#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 Castle.ActiveRecord;
using Pithos.Interfaces;
using Pithos.Network;
using log4net;

namespace Pithos.Core.Agents
{
    using System;
    using System.Collections.Generic;
    using System.Linq;

    [DebuggerDisplay("{FilePath} C:{C} L:{L} S:{S}")]
    public class StateTuple
    {
        public string FilePath { get; private set; }

        public string MD5 { get; set; }

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

        private string _c;
        public string C
        {
            get { return _c; }
            set {
                _c = String.IsNullOrWhiteSpace(value) ? null : value;
            }
        }

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

        private FileSystemInfo _fileInfo;
        private TreeHash _merkle;

        public FileSystemInfo FileInfo
        {
            get { return _fileInfo; }
            set
            {
                _fileInfo = value;
                FilePath = value.FullName;
            }
        }

        public FileState FileState { get; set; }
        public ObjectInfo ObjectInfo{ get; set; }


        public TreeHash Merkle
        {
            get {
                return _merkle;
            }
            set {
                _merkle = value;
                C = _merkle.TopHash.ToHashString();
            }
        }

        public StateTuple() { }

        public StateTuple(FileSystemInfo info)
        {
            FileInfo = info;
        }


    }


    /// <summary>
    /// PollAgent periodically polls the server to detect object changes. The agent retrieves a listing of all
    /// objects and compares it with a previously cached version to detect differences. 
    /// New files are downloaded, missing files are deleted from the local file system and common files are compared
    /// to determine the appropriate action
    /// </summary>
    [Export]
    public class PollAgent
    {
        private static readonly ILog Log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);

        [System.ComponentModel.Composition.Import]
        public IStatusKeeper StatusKeeper { get; set; }

        [System.ComponentModel.Composition.Import]
        public IPithosSettings Settings { get; set; }

        [System.ComponentModel.Composition.Import]
        public NetworkAgent NetworkAgent { get; set; }

        [System.ComponentModel.Composition.Import]
        public Selectives Selectives { get; set; }

        public IStatusNotification StatusNotification { get; set; }

        private CancellationTokenSource _currentOperationCancellation = new CancellationTokenSource();

        public void CancelCurrentOperation()
        {
            //What does it mean to cancel the current upload/download?
            //Obviously, the current operation will be cancelled by throwing
            //a cancellation exception.
            //
            //The default behavior is to retry any operations that throw.
            //Obviously this is not what we want in this situation.
            //The cancelled operation should NOT bea retried. 
            //
            //This can be done by catching the cancellation exception
            //and avoiding the retry.
            //

            //Have to reset the cancellation source - it is not possible to reset the source
            //Have to prevent a case where an operation requests a token from the old source
            var oldSource = Interlocked.Exchange(ref _currentOperationCancellation, new CancellationTokenSource());
            oldSource.Cancel();

        }

        public bool Pause
        {
            get {
                return _pause;
            }
            set {
                _pause = value;                
                if (!_pause)
                    _unPauseEvent.Set();
                else
                {
                    _unPauseEvent.Reset();
                }
            }
        }

        private bool _firstPoll = true;

        //The Sync Event signals a manual synchronisation
        private readonly AsyncManualResetEvent _syncEvent = new AsyncManualResetEvent();

        private readonly AsyncManualResetEvent _unPauseEvent = new AsyncManualResetEvent(true);

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


        /// <summary>
        /// Start a manual synchronization
        /// </summary>
        public void SynchNow(IEnumerable<string> paths=null)
        {            
            //_batchQueue.Enqueue(paths);
            _syncEvent.Set();
        }

        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 async Task 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
                {
                    await _unPauseEvent.WaitAsync();
                    UpdateStatus(PithosStatus.PollSyncing);

                    var accountBatches=new Dictionary<Uri, IEnumerable<string>>();
                    IEnumerable<string> batch = null;
                    if (_batchQueue.TryDequeue(out batch) && batch != null)
                        foreach (var account in _accounts.Values)
                        {
                            var accountBatch = batch.Where(path => path.IsAtOrBelow(account.AccountPath));
                            accountBatches[account.AccountKey] = accountBatch;
                        }


                    IEnumerable<Task<DateTime?>> tasks = new List<Task<DateTime?>>();
                    foreach(var accountInfo in _accounts.Values)
                    {
                        IEnumerable<string> accountBatch ;
                        accountBatches.TryGetValue(accountInfo.AccountKey,out accountBatch);
                        ProcessAccountFiles (accountInfo, accountBatch, since);
                    }

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

                    _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 = await WaitForScheduledOrManualPoll(nextSince);
                }
                finally
                {
                    //Ensure polling is scheduled even in case of error
                    TaskEx.Run(() => PollRemoteFiles(nextSince));                        
                }
            }
        }

        /// <summary>
        /// Wait for the polling period to expire or a manual sync request
        /// </summary>
        /// <param name="since"></param>
        /// <returns></returns>
        private async Task<DateTime?> WaitForScheduledOrManualPoll(DateTime? since)
        {
            var sync = _syncEvent.WaitAsync();
            var wait = TaskEx.Delay(TimeSpan.FromSeconds(Settings.PollingInterval));
            
            var signaledTask = await TaskEx.WhenAny(sync, wait);
            
            //Pausing takes precedence over manual sync or awaiting
            _unPauseEvent.Wait();
            
            //Wait for network processing to finish before polling
            var pauseTask=NetworkAgent.ProceedEvent.WaitAsync();
            await TaskEx.WhenAll(signaledTask, pauseTask);

            //If polling is signalled by SynchNow, ignore the since tag
            if (sync.IsCompleted)
            {
                //TODO: Must convert to AutoReset
                _syncEvent.Reset();
                return null;
            }
            return since;
        }

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


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

                await NetworkAgent.GetDeleteAwaiter();

                Log.Info("Scheduled");
                var client = new CloudFilesClient(accountInfo);

                //We don't need to check the trash container
                var containers = client.ListContainers(accountInfo.UserName)
                    .Where(c=>c.Name!="trash")
                    .ToList();


                CreateContainerFolders(accountInfo, containers);

                //The nextSince time fallback time is the same as the current.
                //If polling succeeds, the next Since time will be the smallest of the maximum modification times
                //of the shared and account objects
                var nextSince = since;

                try
                {
                    //Wait for any deletions to finish
                    await NetworkAgent.GetDeleteAwaiter();
                    //Get the poll time now. We may miss some deletions but it's better to keep a file that was deleted
                    //than delete a file that was created while we were executing the poll                    

                    //Get the list of server objects changed since the last check
                    //The name of the container is passed as state in order to create a dictionary of tasks in a subsequent step
                    var listObjects = (from container in containers
                                       select Task<IList<ObjectInfo>>.Factory.StartNew(_ =>
                                             client.ListObjects(accountInfo.UserName, container.Name, since), container.Name)).ToList();

                    var listShared = Task<IList<ObjectInfo>>.Factory.StartNew(_ => 
                        client.ListSharedObjects(since), "shared");
                    listObjects.Add(listShared);
                    var listTasks = await Task.Factory.WhenAll(listObjects.ToArray());

                    using (ThreadContext.Stacks["SCHEDULE"].Push("Process Results"))
                    {
                        var dict = listTasks.ToDictionary(t => t.AsyncState);

                        //Get all non-trash objects. Remember, the container name is stored in AsyncState
                        var remoteObjects = (from objectList in listTasks
                                            where (string)objectList.AsyncState != "trash"
                                            from obj in objectList.Result
                                            orderby obj.Bytes ascending 
                                            select obj).ToList();
                        
                        //Get the latest remote object modification date, only if it is after
                        //the original since date
                        nextSince = GetLatestDateAfter(nextSince, remoteObjects);

                        var sharedObjects = dict["shared"].Result;
                        nextSince = GetLatestDateBefore(nextSince, sharedObjects);

                        //DON'T process trashed files
                        //If some files are deleted and added again to a folder, they will be deleted
                        //even though they are new.
                        //We would have to check file dates and hashes to ensure that a trashed file
                        //can be deleted safely from the local hard drive.
                        /*
                        //Items with the same name, hash may be both in the container and the trash
                        //Don't delete items that exist in the container
                        var realTrash = from trash in trashObjects
                                        where
                                            !remoteObjects.Any(
                                                info => info.Name == trash.Name && info.Hash == trash.Hash)
                                   8     select trash;
                        ProcessTrashedFiles(accountInfo, realTrash);
*/

                        var cleanRemotes = (from info in remoteObjects.Union(sharedObjects)
                                            let name = info.Name??""
                                            where !name.EndsWith(".ignore", StringComparison.InvariantCultureIgnoreCase) &&
                                                  !name.StartsWith(FolderConstants.CacheFolder + "/",
                                                                   StringComparison.InvariantCultureIgnoreCase)
                                            select info).ToList();

                        if (_firstPoll)
                            StatusKeeper.CleanupOrphanStates();
                        StatusKeeper.CleanupStaleStates(accountInfo, cleanRemotes);
                        
                        //var differencer = _differencer.PostSnapshot(accountInfo, cleanRemotes);

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


                        //Get the local files here                        
                        var agent = AgentLocator<FileAgent>.Get(accountInfo.AccountPath);

                        var files = LoadLocalFileTuples(accountInfo);

                        var states = FileState.Queryable.ToList();                        
                        

                        var infos = (from remote in cleanRemotes
                                    let path = remote.RelativeUrlToFilePath(accountInfo.UserName)
                                    let info=agent.GetFileSystemInfo(path)
                                    select Tuple.Create(info.FullName,remote))
                                    .ToList();

                        var token = _currentOperationCancellation.Token;

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


                        var stateTuples = accountBatch==null?tuples:tuples.Where(t => accountBatch.Contains(t.FilePath));
                        foreach (var tuple in stateTuples)
                        {
                            await _unPauseEvent.WaitAsync();

                            //Set the Merkle Hash
                            SetMerkleHash(accountInfo, tuple);

                            SyncSingleItem(accountInfo, tuple, agent, token);

                        }


                        //On the first run
/*
                        if (_firstPoll)
                        {
                            MarkSuspectedDeletes(accountInfo, cleanRemotes);
                        }
*/


                        Log.Info("[LISTENER] End Processing");
                    }
                }
                catch (Exception ex)
                {
                    Log.ErrorFormat("[FAIL] ListObjects for{0} in ProcessRemoteFiles with {1}", accountInfo.UserName, ex);
                    return nextSince;
                }

                Log.Info("[LISTENER] Finished");
                return nextSince;
            }
        }

        private static void SetMerkleHash(AccountInfo accountInfo, StateTuple tuple)
        {
            //The Merkle hash for directories is that of an empty buffer
            if (tuple.FileInfo is DirectoryInfo)
                tuple.C = MERKLE_EMPTY;
            else if (tuple.FileState != null && tuple.MD5 == tuple.FileState.ShortHash)
            {
                //If there is a state whose MD5 matches, load the merkle hash from the file state
                //insteaf of calculating it
                tuple.C = tuple.FileState.Checksum;                              
            }
            else
            {
                tuple.Merkle = Signature.CalculateTreeHash(tuple.FileInfo, accountInfo.BlockSize, accountInfo.BlockHash);
                //tuple.C=tuple.Merkle.TopHash.ToHashString();                
            }
        }

        private static List<Tuple<FileSystemInfo, string>> LoadLocalFileTuples(AccountInfo accountInfo)
        {
            using (ThreadContext.Stacks["Account Files Hashing"].Push(accountInfo.UserName))
            {

                var localInfos = AgentLocator<FileAgent>.Get(accountInfo.AccountPath).EnumerateFileSystemInfos();
                //Use the queue to retry locked file hashing
                var fileQueue = new Queue<FileSystemInfo>(localInfos);
                var hasher = MD5.Create();

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

                while (fileQueue.Count > 0)
                {
                    var file = fileQueue.Dequeue();
                    using (ThreadContext.Stacks["File"].Push(file.FullName))
                    {
                        /*
                                                Signature.CalculateTreeHash(file, accountInfo.BlockSize,
                                                                                                 accountInfo.BlockHash).
                                                                         TopHash.ToHashString()
                        */
                        try
                        {
                            //Replace MD5 here, do the calc while syncing individual files
                            string hash ;
                            if (file is DirectoryInfo)
                                hash = MERKLE_EMPTY;
                            else
                            {
                                using (StatusNotification.GetNotifier("Hashing ", "{0}", file.Name))
                                using (var stream = (file as FileInfo).OpenRead())
                                {                                    
                                    hash = hasher.ComputeHash(stream).ToHashString();
                                }
                            }                            
                            results.Add(Tuple.Create(file, hash));
                        }
                        catch (IOException exc)
                        {
                            Log.WarnFormat("[HASH] File in use, will retry [{0}]", exc);
                            fileQueue.Enqueue(file);
                        }
                    }
                }

                return results;
            }
        }

        private void SyncSingleItem(AccountInfo accountInfo, StateTuple tuple, FileAgent agent, CancellationToken token)
        {
            Log.DebugFormat("Sync [{0}] C:[{1}] L:[{2}] S:[{3}]",tuple.FilePath,tuple.C,tuple.L,tuple.S);

            var localFilePath = tuple.FilePath;
            //Don't use the tuple info, it may have been deleted
            var localInfo = FileInfoExtensions.FromPath(localFilePath);


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

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

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

            // Local file unchanged? If both C and L are null, make sure it's because 
            //both the file is missing and the state checksum is not missing
            if (tuple.C == tuple.L /*&& (localInfo.Exists || tuple.FileState == null)*/)
            {
                //No local changes
                //Server unchanged?
                if (tuple.S == tuple.L)
                {
                    // No server changes
                    //Has the file been renamed on the server?
                    MoveForServerMove(accountInfo, tuple);
                }
                else
                {
                    //Different from server
                    //Does the server file exist?
                    if (tuple.S == null)
                    {
                        //Server file doesn't exist
                        //deleteObjectFromLocal()
                        StatusKeeper.SetFileState(localFilePath, FileStatus.Deleted,
                                                  FileOverlayStatus.Deleted, "");
                        agent.Delete(localFilePath);
                        //updateRecord(Remove C, L)
                        StatusKeeper.ClearFileStatus(localFilePath);
                    }
                    else
                    {
                        //Server file exists
                        //downloadServerObject() // Result: L = S
                        //If the file has moved on the server, move it locally before downloading
                        var targetPath = MoveForServerMove(accountInfo, tuple);

                        StatusKeeper.SetFileState(targetPath, FileStatus.Modified,
                                                  FileOverlayStatus.Modified, "");
                        NetworkAgent.Downloader.DownloadCloudFile(accountInfo,
                                                                  tuple.ObjectInfo,
                                                                  targetPath, tuple.Merkle, token).Wait(token);
                        //updateRecord( L = S )
                        StatusKeeper.UpdateFileChecksum(targetPath, tuple.ObjectInfo.ETag,
                                                        tuple.ObjectInfo.X_Object_Hash);

                        StatusKeeper.StoreInfo(targetPath, tuple.ObjectInfo);

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

            }
            else
            {
                //Local changes found

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

                            //Debug.Assert(tuple.FileState !=null);
                            var action = new CloudUploadAction(accountInfo, localInfo, tuple.FileState,
                                                               accountInfo.BlockSize, accountInfo.BlockHash,
                                                               "Poll", isUnselectedRootFolder);
                            NetworkAgent.Uploader.UploadCloudFile(action, tuple.Merkle, token).Wait(token);

                            //updateRecord( S = C )
                            //State updated by the uploader

                            if (isUnselectedRootFolder)
                            {
                                ProcessChildren(accountInfo, tuple, agent, token);
                            }
                        }
                    }
                }
                else
                {
                    if (tuple.C == tuple.S)
                    {
                        // (Identical Changes) Result: L = S
                        //doNothing()
                        //Detect server moves
                        var targetPath = MoveForServerMove(accountInfo, tuple);
                        StatusKeeper.StoreInfo(targetPath, tuple.ObjectInfo);
                    }
                    else
                    {
                        if ((tuple.C == null || !localInfo.Exists) && tuple.ObjectInfo != null)
                        {
                            //deleteObjectFromServer()
                            DeleteCloudFile(accountInfo, tuple);
                            //updateRecord(Remove L, S)                  
                        }
                            //If both the local and server files are missing, the state is stale
                        else if (!localInfo.Exists && (tuple.S == null || tuple.ObjectInfo == null))
                        {
                            StatusKeeper.ClearFileStatus(localInfo.FullName);
                        }
                        else
                        {
                            ReportConflictForMismatch(localFilePath);
                            //identifyAsConflict() // Manual action required
                        }
                    }
                }
            }
        }

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

            if (tuple.FileInfo.Exists)
            {                    
                var fi = tuple.FileInfo as FileInfo;
                if (fi != null)
                    fi.MoveTo(serverPath);
                var di = tuple.FileInfo as DirectoryInfo;
                if (di != null)
                    di.MoveTo(serverPath);
                StatusKeeper.StoreInfo(serverPath, tuple.ObjectInfo);
            }
            else
            {
                Debug.Assert(false, "File does not exist");
            }
            return serverPath;
        }

        private void DeleteCloudFile(AccountInfo accountInfo, StateTuple tuple)
        {
            StatusKeeper.SetFileState(tuple.FilePath, FileStatus.Deleted,
                                      FileOverlayStatus.Deleted, "");
            NetworkAgent.DeleteAgent.DeleteCloudFile(accountInfo, tuple.ObjectInfo);
            StatusKeeper.ClearFileStatus(tuple.FilePath);
        }

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

            var dirInfo = tuple.FileInfo as DirectoryInfo;
            var folderTuples = from folder in dirInfo.EnumerateDirectories("*", SearchOption.AllDirectories)
                               select new StateTuple(folder);
            var fileTuples = from file in dirInfo.EnumerateFiles("*", SearchOption.AllDirectories)
                             select new StateTuple(file);
            
            //Process folders first, to ensure folders appear on the sever as soon as possible
            folderTuples.ApplyAction(t => SyncSingleItem(accountInfo, t, agent, token));
            
            fileTuples.ApplyAction(t => SyncSingleItem(accountInfo, t, agent, token));
        }

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

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

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

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

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

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

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

        readonly AccountsDifferencer _differencer = new AccountsDifferencer();
        private Dictionary<Uri, List<Uri>> _selectiveUris = new Dictionary<Uri, List<Uri>>();
        private bool _pause;
        private static string MERKLE_EMPTY = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855";

        /// <summary>
        /// Deletes local files that are not found in the list of cloud files
        /// </summary>
        /// <param name="accountInfo"></param>
        /// <param name="cloudFiles"></param>
        private void ProcessDeletedFiles(AccountInfo accountInfo, IEnumerable<ObjectInfo> cloudFiles)
        {
            if (accountInfo == null)
                throw new ArgumentNullException("accountInfo");
            if (String.IsNullOrWhiteSpace(accountInfo.AccountPath))
                throw new ArgumentException("The AccountInfo.AccountPath is empty", "accountInfo");
            if (cloudFiles == null)
                throw new ArgumentNullException("cloudFiles");
            Contract.EndContractBlock();

            var deletedFiles = new List<FileSystemInfo>();
            foreach (var objectInfo in cloudFiles)
            {
                if (Log.IsDebugEnabled)
                    Log.DebugFormat("Handle deleted [{0}]", objectInfo.Uri);
                var relativePath = objectInfo.RelativeUrlToFilePath(accountInfo.UserName);
                var item = FileAgent.GetFileAgent(accountInfo).GetFileSystemInfo(relativePath);
                if (Log.IsDebugEnabled)
                    Log.DebugFormat("Will delete [{0}] for [{1}]", item.FullName, objectInfo.Uri);
                if (item.Exists)
                {
                    if ((item.Attributes & FileAttributes.ReadOnly) == FileAttributes.ReadOnly)
                    {
                        item.Attributes = item.Attributes & ~FileAttributes.ReadOnly;

                    }


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

                    var directory = item as DirectoryInfo;
                    if (directory != null)
                        directory.Delete(true);
                    else
                        item.Delete();
                    Log.DebugFormat("Deleted [{0}] for [{1}]", item.FullName, objectInfo.Uri);
                    DateTime lastDate;
                    _lastSeen.TryRemove(item.FullName, out lastDate);
                    deletedFiles.Add(item);
                }
                StatusKeeper.SetFileState(item.FullName, FileStatus.Deleted, FileOverlayStatus.Deleted, "File Deleted");
            }
            Log.InfoFormat("[{0}] files were deleted", deletedFiles.Count);
            StatusNotification.NotifyForFiles(deletedFiles, String.Format("{0} files were deleted", deletedFiles.Count),
                                              TraceLevel.Info);

        }

        private void MarkSuspectedDeletes(AccountInfo accountInfo, IEnumerable<ObjectInfo> cloudFiles)
        {
//Only consider files that are not being modified, ie they are in the Unchanged state            
            var deleteCandidates = FileState.Queryable.Where(state =>
                                                             state.FilePath.StartsWith(accountInfo.AccountPath)
                                                             && state.FileStatus == FileStatus.Unchanged).ToList();


            //TODO: filesToDelete must take into account the Others container            
            var filesToDelete = (from deleteCandidate in deleteCandidates
                                 let localFile = FileInfoExtensions.FromPath(deleteCandidate.FilePath)
                                 let relativeFilePath = localFile.AsRelativeTo(accountInfo.AccountPath)
                                 where
                                     !cloudFiles.Any(r => r.RelativeUrlToFilePath(accountInfo.UserName) == relativeFilePath)
                                 select localFile).ToList();


            //Set the status of missing files to Conflict
            foreach (var item in filesToDelete)
            {
                //Try to acquire a gate on the file, to take into account files that have been dequeued
                //and are being processed
                using (var gate = NetworkGate.Acquire(item.FullName, NetworkOperation.Deleting))
                {
                    if (gate.Failed)
                        continue;
                    StatusKeeper.SetFileState(item.FullName, FileStatus.Conflict, FileOverlayStatus.Deleted,
                                              "Local file missing from server");
                }
            }
            UpdateStatus(PithosStatus.HasConflicts);
            StatusNotification.NotifyConflicts(filesToDelete,
                                               String.Format(
                                                   "{0} local files are missing from Pithos, possibly because they were deleted",
                                                   filesToDelete.Count));
            StatusNotification.NotifyForFiles(filesToDelete, String.Format("{0} files were deleted", filesToDelete.Count),
                                              TraceLevel.Info);
        }

        private void ReportConflictForMismatch(string localFilePath)
        {
            if (String.IsNullOrWhiteSpace(localFilePath))
                throw new ArgumentNullException("localFilePath");
            Contract.EndContractBlock();

            StatusKeeper.SetFileState(localFilePath, FileStatus.Conflict, FileOverlayStatus.Conflict, "File changed at the server");
            UpdateStatus(PithosStatus.HasConflicts);
            var message = String.Format("Conflict detected for file {0}", localFilePath);
            Log.Warn(message);
            StatusNotification.NotifyChange(message, TraceLevel.Warning);
        }



        /// <summary>
        /// Creates a Sync action for each changed server file
        /// </summary>
        /// <param name="accountInfo"></param>
        /// <param name="changes"></param>
        /// <returns></returns>
        private IEnumerable<CloudAction> ChangesToActions(AccountInfo accountInfo, IEnumerable<ObjectInfo> changes)
        {
            if (changes == null)
                throw new ArgumentNullException();
            Contract.EndContractBlock();
            var fileAgent = FileAgent.GetFileAgent(accountInfo);

            //In order to avoid multiple iterations over the files, we iterate only once
            //over the remote files
            foreach (var objectInfo in changes)
            {
                var relativePath = objectInfo.RelativeUrlToFilePath(accountInfo.UserName);
                //If a directory object already exists, we may need to sync it
                if (fileAgent.Exists(relativePath))
                {
                    var localFile = fileAgent.GetFileSystemInfo(relativePath);
                    //We don't need to sync directories
                    if (objectInfo.IsDirectory && localFile is DirectoryInfo)
                        continue;
                    using (new SessionScope(FlushAction.Never))
                    {
                        var state = StatusKeeper.GetStateByFilePath(localFile.FullName);
                        _lastSeen[localFile.FullName] = DateTime.Now;
                        //Common files should be checked on a per-case basis to detect differences, which is newer

                        yield return new CloudAction(accountInfo, CloudActionType.MustSynch,
                                                     localFile, objectInfo, state, accountInfo.BlockSize,
                                                     accountInfo.BlockHash,"Poll Changes");
                    }
                }
                else
                {
                    //Remote files should be downloaded
                    yield return new CloudDownloadAction(accountInfo, objectInfo,"Poll Changes");
                }
            }
        }

        /// <summary>
        /// Creates a Local Move action for each moved server file
        /// </summary>
        /// <param name="accountInfo"></param>
        /// <param name="moves"></param>
        /// <returns></returns>
        private IEnumerable<CloudAction> MovesToActions(AccountInfo accountInfo, IEnumerable<ObjectInfo> moves)
        {
            if (moves == null)
                throw new ArgumentNullException();
            Contract.EndContractBlock();
            var fileAgent = FileAgent.GetFileAgent(accountInfo);

            //In order to avoid multiple iterations over the files, we iterate only once
            //over the remote files
            foreach (var objectInfo in moves)
            {
                var previousRelativepath = objectInfo.Previous.RelativeUrlToFilePath(accountInfo.UserName);
                //If the previous file already exists, we can execute a Move operation
                if (fileAgent.Exists(previousRelativepath))
                {
                    var previousFile = fileAgent.GetFileSystemInfo(previousRelativepath);
                    using (new SessionScope(FlushAction.Never))
                    {
                        var state = StatusKeeper.GetStateByFilePath(previousFile.FullName);
                        _lastSeen[previousFile.FullName] = DateTime.Now;

                        //For each moved object we need to move both the local file and update                                                
                        yield return new CloudAction(accountInfo, CloudActionType.RenameLocal,
                                                     previousFile, objectInfo, state, accountInfo.BlockSize,
                                                     accountInfo.BlockHash,"Poll Moves");
                        //For modified files, we need to download the changes as well
                        if (objectInfo.X_Object_Hash != objectInfo.PreviousHash)
                            yield return new CloudDownloadAction(accountInfo,objectInfo, "Poll Moves");
                    }
                }
                //If the previous file does not exist, we need to download it in the new location
                else
                {
                    //Remote files should be downloaded
                    yield return new CloudDownloadAction(accountInfo, objectInfo, "Poll Moves");
                }
            }
        }


        /// <summary>
        /// Creates a download action for each new server file
        /// </summary>
        /// <param name="accountInfo"></param>
        /// <param name="creates"></param>
        /// <returns></returns>
        private IEnumerable<CloudAction> CreatesToActions(AccountInfo accountInfo, IEnumerable<ObjectInfo> creates)
        {
            if (creates == null)
                throw new ArgumentNullException();
            Contract.EndContractBlock();
            var fileAgent = FileAgent.GetFileAgent(accountInfo);

            //In order to avoid multiple iterations over the files, we iterate only once
            //over the remote files
            foreach (var objectInfo in creates)
            {
                if (Log.IsDebugEnabled)
                    Log.DebugFormat("[NEW INFO] {0}",objectInfo.Uri);

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

                //If the object already exists, we should check before uploading or downloading
                if (fileAgent.Exists(relativePath))
                {
                    var localFile= fileAgent.GetFileSystemInfo(relativePath);
                    var state = StatusKeeper.GetStateByFilePath(localFile.WithProperCapitalization().FullName);
                    yield return new CloudAction(accountInfo, CloudActionType.MustSynch,
                                                     localFile, objectInfo, state, accountInfo.BlockSize,
                                                     accountInfo.BlockHash,"Poll Creates");                    
                }
                else
                {
                    //Remote files should be downloaded
                    yield return new CloudDownloadAction(accountInfo, objectInfo,"Poll Creates");
                }

            }
        }

        /// <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);
        }

        public void SetSelectivePaths(AccountInfo accountInfo,Uri[] added, Uri[] removed)
        {
            AbortRemovedPaths(accountInfo,removed);
            //DownloadNewPaths(accountInfo,added);
        }

/*
        private void DownloadNewPaths(AccountInfo accountInfo, Uri[] added)
        {
            var client = new CloudFilesClient(accountInfo);
            foreach (var folderUri in added)
            {
                try
                {

                    string account;
                    string container;
                    var segmentsCount = folderUri.Segments.Length;
                    //Is this an account URL?
                    if (segmentsCount < 3)
                        continue;
                    //Is this a container or  folder URL?
                    if (segmentsCount == 3)
                    {
                        account = folderUri.Segments[1].TrimEnd('/');
                        container = folderUri.Segments[2].TrimEnd('/');
                    }
                    else
                    {
                        account = folderUri.Segments[2].TrimEnd('/');
                        container = folderUri.Segments[3].TrimEnd('/');
                    }
                    IList<ObjectInfo> items;
                    if (segmentsCount > 3)
                    {
                        //List folder
                        var folder = String.Join("", folderUri.Segments.Splice(4));
                        items = client.ListObjects(account, container, folder);
                    }
                    else
                    {
                        //List container
                        items = client.ListObjects(account, container);
                    }
                    var actions = CreatesToActions(accountInfo, items);
                    foreach (var action in actions)
                    {
                        NetworkAgent.Post(action);
                    }
                }
                catch (Exception exc)
                {
                    Log.WarnFormat("Listing of new selective path [{0}] failed with \r\n{1}", folderUri, exc);
                }
            }

            //Need to get a listing of each of the URLs, then post them to the NetworkAgent
            //CreatesToActions(accountInfo,)

/*            NetworkAgent.Post();#1#
        }
*/

        private void AbortRemovedPaths(AccountInfo accountInfo, Uri[] removed)
        {
            /*this.NetworkAgent.*/
        }
    }
}