/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * 
 * @format
 */

/**
     * Copyright 2011 Mozilla Foundation and contributors
     * Licensed under the New BSD license. See LICENSE or:
     * http://opensource.org/licenses/BSD-3-Clause
     *
     * Based on the Base 64 VLQ implementation in Closure Compiler:
     * https://git.io/vymuA
     *
     * Copyright 2011 The Closure Compiler Authors. All rights reserved.
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions are
     * met:
     *
     *  * Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     *  * Redistributions in binary form must reproduce the above
     *    copyright notice, this list of conditions and the following
     *    disclaimer in the documentation and/or other materials provided
     *    with the distribution.
     *  * Neither the name of Google Inc. nor the names of its
     *    contributors may be used to endorse or promote products derived
     *    from this software without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
     * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
     * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
     * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
     * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
     * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     *
     * @copyright
     */

/* eslint-disable no-bitwise */

'use strict';

// A map of values to characters for the b64 encoding
const CHAR_MAP = [
0x41,
0x42,
0x43,
0x44,
0x45,
0x46,
0x47,
0x48,
0x49,
0x4a,
0x4b,
0x4c,
0x4d,
0x4e,
0x4f,
0x50,
0x51,
0x52,
0x53,
0x54,
0x55,
0x56,
0x57,
0x58,
0x59,
0x5a,
0x61,
0x62,
0x63,
0x64,
0x65,
0x66,
0x67,
0x68,
0x69,
0x6a,
0x6b,
0x6c,
0x6d,
0x6e,
0x6f,
0x70,
0x71,
0x72,
0x73,
0x74,
0x75,
0x76,
0x77,
0x78,
0x79,
0x7a,
0x30,
0x31,
0x32,
0x33,
0x34,
0x35,
0x36,
0x37,
0x38,
0x39,
0x2b,
0x2f];


// A single base 64 digit can contain 6 bits of data. For the base 64 variable
// length quantities we use in the source map spec, the first bit is the sign,
// the next four bits are the actual value, and the 6th bit is the
// continuation bit. The continuation bit tells us whether there are more
// digits in this value following this digit.
//
//   Continuation
//   |    Sign
//   |    |
//   V    V
//   101011

const VLQ_BASE_SHIFT = 5;

// binary: 100000
const VLQ_BASE = 1 << VLQ_BASE_SHIFT;

// binary: 011111
const VLQ_BASE_MASK = VLQ_BASE - 1;

// binary: 100000
const VLQ_CONTINUATION_BIT = VLQ_BASE;

/**
                                        * Converts from a two-complement value to a value where the sign bit is
                                        * placed in the least significant bit.  For example, as decimals:
                                        *   1 becomes 2 (10 binary), -1 becomes 3 (11 binary)
                                        *   2 becomes 4 (100 binary), -2 becomes 5 (101 binary)
                                        */
function toVLQSigned(value) {
  return value < 0 ? (-value << 1) + 1 : (value << 1) + 0;
}

/**
   * Encodes a number to base64 VLQ format and appends it to the passed-in buffer
   *
   * DON'T USE COMPOUND OPERATORS (eg `>>>=`) ON `let`-DECLARED VARIABLES!
   * V8 WILL DEOPTIMIZE THIS FUNCTION AND MAP CREATION WILL BE 25% SLOWER!
   *
   * DON'T ADD MORE COMMENTS TO THIS FUNCTION TO KEEP ITS LENGTH SHORT ENOUGH FOR
   * V8 OPTIMIZATION!
   */
function encode(value, buffer, position) {
  let vlq = toVLQSigned(value);
  let digit;
  do {
    digit = vlq & VLQ_BASE_MASK;
    vlq = vlq >>> VLQ_BASE_SHIFT;
    if (vlq > 0) {
      // There are still more digits in this value, so we must make sure the
      // continuation bit is marked.
      digit = digit | VLQ_CONTINUATION_BIT;
    }
    buffer[position++] = CHAR_MAP[digit];
  } while (vlq > 0);

  return position;
}

module.exports = encode;