#include "tcp_receiver.hh"

// Dummy implementation of a TCP receiver

// For Lab 2, please replace with a real implementation that passes the
// automated checks run by `make check_lab2`.

template <typename... Targs>
void DUMMY_CODE(Targs &&.../* unused */) {}

using namespace std;

void TCPReceiver::segment_received(const TCPSegment &seg) {
    if (seg.header().syn) {
        _syn = true;
        // there's no way to know whether connection has been established from bytestream status,
        // so a special member is needed
        _isn = seg.header().seqno;
    }
    if (!_syn)
        return;  // abandon packets before SYN
    uint64_t checkpoint = stream_out().bytes_written();
    uint64_t abs_seqno = unwrap(seg.header().seqno, _isn, checkpoint);
    // In your TCP implementation, you’ll use the index of the last reassembled byte as the checkpoint.
    // So, the bytes_written-1 (Stream Indices) should be this value
    // Watch out for the case when no bytes have been assembled
    if (abs_seqno == 0 && !seg.header().syn)
        return;
    // assertion: when abs_seqno is 0, this packet must be syn
    uint64_t index = abs_seqno - (abs_seqno ? 1 : 0);  // special case for SYN&FIN
    _reassembler.push_substring(seg.payload().copy(), index, seg.header().fin);
    auto _abs_ackno = stream_out().bytes_written() + 1 + (stream_out().input_ended() ? 1 : 0);
    _ackno = wrap(_abs_ackno, _isn);
}

optional<WrappingInt32> TCPReceiver::ackno() const {
    if (_syn)
        return _ackno;
    return {};
}

size_t TCPReceiver::window_size() const {
    // capacity minus the number of bytes holding in the byte stream
    return _capacity - stream_out().buffer_size();
}