Synnefo » Pithos MS Client

// -----------------------------------------------------------------------

// <copyright file="NetworkGate.cs" company="GRNET">

// Copyright 2011 GRNET S.A. All rights reserved.

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//      disclaimer.

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//   2. Redistributions in binary form must reproduce the above

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// THIS SOFTWARE IS PROVIDED BY GRNET S.A. ``AS IS'' AND ANY EXPRESS

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// -----------------------------------------------------------------------

using System;

using System.Collections.Concurrent;

using System.Collections.Generic;

using System.Diagnostics.Contracts;

using System.IO;

namespace Pithos.Core

{

    public enum NetworkOperation

    {

        None,

        Uploading,

        Downloading,

        Deleting,

        Renaming

    }

    //The NetworkGate prevents starting download/uploads for files that are already in the process of downloading,

    //uploading.   

    public class NetworkGate:IDisposable

    {

        public string FilePath { get; private set; }

        public NetworkOperation Operation { get; private set; }

        [ContractInvariantMethod]

        private void Invariants()

        {

            Contract.Invariant(!String.IsNullOrWhiteSpace(FilePath));

            Contract.Invariant(Path.IsPathRooted(FilePath));

        }

        //The state of each file is stored in a thread-safe dictionary

        static readonly ConcurrentDictionary<string, NetworkOperation> NetworkState = new ConcurrentDictionary<string, NetworkOperation>();

        public static NetworkOperation GetNetworkState(string path)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("path must be a rooted path", "path");

            Contract.EndContractBlock();

            NetworkOperation operation;

            var lower = path.ToLower();

            if (NetworkState.TryGetValue(lower, out operation))

                return operation;

            return NetworkOperation.None;

        }

        //Store a network operation for the specified path

        public static void SetNetworkState(string path, NetworkOperation operation)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("path must be a rooted path", "path");

            Contract.EndContractBlock();

            var lower = path.ToLower();

            NetworkState[lower] = operation;            

            //By default, None values don't need to be stored. They are stored anyway

            //because TryRemove may fail.

            if (operation == NetworkOperation.None)

            {

                NetworkOperation oldOperation;

                NetworkState.TryRemove(lower, out oldOperation);

            }

        }

        //Clients should acquire a NetworkGate before starting any network operation.

        //If Acquire fails, another network operation is already in progress

        public static NetworkGate Acquire(string path, NetworkOperation operation)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("path must be a rooted path", "path");

            Contract.EndContractBlock();

            var lower = path.ToLower();

            var state = GetNetworkState(lower);

            //If no operation is in progress, return a NetworkGate

            return (state == NetworkOperation.None)

                       ? new NetworkGate(lower, operation)

                   //otherwise return a gate with Fail flagged

                       : new NetworkGate(lower, NetworkOperation.None);

        }

        private NetworkGate(string path,NetworkOperation operation)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("path must be rooted","path");

            Contract.EndContractBlock();

            Operation = operation;

            FilePath = path.ToLower();            

            //Skip dummy operations (those with Operation == None)

            if (Operation != NetworkOperation.None)

                //and store the file's operation

                SetNetworkState(FilePath, operation);

        }

        //A NetworkGate has Failed if its operation is None

        public bool Failed { get { return Operation == NetworkOperation.None; } }

        //Release a gate by setting the NetworkOperation to None

        public void Release()

        {

            //Skip Failed flags

            if (!Failed)

                //And reset the operation state for the file

                SetNetworkState(FilePath,NetworkOperation.None);

        }

        public void Dispose()

        {

            Dispose(true);

            GC.SuppressFinalize(this);

        }

        protected void Dispose(bool disposing)

        {

            if (disposing)

            {

                Release();

            }

        }

    }

}