// 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_bit_writer.h"

#include <string.h>  // memcpy

#include "lib/jxl/base/byte_order.h"

#include "lib/jxl/dec_bit_reader.h"

namespace jxl {

BitWriter::Allotment::Allotment(BitWriter* JXL_RESTRICT writer, size_t max_bits)

    : max_bits_(max_bits) {

  if (writer == nullptr) return;

  prev_bits_written_ = writer->BitsWritten();

  const size_t prev_bytes = writer->storage_.size();

  const size_t next_bytes = DivCeil(max_bits, kBitsPerByte);

  writer->storage_.resize(prev_bytes + next_bytes);

  parent_ = writer->current_allotment_;

  writer->current_allotment_ = this;

}

BitWriter::Allotment::~Allotment() {

  if (!called_) {

    // Not calling is a bug - unused storage will not be reclaimed.

    JXL_ABORT("Did not call Allotment::ReclaimUnused");

  }

}

void BitWriter::Allotment::FinishedHistogram(BitWriter* JXL_RESTRICT writer) {

  if (writer == nullptr) return;

  JXL_ASSERT(!called_);              // Call before ReclaimUnused

  JXL_ASSERT(histogram_bits_ == 0);  // Do not call twice

  JXL_ASSERT(writer->BitsWritten() >= prev_bits_written_);

  histogram_bits_ = writer->BitsWritten() - prev_bits_written_;

}

void BitWriter::Allotment::PrivateReclaim(BitWriter* JXL_RESTRICT writer,

                                          size_t* JXL_RESTRICT used_bits,

                                          size_t* JXL_RESTRICT unused_bits) {

  JXL_ASSERT(!called_);  // Do not call twice

  called_ = true;

  if (writer == nullptr) return;

  JXL_ASSERT(writer->BitsWritten() >= prev_bits_written_);

  *used_bits = writer->BitsWritten() - prev_bits_written_;

  JXL_ASSERT(*used_bits <= max_bits_);

  *unused_bits = max_bits_ - *used_bits;

  // Reclaim unused bytes whole bytes from writer's allotment.

  const size_t unused_bytes = *unused_bits / kBitsPerByte;  // truncate

  JXL_ASSERT(writer->storage_.size() >= unused_bytes);

  writer->storage_.resize(writer->storage_.size() - unused_bytes);

  writer->current_allotment_ = parent_;

  // Ensure we don't also charge the parent for these bits.

  auto parent = parent_;

  while (parent != nullptr) {

    parent->prev_bits_written_ += *used_bits;

    parent = parent->parent_;

  }

}

void BitWriter::AppendByteAligned(const Span<const uint8_t>& span) {

  if (!span.size()) return;

  storage_.resize(storage_.size() + span.size() + 1);  // extra zero padding

  // Concatenate by copying bytes because both source and destination are bytes.

  JXL_ASSERT(BitsWritten() % kBitsPerByte == 0);

  size_t pos = BitsWritten() / kBitsPerByte;

  memcpy(storage_.data() + pos, span.data(), span.size());

  pos += span.size();

  storage_[pos++] = 0;  // for next Write

  JXL_ASSERT(pos <= storage_.size());

  bits_written_ += span.size() * kBitsPerByte;

}

void BitWriter::AppendByteAligned(const BitWriter& other) {

  JXL_ASSERT(other.BitsWritten() % kBitsPerByte == 0);

  JXL_ASSERT(other.BitsWritten() / kBitsPerByte != 0);

  AppendByteAligned(other.GetSpan());

}

void BitWriter::AppendByteAligned(const std::vector<BitWriter>& others) {

  // Total size to add so we can preallocate

  size_t other_bytes = 0;

  for (const BitWriter& writer : others) {

    JXL_ASSERT(writer.BitsWritten() % kBitsPerByte == 0);

    other_bytes += writer.BitsWritten() / kBitsPerByte;

  }

  if (other_bytes == 0) {

    // No bytes to append: this happens for example when creating per-group

    // storage for groups, but not writing anything in them for e.g. lossless

    // images with no alpha. Do nothing.

    return;

  }

  storage_.resize(storage_.size() + other_bytes + 1);  // extra zero padding

  // Concatenate by copying bytes because both source and destination are bytes.

  JXL_ASSERT(BitsWritten() % kBitsPerByte == 0);

  size_t pos = BitsWritten() / kBitsPerByte;

  for (const BitWriter& writer : others) {

    const Span<const uint8_t> span = writer.GetSpan();

    if (!span.empty()) {

      memcpy(storage_.data() + pos, span.data(), span.size());

      pos += span.size();

    }

  }

  storage_[pos++] = 0;  // for next Write

  JXL_ASSERT(pos <= storage_.size());

  bits_written_ += other_bytes * kBitsPerByte;

}

// TODO(lode): avoid code duplication

void BitWriter::AppendByteAligned(

    const std::vector<std::unique_ptr<BitWriter>>& others) {

  // Total size to add so we can preallocate

  size_t other_bytes = 0;

  for (const auto& writer : others) {

    JXL_ASSERT(writer->BitsWritten() % kBitsPerByte == 0);

    other_bytes += writer->BitsWritten() / kBitsPerByte;

  }

  if (other_bytes == 0) {

    // No bytes to append: this happens for example when creating per-group

    // storage for groups, but not writing anything in them for e.g. lossless

    // images with no alpha. Do nothing.

    return;

  }

  storage_.resize(storage_.size() + other_bytes + 1);  // extra zero padding

  // Concatenate by copying bytes because both source and destination are bytes.

  JXL_ASSERT(BitsWritten() % kBitsPerByte == 0);

  size_t pos = BitsWritten() / kBitsPerByte;

  for (const auto& writer : others) {

    const Span<const uint8_t> span = writer->GetSpan();

    memcpy(storage_.data() + pos, span.data(), span.size());

    pos += span.size();

  }

  storage_[pos++] = 0;  // for next Write

  JXL_ASSERT(pos <= storage_.size());

  bits_written_ += other_bytes * kBitsPerByte;

}

// Example: let's assume that 3 bits (Rs below) have been written already:

// BYTE+0       BYTE+1       BYTE+2

// 0000 0RRR    ???? ????    ???? ????

//

// Now, we could write up to 5 bits by just shifting them left by 3 bits and

// OR'ing to BYTE-0.

//

// For n > 5 bits, we write the lowest 5 bits as above, then write the next

// lowest bits into BYTE+1 starting from its lower bits and so on.

void BitWriter::Write(size_t n_bits, uint64_t bits) {

  JXL_DASSERT((bits >> n_bits) == 0);

  JXL_DASSERT(n_bits <= kMaxBitsPerCall);

  uint8_t* p = &storage_[bits_written_ / kBitsPerByte];

  const size_t bits_in_first_byte = bits_written_ % kBitsPerByte;

  bits <<= bits_in_first_byte;

#if JXL_BYTE_ORDER_LITTLE

  uint64_t v = *p;

  // Last (partial) or next byte to write must be zero-initialized!

  // PaddedBytes initializes the first, and Write/Append maintain this.

  JXL_DASSERT(v >> bits_in_first_byte == 0);

  v |= bits;

  memcpy(p, &v, sizeof(v));  // Write bytes: possibly more than n_bits/8

#else

  *p++ |= static_cast<uint8_t>(bits & 0xFF);

  for (size_t bits_left_to_write = n_bits + bits_in_first_byte;

       bits_left_to_write >= 9; bits_left_to_write -= 8) {

    bits >>= 8;

    *p++ = static_cast<uint8_t>(bits & 0xFF);

  }

  *p = 0;

#endif

  bits_written_ += n_bits;

}

}  // namespace jxl