#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;

        HashSet<string> _knwonContainers = 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)
            {
                //TODO: Must convert to AutoReset
                _syncEvent.Reset();
                return null;
            }
            return since;
        }

        

        public async Task<DateTime?> ProcessAccountFiles(AccountInfo accountInfo, IEnumerable<string> accountBatch, DateTime? since = null)
        {
            if (accountInfo == null)
                throw new ArgumentNullException("accountInfo");
            if (String.IsNullOrWhiteSpace(accountInfo.AccountPath))
                throw new ArgumentException("The AccountInfo.AccountPath is empty", "accountInfo");
            Contract.EndContractBlock();


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

                await NetworkAgent.GetDeleteAwaiter().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(_knwonContainers,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 = await 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)
                        {
                            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.ShortHash)
            {
                //If there is a state whose MD5 matches, load the merkle hash from the file state
                //insteaf of calculating it
                tuple.C = tuple.FileState.Checksum;                              
            }
            else
            {
                tuple.Merkle = Signature.CalculateTreeHashAsync((FileInfo)tuple.FileInfo, accountInfo.BlockSize, accountInfo.BlockHash,1);
                //tuple.C=tuple.Merkle.TopHash.ToHashString();                
            }
        }

        private async Task<List<Tuple<FileSystemInfo, string>>> LoadLocalFileTuples(AccountInfo accountInfo,IEnumerable<string> batch )
        {
            using (ThreadContext.Stacks["Account Files Hashing"].Push(accountInfo.UserName))
            {
                var batchPaths = (batch==null)?new List<string>():batch.ToList();
                IEnumerable<FileSystemInfo> localInfos=AgentLocator<FileAgent>.Get(accountInfo.AccountPath)
                                                        .EnumerateFileSystemInfos();
                if (batchPaths.Count>0)
                    localInfos= localInfos.Where(fi => batchPaths.Contains(fi.FullName));
                
                //Use the queue to retry locked file hashing
                var fileQueue = new 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;
            }
        }

        /// <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);

            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, "");
                            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);
                        }

                        /*
                                                        StatusKeeper.SetFileState(targetPath, FileStatus.Unchanged,
                                                                                  FileOverlayStatus.Normal, "");
                            */
                    }
                }

            }
            else
            {
                //Local changes found

                //Server unchanged?
                if (tuple.S == tuple.L)
                {
                    //The FileAgent selective sync checks for new root folder files
                    if (!agent.Ignore(localFilePath))
                    {
                        if ((tuple.C == null || !localInfo.Exists) && tuple.ObjectInfo != null)
                        {
                            //deleteObjectFromServer()
                            DeleteCloudFile(accountInfo, tuple);
                            //updateRecord( Remove L, S)                  
                        }
                        else
                        {
                            //uploadLocalObject() // Result: S = C, L = S                        

                            //Debug.Assert(tuple.FileState !=null);
                            var action = new CloudUploadAction(accountInfo, localInfo, tuple.FileState,
                                                               accountInfo.BlockSize, accountInfo.BlockHash,
                                                               "Poll", isUnselectedRootFolder);
                            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()
                        //Detect server moves
                        var targetPath = MoveForServerMove(accountInfo, tuple);
                        StatusKeeper.StoreInfo(targetPath, tuple.ObjectInfo);
                    }
                    else
                    {
                        if ((tuple.C == null || !localInfo.Exists) && tuple.ObjectInfo != null)
                        {
                            //deleteObjectFromServer()
                            DeleteCloudFile(accountInfo, tuple);
                            //updateRecord(Remove L, S)                  
                        }
                            //If both the local and server files are missing, the state is stale
                        else if (!localInfo.Exists && (tuple.S == null || tuple.ObjectInfo == null))
                        {
                            StatusKeeper.ClearFileStatus(localInfo.FullName);
                        }
                        else
                        {
                            ReportConflictForMismatch(localFilePath);
                            //identifyAsConflict() // Manual action required
                        }
                    }
                }
            }
        }

        private string MoveForServerMove(AccountInfo accountInfo, StateTuple tuple)
        {
            if (tuple.ObjectInfo == null)
                return null;
            var relativePath = tuple.ObjectInfo.RelativeUrlToFilePath(accountInfo.UserName);
            var serverPath = Path.Combine(accountInfo.AccountPath, relativePath);
            
            //Compare Case Insensitive
            if (String.Equals(tuple.FilePath ,serverPath,StringComparison.InvariantCultureIgnoreCase)) return serverPath;

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

        private static IEnumerable<StateTuple> MergeSources(
            IEnumerable<Tuple<string, ObjectInfo>> infos, 
            IEnumerable<Tuple<FileSystemInfo, string>> files, 
            IEnumerable<FileState> states)
        {
            var tuplesByPath = new Dictionary<string, StateTuple>();
            foreach (var file in files)
            {
                var fsInfo = file.Item1;
                var fileHash = fsInfo is DirectoryInfo? MD5_EMPTY:file.Item2;

                tuplesByPath[fsInfo.FullName] = new StateTuple {FileInfo = fsInfo, C=fileHash,MD5 = fileHash};
            }
            foreach (var state in states)
            {
                StateTuple hashTuple;
                if (tuplesByPath.TryGetValue(state.FilePath, out hashTuple))
                {
                    hashTuple.FileState = state;
                }
                else
                {
                    var fsInfo = FileInfoExtensions.FromPath(state.FilePath);
                    hashTuple = new StateTuple {FileInfo = fsInfo, FileState = state};
                    tuplesByPath[state.FilePath] = hashTuple;
                }
            }

            var tuplesByID = tuplesByPath.Values
                .Where(tuple => tuple.FileState != null && tuple.FileState.ObjectID!=null)
                .ToDictionary(tuple=>tuple.FileState.ObjectID,tuple=>tuple);//new Dictionary<Guid, StateTuple>();

            foreach (var info in infos)
            {
                StateTuple hashTuple;
                var filePath = info.Item1;
                var objectInfo = info.Item2;
                var objectID = objectInfo.UUID;

                if (tuplesByID.TryGetValue(objectID, out hashTuple))
                {
                    hashTuple.ObjectInfo = objectInfo;                    
                }
                else if (tuplesByPath.TryGetValue(filePath, out hashTuple))
                {
                    hashTuple.ObjectInfo = objectInfo;
                }
                else
                {
                    var fsInfo = FileInfoExtensions.FromPath(filePath);
                    hashTuple= new StateTuple {FileInfo = fsInfo, ObjectInfo = objectInfo};
                    tuplesByPath[filePath] = hashTuple;
                    tuplesByID[objectInfo.UUID] = hashTuple;
                }
            }
            Debug.Assert(tuplesByPath.Values.All(t => t.HashesValid()));
            return tuplesByPath.Values;
        }

        /// <summary>
        /// Returns the latest LastModified date from the list of objects, but only if it is before
        /// than the threshold value
        /// </summary>
        /// <param name="threshold"></param>
        /// <param name="cloudObjects"></param>
        /// <returns></returns>
        private static DateTime? GetLatestDateBefore(DateTime? threshold, IList<ObjectInfo> cloudObjects)
        {
            DateTime? maxDate = null;
            if (cloudObjects!=null &&  cloudObjects.Count > 0)
                maxDate = cloudObjects.Max(obj => obj.Last_Modified);
            if (maxDate == null || maxDate == DateTime.MinValue)
                return threshold;
            if (threshold == null || threshold == DateTime.MinValue || threshold > maxDate)
                return maxDate;
            return threshold;
        }

        /// <summary>
        /// Returns the latest LastModified date from the list of objects, but only if it is after
        /// the threshold value
        /// </summary>
        /// <param name="threshold"></param>
        /// <param name="cloudObjects"></param>
        /// <returns></returns>
        private static DateTime? GetLatestDateAfter(DateTime? threshold, IList<ObjectInfo> cloudObjects)
        {
            DateTime? maxDate = null;
            if (cloudObjects!=null &&  cloudObjects.Count > 0)
                maxDate = cloudObjects.Max(obj => obj.Last_Modified);
            if (maxDate == null || maxDate == DateTime.MinValue)
                return threshold;
            if (threshold == null || threshold == DateTime.MinValue || threshold < maxDate)
                return maxDate;
            return threshold;
        }

        readonly AccountsDifferencer _differencer = new AccountsDifferencer();
        private bool _pause;
        
        const string MERKLE_EMPTY = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855";
        const string MD5_EMPTY = "d41d8cd98f00b204e9800998ecf8427e";


        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);
        }
       
    }
}