//////////////////////////////////////////////////////////////////////////////
//
//  Microsoft Research Singularity
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
//  File:   Dispatcher.sg
//
//  Note:
//     This file holds the Singularity-specific web app dispatcher that knows
//     how to invoke web apps under Singularity.
//

using System;
using System.Collections;
using Microsoft.SingSharp;
using Microsoft.SingSharp.Runtime;
using Microsoft.Singularity;
using Microsoft.Singularity.Channels;
using Microsoft.Singularity.V1.Services;
using Microsoft.Singularity.WebApps;
using Microsoft.Singularity.WebApps.Contracts;
using System.Diagnostics;
using System.Web;

namespace Microsoft.Singularity.WebServer
{
    internal sealed class Application
    {
        private static Hashtable applications = new Hashtable();

        public static Application FindOrCreateApplication(Request! request)
        {
            // For now, we have an extremely lame way of mapping from a request
            // to the appropriate application.  We simply take the FilePath
            // after the leading slash.  That better be the name of a launchable
            // application.
            //
            // TODO: Eventually this will be based on manifests and the mapping
            // configuration of the WebServer, passed to the WebServer at
            // startup.

            string filePath = request.GetFilePath();
            string appName = filePath.Substring(1);

            Application app = (Application) applications[appName];

            if (app == null) {
                // No races around inserting unstarted applications into the hashtable.
                lock (applications) {
                    // Perhaps it's there now.
                    app = (Application) applications[appName];
                    if (app == null) {
                        app = new Application(appName);

                        // Regardless of whether the app starts successfully,
                        // record it in our set of applications.
                        app.Start();
                        applications[appName] = app;
                    }
                }
            }
            // If an app failed to start, we keep it in the hashtable so we
            // don't keep re-trying on every client request.
            return ((app != null && app.started)
                    ? app
                    : null);
        }

        private TRef<WebAppContract.Imp:ProcessingState> wrapAppConn;
        private string! name;
        private bool    started;

        // statistics
        private ulong totalServed = 0;
        private ulong totalTime = 0;

        public Application(string! name)
        {
            this.name = name;
            this.started = false;
            base();
        }

        public void Process(Request! request)
        {
            ulong startTime = Processor.CycleCount;

            // Make a local request object
            IHttpRequest localRequest = new LocalHttpRequest(request);

            HttpRequestContract.Imp! reqConnImp;
            HttpRequestContract.Exp! reqConnExp;
            HttpRequestContract.NewChannel(out reqConnImp, out reqConnExp);

            WebAppContract.Imp appConn = wrapAppConn.Acquire();

            try {
                // Start processing this request
                appConn.SendProcess(reqConnImp);
                appConn.RecvOK();
            }
            finally {
                wrapAppConn.Release(appConn);
            }

            // Start servicing the request contract
            RequestExporter.ServiceRequestChannel(localRequest, reqConnExp);

            // Clean up
            delete reqConnExp;

            request.CloseConnection();

            totalServed++;
            totalTime += Processor.CycleCount - startTime;
        }

        public void Start()
        {
            string[] args = new string[1];

            args[0] = name;

            WebAppContract.Imp! appConnImp;
            WebAppContract.Exp! appConnExp;
            WebAppContract.NewChannel(out appConnImp, out appConnExp);

            try {
                Process child = new Process(args, (Endpoint * in ExHeap) appConnExp);
                child.Start();
                appConnImp.RecvWebAppReady();
                wrapAppConn = new TRef<WebAppContract.Imp:ProcessingState>(appConnImp);
            }
            catch (Exception) {
                // TODO: The exception story of Singularity needs work.  For now,
                // just record the fact that this app won't start.
                return;
            }
            started = true;
        }

        internal class RequestExporter
        {
            public static void ServiceRequestChannel(IHttpRequest! request, HttpRequestContract.Exp! conn)
            {
                bool done = false;

                while(!done) {
                    switch receive {
                        case conn.GetUriPath() :
                            conn.SendUriPath(Bitter.FromString2(request.GetUriPath()));
                            break;

                        case conn.GetQueryString() :
                            conn.SendQueryString(Bitter.FromString(request.GetQueryString()));
                            break;

                        case conn.GetVerb() :
                            conn.SendVerb(Bitter.FromString(request.GetVerb()));
                            break;

                        case conn.GetHeader(char[]! in ExHeap headerChars) :
                            string headerName = Bitter.ToString(headerChars);
                            delete headerChars;
                            string headerVal = request.GetHeader(headerName);
                            if (headerVal != null) {
                                conn.SendHeaderValue(Bitter.FromString(headerVal));
                            } else {
                                conn.SendHeaderValue(null);
                            }
                            break;

                        case conn.GetBody() :
                            byte[] bodyData = request.GetBodyData();

                            if (bodyData != null) {
                                conn.SendBodyData(Bitter.FromByteArray(bodyData));
                            } else {
                                conn.SendBodyData(null);
                            }
                            break;

                        case conn.GetRemoteAddress() :
                            conn.SendRemoteAddress(Bitter.FromString(request.GetRemoteAddress()));
                            break;

                        case conn.SendStatus(int code, char[]! in ExHeap descChars) :
                        {
                            string description = Bitter.ToString(descChars);
                            delete descChars;
                            request.SendStatus(code, description);
                            conn.SendOK();
                        }
                        break;

                        case conn.SendHeader(char[]! in ExHeap nameChars, char[]! in ExHeap valChars) :
                        {
                            string name = Bitter.ToString(nameChars);
                            delete nameChars;

                            string value = Bitter.ToString(valChars);
                            delete valChars;

                            request.SendHeader(name, value);
                            conn.SendOK();
                        }
                        break;

                        case conn.SendBodyData(byte[]! in ExHeap dataBytes) :
                        {
                            request.SendBodyData(dataBytes);
                            conn.SendOK();
                        }
                        break;

                        case conn.Done() :
                            request.Done();
                            done = true;
                            break;

                        case conn.ChannelClosed() :
                            // This is unexpected
                            DebugStub.Break();
                            done = true;
                            break;

                        case unsatisfiable :
                            // This is even more unexpected
                            DebugStub.Break();
                            done = true;
                            break;
                    }
                }
            }
        }
    }
}