var createPadding = require('./internal/createPadding'),
    stringSize = require('./internal/stringSize'),
    toInteger = require('./toInteger'),
    toString = require('./toString');

/* Built-in method references for those with the same name as other `lodash` methods. */
var nativeCeil = Math.ceil,
    nativeFloor = Math.floor;

/**
 * Pads `string` on the left and right sides if it's shorter than `length`.
 * Padding characters are truncated if they can't be evenly divided by `length`.
 *
 * @static
 * @memberOf _
 * @category String
 * @param {string} [string=''] The string to pad.
 * @param {number} [length=0] The padding length.
 * @param {string} [chars=' '] The string used as padding.
 * @returns {string} Returns the padded string.
 * @example
 *
 * _.pad('abc', 8);
 * // => '  abc   '
 *
 * _.pad('abc', 8, '_-');
 * // => '_-abc_-_'
 *
 * _.pad('abc', 3);
 * // => 'abc'
 */
function pad(string, length, chars) {
  string = toString(string);
  length = toInteger(length);

  var strLength = stringSize(string);
  if (!length || strLength >= length) {
    return string;
  }
  var mid = (length - strLength) / 2,
      leftLength = nativeFloor(mid),
      rightLength = nativeCeil(mid);

  return createPadding('', leftLength, chars) + string + createPadding('', rightLength, chars);
}

module.exports = pad;
