// 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/jpegli/huffman.h"

#include <limits>
#include <vector>

#include "lib/jpegli/common.h"
#include "lib/jpegli/error.h"

namespace jpegli {

// Returns the table width of the next 2nd level table, count is the histogram
// of bit lengths for the remaining symbols, len is the code length of the next
// processed symbol.
static inline int NextTableBitSize(const int* count, int len) {
  int left = 1 << (len - kJpegHuffmanRootTableBits);
  while (len < static_cast<int>(kJpegHuffmanMaxBitLength)) {
    left -= count[len];
    if (left <= 0) break;
    ++len;
    left <<= 1;
  }
  return len - kJpegHuffmanRootTableBits;
}

void BuildJpegHuffmanTable(const uint32_t* count, const uint32_t* symbols,
                           HuffmanTableEntry* lut) {
  HuffmanTableEntry code;    // current table entry
  HuffmanTableEntry* table;  // next available space in table
  int len;                   // current code length
  int idx;                   // symbol index
  int key;                   // prefix code
  int reps;                  // number of replicate key values in current table
  int low;                   // low bits for current root entry
  int table_bits;            // key length of current table
  int table_size;            // size of current table

  // Make a local copy of the input bit length histogram.
  int tmp_count[kJpegHuffmanMaxBitLength + 1] = {0};
  int total_count = 0;
  for (len = 1; len <= static_cast<int>(kJpegHuffmanMaxBitLength); ++len) {
    tmp_count[len] = count[len];
    total_count += tmp_count[len];
  }

  table = lut;
  table_bits = kJpegHuffmanRootTableBits;
  table_size = 1 << table_bits;

  // Special case code with only one value.
  if (total_count == 1) {
    code.bits = 0;
    code.value = symbols[0];
    for (key = 0; key < table_size; ++key) {
      table[key] = code;
    }
    return;
  }

  // Fill in root table.
  key = 0;
  idx = 0;
  for (len = 1; len <= kJpegHuffmanRootTableBits; ++len) {
    for (; tmp_count[len] > 0; --tmp_count[len]) {
      code.bits = len;
      code.value = symbols[idx++];
      reps = 1 << (kJpegHuffmanRootTableBits - len);
      while (reps--) {
        table[key++] = code;
      }
    }
  }

  // Fill in 2nd level tables and add pointers to root table.
  table += table_size;
  table_size = 0;
  low = 0;
  for (len = kJpegHuffmanRootTableBits + 1;
       len <= static_cast<int>(kJpegHuffmanMaxBitLength); ++len) {
    for (; tmp_count[len] > 0; --tmp_count[len]) {
      // Start a new sub-table if the previous one is full.
      if (low >= table_size) {
        table += table_size;
        table_bits = NextTableBitSize(tmp_count, len);
        table_size = 1 << table_bits;
        low = 0;
        lut[key].bits = table_bits + kJpegHuffmanRootTableBits;
        lut[key].value = (table - lut) - key;
        ++key;
      }
      code.bits = len - kJpegHuffmanRootTableBits;
      code.value = symbols[idx++];
      reps = 1 << (table_bits - code.bits);
      while (reps--) {
        table[low++] = code;
      }
    }
  }
}

// A node of a Huffman tree.
struct HuffmanTree {
  HuffmanTree(uint32_t count, int16_t left, int16_t right)
      : total_count(count), index_left(left), index_right_or_value(right) {}
  uint32_t total_count;
  int16_t index_left;
  int16_t index_right_or_value;
};

void SetDepth(const HuffmanTree& p, HuffmanTree* pool, uint8_t* depth,
              uint8_t level) {
  if (p.index_left >= 0) {
    ++level;
    SetDepth(pool[p.index_left], pool, depth, level);
    SetDepth(pool[p.index_right_or_value], pool, depth, level);
  } else {
    depth[p.index_right_or_value] = level;
  }
}

// Sort the root nodes, least popular first.
static JXL_INLINE bool Compare(const HuffmanTree& v0, const HuffmanTree& v1) {
  return v0.total_count < v1.total_count;
}

// This function will create a Huffman tree.
//
// The catch here is that the tree cannot be arbitrarily deep.
// Brotli specifies a maximum depth of 15 bits for "code trees"
// and 7 bits for "code length code trees."
//
// count_limit is the value that is to be faked as the minimum value
// and this minimum value is raised until the tree matches the
// maximum length requirement.
//
// This algorithm is not of excellent performance for very long data blocks,
// especially when population counts are longer than 2**tree_limit, but
// we are not planning to use this with extremely long blocks.
//
// See http://en.wikipedia.org/wiki/Huffman_coding
void CreateHuffmanTree(const uint32_t* data, const size_t length,
                       const int tree_limit, uint8_t* depth) {
  // For block sizes below 64 kB, we never need to do a second iteration
  // of this loop. Probably all of our block sizes will be smaller than
  // that, so this loop is mostly of academic interest. If we actually
  // would need this, we would be better off with the Katajainen algorithm.
  for (uint32_t count_limit = 1;; count_limit *= 2) {
    std::vector<HuffmanTree> tree;
    tree.reserve(2 * length + 1);

    for (size_t i = length; i != 0;) {
      --i;
      if (data[i]) {
        const uint32_t count = std::max(data[i], count_limit - 1);
        tree.emplace_back(count, -1, static_cast<int16_t>(i));
      }
    }

    const size_t n = tree.size();
    if (n == 1) {
      // Fake value; will be fixed on upper level.
      depth[tree[0].index_right_or_value] = 1;
      break;
    }

    std::stable_sort(tree.begin(), tree.end(), Compare);

    // The nodes are:
    // [0, n): the sorted leaf nodes that we start with.
    // [n]: we add a sentinel here.
    // [n + 1, 2n): new parent nodes are added here, starting from
    //              (n+1). These are naturally in ascending order.
    // [2n]: we add a sentinel at the end as well.
    // There will be (2n+1) elements at the end.
    const HuffmanTree sentinel(std::numeric_limits<uint32_t>::max(), -1, -1);
    tree.push_back(sentinel);
    tree.push_back(sentinel);

    size_t i = 0;      // Points to the next leaf node.
    size_t j = n + 1;  // Points to the next non-leaf node.
    for (size_t k = n - 1; k != 0; --k) {
      size_t left;
      size_t right;
      if (tree[i].total_count <= tree[j].total_count) {
        left = i;
        ++i;
      } else {
        left = j;
        ++j;
      }
      if (tree[i].total_count <= tree[j].total_count) {
        right = i;
        ++i;
      } else {
        right = j;
        ++j;
      }

      // The sentinel node becomes the parent node.
      size_t j_end = tree.size() - 1;
      tree[j_end].total_count =
          tree[left].total_count + tree[right].total_count;
      tree[j_end].index_left = static_cast<int16_t>(left);
      tree[j_end].index_right_or_value = static_cast<int16_t>(right);

      // Add back the last sentinel node.
      tree.push_back(sentinel);
    }
    JXL_DASSERT(tree.size() == 2 * n + 1);
    SetDepth(tree[2 * n - 1], tree.data(), depth, 0);

    // We need to pack the Huffman tree in tree_limit bits.
    // If this was not successful, add fake entities to the lowest values
    // and retry.
    if (*std::max_element(&depth[0], &depth[length]) <= tree_limit) {
      break;
    }
  }
}

void ValidateHuffmanTable(j_common_ptr cinfo, const JHUFF_TBL* table,
                          bool is_dc) {
  size_t total_symbols = 0;
  size_t total_p = 0;
  size_t max_depth = 0;
  for (size_t d = 1; d <= kJpegHuffmanMaxBitLength; ++d) {
    uint8_t count = table->bits[d];
    if (count) {
      total_symbols += count;
      total_p += (1u << (kJpegHuffmanMaxBitLength - d)) * count;
      max_depth = d;
    }
  }
  total_p += 1u << (kJpegHuffmanMaxBitLength - max_depth);  // sentinel symbol
  if (total_symbols == 0) {
    JPEGLI_ERROR("Empty Huffman table");
  }
  if (total_symbols > kJpegHuffmanAlphabetSize) {
    JPEGLI_ERROR("Too many symbols in Huffman table");
  }
  if (total_p != (1u << kJpegHuffmanMaxBitLength)) {
    JPEGLI_ERROR("Invalid bit length distribution");
  }
  uint8_t symbol_seen[kJpegHuffmanAlphabetSize] = {};
  for (size_t i = 0; i < total_symbols; ++i) {
    uint8_t symbol = table->huffval[i];
    if (symbol_seen[symbol]) {
      JPEGLI_ERROR("Duplicate symbol %d in Huffman table", symbol);
    }
    symbol_seen[symbol] = 1;
  }
}

void AddStandardHuffmanTables(j_common_ptr cinfo, bool is_dc) {
  // Huffman tables from the JPEG standard.
  static constexpr JHUFF_TBL kStandardDCTables[2] = {
      // DC luma
      {{0, 0, 1, 5, 1, 1, 1, 1, 1, 1},
       {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11},
       FALSE},
      // DC chroma
      {{0, 0, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1},
       {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11},
       FALSE}};
  static constexpr JHUFF_TBL kStandardACTables[2] = {
      // AC luma
      {{0, 0, 2, 1, 3, 3, 2, 4, 3, 5, 5, 4, 4, 0, 0, 1, 125},
       {0x01, 0x02, 0x03, 0x00, 0x04, 0x11, 0x05, 0x12, 0x21, 0x31, 0x41, 0x06,
        0x13, 0x51, 0x61, 0x07, 0x22, 0x71, 0x14, 0x32, 0x81, 0x91, 0xa1, 0x08,
        0x23, 0x42, 0xb1, 0xc1, 0x15, 0x52, 0xd1, 0xf0, 0x24, 0x33, 0x62, 0x72,
        0x82, 0x09, 0x0a, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x25, 0x26, 0x27, 0x28,
        0x29, 0x2a, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x43, 0x44, 0x45,
        0x46, 0x47, 0x48, 0x49, 0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59,
        0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x73, 0x74, 0x75,
        0x76, 0x77, 0x78, 0x79, 0x7a, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89,
        0x8a, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9a, 0xa2, 0xa3,
        0xa4, 0xa5, 0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6,
        0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9,
        0xca, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda, 0xe1, 0xe2,
        0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9, 0xea, 0xf1, 0xf2, 0xf3, 0xf4,
        0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa},
       FALSE},
      // AC chroma
      {{0, 0, 2, 1, 2, 4, 4, 3, 4, 7, 5, 4, 4, 0, 1, 2, 119},
       {0x00, 0x01, 0x02, 0x03, 0x11, 0x04, 0x05, 0x21, 0x31, 0x06, 0x12, 0x41,
        0x51, 0x07, 0x61, 0x71, 0x13, 0x22, 0x32, 0x81, 0x08, 0x14, 0x42, 0x91,
        0xa1, 0xb1, 0xc1, 0x09, 0x23, 0x33, 0x52, 0xf0, 0x15, 0x62, 0x72, 0xd1,
        0x0a, 0x16, 0x24, 0x34, 0xe1, 0x25, 0xf1, 0x17, 0x18, 0x19, 0x1a, 0x26,
        0x27, 0x28, 0x29, 0x2a, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x43, 0x44,
        0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58,
        0x59, 0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x73, 0x74,
        0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
        0x88, 0x89, 0x8a, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9a,
        0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4,
        0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
        0xc8, 0xc9, 0xca, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda,
        0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9, 0xea, 0xf2, 0xf3, 0xf4,
        0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa},
       FALSE}};
  const JHUFF_TBL* std_tables = is_dc ? kStandardDCTables : kStandardACTables;
  JHUFF_TBL** tables;
  if (cinfo->is_decompressor) {
    j_decompress_ptr cinfo_d = reinterpret_cast<j_decompress_ptr>(cinfo);
    tables = is_dc ? cinfo_d->dc_huff_tbl_ptrs : cinfo_d->ac_huff_tbl_ptrs;
  } else {
    j_compress_ptr cinfo_c = reinterpret_cast<j_compress_ptr>(cinfo);
    tables = is_dc ? cinfo_c->dc_huff_tbl_ptrs : cinfo_c->ac_huff_tbl_ptrs;
  }
  for (int i = 0; i < 2; ++i) {
    if (tables[i] == nullptr) {
      tables[i] = jpegli_alloc_huff_table(cinfo);
      memcpy(tables[i], &std_tables[i], sizeof(JHUFF_TBL));
      ValidateHuffmanTable(cinfo, tables[i], is_dc);
    }
  }
}

}  // namespace jpegli
