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; }

    }*/

    /// <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;

        readonly HashSet<string> _knownContainers = new HashSet<string>();

        /// <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;

                        }

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

                    foreach(var accountInfo in _accounts.Values)

                    {

                        IEnumerable<string> accountBatch ;

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

                        var t=ProcessAccountFiles (accountInfo, accountBatch, since);

                        tasks.Add(t);

                    }

                    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

                    TaskEx.Run(()=>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).ConfigureAwait(false);

            //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).ConfigureAwait(false);

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

            if (sync.IsCompleted)

            {                

                _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().ConfigureAwait(false);

                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().ConfigureAwait(false);

                    //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(_knownContainers,since), "shared");

                    listObjects.Add(listShared);

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

                    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;

                        //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();

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

                        var currentRemotes = differencer.Current.ToList();

                        StatusKeeper.CleanupStaleStates(accountInfo, currentRemotes);

                        //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().ConfigureAwait(false);

                        //Get the local files here                        

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

                        var files = LoadLocalFileTuples(accountInfo, accountBatch);

                        var states = FileState.Queryable.ToList();                        

                        var infos = (from remote in currentRemotes

                                    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.Where(s=>!s.Locked))

                        {

                            await _unPauseEvent.WaitAsync().ConfigureAwait(false);

                            //Set the Merkle Hash

                            //SetMerkleHash(accountInfo, tuple);

                            await SyncSingleItem(accountInfo, tuple, agent, token).ConfigureAwait(false);

                        }

                        //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.ETag)

            {

                //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 = Signature.CalculateTreeHashAsync((FileInfo)tuple.FileInfo, accountInfo.BlockSize, accountInfo.BlockHash,1,progress);

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

            }

        }

*/

        private IEnumerable<FileSystemInfo> 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));

                return localInfos;

            }

        }

        /// <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).ConfigureAwait(false);

            Pause = false;

        }

        private async Task 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);

            try

            {

                bool isInferredParent = tuple.ObjectInfo != null && tuple.ObjectInfo.UUID.StartsWith("00000000-0000-0000");

                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()

                            using (

                                StatusNotification.GetNotifier("Deleting local {0}", "Deleted local {0}",

                                                               Path.GetFileName(localFilePath)))

                            {

                                StatusKeeper.SetFileState(localFilePath, FileStatus.Deleted,

                                                          FileOverlayStatus.Deleted, "");

                                using (NetworkGate.Acquire(localFilePath, NetworkOperation.Deleting))

                                {

                                    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

                            using (

                                StatusNotification.GetNotifier("Downloading {0}", "Downloaded {0}",

                                                               Path.GetFileName(localFilePath)))

                            {

                                var targetPath = MoveForServerMove(accountInfo, tuple);

                                StatusKeeper.SetFileState(targetPath, FileStatus.Modified, FileOverlayStatus.Modified,

                                                          "");

                                await

                                    NetworkAgent.Downloader.DownloadCloudFile(accountInfo, tuple.ObjectInfo, targetPath,

                                                                              token)

                                        .ConfigureAwait(false);

                                //updateRecord( L = S )

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

                                                                tuple.ObjectInfo.X_Object_Hash);

                                StatusKeeper.StoreInfo(targetPath, tuple.ObjectInfo);

                                AddRootFolderToSelectives(accountInfo, tuple, targetPath);

                            }

                            /*

                                                            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                        

                                var progress = new Progress<double>(d =>

                                    StatusNotification.Notify(new StatusNotification(String.Format("Merkle Hashing for Upload {0:p} of {1}", d, localInfo.Name))));

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

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

                                                                   accountInfo.BlockSize, accountInfo.BlockHash,

                                                                   "Poll", isUnselectedRootFolder,progress);

                                using (

                                    StatusNotification.GetNotifier("Uploading {0}", "Uploaded {0}",

                                                                   Path.GetFileName(localFilePath)))

                                {

                                    await NetworkAgent.Uploader.UploadCloudFile(action, token).ConfigureAwait(false);

                                }

                                //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()

                            //Don't update anything for nonexistend server files

                            if (tuple.S != null)

                            {

                                //Detect server moves

                                var targetPath = MoveForServerMove(accountInfo, tuple);

                                StatusKeeper.StoreInfo(targetPath, tuple.ObjectInfo);

                                AddRootFolderToSelectives(accountInfo, tuple, targetPath);

                            }

                            else

                            {

                                //At this point, C==S==NULL and we have a stale state (L)

                                //Log the stale tuple for investigation

                                Log.WarnFormat("Stale tuple detected FilePathPath:[{0}], State:[{1}], LocalFile:[{2}]", tuple.FilePath, tuple.FileState, tuple.FileInfo);

                                //And remove it

                                if (!String.IsNullOrWhiteSpace(tuple.FilePath))

                                    StatusKeeper.ClearFileStatus(tuple.FilePath);

                            }

                        }

                        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

                            }

                        }

                    }

                }

            }

            catch (Exception exc)

            {

                //In case of error log and retry with the next poll

                Log.ErrorFormat("[SYNC] Failed for file {0}. Will Retry.\r\n{1}",tuple.FilePath,exc);

            }

        }

        private void AddRootFolderToSelectives(AccountInfo accountInfo, StateTuple tuple, string targetPath)

        {

            //Also ensure that any newly created folders are added to the selectives, if the original folder was selected

            var containerPath = Path.Combine(accountInfo.AccountPath, tuple.ObjectInfo.Container);

            //If this is a root folder encountered for the first time

            if (tuple.L == null && Directory.Exists(tuple.FileInfo.FullName) 

                && (tuple.FileInfo.FullName.IsAtOrDirectlyBelow(containerPath)))

            {

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

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

                var hasMoved = true;// !initialPath.Equals(targetPath);

                if (hasMoved && Selectives.IsSelected(accountInfo, initialPath))

                {

                    Selectives.AddUri(accountInfo, tuple.ObjectInfo.Uri);

                    Selectives.Save(accountInfo);

                }

            }

        }

        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)

            {

                using (StatusNotification.GetNotifier("Moving local {0}", "Moved local {0}", Path.GetFileName(tuple.FilePath)))

                using(NetworkGate.Acquire(tuple.FilePath,NetworkOperation.Renaming))

                {

                    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)

        {

            using (StatusNotification.GetNotifier("Deleting server {0}", "Deleted server {0}", Path.GetFileName(tuple.FilePath)))

            {

                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(async t =>await SyncSingleItem(accountInfo, t, agent, token).ConfigureAwait(false));

            fileTuples.ApplyAction(async t => await SyncSingleItem(accountInfo, t, agent, token).ConfigureAwait(false));

        }

        /*

         *                 //Use the queue to retry locked file hashing

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

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

                var backoff = 0;

                while (fileQueue.Count > 0)

                {

                    FileSystemInfo file;

                    fileQueue.TryDequeue(out file);

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

                    {

                        try

                        {

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

                            string hash ;

                            if (file is DirectoryInfo)

                                hash = MD5_EMPTY;

                            else

                            {

                                //Wait in case the FileAgent has requested a Pause

                                await _unPauseEvent.WaitAsync().ConfigureAwait(false);

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

                                {

                                    hash = ((FileInfo)file).ComputeShortHash(StatusNotification);

                                    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).ConfigureAwait(false);

                    }

                }

                return results;

         */

        private IEnumerable<StateTuple> MergeSources(

            IEnumerable<Tuple<string, ObjectInfo>> infos, 

            IEnumerable<FileSystemInfo> files, 

            IEnumerable<FileState> states)

        {

            var tuplesByPath = files.ToDictionary(f => f.FullName, f => new StateTuple {FileInfo = f}); new Dictionary<string, StateTuple>();

            //For files that have state

            foreach (var state in states)

            {

                StateTuple hashTuple;

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

                {

                    hashTuple.FileState = state;

                    UpdateMD5(hashTuple);

                }

                else

                {

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

                    hashTuple = new StateTuple {FileInfo = fsInfo, FileState = state};

                    tuplesByPath[state.FilePath] = hashTuple;

                }

            }

            //for files that don't have state

            foreach (var tuple in tuplesByPath.Values.Where(t => t.FileState == null))

            {

                UpdateMD5(tuple);

            }

            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 (objectID != _emptyGuid &&  tuplesByID.TryGetValue(objectID, out hashTuple))

                {

                    hashTuple.ObjectInfo = objectInfo;                    

                }

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

                {

                    hashTuple.ObjectInfo = objectInfo;

                }

                else

                {

                    var fsInfo = FileInfoExtensions.FromPath(filePath);

                    hashTuple= new StateTuple {FileInfo = fsInfo, ObjectInfo = objectInfo};

                    tuplesByPath[filePath] = hashTuple;

                    if (objectInfo.UUID!=_emptyGuid)

                        tuplesByID[objectInfo.UUID] = hashTuple;

                }

            }

            Debug.Assert(tuplesByPath.Values.All(t => t.HashesValid()));

            return tuplesByPath.Values;

        }

        private void  UpdateMD5(StateTuple hashTuple)

        {

            try

            {

                var hash = Signature.MD5_EMPTY;

                if (hashTuple.FileInfo is FileInfo)

                {

                    var file = hashTuple.FileInfo as FileInfo;

                    var stateDate = hashTuple.NullSafe(h => h.FileState).NullSafe(s => s.LastWriteDate) ??

                                    DateTime.MinValue;

                    if (file.LastWriteTime - stateDate < TimeSpan.FromSeconds(1) &&

                        hashTuple.FileState.LastLength == file.Length)

                    {

                        hash = hashTuple.FileState.LastMD5;

                    }

                    else

                    {

                        //Modified, must calculate hash

                        hash = file.ComputeShortHash(StatusNotification);

                        StatusKeeper.UpdateLastMD5(file, hash);

                    }

                }

                hashTuple.C = hash;

                hashTuple.MD5 = hash;

            }

            catch (IOException)

            {

                hashTuple.Locked = true;

            }            

        }

        /// <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 bool _pause;

        private readonly string _emptyGuid = Guid.Empty.ToString();

        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);

            StatusNotification.NotifyChange(message, TraceLevel.Warning);

        }

        /// <summary>

        /// Notify the UI to update the visual status

        /// </summary>

        /// <param name="status"></param>

        private void UpdateStatus(PithosStatus status)

        {

            try

            {

                StatusNotification.SetPithosStatus(status);

                //StatusNotification.Notify(new Notification());

            }

            catch (Exception exc)

            {

                //Failure is not critical, just log it

                Log.Warn("Error while updating status", exc);

            }

        }

        private static void CreateContainerFolders(AccountInfo accountInfo, IEnumerable<ContainerInfo> containers)

        {

            var containerPaths = from container in containers

                                 let containerPath = Path.Combine(accountInfo.AccountPath, container.Name)

                                 where container.Name != FolderConstants.TrashContainer && !Directory.Exists(containerPath)

                                 select containerPath;

            foreach (var path in containerPaths)

            {

                Directory.CreateDirectory(path);

            }

        }

        public void AddAccount(AccountInfo accountInfo)

        {

            //Avoid adding a duplicate accountInfo

            _accounts.TryAdd(accountInfo.AccountKey, accountInfo);

        }

        public void RemoveAccount(AccountInfo accountInfo)

        {

            AccountInfo account;

            _accounts.TryRemove(accountInfo.AccountKey, out account);

            SnapshotDifferencer differencer;

            _differencer.Differencers.TryRemove(accountInfo.AccountKey, out differencer);

        }

    }

}