/**
 * lodash 4.1.1 (Custom Build) <https://lodash.com/>
 * Build: `lodash modularize exports="npm" -o ./`
 * Copyright 2012-2016 The Dojo Foundation <http://dojofoundation.org/>
 * Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE>
 * Copyright 2009-2016 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
 * Available under MIT license <https://lodash.com/license>
 */
var charsStartIndex = require('lodash._charsstartindex'),
    toString = require('lodash.tostring');

/** Used to match leading and trailing whitespace. */
var reTrimStart = /^\s+/;

/** Used to compose unicode character classes. */
var rsAstralRange = '\\ud800-\\udfff',
    rsComboMarksRange = '\\u0300-\\u036f\\ufe20-\\ufe23',
    rsComboSymbolsRange = '\\u20d0-\\u20f0',
    rsVarRange = '\\ufe0e\\ufe0f';

/** Used to compose unicode capture groups. */
var rsAstral = '[' + rsAstralRange + ']',
    rsCombo = '[' + rsComboMarksRange + rsComboSymbolsRange + ']',
    rsFitz = '\\ud83c[\\udffb-\\udfff]',
    rsModifier = '(?:' + rsCombo + '|' + rsFitz + ')',
    rsNonAstral = '[^' + rsAstralRange + ']',
    rsRegional = '(?:\\ud83c[\\udde6-\\uddff]){2}',
    rsSurrPair = '[\\ud800-\\udbff][\\udc00-\\udfff]',
    rsZWJ = '\\u200d';

/** Used to compose unicode regexes. */
var reOptMod = rsModifier + '?',
    rsOptVar = '[' + rsVarRange + ']?',
    rsOptJoin = '(?:' + rsZWJ + '(?:' + [rsNonAstral, rsRegional, rsSurrPair].join('|') + ')' + rsOptVar + reOptMod + ')*',
    rsSeq = rsOptVar + reOptMod + rsOptJoin,
    rsSymbol = '(?:' + [rsNonAstral + rsCombo + '?', rsCombo, rsRegional, rsSurrPair, rsAstral].join('|') + ')';

/** Used to match [string symbols](https://mathiasbynens.be/notes/javascript-unicode). */
var reComplexSymbol = RegExp(rsFitz + '(?=' + rsFitz + ')|' + rsSymbol + rsSeq, 'g');

/**
 * Converts `string` to an array.
 *
 * @private
 * @param {string} string The string to convert.
 * @returns {Array} Returns the converted array.
 */
function stringToArray(string) {
  return string.match(reComplexSymbol);
}

/**
 * Removes leading whitespace or specified characters from `string`.
 *
 * @static
 * @memberOf _
 * @category String
 * @param {string} [string=''] The string to trim.
 * @param {string} [chars=whitespace] The characters to trim.
 * @param- {Object} [guard] Enables use as an iteratee for functions like `_.map`.
 * @returns {string} Returns the trimmed string.
 * @example
 *
 * _.trimStart('  abc  ');
 * // => 'abc  '
 *
 * _.trimStart('-_-abc-_-', '_-');
 * // => 'abc-_-'
 */
function trimStart(string, chars, guard) {
  string = toString(string);
  if (!string) {
    return string;
  }
  if (guard || chars === undefined) {
    return string.replace(reTrimStart, '');
  }
  chars = (chars + '');
  if (!chars) {
    return string;
  }
  var strSymbols = stringToArray(string);
  return strSymbols.slice(charsStartIndex(strSymbols, stringToArray(chars))).join('');
}

module.exports = trimStart;