9]+/g;

/** Used to match complex or compound words. */
var reComplexWord = RegExp([
  rsUpper + '?' + rsLower + '+(?=' + [rsBreak, rsUpper, '$'].join('|') + ')',
  rsUpperMisc + '+(?=' + [rsBreak, rsUpper + rsLowerMisc, '$'].join('|') + ')',
  rsUpper + '?' + rsLowerMisc + '+',
  rsUpper + '+',
  rsDigits,
  rsEmoji
].join('|'), 'g');

/** Used to detect strings that need a more robust regexp to match words. */
var reHasComplexWord = /[a-z][A-Z]|[A-Z]{2,}[a-z]|[0-9][a-zA-Z]|[a-zA-Z][0-9]|[^a-zA-Z0-9 ]/;

/**
 * Splits `string` into an array of its words.
 *
 * @static
 * @memberOf _
 * @since 3.0.0
 * @category String
 * @param {string} [string=''] The string to inspect.
 * @param {RegExp|string} [pattern] The pattern to match words.
 * @param- {Object} [guard] Enables use as an iteratee for methods like `_.map`.
 * @returns {Array} Returns the words of `string`.
 * @example
 *
 * _.words('fred, barney, & pebbles');
 * // => ['fred', 'barney', 'pebbles']
 *
 * _.words('fred, barney, & pebbles', /[^, ]+/g);
 * // => ['fred', 'barney', '&', 'pebbles']
 */
function words(string, pattern, guard) {
  string = toString(string);
  pattern = guard ? undefined : pattern;

  if (pattern === undefined) {
    pattern = reHasComplexWord.test(string) ? reComplexWord : reBasicWord;
  }
  return string.match(pattern) || [];
}

module.exports = words;