trunc.js

var baseToString = require('../internal/baseToString'),
    isIterateeCall = require('../internal/isIterateeCall'),
    isObject = require('../lang/isObject'),
    isRegExp = require('../lang/isRegExp');

/** Used as default options for `_.trunc`. */
var DEFAULT_TRUNC_LENGTH = 30,
    DEFAULT_TRUNC_OMISSION = '...';

/** Used to match `RegExp` flags from their coerced string values. */
var reFlags = /\w*$/;

/**
 * Truncates `string` if it's longer than the given maximum string length.
 * The last characters of the truncated string are replaced with the omission
 * string which defaults to "...".
 *
 * @static
 * @memberOf _
 * @category String
 * @param {string} [string=''] The string to truncate.
 * @param {Object|number} [options] The options object or maximum string length.
 * @param {number} [options.length=30] The maximum string length.
 * @param {string} [options.omission='...'] The string to indicate text is omitted.
 * @param {RegExp|string} [options.separator] The separator pattern to truncate to.
 * @param- {Object} [guard] Enables use as a callback for functions like `_.map`.
 * @returns {string} Returns the truncated string.
 * @example
 *
 * _.trunc('hi-diddly-ho there, neighborino');
 * // => 'hi-diddly-ho there, neighbo...'
 *
 * _.trunc('hi-diddly-ho there, neighborino', 24);
 * // => 'hi-diddly-ho there, n...'
 *
 * _.trunc('hi-diddly-ho there, neighborino', {
 *   'length': 24,
 *   'separator': ' '
 * });
 * // => 'hi-diddly-ho there,...'
 *
 * _.trunc('hi-diddly-ho there, neighborino', {
 *   'length': 24,
 *   'separator': /,? +/
 * });
 * // => 'hi-diddly-ho there...'
 *
 * _.trunc('hi-diddly-ho there, neighborino', {
 *   'omission': ' [...]'
 * });
 * // => 'hi-diddly-ho there, neig [...]'
 */
function trunc(string, options, guard) {
  if (guard && isIterateeCall(string, options, guard)) {
    options = null;
  }
  var length = DEFAULT_TRUNC_LENGTH,
      omission = DEFAULT_TRUNC_OMISSION;

  if (options != null) {
    if (isObject(options)) {
      var separator = 'separator' in options ? options.separator : separator;
      length = 'length' in options ? (+options.length || 0) : length;
      omission = 'omission' in options ? baseToString(options.omission) : omission;
    } else {
      length = +options || 0;
    }
  }
  string = baseToString(string);
  if (length >= string.length) {
    return string;
  }
  var end = length - omission.length;
  if (end < 1) {
    return omission;
  }
  var result = string.slice(0, end);
  if (separator == null) {
    return result + omission;
  }
  if (isRegExp(separator)) {
    if (string.slice(end).search(separator)) {
      var match,
          newEnd,
          substring = string.slice(0, end);

      if (!separator.global) {
        separator = RegExp(separator.source, (reFlags.exec(separator) || '') + 'g');
      }
      separator.lastIndex = 0;
      while ((match = separator.exec(substring))) {
        newEnd = match.index;
      }
      result = result.slice(0, newEnd == null ? end : newEnd);
    }
  } else if (string.indexOf(separator, end) != end) {
    var index = result.lastIndexOf(separator);
    if (index > -1) {
      result = result.slice(0, index);
    }
  }
  return result + omission;
}

module.exports = trunc;