// Copyright (c) Google LLC 2019

//

// Use of this source code is governed by an MIT-style

// license that can be found in the LICENSE file or at

// https://opensource.org/licenses/MIT.

#include "./context_map_decode.h"

#include "../common/constants.h"

#include "../common/platform.h"

#include <brunsli/status.h>

#include <brunsli/types.h>

#include "./bit_reader.h"

#include "./huffman_decode.h"

namespace brunsli {

namespace {

void MoveToFront(uint8_t* v, uint8_t index) {

  uint8_t value = v[index];

  uint8_t i = index;

  for (; i; --i) v[i] = v[i - 1];

  v[0] = value;

}

void InverseMoveToFrontTransform(uint8_t* v, size_t v_len) {

  uint8_t mtf[256];

  for (size_t i = 0; i < 256; ++i) {

    mtf[i] = static_cast<uint8_t>(i);

  }

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

    uint8_t index = v[i];

    v[i] = mtf[index];

    if (index) MoveToFront(mtf, index);

  }

}

}  // namespace

BrunsliStatus DecodeContextMap(const HuffmanDecodingData& entropy,

                               size_t max_run_length_prefix, size_t* index,

                               std::vector<uint8_t>* context_map,

                               BrunsliBitReader* br) {

  size_t& i = *index;

  uint8_t* map = context_map->data();

  const size_t length = context_map->size();

  while (i < length) {

    // Check there is enough deta for Huffman code, RLE and IMTF bit.

    if (!BrunsliBitReaderCanRead(br, 15 + max_run_length_prefix + 1)) {

      return BRUNSLI_NOT_ENOUGH_DATA;

    }

    uint32_t code = entropy.ReadSymbol(br);

    if (code == 0) {

      map[i] = 0;

      ++i;

    } else if (code <= max_run_length_prefix) {

      size_t reps = 1u + (1u << code) + (int)BrunsliBitReaderRead(br, code);

      while (--reps) {

        if (i >= length) return BRUNSLI_INVALID_BRN;

        map[i] = 0;

        ++i;

      }

    } else {

      map[i] = (uint8_t)(code - max_run_length_prefix);

      ++i;

    }

  }

  if (BrunsliBitReaderRead(br, 1)) {

    InverseMoveToFrontTransform(map, length);

  }

  return BrunsliBitReaderIsHealthy(br) ? BRUNSLI_OK : BRUNSLI_INVALID_BRN;

}

}  // namespace brunsli