///////////////////////////////////////////////////////////////////////////////
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//

namespace Microsoft.Singularity.Security
{
    using System;
    using System.Collections;
    using System.Threading;

    using Microsoft.SingSharp;
    using Microsoft.Contracts;
    using Microsoft.Singularity.Channels;
    using Microsoft.Singularity.Directory;

    /// <summary>
    /// A <code>ChannelPool</code> maintains a pool of open channels.
    /// (to the security service). It should be possible to parameterize this
    /// class for general use.
    /// </summary>
    internal class ChannelPool
    {

#if POOLED
        const int POOL_CAPACITY = 10;
#else
        const int POOL_CAPACITY = 1;
#endif

        /// <summary>
        /// The unused channels
        /// </summary>
        TRef<SecurityDiagnosticsContract.Imp, SecurityDiagnosticsContract.ReadyState>[]! trefs;
        int capacity = POOL_CAPACITY;
        int nalloc = 0;
        int navail = 0;
        /// <summary>
        /// Synchronization token
        /// </summary>
        object token;
        bool disposed;

        public ChannelPool()
        {
            int i;
            trefs = new TRef<SecurityDiagnosticsContract.Imp, SecurityDiagnosticsContract.ReadyState>[capacity];
            token = new object();
            disposed = false;
        }

        // opens a connection to the security service
        private static SecurityDiagnosticsContract.Imp  OpenChannel()
        {
            SecurityDiagnosticsContract.Imp! imp;
            SecurityDiagnosticsContract.Exp! exp;
            SecurityDiagnosticsContract.NewChannel(out imp, out exp);
            // open a channel to the nameservice
            DirectoryServiceContract.Imp ns = DirectoryService.NewClientEndpoint();
            // try to bind
            ns.SendBind(Bitter.FromString2(SecurityDiagnosticsContract.ModuleName), exp);

            switch receive
            {
            case ns.AckBind():
                break;
            case ns.NakBind(rejected, error):
                delete imp;
                delete rejected;
                delete ns;
                return null;
            }
            delete ns;

            imp.RecvReady();
            return imp;
        }

        /// <summary>
        /// Returns a free channel. Blocks if none is available.
        /// </summary>
        public SecurityDiagnosticsContract.Imp! Acquire()
        {
            lock (token)
            {
                // wait if no channel is available
                while (true) {
                    if (navail != 0) {
                        navail--;
                        return ((!)trefs[navail]).Acquire();
                    }
                    if (nalloc < capacity) {
                        SecurityDiagnosticsContract.Imp imp = OpenChannel();
                        if (imp != null) {
                            trefs[nalloc] = new
                                TRef<SecurityDiagnosticsContract.Imp, SecurityDiagnosticsContract.ReadyState>
                                (imp);
                            return ((!)trefs[nalloc++]).Acquire();
                        }
                    }
                    Monitor.Wait(token);
                }
            }
        }

        /// <summary>
        /// Releases a channel
        /// </summary>
        public void Release([Claims]SecurityDiagnosticsContract.Imp! imp)
        {
            lock (token)
            {
                ((!)trefs[navail++]).Release(imp);
                Monitor.PulseAll(token);
            }
        }

        /// <summary>
        /// Closes the channels
        /// </summary>
        public void Dispose()
        {
            lock (token)
            {
                if (!disposed){
                    int i;
                    for (i=0; i<navail; i++) {
                        SecurityDiagnosticsContract.Imp! imp = ((!)trefs[i]).Acquire();
                        delete imp;
                    }
                    disposed = true;
                }
            }
        }
    }
}