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.Reflection;

using System.Threading;

using System.Threading.Tasks;

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();

                }

            }

        }

        public CancellationToken CancellationToken

        {

            get { return _currentOperationCancellation.Token; }

        }

        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.SetAsync();                

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

        }

        /// <summary>

        /// Start a manual synchronization

        /// </summary>

        public Task SynchNowAsync(IEnumerable<string> paths=null)

        {

            _batchQueue.Enqueue(paths);

            return _syncEvent.SetAsync();                

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

        }

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

        ConcurrentDictionary<string,MovedEventArgs> _moves=new ConcurrentDictionary<string, MovedEventArgs>(); 

        public void PostMove(MovedEventArgs args)

        {

            TaskEx.Run(() => _moves.AddOrUpdate(args.OldFullPath, args,(s,e)=>e));            

        }

        private bool _hasConnection;

        /// <summary>

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

        /// </summary>

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

        /// <returns></returns>

        public  async Task PollRemoteFiles(DateTimeOffset? 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

                DateTimeOffset? nextSince = since;

                try

                {

                    _unPauseEvent.Wait();

                    UpdateStatus(PithosStatus.PollSyncing);

                    if (!NetworkAgent.IsConnectedToInternet)

                    {

                        if (_hasConnection)

                        {

                            StatusNotification.Notify(new Notification

                            {

                                Level = TraceLevel.Error,

                                Title = "Internet Connection problem",

                                Message ="Internet connectivity was lost. Synchronization will continue when connectivity is restored"

                            });

                        }

                        _hasConnection = false;

                    }

                    else

                    {

                        if (!_hasConnection)

                        {

                            StatusNotification.Notify(new Notification

                            {

                                Level = TraceLevel.Info,

                                Title = "Internet Connection",

                                Message = "Internet connectivity restored."

                            });

                        }

                        _hasConnection = true;

                        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 moves = Interlocked.Exchange(ref _moves, new ConcurrentDictionary<string, MovedEventArgs>());

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

                        foreach (var accountInfo in _accounts.Values)

                        {

                            IEnumerable<string> accountBatch;

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

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

                            tasks.Add(t);

                        }

                        var taskList = tasks.ToList();

                        var nextTimes = await TaskEx.WhenAll(taskList).ConfigureAwait(false);

                        _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 for changes since [{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 = await WaitForScheduledOrManualPoll(nextSince).ConfigureAwait(false);

                }

                finally

                {

                    //Ensure polling is scheduled even in case of error

#pragma warning disable 4014

                    TaskEx.Run(()=>PollRemoteFiles(nextSince));

#pragma warning restore 4014

                    //_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<DateTimeOffset?> WaitForScheduledOrManualPoll(DateTimeOffset? since)

        {

            var sync = _syncEvent.WaitAsync();

            var delay = TimeSpan.FromSeconds(Settings.PollingInterval);

            if (Log.IsDebugEnabled)

                Log.DebugFormat("Next Poll at [{0}]", DateTime.Now.Add(delay));

            var wait = TaskEx.Delay(delay);

            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<DateTimeOffset?> ProcessAccountFiles(AccountInfo accountInfo, IEnumerable<string> accountBatch, ConcurrentDictionary<string, MovedEventArgs> moves, DateTimeOffset? 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 allContainers=await client.ListContainers(accountInfo.UserName).ConfigureAwait(false);

                var containers = allContainers

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

                DateTimeOffset? 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                    

                    var token = _currentOperationCancellation.Token;

                    //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,token)).ToList();

                    var selectiveEnabled = Selectives.IsSelectiveEnabled(accountInfo.AccountKey);

                    var listShared = selectiveEnabled?

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

                                    client.ListSharedObjects(_knownContainers,since), "shared",token)

                                :Task.Factory.FromResult((IList<ObjectInfo>) new List<ObjectInfo>(),"shared");

                    listObjects.Add(listShared);

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

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

                    {

                        //In case of cancellation, retry for the current date

                        if (token.IsCancellationRequested) return since;

                        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 objectList.AsyncState.ToString() != "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.ToUnescapedString()??""

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

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

                                                                   StringComparison.InvariantCultureIgnoreCase)

                                            select info).ToList();

                        //In case of cancellation, retry for the current date

                        if (token.IsCancellationRequested) return since;

                        if (_firstPoll)

                            StatusKeeper.CleanupOrphanStates();

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

                        var currentRemotes = differencer.Current.ToList();

                        //In case of cancellation, retry for the current date

                        if (token.IsCancellationRequested) return since;

                        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);

                        //In case of cancellation, retry for the current date

                        if (token.IsCancellationRequested) return since;

                        //Get the local files here                        

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

                        var files = LoadLocalFileTuples(accountInfo, accountBatch);

                        //WARNING: GetFileSystemInfo may create state entries.

                        //TODO: Find a different way to create the tuples and block long filenames

                        var infos = (from remote in currentRemotes

                                    let path = remote.RelativeUrlToFilePath(accountInfo.UserName)

                                    let info=agent.GetFileSystemInfo(path)

                                    where info != null

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

                                    .ToList();

                        var states = StatusKeeper.GetAllStates();

                        var tupleBuilder = new TupleBuilder(CancellationToken,StatusKeeper,StatusNotification,Settings);

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

                        var processedPaths = new HashSet<string>();

                        //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);

                            //In case of cancellation, retry for the current date

                            if (token.IsCancellationRequested) return since;

                            //Set the Merkle Hash

                            //SetMerkleHash(accountInfo, tuple);

                            await SyncSingleItem(accountInfo, tuple, agent, moves,processedPaths,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, ConcurrentDictionary<string, MovedEventArgs> moves,HashSet<string> processedPaths, CancellationToken token)

        {

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

            //If the processed paths already contain the current path, exit

            if (!processedPaths.Add(tuple.FilePath))

                return;

            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 locally?

                        if (!await MoveForLocalMove(accountInfo,tuple))

                            //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}",true,

                                                               localInfo.Name))

                            {

                                DeleteLocalFile(agent, 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}",true,

                                                               localInfo.Name))

                            {

                                var targetPath = MoveForServerMove(accountInfo, tuple);

                                if (targetPath != null)

                                {

                                    await DownloadCloudFile(accountInfo, tuple, token, targetPath).ConfigureAwait(false);

                                    AddOwnFolderToSelectives(accountInfo, tuple, targetPath);

                                }

                            }

                        }

                    }

                }

                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()

                                await DeleteCloudFile(accountInfo, tuple);

                                //updateRecord( Remove L, S)                  

                            }

                            else

                            {

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

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

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

                                //Is it an unselected root folder

                                var isCreation = isUnselectedRootFolder ||//or a new folder under a selected parent?

                                        (localInfo is DirectoryInfo && Selectives.IsSelected(accountInfo, localInfo) && tuple.FileState == null && tuple.ObjectInfo == null);

                                //Is this a result of a FILE move with no modifications? Then try to move it,

                                //to avoid an expensive hash

                                if (!await MoveForLocalMove(accountInfo, tuple))

                                {

                                    await UploadLocalFile(accountInfo, tuple, token, isCreation, localInfo,processedPaths, progress).ConfigureAwait(false);

                                }

                                //updateRecord( S = C )

                                //State updated by the uploader

                                if (isCreation )

                                {                                    

                                    ProcessChildren(accountInfo, tuple, agent, moves,processedPaths,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);

                                if (targetPath != null)

                                {

                                    Debug.Assert(tuple.Merkle != null);

                                    StatusKeeper.StoreInfo(targetPath, tuple.ObjectInfo, tuple.Merkle);

                                    AddOwnFolderToSelectives(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()

                                await 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 DeleteLocalFile(FileAgent agent, string localFilePath)

        {

            StatusKeeper.SetFileState(localFilePath, FileStatus.Deleted,

                                      FileOverlayStatus.Deleted, "");

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

            {

                agent.Delete(localFilePath);

            }

            //updateRecord(Remove C, L)

            StatusKeeper.ClearFileStatus(localFilePath);

        }

        private async Task DownloadCloudFile(AccountInfo accountInfo, StateTuple tuple, CancellationToken token, string targetPath)

        {                        

            //Don't create a new state for non-existent files

            if (File.Exists(targetPath) || Directory.Exists(targetPath))

                StatusKeeper.SetFileState(targetPath, FileStatus.Modified, FileOverlayStatus.Modified,"");

            var finalHash=await

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

                                                          token)

                    .ConfigureAwait(false);

            //updateRecord( L = S )

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

                                            finalHash);

            StatusKeeper.StoreInfo(targetPath, tuple.ObjectInfo,finalHash);

        }

        private async Task UploadLocalFile(AccountInfo accountInfo, StateTuple tuple, CancellationToken token,

                                     bool isUnselectedRootFolder, FileSystemInfo localInfo, HashSet<string> processedPaths, IProgress<HashProgress> progress)

        {

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

                                               accountInfo.BlockSize, accountInfo.BlockHash,

                                               "Poll", isUnselectedRootFolder, token, progress,tuple.Merkle);            

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

                                                  localInfo.Name))

            {

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

            }

            if (isUnselectedRootFolder)

            {

                var dirActions =(

                    from dir in ((DirectoryInfo) localInfo).EnumerateDirectories("*", SearchOption.AllDirectories)

                    let subAction = new CloudUploadAction(accountInfo, dir, null,

                                                          accountInfo.BlockSize, accountInfo.BlockHash,

                                                          "Poll", true, token, progress)

                    select subAction).ToList();

                foreach (var dirAction in dirActions)

                {

                    processedPaths.Add(dirAction.LocalFile.FullName);

                }

                await TaskEx.WhenAll(dirActions.Select(a=>NetworkAgent.Uploader.UploadCloudFile(a,token)).ToArray());

            }

        }

        private async Task<bool> MoveForLocalMove(AccountInfo accountInfo, StateTuple tuple)

        {

            //Is the previous path missing?

            if (String.IsNullOrWhiteSpace(tuple.OldFullPath))

                return false;

            //Has the file locally, in which case it should be uploaded rather than moved?

            if (tuple.OldChecksum != tuple.Merkle.TopHash.ToHashString())

                return false;

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

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

            //Has the file been renamed on the server?

            if (!tuple.OldFullPath.Equals(serverPath))

            {

                ReportConflictForDoubleRename(tuple.FilePath);

                return false;

            }

            try

            {

                var client = new CloudFilesClient(accountInfo);

                var objectInfo = CloudAction.CreateObjectInfoFor(accountInfo, tuple.FileInfo);

                objectInfo.X_Object_Hash = tuple.Merkle.TopHash.ToHashString();

                var containerPath = Path.Combine(accountInfo.AccountPath, objectInfo.Container.ToUnescapedString());

                //TODO: SImplify these multiple conversions from and to Uris

                var oldName = tuple.OldFullPath.AsRelativeTo(containerPath);

                //Then execute a move instead of an upload

                using (StatusNotification.GetNotifier("Moving {0}", "Moved {0}", true,tuple.FileInfo.Name))

                {

                    await client.MoveObject(objectInfo.Account, objectInfo.Container, oldName.Replace('\\','/').ToEscapedUri(),

                                                          objectInfo.Container, objectInfo.Name).ConfigureAwait(false);

                    StatusKeeper.MoveFileState(tuple.OldFullPath, tuple.FilePath, objectInfo, tuple.Merkle);

                    //StatusKeeper.StoreInfo(tuple.FilePath,objectInfo,tuple.Merkle);

                    //StatusKeeper.ClearFolderStatus(tuple.FilePath);

                }

                return true;

            }

            catch (Exception exc)

            {

                Log.ErrorFormat("[MOVE] Failed for [{0}],:\r\n{1}", tuple.FilePath, exc);

                //Return false to force an upload of the file

                return false;

            }

        }

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

        {

            //Not for shared folders

            if (tuple.ObjectInfo.IsShared==true)

                return;

            //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.ToUnescapedString());

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

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

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

            {

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

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

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

                //If the new path is under a selected folder, add it to the selectives as well

                if (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;

            //Has the file been renamed locally?

            if (!String.IsNullOrWhiteSpace(tuple.OldFullPath) &&  !tuple.OldFullPath.Equals(tuple.FilePath))

            {

                ReportConflictForDoubleRename(tuple.FilePath);

                return null;

            }

            tuple.FileInfo.Refresh();

            //The file/folder may not exist if it was moved because its parent moved

            if (!tuple.FileInfo.Exists)

            {

                var target=FileInfoExtensions.FromPath(serverPath);

                if (!target.Exists)

                {

                    Log.ErrorFormat("No source or target found while trying to move {0} to {1}", tuple.FileInfo.FullName, serverPath);

                }

                return serverPath;

            }

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

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

            {

                var fi = tuple.FileInfo as FileInfo;

                if (fi != null)

                {

                    var targetFile = new FileInfo(serverPath);

                    if (!targetFile.Directory.Exists)

                        targetFile.Directory.Create();

                    fi.MoveTo(serverPath);

                }

                var di = tuple.FileInfo as DirectoryInfo;

                if (di != null)

                {

                    var targetDir = new DirectoryInfo(serverPath);

                    if (!targetDir.Parent.Exists)

                        targetDir.Parent.Create();

                    di.MoveTo(serverPath);

                }

            }

            StatusKeeper.StoreInfo(serverPath, tuple.ObjectInfo);

            return serverPath;

        }

        private async Task DeleteCloudFile(AccountInfo accountInfo, StateTuple tuple)

        {

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

            {

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

                                          FileOverlayStatus.Deleted, "");

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

                StatusKeeper.ClearFileStatus(tuple.FilePath);

            }

        }

        private void ProcessChildren(AccountInfo accountInfo, StateTuple tuple, FileAgent agent, ConcurrentDictionary<string, MovedEventArgs> moves,HashSet<string> processedPaths,CancellationToken token)

        {

            var dirInfo = tuple.FileInfo as DirectoryInfo;

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

                               select new StateTuple(folder){C=Signature.MERKLE_EMPTY};

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

                             let state=StatusKeeper.GetStateByFilePath(file.FullName)

                             select new StateTuple(file){

                                            Merkle=StatusAgent.CalculateTreeHash(file,accountInfo,state,

                                            Settings.HashingParallelism,token,null)

                                        };

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

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

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

        }

        /// <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 DateTimeOffset? GetLatestDateBefore(DateTime? threshold, IList<ObjectInfo> cloudObjects)

        {

            DateTimeOffset? maxDate = null;

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

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

            if (!maxDate.HasValue)

                return threshold;

            if (!threshold.HasValue|| 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 DateTimeOffset? GetLatestDateAfter(DateTimeOffset? threshold, IList<ObjectInfo> cloudObjects)

        {

            DateTimeOffset? maxDate = null;

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

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

            if (!maxDate.HasValue)

                return threshold;

            if (!threshold.HasValue|| threshold < maxDate)

                return maxDate;

            return threshold;

        }

        readonly AccountsDifferencer _differencer = new AccountsDifferencer();

        private bool _pause;

        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);

        }

        private void ReportConflictForDoubleRename(string localFilePath)

        {

            if (String.IsNullOrWhiteSpace(localFilePath))

                throw new ArgumentNullException("localFilePath");

            Contract.EndContractBlock();

            StatusKeeper.SetFileState(localFilePath, FileStatus.Conflict, FileOverlayStatus.Conflict, "File renamed both locally and on the server");

            UpdateStatus(PithosStatus.HasConflicts);

            var message = String.Format("Double rename 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.ToUnescapedString())

                                 where container.Name.ToString() != 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)

        {

            if (accountInfo == null)

                return;

            AccountInfo account;

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

            SnapshotDifferencer differencer;

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

        }

    }

}