// Copyright (c) Google LLC 2020

//

// 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 "./bit_reader.h"

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

namespace brunsli {

void BrunsliBitReaderInit(BrunsliBitReader* br) {

  br->num_bits_ = 0;

  br->bits_ = 0;

  br->num_debt_bytes_ = 0;

  br->is_healthy_ = true;

  br->is_optimistic_ = false;

}

void BrunsliBitReaderResume(BrunsliBitReader* br, const uint8_t* buffer,

                              size_t length) {

  br->next_ = buffer;

  br->end_ = buffer + length;

  br->is_optimistic_ = false;

}

/*

   Tries to return "debt" if any, and normalize the state.

   Normal state means that less than 8 bits are held in bit buffer.

   Peeking (BrunsliBitReaderGet) more bits than actually using

   (BrunsliBitReaderDrop) could put bit reader into denormal state.

*/

static BRUNSLI_INLINE void BrunsliBitReaderUnload(BrunsliBitReader* br) {

  // Cancel the overdraft.

  while ((br->num_debt_bytes_ > 0) && (br->num_bits_ >= 8)) {

    br->num_debt_bytes_--;

    br->num_bits_ -= 8;

  }

  // Return unused bytes.

  while (br->num_bits_ >= 8) {

    br->next_--;

    br->num_bits_ -= 8;

  }

  br->bits_ &= BrunsliBitReaderBitMask(br->num_bits_);

}

size_t BrunsliBitReaderSuspend(BrunsliBitReader* br) {

  BrunsliBitReaderUnload(br);

  size_t unused_bytes = br->end_ - br->next_;

  br->next_ = nullptr;

  br->end_ = nullptr;

  return unused_bytes;

}

void BrunsliBitReaderFinish(BrunsliBitReader* br) {

  uint32_t n_bits = br->num_bits_;

  // Likely, did not invoke Suspend before.

  if (n_bits >= 8) {

    br->is_healthy_ = false;

    return;

  }

  if (n_bits > 0) {

    uint32_t padding_bits = BrunsliBitReaderRead(br, n_bits);

    if (padding_bits != 0) br->is_healthy_ = false;

  }

}

bool BrunsliBitReaderIsHealthy(BrunsliBitReader* br) {

  BrunsliBitReaderUnload(br);

  return (br->num_debt_bytes_ == 0) && (br->is_healthy_);

}

void BrunsliBitReaderSetOptimistic(BrunsliBitReader* br) {

  br->is_optimistic_ = true;

}

bool BrunsliBitReaderCanRead(BrunsliBitReader* br, size_t n_bits) {

  if (br->is_optimistic_) return true;

  if (br->num_debt_bytes_ != 0) return false;

  if (br->num_bits_ >= n_bits) return true;

  size_t num_extra_bytes = (n_bits - br->num_bits_ + 7) >> 3;

  return (br->next_ + num_extra_bytes <= br->end_);

}

}  // namespace brunsli