var castSlice = require('./_castSlice'),
    charsStartIndex = require('./_charsStartIndex'),
    stringToArray = require('./_stringToArray'),
    toString = require('./toString');

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

/**
 * Removes leading whitespace or specified characters from `string`.
 *
 * @static
 * @memberOf _
 * @since 4.0.0
 * @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 methods 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, '');
  }
  if (!(chars += '')) {
    return string;
  }
  var strSymbols = stringToArray(string),
      start = charsStartIndex(strSymbols, stringToArray(chars));

  return castSlice(strSymbols, start).join('');
}

module.exports = trimStart;
