
/* -*- Mode: js; js-indent-level: 2; -*- */
/*
 * Copyright 2011 Mozilla Foundation and contributors
 * Licensed under the New BSD license. See LICENSE or:
 * http://opensource.org/licenses/BSD-3-Clause
 */

var intToCharMap = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'.split('');

/**
 * Encode an integer in the range of 0 to 63 to a single base 64 digit.
 */
exports.encode = function (number) {
  if (0 <= number && number < intToCharMap.length) {
    return intToCharMap[number];
  }
  throw new TypeError("Must be between 0 and 63: " + number);
};

/**
 * Decode a single base 64 character code digit to an integer. Returns -1 on
 * failure.
 */
exports.decode = function (charCode) {
  var bigA = 65;     // 'A'
  var bigZ = 90;     // 'Z'

  var littleA = 97;  // 'a'
  var littleZ = 122; // 'z'

  var zero = 48;     // '0'
  var nine = 57;     // '9'

  var plus = 43;     // '+'
  var slash = 47;    // '/'

  var littleOffset = 26;
  var numberOffset = 52;

  // 0 - 25: ABCDEFGHIJKLMNOPQRSTUVWXYZ
  if (bigA <= charCode && charCode <= bigZ) {
    return (charCode - bigA);
  }

  // 26 - 51: abcdefghijklmnopqrstuvwxyz
  if (littleA <= charCode && charCode <= littleZ) {
    return (charCode - littleA + littleOffset);
  }

  // 52 - 61: 0123456789
  if (zero <= charCode && charCode <= nine) {
    return (charCode - zero + numberOffset);
  }

  // 62: +
  if (charCode == plus) {
    return 62;
  }

  // 63: /
  if (charCode == slash) {
    return 63;
  }

  // Invalid base64 digit.
  return -1;
};