// 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.

library crypto.base64;

import 'dart:convert';
import 'dart:typed_data';

/// An instance of the default implementation of [Base64Codec].
///
/// This provides convenient access to most common Base64 use-cases.
const Base64Codec BASE64 = const Base64Codec();

/// A mapping from ASCII character codes to their corresponding Base64 values.
///
/// Characters with a value of -2 are invalid. Characters with a value of -1
/// should be ignored. The padding character, "=", is represented as 0.
const List<int> _decodeTable = const [
  -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,  0, -2, -2,
  -2,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 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
];

/// A String representing a mapping from numbers between 0 and 63, inclusive, to
/// their corresponding encoded character.
///
/// This is the table for URL-safe encodings.
const String _encodeTableUrlSafe =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";

/// A String representing a mapping from numbers between 0 and 63, inclusive, to
/// their corresponding encoded character.
///
/// This is the table for URL-unsafe encodings.
const String _encodeTable =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

/// The line length for Base64 strings with line separators.
const int _LINE_LENGTH = 76;

/// A carriage return.
const int _CR = 13; // '\r'

/// A line feed.
const int _LF = 10; // '\n'

/// The byte sequence representing non-URL-encoded padding.
const List<int> _PAD_BYTES = const [61]; // '='

/// The byte sequence representing URL-encoded padding.
const List<int> _ENCODED_PAD_BYTES = const [37, 51, 68]; // '%3D'

/// The string representing non-URL-encoded padding.
const String _PAD = "=";

/// The string representing URL-encoded padding.
const String _ENCODED_PAD = "%3D";

/// A codec that converts between binary data and [Base64][rfc]-encoded strings.
///
/// [rfc]: https://tools.ietf.org/html/rfc4648
class Base64Codec extends Codec<List<int>, String> {
  final bool _urlSafe;
  final bool _addLineSeparator;
  final bool _encodePaddingCharacter;

  /// Creates a new [Base64Codec].
  ///
  /// The default [BASE64] codec will be good enough for most cases. A new codec
  /// only needs to be instantiated when you want to do multiple conversions
  /// with the same configuration.
  ///
  /// If [urlSafe] is `true`, a URL-safe alphabet will be used when encoding.
  /// Specifically, the characters `-` and `_` will be used instead of `+` and
  /// `/`.
  ///
  /// If [addLineSeparator] is `true`, `\r\n` line separators will be added
  /// every 76 characters when encoding.
  ///
  /// If [encodePaddingCharacter] is `true`, the padding character `=` will be
  /// written as `%3D` when encoding.
  const Base64Codec(
      {bool urlSafe: false,
      bool addLineSeparator: false,
      bool encodePaddingCharacter: false})
      : _urlSafe = urlSafe,
        _addLineSeparator = addLineSeparator,
        _encodePaddingCharacter = encodePaddingCharacter;

  String get name => "base64";

  /// Encodes [bytes] into a Base64 string.
  ///
  /// If [urlSafe] is `true`, a URL-safe alphabet will be used when encoding.
  /// Specifically, the characters `-` and `_` will be used instead of `+` and
  /// `/`.
  ///
  /// If [addLineSeparator] is `true`, `\r\n` line separators will be added
  /// every 76 characters when encoding.
  ///
  /// If [encodePaddingCharacter] is `true`, the padding character `=` will be
  /// written as `%3D` when encoding.
  ///
  /// Any flags passed to this method take precedence over the flags passed to
  /// the codec itself.
  String encode(List<int> bytes,
      {bool urlSafe, bool addLineSeparator, bool encodePaddingCharacter}) {
    if (urlSafe == null) urlSafe = _urlSafe;
    if (addLineSeparator == null) addLineSeparator = _addLineSeparator;
    if (encodePaddingCharacter == null) {
      encodePaddingCharacter = _encodePaddingCharacter;
    }
    return new Base64Encoder(
        urlSafe: urlSafe,
        addLineSeparator: addLineSeparator,
        encodePaddingCharacter: encodePaddingCharacter).convert(bytes);
  }

  Base64Encoder get encoder => new Base64Encoder(
      urlSafe: _urlSafe,
      addLineSeparator: _addLineSeparator,
      encodePaddingCharacter: _encodePaddingCharacter);

  Base64Decoder get decoder => new Base64Decoder();
}

/// An encoder that converts sequences of bytes to strings using [Base64][rfc].
///
/// [rfc]: https://tools.ietf.org/html/rfc4648
class Base64Encoder extends Converter<List<int>, String> {
  /// Whether this encoder generates URL-safe strings.
  final bool _urlSafe;

  /// Whether this encoder adds line breaks to the output.
  final bool _addLineSeparator;

  /// Whether this encoder URL-encodes trailing padding characters.
  final bool _encodePaddingCharacter;

  /// The sequence of bytes to use as a padding character.
  final List<int> _pad;

  /// Creates a new [Base64Encoder].
  ///
  /// The default [BASE64.encoder] will be good enough for most cases. A new
  /// codec only needs to be instantiated when you want to do multiple
  /// conversions with the same configuration.
  ///
  /// If [urlSafe] is `true`, a URL-safe alphabet will be used. Specifically,
  /// the characters `-` and `_` will be used instead of `+` and `/`.
  ///
  /// If [addLineSeparator] is `true`, `\r\n` line separators will be added
  /// every 76 characters.
  ///
  /// If [encodePaddingCharacter] is `true`, the padding character `=` will be
  /// written as `%3D`.
  const Base64Encoder(
      {bool urlSafe: false,
      bool addLineSeparator: false,
      bool encodePaddingCharacter: false})
      : _urlSafe = urlSafe,
        _addLineSeparator = addLineSeparator,
        _encodePaddingCharacter = encodePaddingCharacter,
        _pad = encodePaddingCharacter == true ? _ENCODED_PAD_BYTES : _PAD_BYTES;

  /// Converts [bytes] to Base64.
  ///
  /// If [start] and [end] are provided, only the sublist `bytes.sublist(start,
  /// end)` is converted.
  String convert(List<int> bytes, [int start = 0, int end]) {
    int bytes_length = bytes.length;
    RangeError.checkValidRange(start, end, bytes_length);
    if (end == null) end = bytes_length;
    int length = end - start;
    if (length == 0) {
      return "";
    }
    final String lookup = _urlSafe ? _encodeTableUrlSafe : _encodeTable;
    // Size of 24 bit chunks.
    final int remainderLength = length.remainder(3);
    final int chunkLength = length - remainderLength;
    // Size of base output.
    int baseOutputLength = ((length ~/ 3) * 4);
    int remainderOutputLength;
    if (_encodePaddingCharacter) {
      remainderOutputLength = ((remainderLength > 0) ? 6 : 0);
    } else {
      remainderOutputLength = ((remainderLength > 0) ? 4 : 0);
    }

    int outputLength = baseOutputLength + remainderOutputLength;
    // Add extra for line separators.
    if (_addLineSeparator) {
      outputLength += ((outputLength - 1) ~/ _LINE_LENGTH) << 1;
    }
    List<int> out = new List<int>(outputLength);

    // Encode 24 bit chunks.
    int j = 0, i = start, c = 0;
    while (i < chunkLength) {
      int x = ((bytes[i++] << 16) & 0x00FFFFFF) |
          ((bytes[i++] << 8) & 0x00FFFFFF) |
          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 < outputLength - 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.setRange(j, j + _pad.length, _pad);
      out.setRange(j + _pad.length, j + 2 * _pad.length, _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.setRange(j, j + _pad.length, _pad);
    }

    return new String.fromCharCodes(out);
  }

  _Base64EncoderSink startChunkedConversion(Sink<String> sink) {
    StringConversionSink stringSink;
    if (sink is StringConversionSink) {
      stringSink = sink;
    } else {
      stringSink = new StringConversionSink.from(sink);
    }
    return new _Base64EncoderSink(stringSink, _urlSafe, _addLineSeparator);
  }
}

/// A [ChunkedConversionSink] for encoding chunks of data to Base64.
class _Base64EncoderSink extends ChunkedConversionSink<List<int>> {
  /// The encoder used to encode each chunk.
  final Base64Encoder _encoder;

  /// The underlying sink to which to emit the encoded strings.
  final ChunkedConversionSink<String> _outSink;

  /// The buffer of as-yet-unconverted bytes.
  ///
  /// This is used to ensure that we don't generate interstitial padding
  /// characters.
  final List<int> _buffer = new List<int>();

  /// The length of [_buffer]; that is, the number of unconverted bytes.
  int _bufferCount = 0;

  _Base64EncoderSink(this._outSink, urlSafe, addLineSeparator)
      : _encoder = new Base64Encoder(
            urlSafe: urlSafe, addLineSeparator: addLineSeparator);

  void add(List<int> chunk) {
    var nextBufferCount = (chunk.length + _bufferCount) % 3;

    int decodableLength = _bufferCount + chunk.length - nextBufferCount;

    if (_bufferCount + chunk.length > _buffer.length) {
      _buffer.replaceRange(_bufferCount, _buffer.length,
          chunk.sublist(0, _buffer.length - _bufferCount));
      _buffer.addAll(chunk.sublist(_buffer.length - _bufferCount));
    } else {
      _buffer.replaceRange(_bufferCount, _bufferCount + chunk.length, chunk);
    }

    _outSink.add(_encoder.convert(_buffer, 0, decodableLength));
    _buffer.removeRange(0, decodableLength);
    _bufferCount = nextBufferCount;
  }

  void close() {
    if (_bufferCount > 0) {
      _outSink.add(_encoder.convert(_buffer.sublist(0, _bufferCount)));
    }
    _outSink.close();
  }
}

/// An encoder that converts [Base64][rfc] strings to sequences of bytes.
///
/// [rfc]: https://tools.ietf.org/html/rfc4648
class Base64Decoder extends Converter<String, List<int>> {
  const Base64Decoder();

  List<int> convert(String input) {
    int length = input.length;
    if (length == 0) {
      return new Uint8List(0);
    }

    int normalLength = 0;
    int i = 0;
    // Count '\r', '\n' and illegal characters, check if
    // '/', '+' / '-', '_' are used consistently, for illegal characters,
    // throw an exception.

    while (i < length) {
      int codeUnit = input.codeUnitAt(i);
      int c = _decodeTable[codeUnit];
      if (c == -2) {
        if (codeUnit == _ENCODED_PAD_BYTES[0] &&
            i < length - 2 &&
            input.codeUnitAt(i + 1) == _ENCODED_PAD_BYTES[1] &&
            input.codeUnitAt(i + 2) == _ENCODED_PAD_BYTES[2]) {
          normalLength++;
          i += 2;
        } else {
          throw new FormatException('Invalid character', input, i);
        }
      }
      if (c >= 0) normalLength++;
      i++;
    }

    if (normalLength % 4 != 0) {
      throw new FormatException(
          '''Size of Base 64 characters in Input
          must be a multiple of 4''',
          input,
          normalLength);
    }

    // Count pad characters.
    int padLength = 0;
    i = length - 1;
    while (i >= 0) {
      int currentCodeUnit = input.codeUnitAt(i);
      if (currentCodeUnit == _ENCODED_PAD_BYTES[2] &&
          i >= 2 &&
          input.codeUnitAt(i - 1) == _ENCODED_PAD_BYTES[1] &&
          input.codeUnitAt(i - 2) == _ENCODED_PAD_BYTES[0]) {
        padLength++;
        i -= 2;
      } else if (_decodeTable[currentCodeUnit] > 0) {
        break;
      } else if (currentCodeUnit == _PAD_BYTES[0]) {
        padLength++;
      }
      i--;
    }
    int outputLength = ((normalLength * 6) >> 3) - padLength;
    List<int> out = new Uint8List(outputLength);

    for (int i = 0, o = 0; o < outputLength;) {
      // 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) & 0x00FFFFFF) | c;
          j--;
        }
      }
      out[o++] = x >> 16;
      if (o < outputLength) {
        out[o++] = (x >> 8) & 0xFF;
        if (o < outputLength) out[o++] = x & 0xFF;
      }
    }

    return out;
  }

  _Base64DecoderSink startChunkedConversion(Sink<List<int>> sink) {
    if (sink is! ByteConversionSink) {
      sink = new ByteConversionSink.from(sink);
    }
    return new _Base64DecoderSink(sink);
  }
}

/// A [ChunkedConversionSink] for decoding chunks of Base64 strings to data.
class _Base64DecoderSink extends ChunkedConversionSink<String> {
  /// The encoder used to decode each chunk.
  final Base64Decoder _decoder = new Base64Decoder();

  /// The underlying sink to which to emit the decoded strings.
  final ChunkedConversionSink<List<int>> _outSink;

  /// The as-yet-unconverted text.
  ///
  /// This is used to handle a chunk stopping partway in the middle of a
  /// URL-encoded `=` character.
  String _unconverted = "";

  _Base64DecoderSink(this._outSink);

  void add(String chunk) {
    if (chunk.isEmpty) return;
    if (_unconverted.isNotEmpty) {
      chunk = _unconverted + chunk;
    }
    chunk = chunk.replaceAll(_ENCODED_PAD, _PAD);
    int decodableLength = chunk.length;
    // If chunk ends in "%" or "%3", it may be a partial encoded pad.
    // If chunk is smaller than 4 characters, don't bother checking.
    if (chunk.length > 3 && chunk.contains(_ENCODED_PAD[0], chunk.length - 2)) {
      decodableLength = chunk.lastIndexOf(_ENCODED_PAD[0]);
    }
    decodableLength -= decodableLength % 4;
    _unconverted = chunk.substring(decodableLength);
    if (decodableLength > 0) {
      _outSink.add(_decoder.convert(chunk.substring(0, decodableLength)));
    }
  }

  void close() {
    if (_unconverted.isNotEmpty) {
      _outSink.add(_decoder.convert(_unconverted));
    }
    _outSink.close();
  }
}