// Copyright (c) the JPEG XL Project Authors. All rights reserved.

//

// Use of this source code is governed by a BSD-style

// license that can be found in the LICENSE file.

#include "lib/jxl/enc_huffman.h"

#include <algorithm>

#include <memory>

#include "lib/jxl/huffman_tree.h"

namespace jxl {

namespace {

constexpr int kCodeLengthCodes = 18;

void StoreHuffmanTreeOfHuffmanTreeToBitMask(const int num_codes,

                                            const uint8_t* code_length_bitdepth,

                                            BitWriter* writer) {

  static const uint8_t kStorageOrder[kCodeLengthCodes] = {

      1, 2, 3, 4, 0, 5, 17, 6, 16, 7, 8, 9, 10, 11, 12, 13, 14, 15};

  // The bit lengths of the Huffman code over the code length alphabet

  // are compressed with the following static Huffman code:

  //   Symbol   Code

  //   ------   ----

  //   0          00

  //   1        1110

  //   2         110

  //   3          01

  //   4          10

  //   5        1111

  static const uint8_t kHuffmanBitLengthHuffmanCodeSymbols[6] = {0, 7, 3,

                                                                 2, 1, 15};

  static const uint8_t kHuffmanBitLengthHuffmanCodeBitLengths[6] = {2, 4, 3,

                                                                    2, 2, 4};

  // Throw away trailing zeros:

  size_t codes_to_store = kCodeLengthCodes;

  if (num_codes > 1) {

    for (; codes_to_store > 0; --codes_to_store) {

      if (code_length_bitdepth[kStorageOrder[codes_to_store - 1]] != 0) {

        break;

      }

    }

  }

  size_t skip_some = 0;  // skips none.

  if (code_length_bitdepth[kStorageOrder[0]] == 0 &&

      code_length_bitdepth[kStorageOrder[1]] == 0) {

    skip_some = 2;  // skips two.

    if (code_length_bitdepth[kStorageOrder[2]] == 0) {

      skip_some = 3;  // skips three.

    }

  }

  writer->Write(2, skip_some);

  for (size_t i = skip_some; i < codes_to_store; ++i) {

    size_t l = code_length_bitdepth[kStorageOrder[i]];

    writer->Write(kHuffmanBitLengthHuffmanCodeBitLengths[l],

                  kHuffmanBitLengthHuffmanCodeSymbols[l]);

  }

}

void StoreHuffmanTreeToBitMask(const size_t huffman_tree_size,

                               const uint8_t* huffman_tree,

                               const uint8_t* huffman_tree_extra_bits,

                               const uint8_t* code_length_bitdepth,

                               const uint16_t* code_length_bitdepth_symbols,

                               BitWriter* writer) {

  for (size_t i = 0; i < huffman_tree_size; ++i) {

    size_t ix = huffman_tree[i];

    writer->Write(code_length_bitdepth[ix], code_length_bitdepth_symbols[ix]);

    // Extra bits

    switch (ix) {

      case 16:

        writer->Write(2, huffman_tree_extra_bits[i]);

        break;

      case 17:

        writer->Write(3, huffman_tree_extra_bits[i]);

        break;

    }

  }

}

void StoreSimpleHuffmanTree(const uint8_t* depths, size_t symbols[4],

                            size_t num_symbols, size_t max_bits,

                            BitWriter* writer) {

  // value of 1 indicates a simple Huffman code

  writer->Write(2, 1);

  writer->Write(2, num_symbols - 1);  // NSYM - 1

  // Sort

  for (size_t i = 0; i < num_symbols; i++) {

    for (size_t j = i + 1; j < num_symbols; j++) {

      if (depths[symbols[j]] < depths[symbols[i]]) {

        std::swap(symbols[j], symbols[i]);

      }

    }

  }

  if (num_symbols == 2) {

    writer->Write(max_bits, symbols[0]);

    writer->Write(max_bits, symbols[1]);

  } else if (num_symbols == 3) {

    writer->Write(max_bits, symbols[0]);

    writer->Write(max_bits, symbols[1]);

    writer->Write(max_bits, symbols[2]);

  } else {

    writer->Write(max_bits, symbols[0]);

    writer->Write(max_bits, symbols[1]);

    writer->Write(max_bits, symbols[2]);

    writer->Write(max_bits, symbols[3]);

    // tree-select

    writer->Write(1, depths[symbols[0]] == 1 ? 1 : 0);

  }

}

// num = alphabet size

// depths = symbol depths

void StoreHuffmanTree(const uint8_t* depths, size_t num, BitWriter* writer) {

  // Write the Huffman tree into the compact representation.

  std::unique_ptr<uint8_t[]> arena(new uint8_t[2 * num]);

  uint8_t* huffman_tree = arena.get();

  uint8_t* huffman_tree_extra_bits = arena.get() + num;

  size_t huffman_tree_size = 0;

  WriteHuffmanTree(depths, num, &huffman_tree_size, huffman_tree,

                   huffman_tree_extra_bits);

  // Calculate the statistics of the Huffman tree in the compact representation.

  uint32_t huffman_tree_histogram[kCodeLengthCodes] = {0};

  for (size_t i = 0; i < huffman_tree_size; ++i) {

    ++huffman_tree_histogram[huffman_tree[i]];

  }

  int num_codes = 0;

  int code = 0;

  for (int i = 0; i < kCodeLengthCodes; ++i) {

    if (huffman_tree_histogram[i]) {

      if (num_codes == 0) {

        code = i;

        num_codes = 1;

      } else if (num_codes == 1) {

        num_codes = 2;

        break;

      }

    }

  }

  // Calculate another Huffman tree to use for compressing both the

  // earlier Huffman tree with.

  uint8_t code_length_bitdepth[kCodeLengthCodes] = {0};

  uint16_t code_length_bitdepth_symbols[kCodeLengthCodes] = {0};

  CreateHuffmanTree(&huffman_tree_histogram[0], kCodeLengthCodes, 5,

                    &code_length_bitdepth[0]);

  ConvertBitDepthsToSymbols(code_length_bitdepth, kCodeLengthCodes,

                            &code_length_bitdepth_symbols[0]);

  // Now, we have all the data, let's start storing it

  StoreHuffmanTreeOfHuffmanTreeToBitMask(num_codes, code_length_bitdepth,

                                         writer);

  if (num_codes == 1) {

    code_length_bitdepth[code] = 0;

  }

  // Store the real huffman tree now.

  StoreHuffmanTreeToBitMask(huffman_tree_size, huffman_tree,

                            huffman_tree_extra_bits, &code_length_bitdepth[0],

                            code_length_bitdepth_symbols, writer);

}

}  // namespace

void BuildAndStoreHuffmanTree(const uint32_t* histogram, const size_t length,

                              uint8_t* depth, uint16_t* bits,

                              BitWriter* writer) {

  size_t count = 0;

  size_t s4[4] = {0};

  for (size_t i = 0; i < length; i++) {

    if (histogram[i]) {

      if (count < 4) {

        s4[count] = i;

      } else if (count > 4) {

        break;

      }

      count++;

    }

  }

  size_t max_bits_counter = length - 1;

  size_t max_bits = 0;

  while (max_bits_counter) {

    max_bits_counter >>= 1;

    ++max_bits;

  }

  if (count <= 1) {

    // Output symbol bits and depths are initialized with 0, nothing to do.

    writer->Write(4, 1);

    writer->Write(max_bits, s4[0]);

    return;

  }

  CreateHuffmanTree(histogram, length, 15, depth);

  ConvertBitDepthsToSymbols(depth, length, bits);

  if (count <= 4) {

    StoreSimpleHuffmanTree(depth, s4, count, max_bits, writer);

  } else {

    StoreHuffmanTree(depth, length, writer);

  }

}

}  // namespace jxl