// Copyright (c) 2015 The Chromium 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 "net/quic/stream_sequencer_buffer.h"

#include "base/basictypes.h"
#include "base/logging.h"

using std::min;

namespace net {

StreamSequencerBuffer::Gap::Gap(QuicStreamOffset begin_offset,
                                QuicStreamOffset end_offset)
    : begin_offset(begin_offset), end_offset(end_offset) {}

StreamSequencerBuffer::FrameInfo::FrameInfo()
    : length(1), timestamp(QuicTime::Zero()) {}

StreamSequencerBuffer::FrameInfo::FrameInfo(size_t length, QuicTime timestamp)
    : length(length), timestamp(timestamp) {}

StreamSequencerBuffer::StreamSequencerBuffer(size_t max_capacity_bytes)
    : max_buffer_capacity_bytes_(max_capacity_bytes),
      blocks_count_(
          ceil(static_cast<double>(max_capacity_bytes) / kBlockSizeBytes)),
      total_bytes_read_(0),
      blocks_(blocks_count_) {
  Clear();
}

StreamSequencerBuffer::~StreamSequencerBuffer() {
  Clear();
}

void StreamSequencerBuffer::Clear() {
  for (size_t i = 0; i < blocks_count_; ++i) {
    if (blocks_[i] != nullptr) {
      RetireBlock(i);
    }
  }
  num_bytes_buffered_ = 0;
  // Reset gaps_ so that buffer is in a state as if all data before
  // total_bytes_read_ has been consumed, and those after total_bytes_read_
  // has never arrived.
  gaps_ = std::list<Gap>(
      1, Gap(total_bytes_read_, std::numeric_limits<QuicStreamOffset>::max())),
  frame_arrival_time_map_.clear();
}

void StreamSequencerBuffer::RetireBlock(size_t idx) {
  DCHECK(blocks_[idx] != nullptr);
  delete blocks_[idx];
  blocks_[idx] = nullptr;
  DVLOG(1) << "Retired block" << idx;
}

QuicErrorCode StreamSequencerBuffer::OnStreamData(
    QuicStreamOffset starting_offset,
    base::StringPiece data,
    QuicTime timestamp,
    size_t* const bytes_buffered) {
  *bytes_buffered = 0;
  QuicStreamOffset offset = starting_offset;
  size_t size = data.size();
  if (size == 0) {
    LOG(DFATAL) << "Attempted to write 0 bytes of data.";
    return QUIC_INVALID_STREAM_FRAME;
  }

  // Find the first gap not ending before |offset|. This gap maybe the gap to
  // fill if the arriving frame doesn't overlaps with previous ones.
  std::list<Gap>::iterator current_gap = gaps_.begin();
  while (current_gap != gaps_.end() && current_gap->end_offset <= offset) {
    ++current_gap;
  }

  DCHECK(current_gap != gaps_.end());

  // "duplication": might duplicate with data alread filled,but also might
  // overlap across different base::StringPiece objects already written.
  // In both cases, don't write the data,
  // and allow the caller of this method to handle the result.
  if (offset < current_gap->begin_offset &&
      offset + size <= current_gap->begin_offset) {
    DVLOG(1) << "duplicated data at offset:" << offset << " len: " << size;
    return QUIC_NO_ERROR;
  }
  if (offset < current_gap->begin_offset &&
      offset + size > current_gap->begin_offset) {
    // Beginning of new data overlaps data before current gap.
    return QUIC_INVALID_STREAM_DATA;
  }
  if (offset + size > current_gap->end_offset) {
    // End of new data overlaps with data after current gap.
    return QUIC_INVALID_STREAM_DATA;
  }

  // Write beyond the current range this buffer is covering.
  if (offset + size > total_bytes_read_ + max_buffer_capacity_bytes_) {
    return QUIC_INTERNAL_ERROR;
  }

  size_t total_written = 0;
  size_t source_remaining = size;
  const char* source = data.data();
  // Write data block by block. If corresponding block has not created yet,
  // create it first.
  // Stop when all data are written or reaches the logical end of the buffer.
  while (source_remaining > 0) {
    const size_t write_block_num = GetBlockIndex(offset);
    const size_t write_block_offset = GetInBlockOffset(offset);
    DCHECK_GT(blocks_count_, write_block_num);

    size_t block_capacity = GetBlockCapacity(write_block_num);
    size_t bytes_avail = block_capacity - write_block_offset;

    // If this write meets the upper boundary of the buffer,
    // reduce the available free bytes.
    if (offset + bytes_avail > total_bytes_read_ + max_buffer_capacity_bytes_) {
      bytes_avail = total_bytes_read_ + max_buffer_capacity_bytes_ - offset;
    }

    if (blocks_[write_block_num] == nullptr) {
      // TODO(danzh): Investigate if using a freelist would improve performance.
      // Same as RetireBlock().
      blocks_[write_block_num] = new BufferBlock();
    }

    const size_t bytes_to_copy = min<size_t>(bytes_avail, source_remaining);
    char* dest = blocks_[write_block_num]->buffer + write_block_offset;
    DVLOG(1) << "write at offset: " << offset << " len: " << bytes_to_copy;
    memcpy(dest, source, bytes_to_copy);
    source += bytes_to_copy;
    source_remaining -= bytes_to_copy;
    offset += bytes_to_copy;
    total_written += bytes_to_copy;
  }

  DCHECK_GT(total_written, 0u);
  *bytes_buffered = total_written;
  UpdateGapList(current_gap, starting_offset, total_written);

  frame_arrival_time_map_.insert(
      std::make_pair(starting_offset, FrameInfo(size, timestamp)));
  num_bytes_buffered_ += total_written;
  return QUIC_NO_ERROR;
}

inline void StreamSequencerBuffer::UpdateGapList(
    std::list<Gap>::iterator gap_with_new_data_written,
    QuicStreamOffset start_offset,
    size_t bytes_written) {
  if (gap_with_new_data_written->begin_offset == start_offset &&
      gap_with_new_data_written->end_offset > start_offset + bytes_written) {
    // New data has been written into the left part of the buffer.
    gap_with_new_data_written->begin_offset = start_offset + bytes_written;
  } else if (gap_with_new_data_written->begin_offset < start_offset &&
             gap_with_new_data_written->end_offset ==
                 start_offset + bytes_written) {
    // New data has been written into the right part of the buffer.
    gap_with_new_data_written->end_offset = start_offset;
  } else if (gap_with_new_data_written->begin_offset < start_offset &&
             gap_with_new_data_written->end_offset >
                 start_offset + bytes_written) {
    // New data has been written into the middle of the buffer.
    auto current = gap_with_new_data_written++;
    size_t current_end = current->end_offset;
    current->end_offset = start_offset;
    gaps_.insert(gap_with_new_data_written,
                 Gap(start_offset + bytes_written, current_end));
  } else if (gap_with_new_data_written->begin_offset == start_offset &&
             gap_with_new_data_written->end_offset ==
                 start_offset + bytes_written) {
    // This gap has been filled with new data. So it's no longer a gap.
    gaps_.erase(gap_with_new_data_written);
  }
}

size_t StreamSequencerBuffer::Readv(const iovec* dest_iov, size_t dest_count) {
  size_t bytes_read = 0;
  for (size_t i = 0; i < dest_count && ReadableBytes() > 0; ++i) {
    char* dest = reinterpret_cast<char*>(dest_iov[i].iov_base);
    size_t dest_remaining = dest_iov[i].iov_len;
    while (dest_remaining > 0 && ReadableBytes() > 0) {
      size_t block_idx = NextBlockToRead();
      size_t start_offset_in_block = ReadOffset();
      size_t block_capacity = GetBlockCapacity(block_idx);
      size_t bytes_available_in_block =
          min<size_t>(ReadableBytes(), block_capacity - start_offset_in_block);
      size_t bytes_to_copy =
          min<size_t>(bytes_available_in_block, dest_remaining);
      DCHECK_GT(bytes_to_copy, 0u);
      DCHECK_NE(static_cast<BufferBlock*>(nullptr), blocks_[block_idx]);
      memcpy(dest, blocks_[block_idx]->buffer + start_offset_in_block,
             bytes_to_copy);
      dest += bytes_to_copy;
      dest_remaining -= bytes_to_copy;
      num_bytes_buffered_ -= bytes_to_copy;
      total_bytes_read_ += bytes_to_copy;
      bytes_read += bytes_to_copy;

      // Retire the block if all the data is read out
      // and no other data is stored in this block.
      if (bytes_to_copy == bytes_available_in_block) {
        RetireBlockIfEmpty(block_idx);
      }
    }
  }

  if (bytes_read > 0) {
    UpdateFrameArrivalMap(total_bytes_read_);
  }
  return bytes_read;
}

int StreamSequencerBuffer::GetReadableRegions(struct iovec* iov,
                                              int iov_count) const {
  DCHECK(iov != nullptr);
  DCHECK_GT(iov_count, 0);

  if (ReadableBytes() == 0) {
    iov[0].iov_base = nullptr;
    iov[0].iov_len = 0;
    return 0;
  }

  size_t start_block_idx = NextBlockToRead();
  QuicStreamOffset readable_offset_end = gaps_.front().begin_offset - 1;
  DCHECK_GE(readable_offset_end + 1, total_bytes_read_);
  size_t end_block_offset = GetInBlockOffset(readable_offset_end);
  size_t end_block_idx = GetBlockIndex(readable_offset_end);

  // If readable region is within one block, deal with it seperately.
  if (start_block_idx == end_block_idx && ReadOffset() <= end_block_offset) {
    iov[0].iov_base = blocks_[start_block_idx]->buffer + ReadOffset();
    iov[0].iov_len = ReadableBytes();
    DVLOG(1) << "get only block" << start_block_idx;
    return 1;
  }

  // Get first block
  iov[0].iov_base = blocks_[start_block_idx]->buffer + ReadOffset();
  iov[0].iov_len = GetBlockCapacity(start_block_idx) - ReadOffset();
  DVLOG(1) << "get first block" << start_block_idx << " with len "
           << iov[0].iov_len;
  DCHECK_GT(readable_offset_end + 1, total_bytes_read_ + iov[0].iov_len)
      << "there should be more available data";

  // Get readable regions of the rest blocks till either 2nd to last block
  // before gap is met or |iov| is filled. For these blocks, one whole block is
  // a region.
  int iov_used = 1;
  size_t block_idx = (start_block_idx + iov_used) % blocks_count_;
  while (block_idx != end_block_idx && iov_used < iov_count) {
    DCHECK_NE(static_cast<BufferBlock*>(nullptr), blocks_[block_idx]);
    iov[iov_used].iov_base = blocks_[block_idx]->buffer;
    iov[iov_used].iov_len = GetBlockCapacity(block_idx);
    DVLOG(1) << "get block" << block_idx;
    ++iov_used;
    block_idx = (start_block_idx + iov_used) % blocks_count_;
  }

  // Deal with last block if |iov| can hold more.
  if (iov_used < iov_count) {
    DCHECK_NE(static_cast<BufferBlock*>(nullptr), blocks_[block_idx]);
    iov[iov_used].iov_base = blocks_[end_block_idx]->buffer;
    iov[iov_used].iov_len = end_block_offset + 1;
    DVLOG(1) << "get last block " << end_block_idx;
    ++iov_used;
  }
  return iov_used;
}

bool StreamSequencerBuffer::GetReadableRegion(iovec* iov,
                                              QuicTime* timestamp) const {
  if (ReadableBytes() == 0) {
    iov[0].iov_base = nullptr;
    iov[0].iov_len = 0;
    return false;
  }

  size_t start_block_idx = NextBlockToRead();
  iov->iov_base = blocks_[start_block_idx]->buffer + ReadOffset();
  size_t readable_bytes_in_block = min<size_t>(
      GetBlockCapacity(start_block_idx) - ReadOffset(), ReadableBytes());
  size_t region_len = 0;
  auto iter = frame_arrival_time_map_.begin();
  *timestamp = iter->second.timestamp;
  DVLOG(1) << "readable bytes in block: " << readable_bytes_in_block;
  for (; iter != frame_arrival_time_map_.end() &&
         region_len + iter->second.length <= readable_bytes_in_block;
       ++iter) {
    if (iter->second.timestamp != *timestamp) {
      // If reaches a frame arrive at another timestamp, stop expanding current
      // region.
      DVLOG(1) << "Meet frame with different timestamp.";
      break;
    }
    region_len += iter->second.length;
    DVLOG(1) << "Add bytes to region: " << iter->second.length;
  }
  if (iter == frame_arrival_time_map_.end() ||
      iter->second.timestamp == *timestamp) {
    // If encountered the end of readable bytes before reaching a different
    // timestamp.
    DVLOG(1) << "Get all readable bytes in first block.";
    region_len = readable_bytes_in_block;
  }
  iov->iov_len = region_len;
  return true;
}

bool StreamSequencerBuffer::MarkConsumed(size_t bytes_used) {
  if (bytes_used > ReadableBytes()) {
    return false;
  }
  size_t bytes_to_consume = bytes_used;
  while (bytes_to_consume > 0) {
    size_t block_idx = NextBlockToRead();
    size_t offset_in_block = ReadOffset();
    size_t bytes_available = min<size_t>(
        ReadableBytes(), GetBlockCapacity(block_idx) - offset_in_block);
    size_t bytes_read = min<size_t>(bytes_to_consume, bytes_available);
    total_bytes_read_ += bytes_read;
    num_bytes_buffered_ -= bytes_read;
    bytes_to_consume -= bytes_read;
    // If advanced to the end of current block and end of buffer hasn't wrapped
    // to this block yet.
    if (bytes_available == bytes_read) {
      RetireBlockIfEmpty(block_idx);
    }
  }
  if (bytes_used > 0) {
    UpdateFrameArrivalMap(total_bytes_read_);
  }
  return true;
}

size_t StreamSequencerBuffer::FlushBufferedFrames() {
  size_t prev_total_bytes_read = total_bytes_read_;
  total_bytes_read_ = gaps_.back().begin_offset;
  Clear();
  return total_bytes_read_ - prev_total_bytes_read;
}

size_t StreamSequencerBuffer::ReadableBytes() const {
  return gaps_.front().begin_offset - total_bytes_read_;
}

bool StreamSequencerBuffer::HasBytesToRead() const {
  return ReadableBytes() > 0;
}

QuicStreamOffset StreamSequencerBuffer::BytesConsumed() const {
  return total_bytes_read_;
}

size_t StreamSequencerBuffer::BytesBuffered() const {
  return num_bytes_buffered_;
}

size_t StreamSequencerBuffer::GetBlockIndex(QuicStreamOffset offset) const {
  return (offset % max_buffer_capacity_bytes_) / kBlockSizeBytes;
}

size_t StreamSequencerBuffer::GetInBlockOffset(QuicStreamOffset offset) const {
  return (offset % max_buffer_capacity_bytes_) % kBlockSizeBytes;
}

size_t StreamSequencerBuffer::ReadOffset() const {
  return GetInBlockOffset(total_bytes_read_);
}

size_t StreamSequencerBuffer::NextBlockToRead() const {
  return GetBlockIndex(total_bytes_read_);
}

void StreamSequencerBuffer::RetireBlockIfEmpty(size_t block_index) {
  DCHECK(ReadableBytes() == 0 || GetInBlockOffset(total_bytes_read_) == 0)
      << "RetireBlockIfEmpty() should only be called when advancing to next "
         "block"
         " or a gap has been reached.";
  // If the whole buffer becomes empty, the last piece of data has been read.
  if (Empty()) {
    RetireBlock(block_index);
    return;
  }

  // Check where the logical end of this buffer is.
  // Not empty if the end of circular buffer has been wrapped to this block.
  if (GetBlockIndex(gaps_.back().begin_offset - 1) == block_index) {
    return;
  }

  // Read index remains in this block, which means a gap has been reached.
  if (NextBlockToRead() == block_index) {
    Gap first_gap = gaps_.front();
    DCHECK(first_gap.begin_offset == total_bytes_read_);
    // Check where the next piece data is.
    // Not empty if next piece of data is still in this chunk.
    bool gap_extends_to_infinity =
        (first_gap.end_offset != std::numeric_limits<QuicStreamOffset>::max());
    bool gap_ends_in_this_block =
        (GetBlockIndex(first_gap.end_offset) == block_index);
    if (gap_extends_to_infinity || gap_ends_in_this_block) {
      return;
    }
  }
  RetireBlock(block_index);
}

bool StreamSequencerBuffer::Empty() const {
  return gaps_.size() == 1 && gaps_.front().begin_offset == total_bytes_read_;
}

size_t StreamSequencerBuffer::GetBlockCapacity(size_t block_index) const {
  if ((block_index + 1) == blocks_count_) {
    size_t result = max_buffer_capacity_bytes_ % kBlockSizeBytes;
    if (result == 0) {  // whole block
      result = kBlockSizeBytes;
    }
    return result;
  } else {
    return kBlockSizeBytes;
  }
}

void StreamSequencerBuffer::UpdateFrameArrivalMap(QuicStreamOffset offset) {
  // Get the frame before which all frames should be removed.
  auto next_frame = frame_arrival_time_map_.upper_bound(offset);
  DCHECK(next_frame != frame_arrival_time_map_.begin());
  auto iter = frame_arrival_time_map_.begin();
  while (iter != next_frame) {
    auto erased = *iter;
    iter = frame_arrival_time_map_.erase(iter);
    DVLOG(1) << "remove FrameInfo with offsest: " << erased.first
             << " len: " << erased.second.length;
    if (erased.first + erased.second.length > offset) {
      // If last frame is partially read out, update this FrameInfo and insert
      // it back.
      auto updated = std::make_pair(
          offset, FrameInfo(erased.first + erased.second.length - offset,
                            erased.second.timestamp));
      DVLOG(1) << "insert back FrameInfo with offset: " << updated.first
               << " len: " << updated.second.length;
      frame_arrival_time_map_.insert(updated);
    }
  }
}

}  //  namespace net