// Copyright (c) 2012 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/quic_stream_sequencer.h"

#include <algorithm>
#include <limits>

#include "base/logging.h"
#include "net/quic/reliable_quic_stream.h"

using std::min;
using std::numeric_limits;

namespace net {

QuicStreamSequencer::QuicStreamSequencer(ReliableQuicStream* quic_stream)
    : stream_(quic_stream),
      num_bytes_consumed_(0),
      max_frame_memory_(numeric_limits<size_t>::max()),
      close_offset_(numeric_limits<QuicStreamOffset>::max()),
      half_close_(true) {
}

QuicStreamSequencer::QuicStreamSequencer(size_t max_frame_memory,
                                         ReliableQuicStream* quic_stream)
    : stream_(quic_stream),
      num_bytes_consumed_(0),
      max_frame_memory_(max_frame_memory),
      close_offset_(numeric_limits<QuicStreamOffset>::max()),
      half_close_(true) {
  if (max_frame_memory < kMaxPacketSize) {
    LOG(DFATAL) << "Setting max frame memory to " << max_frame_memory
                << ".  Some frames will be impossible to handle.";
  }
}

QuicStreamSequencer::~QuicStreamSequencer() {
}

bool QuicStreamSequencer::WillAcceptStreamFrame(
    const QuicStreamFrame& frame) const {
  size_t data_len = frame.data.size();
  DCHECK_LE(data_len, max_frame_memory_);

  QuicStreamOffset byte_offset = frame.offset;
  if (byte_offset < num_bytes_consumed_ ||
      frames_.find(byte_offset) != frames_.end()) {
    return false;
  }
  if (data_len > max_frame_memory_) {
    // We're never going to buffer this frame and we can't pass it up.
    // The stream might only consume part of it and we'd need a partial ack.
    //
    // Ideally this should never happen, as we check that
    // max_frame_memory_ > kMaxPacketSize and lower levels should reject
    // frames larger than that.
    return false;
  }
  if (byte_offset + data_len - num_bytes_consumed_ > max_frame_memory_) {
    // We can buffer this but not right now.  Toss it.
    // It might be worth trying an experiment where we try best-effort buffering
    return false;
  }
  return true;
}

bool QuicStreamSequencer::OnStreamFrame(const QuicStreamFrame& frame) {
  if (!WillAcceptStreamFrame(frame)) {
    // This should not happen, as WillAcceptFrame should be called before
    // OnStreamFrame.  Error handling should be done by the caller.
    return false;
  }

  QuicStreamOffset byte_offset = frame.offset;
  const char* data = frame.data.data();
  size_t data_len = frame.data.size();

  if (byte_offset == num_bytes_consumed_) {
    DVLOG(1) << "Processing byte offset " << byte_offset;
    size_t bytes_consumed = stream_->ProcessData(data, data_len);
    num_bytes_consumed_ += bytes_consumed;

    if (MaybeCloseStream()) {
      return true;
    }
    if (bytes_consumed > data_len) {
      stream_->Close(QUIC_SERVER_ERROR_PROCESSING_STREAM);
      return false;
    } else if (bytes_consumed == data_len) {
      FlushBufferedFrames();
      return true;  // it's safe to ack this frame.
    } else {
      // Set ourselves up to buffer what's left
      data_len -= bytes_consumed;
      data += bytes_consumed;
      byte_offset += bytes_consumed;
    }
  }

  DVLOG(1) << "Buffering packet at offset " << byte_offset;
  frames_.insert(make_pair(byte_offset, string(data, data_len)));
  return true;
}

void QuicStreamSequencer::CloseStreamAtOffset(QuicStreamOffset offset,
                                              bool half_close) {
  const QuicStreamOffset kMaxOffset = numeric_limits<QuicStreamOffset>::max();

  // If we have a scheduled termination or close, any new offset should match
  // it.
  if (close_offset_ != kMaxOffset && offset != close_offset_) {
      stream_->Close(QUIC_MULTIPLE_TERMINATION_OFFSETS);
      return;
  }

  close_offset_ = offset;
  // Full close overrides half close.
  if (half_close == false) {
    half_close_ = false;
  }

  MaybeCloseStream();
}

bool QuicStreamSequencer::MaybeCloseStream() {
  if (IsHalfClosed()) {
    DVLOG(1) << "Passing up termination, as we've processed "
             << num_bytes_consumed_ << " of " << close_offset_
             << " bytes.";
    // Technically it's an error if num_bytes_consumed isn't exactly
    // equal, but error handling seems silly at this point.
    stream_->TerminateFromPeer(half_close_);
    return true;
  }
  return false;
}

bool QuicStreamSequencer::HasBytesToRead() const {
  FrameMap::const_iterator it = frames_.begin();

  return it != frames_.end() && it->first == num_bytes_consumed_;
}

bool QuicStreamSequencer::IsHalfClosed() const {
  return num_bytes_consumed_ >= close_offset_;
}

bool QuicStreamSequencer::IsClosed() const {
  return num_bytes_consumed_ >= close_offset_ && half_close_ == false;
}

void QuicStreamSequencer::FlushBufferedFrames() {
  FrameMap::iterator it = frames_.find(num_bytes_consumed_);
  while (it != frames_.end()) {
    DVLOG(1) << "Flushing buffered packet at offset " << it->first;
    string* data = &it->second;
    size_t bytes_consumed = stream_->ProcessData(data->c_str(), data->size());
    num_bytes_consumed_ += bytes_consumed;
    if (MaybeCloseStream()) {
      return;
    }
    if (bytes_consumed > data->size()) {
      stream_->Close(QUIC_SERVER_ERROR_PROCESSING_STREAM);  // Programming error
      return;
    } else if (bytes_consumed == data->size()) {
      frames_.erase(it);
      it = frames_.find(num_bytes_consumed_);
    } else {
      string new_data = it->second.substr(bytes_consumed);
      frames_.erase(it);
      frames_.insert(make_pair(num_bytes_consumed_, new_data));
      return;
    }
  }
}

}  // namespace net