namespace NetStack.Contracts
{
    public enum TcpError
    {
        Unknown = 1,
        AlreadyConnected,       // this connection is already in use
        Refused,                // the receiving host actively refused the connection
        Reset,                  // the connection was reset
        Timeout,                // no response was received
        ProtocolViolation,      // we received a TCP segment that is not acceptable in the current state
        ResourcesExhausted,     // out of memory, etc.
        Closed,                 // remote peer has closed socket
    }

    public contract TcpConnectionContract
    {
        // Requests
        in message Connect(uint dstIP, ushort dstPort);
        in message BindLocalEndPoint(uint dstIP, ushort dstPort);

        //
        // Initial state; there is a gratuitous Ready message to
        // ensure the Exp side has been connected before it accepts
        // any messages.
        //
        out message Ready();

        state Start : Ready! -> ReadyState;

        state ReadyState : one
        {
            Connect? -> ConnectResult; // Can connect without binding first
            BindLocalEndPoint? -> BindResult; // Can't listen without binding first
            Close? -> Closed;
        }

        //
        // Binding to a local endpoint
        //
        state BindResult : one
        {
            OK! -> Bound;
            InvalidEndPoint! -> ReadyState;
        }

        in message Listen(int backlog);

        state Bound : one
        {
            Listen? -> ListenResult;
            Connect? -> ConnectResult;
            Close? -> Closed;
        }

        //
        // Attempts to connect to a remote host
        //
        out message OK();
        out message CouldNotConnect(TcpError error);

        state ConnectResult : one
        {
            CouldNotConnect! -> ReadyState;
            OK! -> Connected;
        }

        //
        // Attempts to listen for inbound connections
        //
        out message CouldNotListen();

        state ListenResult : one
        {
            CouldNotListen! -> ReadyState;
            OK! -> Listening;
        }

        out message InvalidEndPoint();

        in message GetLocalAddress();
        in message GetLocalPort();
        in message Accept(TcpConnectionContract.Exp:PreConnected! newConnection);
        in message IsSessionAvailable(); // Is there a new session waiting to be serviced?

        out message IPAddress(uint ip);
        out message Port(ushort port);
        out message SessionIsAvailable(bool isAvailable);

        state Listening : one
        {
            GetLocalAddress? -> IPAddress! -> Listening;
            GetLocalPort? -> Port! -> Listening;
            IsSessionAvailable? -> SessionIsAvailable! -> Listening;
            Accept? -> OK! -> Listening; // Blocks until a connection is received

            Close? -> Closed;
        }

        //
        // The pre-connected state exists so we can confirm that the endpoint
        // has been wired to the NetStack before accepting messages on it
        //
        state PreConnected : Ready! -> Connected;

        //
        // Operations on an established connection
        //

        // Requests
        in message Read(); // Read as much data as possible without blocking
        in message PollRead(int timeout); // Wait up to timeout ms for data
        in message IsDataAvailable(); // Is there queued data that can be read immediately?
        in message Write(byte[]! in ExHeap data);
        in message Close(); // Performs a non-blocking but graceful shutdown
        in message Abort(); // Performs an immediate, hard close (unsent data is discarded)
        in message GetRemoteAddress();
        in message GetRemotePort();
        in message DoneSending();
        in message DoneReceiving();

        // Response messages
        out message ConnectionClosed(); // Connection has been shut down
        out message NoData(); // There was nothing to read
        out message NoMoreData(); // Will never be more data
        out message CantSend(); // Remote side refuses more data
        out message Data(byte[]! in ExHeap data);
        out message DataIsAvailable(bool isAvailable);

        state Connected : one
        {
            Read? -> ReadResult;
            PollRead? -> PollReadResult;
            Write? -> WriteResult;

            IsDataAvailable? -> (DataIsAvailable!) -> Connected;
            GetLocalAddress? -> IPAddress! -> Connected;
            GetLocalPort? -> Port! -> Connected;
            GetRemoteAddress? -> IPAddress! -> Connected;
            GetRemotePort? -> Port! -> Connected;

            DoneSending? -> ReceiveOnly;
            DoneReceiving? -> SendOnly;
            Close? -> Closed;
            Abort? -> Closed;
        }

        state ReadResult : one
        {
            Data! -> Connected;
            // This indicates that there will never be any more
            // data, but that sending is still allowed
            NoMoreData! -> SendOnly;
            // This indicates that sending has been closed by the
            // remote side
            ConnectionClosed! -> Zombie;
        }

        state PollReadResult : one
        {
            Data! -> Connected;
            // No data available within the poll window; try again
            NoData! -> Connected;
            NoMoreData! -> SendOnly;
            ConnectionClosed! -> Zombie;
        }

        state WriteResult : one
        {
            OK! -> Connected;
            // This indicates that writing has been closed by the
            // remote side, but reading is still allowed.
            CantSend! -> ReceiveOnly;
        }

        //
        // Operations on a receive-only connection (send side has been closed)
        //
        state ReceiveOnly : one
        {
            Read? -> ROReadResult;
            PollRead? -> ROPollReadResult;

            IsDataAvailable? -> (DataIsAvailable!) -> ReceiveOnly;
            GetLocalAddress? -> IPAddress! -> ReceiveOnly;
            GetLocalPort? -> Port! -> ReceiveOnly;
            GetRemoteAddress? -> IPAddress! -> ReceiveOnly;
            GetRemotePort? -> Port! -> ReceiveOnly;

            DoneReceiving? -> Zombie;
            Close? -> Closed;
            Abort? -> Closed;
        }

        state ROReadResult : one
        {
            Data! -> ReceiveOnly;
            // If there is no more data, there's nothing more to do.
            NoMoreData! -> Zombie;
        }

        state ROPollReadResult : one
        {
            Data! -> ReceiveOnly;
            NoData! -> ReceiveOnly;
            NoMoreData! -> Zombie;
        }

        //
        // Operations on a send-only connection (receive side has been closed)
        //
        state SendOnly : one
        {
            Write? -> SOWriteResult;

            GetLocalAddress? -> IPAddress! -> SendOnly;
            GetLocalPort? -> Port! -> SendOnly;
            GetRemoteAddress? -> IPAddress! -> SendOnly;
            GetRemotePort? -> Port! -> SendOnly;

            DoneSending? -> Zombie;
            Close? -> Closed;
            Abort? -> Closed;
        }

        state SOWriteResult : one
        {
            OK! -> SendOnly;
            // Remote side refuses further data
            CantSend! -> Zombie;
        }

        //
        // Zombied connection (nothing left to do but user hasn't explicitly
        // closed yet)
        //
        state Zombie : one
        {
            Close? -> Closed; // Wrap up gracefully
            Abort? -> Closed; // Drop any unsent data
        }

        state Closed : {} // Nothing is acceptable here
    }
}