Synnefo » Pithos MS Client

#region

/* -----------------------------------------------------------------------

 * <copyright file="PollAgent.cs" company="GRNet">

 * 

 * Copyright 2011-2012 GRNET S.A. All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or

 * without modification, are permitted provided that the following

 * conditions are met:

 *

 *   1. Redistributions of source code must retain the above

 *      copyright notice, this list of conditions and the following

 *      disclaimer.

 *

 *   2. Redistributions in binary form must reproduce the above

 *      copyright notice, this list of conditions and the following

 *      disclaimer in the documentation and/or other materials

 *      provided with the distribution.

 *

 *

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

 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL GRNET S.A OR

 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF

 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED

 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN

 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE

 * POSSIBILITY OF SUCH DAMAGE.

 *

 * The views and conclusions contained in the software and

 * documentation are those of the authors and should not be

 * interpreted as representing official policies, either expressed

 * or implied, of GRNET S.A.

 * </copyright>

 * -----------------------------------------------------------------------

 */

#endregion

using System.Collections.Concurrent;

using System.ComponentModel.Composition;

using System.Diagnostics;

using System.Diagnostics.Contracts;

using System.IO;

using System.Linq.Expressions;

using System.Reflection;

using System.Security.Cryptography;

using System.Threading;

using System.Threading.Tasks;

using System.Threading.Tasks.Dataflow;

using Castle.ActiveRecord;

using Pithos.Interfaces;

using Pithos.Network;

using log4net;

namespace Pithos.Core.Agents

{

    using System;

    using System.Collections.Generic;

    using System.Linq;

    public class PollRequest

    {

        public DateTime? Since { get; set; }

        public IEnumerable<string> Batch { get; set; }

    }

    [DebuggerDisplay("{FilePath} C:{C} L:{L} S:{S}")]

    public class StateTuple

    {

        public string FilePath { get; private set; }

        public string MD5 { get; set; }

        public string L

        {

            get { return FileState==null?null:FileState.Checksum; }

        }

        private string _c;

        public string C

        {

            get { return _c; }

            set {

                _c = String.IsNullOrWhiteSpace(value) ? null : value;

            }

        }

        public string S

        {

            get { return ObjectInfo == null ? null : ObjectInfo.X_Object_Hash; }

        }

        private FileSystemInfo _fileInfo;

        private TreeHash _merkle;

        public FileSystemInfo FileInfo

        {

            get { return _fileInfo; }

            set

            {

                _fileInfo = value;

                FilePath = value.FullName;

            }

        }

        public FileState FileState { get; set; }

        public ObjectInfo ObjectInfo{ get; set; }

        public TreeHash Merkle

        {

            get {

                return _merkle;

            }

            set {

                _merkle = value;

                C = _merkle.TopHash.ToHashString();

            }

        }

        public StateTuple() { }

        public StateTuple(FileSystemInfo info)

        {

            FileInfo = info;

        }

    }

    /// <summary>

    /// PollAgent periodically polls the server to detect object changes. The agent retrieves a listing of all

    /// objects and compares it with a previously cached version to detect differences. 

    /// New files are downloaded, missing files are deleted from the local file system and common files are compared

    /// to determine the appropriate action

    /// </summary>

    [Export]

    public class PollAgent

    {

        private static readonly ILog Log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);

        [System.ComponentModel.Composition.Import]

        public IStatusKeeper StatusKeeper { get; set; }

        [System.ComponentModel.Composition.Import]

        public IPithosSettings Settings { get; set; }

        [System.ComponentModel.Composition.Import]

        public NetworkAgent NetworkAgent { get; set; }

        [System.ComponentModel.Composition.Import]

        public Selectives Selectives { get; set; }

        public IStatusNotification StatusNotification { get; set; }

        private CancellationTokenSource _currentOperationCancellation = new CancellationTokenSource();

        public void CancelCurrentOperation()

        {

            //What does it mean to cancel the current upload/download?

            //Obviously, the current operation will be cancelled by throwing

            //a cancellation exception.

            //

            //The default behavior is to retry any operations that throw.

            //Obviously this is not what we want in this situation.

            //The cancelled operation should NOT bea retried. 

            //

            //This can be done by catching the cancellation exception

            //and avoiding the retry.

            //

            //Have to reset the cancellation source - it is not possible to reset the source

            //Have to prevent a case where an operation requests a token from the old source

            var oldSource = Interlocked.Exchange(ref _currentOperationCancellation, new CancellationTokenSource());

            oldSource.Cancel();

        }

        public bool Pause

        {

            get {

                return _pause;

            }

            set {

                _pause = value;                

                if (!_pause)

                    _unPauseEvent.Set();

                else

                {

                    _unPauseEvent.Reset();

                }

            }

        }

        private bool _firstPoll = true;

        //The Sync Event signals a manual synchronisation

        private readonly AsyncManualResetEvent _syncEvent = new AsyncManualResetEvent();

        private readonly AsyncManualResetEvent _unPauseEvent = new AsyncManualResetEvent(true);

        private readonly ConcurrentDictionary<string, DateTime> _lastSeen = new ConcurrentDictionary<string, DateTime>();

        private readonly ConcurrentDictionary<Uri, AccountInfo> _accounts = new ConcurrentDictionary<Uri,AccountInfo>();

        //private readonly ActionBlock<PollRequest>  _pollAction;

        public PollAgent()

        {

            //_pollAction=new ActionBlock<PollRequest>(p=>ProcessPollRequest(p));

        }

        /*private void ProcessPollRequest(PollRequest request)

        {

            if (request.Since == null && request.Batch != null)

            {

                _batchQueue.Enqueue(request.Batch);

                _syncEvent.Set();                

            }

            else 

            {

                PollRemoteFiles(request.Since).Wait();

            }

        }*/

        /// <summary>

        /// Start a manual synchronization

        /// </summary>

        public void SynchNow(IEnumerable<string> paths=null)

        {

            _batchQueue.Enqueue(paths);

            _syncEvent.Set();                

            //_pollAction.Post(new PollRequest {Batch = paths});

        }

        readonly ConcurrentQueue<IEnumerable<string>> _batchQueue=new ConcurrentQueue<IEnumerable<string>>();

        /// <summary>

        /// Remote files are polled periodically. Any changes are processed

        /// </summary>

        /// <param name="since"></param>

        /// <returns></returns>

        public  void PollRemoteFiles(DateTime? since = null)

        {

            if (Log.IsDebugEnabled)

                Log.DebugFormat("Polling changes after [{0}]",since);

            Debug.Assert(Thread.CurrentThread.IsBackground, "Polling Ended up in the main thread!");

            //GC.Collect();

            using (ThreadContext.Stacks["Retrieve Remote"].Push("All accounts"))

            {

                //If this poll fails, we will retry with the same since value

                var nextSince = since;

                try

                {

                    _unPauseEvent.Wait();

                    UpdateStatus(PithosStatus.PollSyncing);

                    var accountBatches=new Dictionary<Uri, IEnumerable<string>>();

                    IEnumerable<string> batch = null;

                    if (_batchQueue.TryDequeue(out batch) && batch != null)

                        foreach (var account in _accounts.Values)

                        {

                            var accountBatch = batch.Where(path => path.IsAtOrBelow(account.AccountPath));

                            accountBatches[account.AccountKey] = accountBatch;

                        }

                    IEnumerable<Task<DateTime?>> tasks = new List<Task<DateTime?>>();

                    foreach(var accountInfo in _accounts.Values)

                    {

                        IEnumerable<string> accountBatch ;

                        accountBatches.TryGetValue(accountInfo.AccountKey,out accountBatch);

                        ProcessAccountFiles (accountInfo, accountBatch, since).Wait();

                    }

                    var nextTimes=TaskEx.WhenAll(tasks.ToList()).Result;

                    _firstPoll = false;

                    //Reschedule the poll with the current timestamp as a "since" value

                    if (nextTimes.Length>0)

                        nextSince = nextTimes.Min();

                    if (Log.IsDebugEnabled)

                        Log.DebugFormat("Next Poll at [{0}]",nextSince);

                }

                catch (Exception ex)

                {

                    Log.ErrorFormat("Error while processing accounts\r\n{0}", ex);

                    //In case of failure retry with the same "since" value

                }

                UpdateStatus(PithosStatus.PollComplete);

                //The multiple try blocks are required because we can't have an await call

                //inside a finally block

                //TODO: Find a more elegant solution for reschedulling in the event of an exception

                try

                {

                    //Wait for the polling interval to pass or the Sync event to be signalled

                    nextSince = WaitForScheduledOrManualPoll(nextSince).Result;

                }

                finally

                {

                    //Ensure polling is scheduled even in case of error

                    PollRemoteFiles(nextSince);

                    //_pollAction.Post(new PollRequest {Since = nextSince});

                }

            }

        }

        /// <summary>

        /// Wait for the polling period to expire or a manual sync request

        /// </summary>

        /// <param name="since"></param>

        /// <returns></returns>

        private async Task<DateTime?> WaitForScheduledOrManualPoll(DateTime? since)

        {

            var sync = _syncEvent.WaitAsync();

            var wait = TaskEx.Delay(TimeSpan.FromSeconds(Settings.PollingInterval));

            var signaledTask = await TaskEx.WhenAny(sync, wait);

            //Pausing takes precedence over manual sync or awaiting

            _unPauseEvent.Wait();

            //Wait for network processing to finish before polling

            var pauseTask=NetworkAgent.ProceedEvent.WaitAsync();

            await TaskEx.WhenAll(signaledTask, pauseTask);

            //If polling is signalled by SynchNow, ignore the since tag

            if (sync.IsCompleted)

            {

                //TODO: Must convert to AutoReset

                _syncEvent.Reset();

                return null;

            }

            return since;

        }

        public async Task<DateTime?> ProcessAccountFiles(AccountInfo accountInfo, IEnumerable<string> accountBatch, DateTime? since = null)

        {

            if (accountInfo == null)

                throw new ArgumentNullException("accountInfo");

            if (String.IsNullOrWhiteSpace(accountInfo.AccountPath))

                throw new ArgumentException("The AccountInfo.AccountPath is empty", "accountInfo");

            Contract.EndContractBlock();

            using (ThreadContext.Stacks["Retrieve Remote"].Push(accountInfo.UserName))

            {

                await NetworkAgent.GetDeleteAwaiter();

                Log.Info("Scheduled");

                var client = new CloudFilesClient(accountInfo);

                //We don't need to check the trash container

                var containers = client.ListContainers(accountInfo.UserName)

                    .Where(c=>c.Name!="trash")

                    .ToList();

                CreateContainerFolders(accountInfo, containers);

                //The nextSince time fallback time is the same as the current.

                //If polling succeeds, the next Since time will be the smallest of the maximum modification times

                //of the shared and account objects

                var nextSince = since;

                try

                {

                    //Wait for any deletions to finish

                    await NetworkAgent.GetDeleteAwaiter();

                    //Get the poll time now. We may miss some deletions but it's better to keep a file that was deleted

                    //than delete a file that was created while we were executing the poll                    

                    //Get the list of server objects changed since the last check

                    //The name of the container is passed as state in order to create a dictionary of tasks in a subsequent step

                    var listObjects = (from container in containers

                                       select Task<IList<ObjectInfo>>.Factory.StartNew(_ =>

                                             client.ListObjects(accountInfo.UserName, container.Name, since), container.Name)).ToList();

                    var listShared = Task<IList<ObjectInfo>>.Factory.StartNew(_ => 

                        client.ListSharedObjects(since), "shared");

                    listObjects.Add(listShared);

                    var listTasks = await Task.Factory.WhenAll(listObjects.ToArray());

                    using (ThreadContext.Stacks["SCHEDULE"].Push("Process Results"))

                    {

                        var dict = listTasks.ToDictionary(t => t.AsyncState);

                        //Get all non-trash objects. Remember, the container name is stored in AsyncState

                        var remoteObjects = (from objectList in listTasks

                                            where (string)objectList.AsyncState != "trash"

                                            from obj in objectList.Result

                                            orderby obj.Bytes ascending 

                                            select obj).ToList();

                        //Get the latest remote object modification date, only if it is after

                        //the original since date

                        nextSince = GetLatestDateAfter(nextSince, remoteObjects);

                        var sharedObjects = dict["shared"].Result;

                        nextSince = GetLatestDateBefore(nextSince, sharedObjects);

                        //DON'T process trashed files

                        //If some files are deleted and added again to a folder, they will be deleted

                        //even though they are new.

                        //We would have to check file dates and hashes to ensure that a trashed file

                        //can be deleted safely from the local hard drive.

                        /*

                        //Items with the same name, hash may be both in the container and the trash

                        //Don't delete items that exist in the container

                        var realTrash = from trash in trashObjects

                                        where

                                            !remoteObjects.Any(

                                                info => info.Name == trash.Name && info.Hash == trash.Hash)

                                   8     select trash;

                        ProcessTrashedFiles(accountInfo, realTrash);

*/

                        var cleanRemotes = (from info in remoteObjects.Union(sharedObjects)

                                            let name = info.Name??""

                                            where !name.EndsWith(".ignore", StringComparison.InvariantCultureIgnoreCase) &&

                                                  !name.StartsWith(FolderConstants.CacheFolder + "/",

                                                                   StringComparison.InvariantCultureIgnoreCase)

                                            select info).ToList();

                        if (_firstPoll)

                            StatusKeeper.CleanupOrphanStates();

                        StatusKeeper.CleanupStaleStates(accountInfo, cleanRemotes);

                        //var differencer = _differencer.PostSnapshot(accountInfo, cleanRemotes);

                        //var filterUris = Selectives.SelectiveUris[accountInfo.AccountKey];

                        //May have to wait if the FileAgent has asked for a Pause, due to local changes

                        await _unPauseEvent.WaitAsync();

                        //Get the local files here                        

                        var agent = AgentLocator<FileAgent>.Get(accountInfo.AccountPath);                        

                        //TODO: Pass the batch here as well

                        var files = await LoadLocalFileTuples(accountInfo, accountBatch);

                        var states = FileState.Queryable.ToList();                        

                        var infos = (from remote in cleanRemotes

                                    let path = remote.RelativeUrlToFilePath(accountInfo.UserName)

                                    let info=agent.GetFileSystemInfo(path)

                                    select Tuple.Create(info.FullName,remote))

                                    .ToList();

                        var token = _currentOperationCancellation.Token;

                        var tuples = MergeSources(infos, files, states).ToList();

                        //Process only the changes in the batch file, if one exists

                        var stateTuples = accountBatch==null?tuples:tuples.Where(t => accountBatch.Contains(t.FilePath));

                        foreach (var tuple in stateTuples)

                        {

                            await _unPauseEvent.WaitAsync();

                            //Set the Merkle Hash

                            SetMerkleHash(accountInfo, tuple);

                            SyncSingleItem(accountInfo, tuple, agent, token);

                        }

                        //On the first run

/*

                        if (_firstPoll)

                        {

                            MarkSuspectedDeletes(accountInfo, cleanRemotes);

                        }

*/

                        Log.Info("[LISTENER] End Processing");

                    }

                }

                catch (Exception ex)

                {

                    Log.ErrorFormat("[FAIL] ListObjects for{0} in ProcessRemoteFiles with {1}", accountInfo.UserName, ex);

                    return nextSince;

                }

                Log.Info("[LISTENER] Finished");

                return nextSince;

            }

        }

        private static void SetMerkleHash(AccountInfo accountInfo, StateTuple tuple)

        {

            //The Merkle hash for directories is that of an empty buffer

            if (tuple.FileInfo is DirectoryInfo)

                tuple.C = MERKLE_EMPTY;

            else if (tuple.FileState != null && tuple.MD5 == tuple.FileState.ShortHash)

            {

                //If there is a state whose MD5 matches, load the merkle hash from the file state

                //insteaf of calculating it

                tuple.C = tuple.FileState.Checksum;                              

            }

            else

            {

                tuple.Merkle = TaskEx.Run(()=> Signature.CalculateTreeHash(tuple.FileInfo, accountInfo.BlockSize, accountInfo.BlockHash)).Result;

                //tuple.C=tuple.Merkle.TopHash.ToHashString();                

            }

        }

        private async Task<List<Tuple<FileSystemInfo, string>>> LoadLocalFileTuples(AccountInfo accountInfo,IEnumerable<string> batch )

        {

            using (ThreadContext.Stacks["Account Files Hashing"].Push(accountInfo.UserName))

            {

                var batchPaths = (batch==null)?new List<string>():batch.ToList();

                IEnumerable<FileSystemInfo> localInfos=AgentLocator<FileAgent>.Get(accountInfo.AccountPath)

                                                        .EnumerateFileSystemInfos();

                if (batchPaths.Count>0)

                    localInfos= localInfos.Where(fi => batchPaths.Contains(fi.FullName));

                //Use the queue to retry locked file hashing

                var fileQueue = new Queue<FileSystemInfo>(localInfos);

                var hasher = MD5.Create();

                var results = new List<Tuple<FileSystemInfo, string>>();

                var backoff = 0;

                while (fileQueue.Count > 0)

                {

                    var file = fileQueue.Dequeue();

                    using (ThreadContext.Stacks["File"].Push(file.FullName))

                    {

                        /*

                                                Signature.CalculateTreeHash(file, accountInfo.BlockSize,

                                                                                                 accountInfo.BlockHash).

                                                                         TopHash.ToHashString()

                        */

                        try

                        {

                            //Replace MD5 here, do the calc while syncing individual files

                            string hash ;

                            if (file is DirectoryInfo)

                                hash = MERKLE_EMPTY;

                            else

                            {

                                //Wait in case the FileAgent has requested a Pause

                                await _unPauseEvent.WaitAsync();

                                using (StatusNotification.GetNotifier("Hashing {0}", "Finished hashing {0}", file.Name))

                                using (var stream = (file as FileInfo).OpenRead())

                                {                                    

                                    hash = hasher.ComputeHash(stream).ToHashString();

                                    backoff = 0;

                                }

                            }                            

                            results.Add(Tuple.Create(file, hash));

                        }

                        catch (IOException exc)

                        {

                            Log.WarnFormat("[HASH] File in use, will retry [{0}]", exc);

                            fileQueue.Enqueue(file);

                            //If this is the only enqueued file                            

                            if (fileQueue.Count != 1) continue;

                            //Increase delay

                            if (backoff<60000)

                                backoff += 10000;

                            //Pause Polling for the specified time

                        }

                        if (backoff>0)

                            await PauseFor(backoff);

                    }

                }

                return results;

            }

        }

        /// <summary>

        /// Wait and Pause the agent while waiting

        /// </summary>

        /// <param name="backoff"></param>

        /// <returns></returns>

        private async Task PauseFor(int backoff)

        {

            Pause = true;

            await TaskEx.Delay(backoff);

            Pause = false;

        }

        private void SyncSingleItem(AccountInfo accountInfo, StateTuple tuple, FileAgent agent, CancellationToken token)

        {

            Log.DebugFormat("Sync [{0}] C:[{1}] L:[{2}] S:[{3}]",tuple.FilePath,tuple.C,tuple.L,tuple.S);

            var localFilePath = tuple.FilePath;

            //Don't use the tuple info, it may have been deleted

            var localInfo = FileInfoExtensions.FromPath(localFilePath);

            var isUnselectedRootFolder = agent.IsUnselectedRootFolder(tuple.FilePath);

            //Unselected root folders that have not yet been uploaded should be uploaded and added to the 

            //selective folders

            if (!Selectives.IsSelected(accountInfo, localFilePath) && !(isUnselectedRootFolder && tuple.ObjectInfo==null) )                

                return;

            // Local file unchanged? If both C and L are null, make sure it's because 

            //both the file is missing and the state checksum is not missing

            if (tuple.C == tuple.L /*&& (localInfo.Exists || tuple.FileState == null)*/)

            {

                //No local changes

                //Server unchanged?

                if (tuple.S == tuple.L)

                {

                    // No server changes

                    //Has the file been renamed on the server?

                    MoveForServerMove(accountInfo, tuple);

                }

                else

                {

                    //Different from server

                    //Does the server file exist?

                    if (tuple.S == null)

                    {

                        //Server file doesn't exist

                        //deleteObjectFromLocal()

                        StatusKeeper.SetFileState(localFilePath, FileStatus.Deleted,

                                                  FileOverlayStatus.Deleted, "");

                        agent.Delete(localFilePath);

                        //updateRecord(Remove C, L)

                        StatusKeeper.ClearFileStatus(localFilePath);

                    }

                    else

                    {

                        //Server file exists

                        //downloadServerObject() // Result: L = S

                        //If the file has moved on the server, move it locally before downloading

                        var targetPath = MoveForServerMove(accountInfo, tuple);

                        StatusKeeper.SetFileState(targetPath, FileStatus.Modified,

                                                  FileOverlayStatus.Modified, "");

                        NetworkAgent.Downloader.DownloadCloudFile(accountInfo,

                                                                  tuple.ObjectInfo,

                                                                  targetPath, tuple.Merkle, token).Wait(token);

                        //updateRecord( L = S )

                        StatusKeeper.UpdateFileChecksum(targetPath, tuple.ObjectInfo.ETag,

                                                        tuple.ObjectInfo.X_Object_Hash);

                        StatusKeeper.StoreInfo(targetPath, tuple.ObjectInfo);

                        /*

                                                        StatusKeeper.SetFileState(targetPath, FileStatus.Unchanged,

                                                                                  FileOverlayStatus.Normal, "");

                            */

                    }

                }

            }

            else

            {

                //Local changes found

                //Server unchanged?

                if (tuple.S == tuple.L)

                {

                    //The FileAgent selective sync checks for new root folder files

                    if (!agent.Ignore(localFilePath))

                    {

                        if ((tuple.C == null || !localInfo.Exists) && tuple.ObjectInfo != null)

                        {

                            //deleteObjectFromServer()

                            DeleteCloudFile(accountInfo, tuple);

                            //updateRecord( Remove L, S)                  

                        }

                        else

                        {

                            //uploadLocalObject() // Result: S = C, L = S                        

                            //Debug.Assert(tuple.FileState !=null);

                            var action = new CloudUploadAction(accountInfo, localInfo, tuple.FileState,

                                                               accountInfo.BlockSize, accountInfo.BlockHash,

                                                               "Poll", isUnselectedRootFolder);

                            NetworkAgent.Uploader.UploadCloudFile(action, tuple.Merkle, token).Wait(token);

                            //updateRecord( S = C )

                            //State updated by the uploader

                            if (isUnselectedRootFolder)

                            {

                                ProcessChildren(accountInfo, tuple, agent, token);

                            }

                        }

                    }

                }

                else

                {

                    if (tuple.C == tuple.S)

                    {

                        // (Identical Changes) Result: L = S

                        //doNothing()

                        //Detect server moves

                        var targetPath = MoveForServerMove(accountInfo, tuple);

                        StatusKeeper.StoreInfo(targetPath, tuple.ObjectInfo);

                    }

                    else

                    {

                        if ((tuple.C == null || !localInfo.Exists) && tuple.ObjectInfo != null)

                        {

                            //deleteObjectFromServer()

                            DeleteCloudFile(accountInfo, tuple);

                            //updateRecord(Remove L, S)                  

                        }

                            //If both the local and server files are missing, the state is stale

                        else if (!localInfo.Exists && (tuple.S == null || tuple.ObjectInfo == null))

                        {

                            StatusKeeper.ClearFileStatus(localInfo.FullName);

                        }

                        else

                        {

                            ReportConflictForMismatch(localFilePath);

                            //identifyAsConflict() // Manual action required

                        }

                    }

                }

            }

        }

        private string MoveForServerMove(AccountInfo accountInfo, StateTuple tuple)

        {

            if (tuple.ObjectInfo == null)

                return null;

            var relativePath = tuple.ObjectInfo.RelativeUrlToFilePath(accountInfo.UserName);

            var serverPath = Path.Combine(accountInfo.AccountPath, relativePath);

            //Compare Case Insensitive

            if (String.Equals(tuple.FilePath ,serverPath,StringComparison.InvariantCultureIgnoreCase)) return serverPath;

            if (tuple.FileInfo.Exists)

            {                    

                var fi = tuple.FileInfo as FileInfo;

                if (fi != null)

                    fi.MoveTo(serverPath);

                var di = tuple.FileInfo as DirectoryInfo;

                if (di != null)

                    di.MoveTo(serverPath);

                StatusKeeper.StoreInfo(serverPath, tuple.ObjectInfo);

            }

            else

            {

                Debug.Assert(false, "File does not exist");

            }

            return serverPath;

        }

        private void DeleteCloudFile(AccountInfo accountInfo, StateTuple tuple)

        {

            StatusKeeper.SetFileState(tuple.FilePath, FileStatus.Deleted,

                                      FileOverlayStatus.Deleted, "");

            NetworkAgent.DeleteAgent.DeleteCloudFile(accountInfo, tuple.ObjectInfo);

            StatusKeeper.ClearFileStatus(tuple.FilePath);

        }

        private void ProcessChildren(AccountInfo accountInfo, StateTuple tuple, FileAgent agent, CancellationToken token)

        {

            var dirInfo = tuple.FileInfo as DirectoryInfo;

            var folderTuples = from folder in dirInfo.EnumerateDirectories("*", SearchOption.AllDirectories)

                               select new StateTuple(folder);

            var fileTuples = from file in dirInfo.EnumerateFiles("*", SearchOption.AllDirectories)

                             select new StateTuple(file);

            //Process folders first, to ensure folders appear on the sever as soon as possible

            folderTuples.ApplyAction(t => SyncSingleItem(accountInfo, t, agent, token));

            fileTuples.ApplyAction(t => SyncSingleItem(accountInfo, t, agent, token));

        }

        private static IEnumerable<StateTuple> MergeSources(

            IEnumerable<Tuple<string, ObjectInfo>> infos, 

            IEnumerable<Tuple<FileSystemInfo, string>> files, 

            IEnumerable<FileState> states)

        {

            var tuplesByPath = new Dictionary<string, StateTuple>();

            foreach (var file in files)

            {

                var fsInfo = file.Item1;

                var fileHash = fsInfo is DirectoryInfo? MERKLE_EMPTY:file.Item2;

                tuplesByPath[fsInfo.FullName] = new StateTuple {FileInfo = fsInfo, MD5 = fileHash};

            }

            foreach (var state in states)

            {

                StateTuple hashTuple;

                if (tuplesByPath.TryGetValue(state.FilePath, out hashTuple))

                {

                    hashTuple.FileState = state;

                }

                else

                {

                    var fsInfo = FileInfoExtensions.FromPath(state.FilePath);

                    tuplesByPath[state.FilePath] = new StateTuple {FileInfo = fsInfo, FileState = state};

                }

            }

            var tuplesByID = tuplesByPath.Values

                .Where(tuple => tuple.FileState != null && tuple.FileState.ObjectID!=null)

                .ToDictionary(tuple=>tuple.FileState.ObjectID,tuple=>tuple);//new Dictionary<Guid, StateTuple>();

            foreach (var info in infos)

            {

                StateTuple hashTuple;

                var filePath = info.Item1;

                var objectInfo = info.Item2;

                var objectID = objectInfo.UUID;

                if (tuplesByID.TryGetValue(objectID, out hashTuple))

                {

                    hashTuple.ObjectInfo = objectInfo;                    

                }

                else if (tuplesByPath.TryGetValue(filePath, out hashTuple))

                {

                    hashTuple.ObjectInfo = objectInfo;

                }

                else

                {

                    var fsInfo = FileInfoExtensions.FromPath(filePath);

                    var tuple = new StateTuple {FileInfo = fsInfo, ObjectInfo = objectInfo};

                    tuplesByPath[filePath] = tuple;

                    tuplesByID[objectInfo.UUID] = tuple;

                }

            }

            return tuplesByPath.Values;

        }

        /// <summary>

        /// Returns the latest LastModified date from the list of objects, but only if it is before

        /// than the threshold value

        /// </summary>

        /// <param name="threshold"></param>

        /// <param name="cloudObjects"></param>

        /// <returns></returns>

        private static DateTime? GetLatestDateBefore(DateTime? threshold, IList<ObjectInfo> cloudObjects)

        {

            DateTime? maxDate = null;

            if (cloudObjects!=null &&  cloudObjects.Count > 0)

                maxDate = cloudObjects.Max(obj => obj.Last_Modified);

            if (maxDate == null || maxDate == DateTime.MinValue)

                return threshold;

            if (threshold == null || threshold == DateTime.MinValue || threshold > maxDate)

                return maxDate;

            return threshold;

        }

        /// <summary>

        /// Returns the latest LastModified date from the list of objects, but only if it is after

        /// the threshold value

        /// </summary>

        /// <param name="threshold"></param>

        /// <param name="cloudObjects"></param>

        /// <returns></returns>

        private static DateTime? GetLatestDateAfter(DateTime? threshold, IList<ObjectInfo> cloudObjects)

        {

            DateTime? maxDate = null;

            if (cloudObjects!=null &&  cloudObjects.Count > 0)

                maxDate = cloudObjects.Max(obj => obj.Last_Modified);

            if (maxDate == null || maxDate == DateTime.MinValue)

                return threshold;

            if (threshold == null || threshold == DateTime.MinValue || threshold < maxDate)

                return maxDate;

            return threshold;

        }

        readonly AccountsDifferencer _differencer = new AccountsDifferencer();

        private Dictionary<Uri, List<Uri>> _selectiveUris = new Dictionary<Uri, List<Uri>>();

        private bool _pause;

        private static string MERKLE_EMPTY = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855";

        /// <summary>

        /// Deletes local files that are not found in the list of cloud files

        /// </summary>

        /// <param name="accountInfo"></param>

        /// <param name="cloudFiles"></param>

        private void ProcessDeletedFiles(AccountInfo accountInfo, IEnumerable<ObjectInfo> cloudFiles)

        {

            if (accountInfo == null)

                throw new ArgumentNullException("accountInfo");

            if (String.IsNullOrWhiteSpace(accountInfo.AccountPath))

                throw new ArgumentException("The AccountInfo.AccountPath is empty", "accountInfo");

            if (cloudFiles == null)

                throw new ArgumentNullException("cloudFiles");

            Contract.EndContractBlock();

            var deletedFiles = new List<FileSystemInfo>();

            foreach (var objectInfo in cloudFiles)

            {

                if (Log.IsDebugEnabled)

                    Log.DebugFormat("Handle deleted [{0}]", objectInfo.Uri);

                var relativePath = objectInfo.RelativeUrlToFilePath(accountInfo.UserName);

                var item = FileAgent.GetFileAgent(accountInfo).GetFileSystemInfo(relativePath);

                if (Log.IsDebugEnabled)

                    Log.DebugFormat("Will delete [{0}] for [{1}]", item.FullName, objectInfo.Uri);

                if (item.Exists)

                {

                    if ((item.Attributes & FileAttributes.ReadOnly) == FileAttributes.ReadOnly)

                    {

                        item.Attributes = item.Attributes & ~FileAttributes.ReadOnly;

                    }

                    Log.DebugFormat("Deleting {0}", item.FullName);

                    var directory = item as DirectoryInfo;

                    if (directory != null)

                        directory.Delete(true);

                    else

                        item.Delete();

                    Log.DebugFormat("Deleted [{0}] for [{1}]", item.FullName, objectInfo.Uri);

                    DateTime lastDate;

                    _lastSeen.TryRemove(item.FullName, out lastDate);

                    deletedFiles.Add(item);

                }

                StatusKeeper.SetFileState(item.FullName, FileStatus.Deleted, FileOverlayStatus.Deleted, "File Deleted");

            }

            Log.InfoFormat("[{0}] files were deleted", deletedFiles.Count);

            StatusNotification.NotifyForFiles(deletedFiles, String.Format("{0} files were deleted", deletedFiles.Count),

                                              TraceLevel.Info);

        }

        private void MarkSuspectedDeletes(AccountInfo accountInfo, IEnumerable<ObjectInfo> cloudFiles)

        {

//Only consider files that are not being modified, ie they are in the Unchanged state            

            var deleteCandidates = FileState.Queryable.Where(state =>

                                                             state.FilePath.StartsWith(accountInfo.AccountPath)

                                                             && state.FileStatus == FileStatus.Unchanged).ToList();

            //TODO: filesToDelete must take into account the Others container            

            var filesToDelete = (from deleteCandidate in deleteCandidates

                                 let localFile = FileInfoExtensions.FromPath(deleteCandidate.FilePath)

                                 let relativeFilePath = localFile.AsRelativeTo(accountInfo.AccountPath)

                                 where

                                     !cloudFiles.Any(r => r.RelativeUrlToFilePath(accountInfo.UserName) == relativeFilePath)

                                 select localFile).ToList();

            //Set the status of missing files to Conflict

            foreach (var item in filesToDelete)

            {

                //Try to acquire a gate on the file, to take into account files that have been dequeued

                //and are being processed

                using (var gate = NetworkGate.Acquire(item.FullName, NetworkOperation.Deleting))

                {

                    if (gate.Failed)

                        continue;

                    StatusKeeper.SetFileState(item.FullName, FileStatus.Conflict, FileOverlayStatus.Deleted,

                                              "Local file missing from server");

                }

            }

            UpdateStatus(PithosStatus.HasConflicts);

            StatusNotification.NotifyConflicts(filesToDelete,

                                               String.Format(

                                                   "{0} local files are missing from Pithos, possibly because they were deleted",

                                                   filesToDelete.Count));

            StatusNotification.NotifyForFiles(filesToDelete, String.Format("{0} files were deleted", filesToDelete.Count),

                                              TraceLevel.Info);

        }

        private void ReportConflictForMismatch(string localFilePath)

        {

            if (String.IsNullOrWhiteSpace(localFilePath))

                throw new ArgumentNullException("localFilePath");

            Contract.EndContractBlock();

            StatusKeeper.SetFileState(localFilePath, FileStatus.Conflict, FileOverlayStatus.Conflict, "File changed at the server");

            UpdateStatus(PithosStatus.HasConflicts);

            var message = String.Format("Conflict detected for file {0}", localFilePath);

            Log.Warn(message);