// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'dart:math';
import 'dart:typed_data';

class CryptoUtils {
  static const int PAD = 61; // '='
  static const int CR = 13; // '\r'
  static const int LF = 10; // '\n'
  static const int LINE_LENGTH = 76;

  static const String _encodeTable =
      "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

  static const String _encodeTableUrlSafe =
      "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";

  // Lookup table used for finding Base 64 alphabet index of a given byte.
  // -2 : Outside Base 64 alphabet.
  // -1 : '\r' or '\n'
  //  0 : = (Padding character).
  // >0 : Base 64 alphabet index of given byte.
  static const List<int> _decodeTable = [
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -1, -2, -2, -1, -2, -2, //
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, //
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, 62, -2, 62, -2, 63, //
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -2, -2, -2, 00, -2, -2, //
    -2, 00, 01, 02, 03, 04, 05, 06, 07, 08, 09, 10, 11, 12, 13, 14, //
    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -2, -2, -2, -2, 63, //
    -2, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, //
    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -2, -2, -2, -2, -2, //
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, //
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, //
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, //
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, //
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, //
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, //
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, //
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2
  ];

  static final Random _rng = Random.secure();

  static Uint8List getRandomBytes(int count) {
    final Uint8List result = Uint8List(count);
    for (int i = 0; i < count; i++) {
      result[i] = _rng.nextInt(0xff);
    }
    return result;
  }

  static String bytesToHex(List<int> bytes) {
    var result = StringBuffer();
    for (var part in bytes) {
      result.write('${part < 16 ? '0' : ''}${part.toRadixString(16)}');
    }
    return result.toString();
  }

  static String bytesToBase64(List<int> bytes,
      [bool urlSafe = false, bool addLineSeparator = false]) {
    int len = bytes.length;
    if (len == 0) {
      return "";
    }
    final String lookup = urlSafe ? _encodeTableUrlSafe : _encodeTable;
    // Size of 24 bit chunks.
    final int remainderLength = len.remainder(3);
    final int chunkLength = len - remainderLength;
    // Size of base output.
    int outputLen = ((len ~/ 3) * 4) + ((remainderLength > 0) ? 4 : 0);
    // Add extra for line separators.
    if (addLineSeparator) {
      outputLen += ((outputLen - 1) ~/ LINE_LENGTH) << 1;
    }
    List<int> out = List<int>.filled(outputLen, null);

    // Encode 24 bit chunks.
    int j = 0, i = 0, c = 0;
    while (i < chunkLength) {
      int x = ((bytes[i++] << 16) & 0xFFFFFF) |
          ((bytes[i++] << 8) & 0xFFFFFF) |
          bytes[i++];
      out[j++] = lookup.codeUnitAt(x >> 18);
      out[j++] = lookup.codeUnitAt((x >> 12) & 0x3F);
      out[j++] = lookup.codeUnitAt((x >> 6) & 0x3F);
      out[j++] = lookup.codeUnitAt(x & 0x3f);
      // Add optional line separator for each 76 char output.
      if (addLineSeparator && ++c == 19 && j < outputLen - 2) {
        out[j++] = CR;
        out[j++] = LF;
        c = 0;
      }
    }

    // If input length if not a multiple of 3, encode remaining bytes and
    // add padding.
    if (remainderLength == 1) {
      int x = bytes[i];
      out[j++] = lookup.codeUnitAt(x >> 2);
      out[j++] = lookup.codeUnitAt((x << 4) & 0x3F);
      out[j++] = PAD;
      out[j++] = PAD;
    } else if (remainderLength == 2) {
      int x = bytes[i];
      int y = bytes[i + 1];
      out[j++] = lookup.codeUnitAt(x >> 2);
      out[j++] = lookup.codeUnitAt(((x << 4) | (y >> 4)) & 0x3F);
      out[j++] = lookup.codeUnitAt((y << 2) & 0x3F);
      out[j++] = PAD;
    }

    return String.fromCharCodes(out);
  }

  static List<int> base64StringToBytes(String input,
      [bool ignoreInvalidCharacters = true]) {
    int len = input.length;
    if (len == 0) {
      return const <int>[];
    }

    // Count '\r', '\n' and illegal characters, For illegal characters,
    // if [ignoreInvalidCharacters] is false, throw an exception.
    int extrasLen = 0;
    for (int i = 0; i < len; i++) {
      int c = _decodeTable[input.codeUnitAt(i)];
      if (c < 0) {
        extrasLen++;
        if (c == -2 && !ignoreInvalidCharacters) {
          throw FormatException('Invalid character: ${input[i]}');
        }
      }
    }

    if ((len - extrasLen) % 4 != 0) {
      throw FormatException('''Size of Base 64 characters in Input
          must be a multiple of 4. Input: $input''');
    }

    // Count pad characters, ignore illegal characters at the end.
    int padLength = 0;
    for (int i = len - 1; i >= 0; i--) {
      int currentCodeUnit = input.codeUnitAt(i);
      if (_decodeTable[currentCodeUnit] > 0) break;
      if (currentCodeUnit == PAD) padLength++;
    }
    int outputLen = (((len - extrasLen) * 6) >> 3) - padLength;
    List<int> out = List<int>.filled(outputLen, null);

    for (int i = 0, o = 0; o < outputLen;) {
      // Accumulate 4 valid 6 bit Base 64 characters into an int.
      int x = 0;
      for (int j = 4; j > 0;) {
        int c = _decodeTable[input.codeUnitAt(i++)];
        if (c >= 0) {
          x = ((x << 6) & 0xFFFFFF) | c;
          j--;
        }
      }
      out[o++] = x >> 16;
      if (o < outputLen) {
        out[o++] = (x >> 8) & 0xFF;
        if (o < outputLen) out[o++] = x & 0xFF;
      }
    }
    return out;
  }
}

// Constants.
const _MASK_8 = 0xff;
const _MASK_32 = 0xffffffff;
const _BITS_PER_BYTE = 8;
const _BYTES_PER_WORD = 4;

// Base class encapsulating common behavior for cryptographic hash
// functions.
abstract class HashBase {
  // Hasher state.
  final int _chunkSizeInWords;
  final int _digestSizeInWords;
  final bool _bigEndianWords;
  int _lengthInBytes = 0;
  List<int> _pendingData;
  List<int> _currentChunk;
  List<int> _h;
  bool _digestCalled = false;

  HashBase(
      this._chunkSizeInWords, this._digestSizeInWords, this._bigEndianWords)
      : _pendingData = [] {
    _currentChunk = List.filled(_chunkSizeInWords, null);
    _h = List.filled(_digestSizeInWords, null);
  }

  // Update the hasher with more data.
  add(List<int> data) {
    if (_digestCalled) {
      throw StateError('Hash update method called after digest was retrieved');
    }
    _lengthInBytes += data.length;
    _pendingData.addAll(data);
    _iterate();
  }

  // Finish the hash computation and return the digest string.
  List<int> close() {
    if (_digestCalled) {
      return _resultAsBytes();
    }
    _digestCalled = true;
    _finalizeData();
    _iterate();
    assert(_pendingData.isEmpty);
    return _resultAsBytes();
  }

  // Returns the block size of the hash in bytes.
  int get blockSize {
    return _chunkSizeInWords * _BYTES_PER_WORD;
  }

  // Create a fresh instance of this Hash.
  newInstance();

  // One round of the hash computation.
  void _updateHash(List<int> m);

  // Helper methods.
  int _add32(int x, int y) => (x + y) & _MASK_32;
  int _roundUp(int val, int n) => (val + n - 1) & -n;

  // Rotate left limiting to unsigned 32-bit values.
  int _rotl32(int val, int shift) {
    var mod_shift = shift & 31;
    return ((val << mod_shift) & _MASK_32) |
        ((val & _MASK_32) >> (32 - mod_shift));
  }

  // Compute the final result as a list of bytes from the hash words.
  List<int> _resultAsBytes() {
    var result = <int>[];
    for (var i = 0; i < _h.length; i++) {
      result.addAll(_wordToBytes(_h[i]));
    }
    return result;
  }

  // Converts a list of bytes to a chunk of 32-bit words.
  _bytesToChunk(List<int> data, int dataIndex) {
    assert((data.length - dataIndex) >= (_chunkSizeInWords * _BYTES_PER_WORD));

    for (var wordIndex = 0; wordIndex < _chunkSizeInWords; wordIndex++) {
      var w3 = _bigEndianWords ? data[dataIndex] : data[dataIndex + 3];
      var w2 = _bigEndianWords ? data[dataIndex + 1] : data[dataIndex + 2];
      var w1 = _bigEndianWords ? data[dataIndex + 2] : data[dataIndex + 1];
      var w0 = _bigEndianWords ? data[dataIndex + 3] : data[dataIndex];
      dataIndex += 4;
      var word = (w3 & 0xff) << 24;
      word |= (w2 & _MASK_8) << 16;
      word |= (w1 & _MASK_8) << 8;
      word |= (w0 & _MASK_8);
      _currentChunk[wordIndex] = word;
    }
  }

  // Convert a 32-bit word to four bytes.
  List<int> _wordToBytes(int word) {
    List<int> bytes = List.filled(_BYTES_PER_WORD, null);
    bytes[0] = (word >> (_bigEndianWords ? 24 : 0)) & _MASK_8;
    bytes[1] = (word >> (_bigEndianWords ? 16 : 8)) & _MASK_8;
    bytes[2] = (word >> (_bigEndianWords ? 8 : 16)) & _MASK_8;
    bytes[3] = (word >> (_bigEndianWords ? 0 : 24)) & _MASK_8;
    return bytes;
  }

  // Iterate through data updating the hash computation for each
  // chunk.
  _iterate() {
    var len = _pendingData.length;
    var chunkSizeInBytes = _chunkSizeInWords * _BYTES_PER_WORD;
    if (len >= chunkSizeInBytes) {
      var index = 0;
      for (; (len - index) >= chunkSizeInBytes; index += chunkSizeInBytes) {
        _bytesToChunk(_pendingData, index);
        _updateHash(_currentChunk);
      }
      _pendingData = _pendingData.sublist(index, len);
    }
  }

  // Finalize the data. Add a 1 bit to the end of the message. Expand with
  // 0 bits and add the length of the message.
  _finalizeData() {
    _pendingData.add(0x80);
    var contentsLength = _lengthInBytes + 9;
    var chunkSizeInBytes = _chunkSizeInWords * _BYTES_PER_WORD;
    var finalizedLength = _roundUp(contentsLength, chunkSizeInBytes);
    var zeroPadding = finalizedLength - contentsLength;
    for (var i = 0; i < zeroPadding; i++) {
      _pendingData.add(0);
    }
    var lengthInBits = _lengthInBytes * _BITS_PER_BYTE;
    assert(lengthInBits < pow(2, 32));
    if (_bigEndianWords) {
      _pendingData.addAll(_wordToBytes(0));
      _pendingData.addAll(_wordToBytes(lengthInBits & _MASK_32));
    } else {
      _pendingData.addAll(_wordToBytes(lengthInBits & _MASK_32));
      _pendingData.addAll(_wordToBytes(0));
    }
  }
}

// The MD5 hasher is used to compute an MD5 message digest.
class MD5 extends HashBase {
  MD5() : super(16, 4, false) {
    _h[0] = 0x67452301;
    _h[1] = 0xefcdab89;
    _h[2] = 0x98badcfe;
    _h[3] = 0x10325476;
  }

  // Returns a new instance of this Hash.
  MD5 newInstance() {
    return MD5();
  }

  static const _k = [
    0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee, 0xf57c0faf, 0x4787c62a, //
    0xa8304613, 0xfd469501, 0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be, //
    0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821, 0xf61e2562, 0xc040b340, //
    0x265e5a51, 0xe9b6c7aa, 0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8, //
    0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed, 0xa9e3e905, 0xfcefa3f8, //
    0x676f02d9, 0x8d2a4c8a, 0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c, //
    0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70, 0x289b7ec6, 0xeaa127fa, //
    0xd4ef3085, 0x04881d05, 0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665, //
    0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039, 0x655b59c3, 0x8f0ccc92, //
    0xffeff47d, 0x85845dd1, 0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1, //
    0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391
  ];

  static const _r = [
    7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 5, 9, 14, //
    20, 5, 9, 14, 20, 5, 9, 14, 20, 5, 9, 14, 20, 4, 11, 16, 23, 4, 11, //
    16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 6, 10, 15, 21, 6, 10, 15, 21, 6, //
    10, 15, 21, 6, 10, 15, 21
  ];

  // Compute one iteration of the MD5 algorithm with a chunk of
  // 16 32-bit pieces.
  void _updateHash(List<int> m) {
    assert(m.length == 16);

    var a = _h[0];
    var b = _h[1];
    var c = _h[2];
    var d = _h[3];

    int t0;
    int t1;

    for (var i = 0; i < 64; i++) {
      if (i < 16) {
        t0 = (b & c) | ((~b & _MASK_32) & d);
        t1 = i;
      } else if (i < 32) {
        t0 = (d & b) | ((~d & _MASK_32) & c);
        t1 = ((5 * i) + 1) % 16;
      } else if (i < 48) {
        t0 = b ^ c ^ d;
        t1 = ((3 * i) + 5) % 16;
      } else {
        t0 = c ^ (b | (~d & _MASK_32));
        t1 = (7 * i) % 16;
      }

      var temp = d;
      d = c;
      c = b;
      b = _add32(
          b, _rotl32(_add32(_add32(a, t0), _add32(_k[i], m[t1])), _r[i]));
      a = temp;
    }

    _h[0] = _add32(a, _h[0]);
    _h[1] = _add32(b, _h[1]);
    _h[2] = _add32(c, _h[2]);
    _h[3] = _add32(d, _h[3]);
  }
}