////////////////////////////////////////////////////////////////////////////////
//
//  Microsoft Research Singularity
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
//  Note:   Multiplexes any number of input pipes to a single output pipe.
//          Also features a channel to submit new input pipes.
//

using System;
using System.Threading;
using Microsoft.SingSharp;
using Microsoft.Singularity;
using Microsoft.Singularity.Channels;
using Tty = Microsoft.Singularity.Io.Tty;

namespace Microsoft.Singularity.Io
{

    public contract PipeMultiplexControl {
        in message NewInput(UnicodePipeContract.Exp:EXPMOVABLE! client);
        out message Ack();

        state START: NewInput? -> Ack! -> START;
    }

    /// <summary>
    /// Allows creating and managing a multiplexer that forwards data from several pipes
    /// to a single output pipe.
    /// </summary>
    public sealed class PipeMultiplexer : ITracked {

        private class PipeThread {
            TRef<UnicodePipeContract.Exp:READY> initialClientArgument;
            TRef<UnicodePipeContract.Imp:READY>! threadStartupArgument1;
            TRef<PipeMultiplexControl.Exp:START>! threadStartupArgument2;


            public PipeThread([Claims] UnicodePipeContract.Imp:READY! output,
                              [Claims] PipeMultiplexControl.Exp:START! control,
                              [Claims] UnicodePipeContract.Exp:READY? initialClient)
            {
                this.threadStartupArgument1 = new TRef<UnicodePipeContract.Imp:READY>(output);
                this.threadStartupArgument2 = new TRef<PipeMultiplexControl.Exp:START>(control);
                if (initialClient != null) {
                    this.initialClientArgument = 
                        new TRef<UnicodePipeContract.Exp:READY>(initialClient);
                }
            }


            public void Start() {
                UnicodePipeContract.Exp:READY? initialClient = null;
                if (this.initialClientArgument != null) {
                    initialClient = this.initialClientArgument.Acquire();
                }
                MessagePump(this.threadStartupArgument1.Acquire(),
                            this.threadStartupArgument2.Acquire(),
                            initialClient);
            }


            private static void MessagePump([Claims] UnicodePipeContract.Imp:READY! output,
                                            [Claims] PipeMultiplexControl.Exp:START! control,
                                            [Claims] UnicodePipeContract.Exp:READY? initialClient)
            {
                ESet<UnicodePipeContract.Imp:ACK> waitingForOutputAck =
                    new ESet<UnicodePipeContract.Imp:ACK>();

                ESet<UnicodePipeContract.Exp:ACK> clientWaitingForAck =
                    new ESet<UnicodePipeContract.Exp:ACK>();

                ESet<UnicodePipeContract.Imp:READY> outputReady =
                    new ESet<UnicodePipeContract.Imp:READY>();

                ESet<UnicodePipeContract.Exp:READY> clients = 
                    new ESet<UnicodePipeContract.Exp:READY>();

                if (initialClient != null) {
                    clients.Add(initialClient);
                }
                outputReady.Add(output);

                bool done = false;

                try {
                    while (!done) {
                        switch receive {

                        case control.NewInput(client):
                            //DebugStub.WriteLine("pipe multiplexer new client [{0}]",
                            //                    __arglist(clients.Count+1));
                            client.SendMoved();
                            clients.Add(client);
                            control.SendAck();
                            break;

                        case control.ChannelClosed():
                            //DebugStub.WriteLine("pipe multiplexer control channel closed");
                            done = true; 
                            break;

                        case client.Write(buffer, index, count) in clients && 
                            outputReady.Head(outputEp):
                            // a client wants to write and the output is ready
                            //DebugStub.WriteLine("pipe multiplexer [{0}] client writes",
                            //                    __arglist(clients.Count+1));
                            outputEp.SendWrite(buffer, index, count);
                            clientWaitingForAck.Add(client);
                            waitingForOutputAck.Add(outputEp);
                            continue;

                        case outputEp.AckWrite(buffer) in waitingForOutputAck &&
                            clientWaitingForAck.Head(client):
                            // a client is waiting for ack and output sent us ack
                            //DebugStub.WriteLine("pipe multiplexer: output Acks");
                            client.SendAckWrite(buffer);
                            clients.Add(client);
                            outputReady.Add(outputEp);
                            continue;

                        case client.ChannelClosed() in clients:
                            //DebugStub.WriteLine("pipe multiplexer: client departs");
                            delete client;
                            continue;

                        case outputEp.ChannelClosed() in waitingForOutputAck:
                            DebugStub.WriteLine("pipe multiplexer: output closes");
                            delete outputEp;
                            done = true;
                            break;
                        }
                    }
                }
                finally {
                    waitingForOutputAck.Dispose();
                    outputReady.Dispose();
                    clientWaitingForAck.Dispose();
                    clients.Dispose();
                    delete control;
                }
            }
        }

        /// Can be null when control channel closed
        private PipeMultiplexControl.Imp:START controlChannel;

        private PipeMultiplexer([Claims] PipeMultiplexControl.Imp:START! control) {
            this.controlChannel = control;
        }

        public static PipeMultiplexer!
        Start([Claims] UnicodePipeContract.Imp:READY! output, 
              [Claims] UnicodePipeContract.Exp:READY? initialClient)
        {
            PipeMultiplexControl.Imp! controlImp;
            PipeMultiplexControl.Exp! controlExp;
            PipeMultiplexControl.NewChannel(out controlImp, out controlExp);

            PipeThread pipeThread = new PipeThread(output, controlExp, initialClient);

            Thread t = new Thread(new ThreadStart(pipeThread.Start));
            t.Start();
            return new PipeMultiplexer(controlImp);
        }

        /// <summary>
        /// Adds a fresh input pipe to the multiplexer and returns the client end.
        /// </summary>
        public UnicodePipeContract.Imp:READY FreshClient() {
            expose (this) {
                PipeMultiplexControl.Imp control = this.controlChannel;
                if (control == null) return null; // channel closed

                UnicodePipeContract.Imp! client;
                UnicodePipeContract.Exp! exp;
                UnicodePipeContract.NewChannel(out client, out exp, UnicodePipeContract.EXPMOVABLE.Value);
                control.SendNewInput(exp);
                switch receive {
                    case control.Ack():
                        // put client into correct state:

                        switch receive {
                        case client.Moved():
                            return client;

                        case client.ChannelClosed():
                            delete client;
                            return null;
                        }

                    case control.ChannelClosed():
                        delete control;
                        delete client;
                        this.controlChannel = null;
                        return null;
                }
            }
            
        }

        public void Dispose()
        {
            delete this.controlChannel;
        }
        
        void ITracked.Acquire() {}
        void ITracked.Release() {}
        void ITracked.Expose() {}
        void ITracked.UnExpose() {}

    }
}