// Copyright 2020 The Pigweed Authors

//

// Licensed under the Apache License, Version 2.0 (the "License"); you may not

// use this file except in compliance with the License. You may obtain a copy of

// the License at

//

//     https://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT

// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the

// License for the specific language governing permissions and limitations under

// the License.

#include "pw_base64/base64.h"

#include <cstdint>

#include "pw_assert/check.h"

namespace pw::base64 {

namespace {

// Encoding functions

constexpr size_t kEncodedGroupSize = 4;

constexpr char kChar62 = '+';  // URL safe encoding uses - instead

constexpr char kChar63 = '/';  // URL safe encoding uses _ instead

constexpr char kPadding = '=';

// Table that encodes a 6-bit pattern as a Base64 character

constexpr char kEncodeTable[64] = {

    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K',     'L',    'M',

    'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',     'Y',    'Z',

    'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k',     'l',    'm',

    'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x',     'y',    'z',

    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', kChar62, kChar63};

constexpr char BitGroup0Char(uint8_t byte0) {

  return kEncodeTable[(byte0 & 0b11111100) >> 2];

}

constexpr char BitGroup1Char(uint8_t byte0, uint8_t byte1 = 0) {

  return kEncodeTable[((byte0 & 0b00000011) << 4) |

                      ((byte1 & 0b11110000) >> 4)];

}

constexpr char BitGroup2Char(uint8_t byte1, uint8_t byte2 = 0) {

  return kEncodeTable[((byte1 & 0b00001111) << 2) |

                      ((byte2 & 0b11000000) >> 6)];

}

constexpr char BitGroup3Char(uint8_t byte2) {

  return kEncodeTable[byte2 & 0b00111111];

}

// Decoding functions

constexpr char kMinValidChar = '+';

constexpr char kMaxValidChar = 'z';

constexpr uint8_t kX = 0xff;  // Value used for invalid characters

// Table that decodes a Base64 character to its 6-bit value. Supports the

// standard (+/) and URL-safe (-_) alphabets. Starts from the lowest-value valid

// character, which is +.

constexpr uint8_t kDecodeTable[] = {

    62, kX, 62, kX, 63, 52, 53, 54, 55, 56,  //  0 - 09

    57, 58, 59, 60, 61, kX, kX, kX, kX, kX,  // 10 - 19

    kX, kX, 0,  1,  2,  3,  4,  5,  6,  7,   // 20 - 29

    8,  9,  10, 11, 12, 13, 14, 15, 16, 17,  // 30 - 39

    18, 19, 20, 21, 22, 23, 24, 25, kX, kX,  // 40 - 49

    kX, kX, 63, kX, 26, 27, 28, 29, 30, 31,  // 50 - 59

    32, 33, 34, 35, 36, 37, 38, 39, 40, 41,  // 60 - 69

    42, 43, 44, 45, 46, 47, 48, 49, 50, 51,  // 70 - 79

};

constexpr uint8_t CharToBits(char ch) {

  return kDecodeTable[ch - kMinValidChar];

}

constexpr uint8_t Byte0(uint8_t bits0, uint8_t bits1) {

  return static_cast<uint8_t>(bits0 << 2) | ((bits1 & 0b110000) >> 4);

}

constexpr uint8_t Byte1(uint8_t bits1, uint8_t bits2) {

  return static_cast<uint8_t>((bits1 & 0b001111) << 4) |

         ((bits2 & 0b111100) >> 2);

}

constexpr uint8_t Byte2(uint8_t bits2, uint8_t bits3) {

  return static_cast<uint8_t>((bits2 & 0b000011) << 6) | bits3;

}

}  // namespace

extern "C" void pw_Base64Encode(const void* binary_data,

                                const size_t binary_size_bytes,

                                char* output) {

  const uint8_t* bytes = static_cast<const uint8_t*>(binary_data);

  // Encode groups of 3 source bytes into 4 output characters.

  size_t remaining = binary_size_bytes;

  for (; remaining >= 3u; remaining -= 3u, bytes += 3) {

    *output++ = BitGroup0Char(bytes[0]);

    *output++ = BitGroup1Char(bytes[0], bytes[1]);

    *output++ = BitGroup2Char(bytes[1], bytes[2]);

    *output++ = BitGroup3Char(bytes[2]);

  }

  // If the source data length isn't a multiple of 3, pad the end with either 1

  // or 2 '=' characters.

  if (remaining > 0u) {

    *output++ = BitGroup0Char(bytes[0]);

    if (remaining == 1u) {

      *output++ = BitGroup1Char(bytes[0]);

      *output++ = kPadding;

    } else {

      *output++ = BitGroup1Char(bytes[0], bytes[1]);

      *output++ = BitGroup2Char(bytes[1]);

    }

    *output++ = kPadding;

  }

}

extern "C" size_t pw_Base64Decode(const char* base64,

                                  const size_t base64_size_bytes,

                                  void* const output) {

  // If empty or missing padding, return 0.

  if (base64_size_bytes == 0 || base64_size_bytes % kEncodedGroupSize != 0) {

    return 0;

  }

  uint8_t* binary = static_cast<uint8_t*>(output);

  size_t ch = 0;

  for (; ch < base64_size_bytes - kEncodedGroupSize; ch += kEncodedGroupSize) {

    const uint8_t char0 = CharToBits(base64[ch + 0]);

    const uint8_t char1 = CharToBits(base64[ch + 1]);

    const uint8_t char2 = CharToBits(base64[ch + 2]);

    const uint8_t char3 = CharToBits(base64[ch + 3]);

    binary[0] = Byte0(char0, char1);

    binary[1] = Byte1(char1, char2);

    binary[2] = Byte2(char2, char3);

    binary += 3;

  }

  // Decode the final group, which may include padding.

  const uint8_t char0 = CharToBits(base64[ch + 0]);

  const uint8_t char1 = CharToBits(base64[ch + 1]);

  const uint8_t char2 = CharToBits(base64[ch + 2]);

  const uint8_t char3 = CharToBits(base64[ch + 3]);

  *binary++ = Byte0(char0, char1);

  if (base64[ch + 2] != kPadding) {

    *binary++ = Byte1(char1, char2);

    if (base64[ch + 3] != kPadding) {

      *binary++ = Byte2(char2, char3);

    }

  }

  return static_cast<size_t>(binary - static_cast<uint8_t*>(output));

}

extern "C" bool pw_Base64IsValidChar(char base64_char) {

  return !(base64_char < kMinValidChar || base64_char > kMaxValidChar ||

           CharToBits(base64_char) == kX /* invalid char */);

}

extern "C" bool pw_Base64IsValid(const char* base64_data, size_t base64_size) {

  if (base64_size == 0u) {

    return true;

  }

  if (base64_size % kEncodedGroupSize != 0) {

    return false;

  }

  // Check up to the last two characters, which are potentially padding.

  for (size_t i = 0; i < base64_size - 2; ++i) {

    if (!pw_Base64IsValidChar(base64_data[i])) {

      return false;

    }

  }

  // Check the last two possibly padding characters.

  if (base64_data[base64_size - 2] == kPadding) {

    return base64_data[base64_size - 1] == kPadding;

  }

  return pw_Base64IsValidChar(base64_data[base64_size - 1]) ||

         base64_data[base64_size - 1] == kPadding;

}

size_t Encode(span<const std::byte> binary, span<char> output_buffer) {

  const size_t required_size = EncodedSize(binary.size_bytes());

  if (output_buffer.size_bytes() < required_size) {

    return 0;

  }

  pw_Base64Encode(binary.data(), binary.size_bytes(), output_buffer.data());

  return required_size;

}

size_t Decode(std::string_view base64, span<std::byte> output_buffer) {

  if (output_buffer.size_bytes() < MaxDecodedSize(base64.size()) ||

      !IsValid(base64)) {

    return 0;

  }

  return Decode(base64, output_buffer.data());

}

void Encode(span<const std::byte> binary, InlineString<>& output) {

  const size_t initial_size = output.size();

  const size_t final_size = initial_size + EncodedSize(binary.size());

  PW_CHECK(final_size <= output.capacity());

  output.resize_and_overwrite([&](char* data, size_t) {

    Encode(binary, data + initial_size);

    return final_size;

  });

}

}  // namespace pw::base64