#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.Set();                

            //_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));            
        }

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

                    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, moves,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 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 = 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 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<DateTime?> ProcessAccountFiles(AccountInfo accountInfo, IEnumerable<string> accountBatch, ConcurrentDictionary<string, MovedEventArgs> moves, 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 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
                var nextSince = since;

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

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

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

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

                        //Get all non-trash objects. Remember, the container name is stored in AsyncState
                        var remoteObjects = (from objectList in listTasks
                                            where (string)objectList.AsyncState.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();

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

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

                        //May have to wait if the FileAgent has asked for a Pause, due to local changes
                        await _unPauseEvent.WaitAsync().ConfigureAwait(false);

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


                        var states = StatusKeeper.GetAllStates();
                        
                        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,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);

                            //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 (!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}",
                                                               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}",
                                                               localInfo.Name))
                            {
                                var targetPath = MoveForServerMove(accountInfo, tuple);
                                if (targetPath != null)
                                {

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

                                    AddOwnFolderToSelectives(accountInfo, tuple, targetPath);
                                }
                            }

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

                    //Local changes found

                    //Server unchanged?
                    if (tuple.S == tuple.L)
                    {
                        //The FileAgent selective sync checks for new root folder files
                        if (!agent.Ignore(localFilePath))
                        {
                            if ((tuple.C == null || !localInfo.Exists) && tuple.ObjectInfo != null)
                            {
                                //deleteObjectFromServer()
                                DeleteCloudFile(accountInfo, tuple);
                                //updateRecord( Remove L, S)                  
                            }
                            else
                            {
                                //uploadLocalObject() // Result: S = C, L = S                        
                                var progress = new Progress<double>(d =>
                                    StatusNotification.Notify(new StatusNotification(String.Format("Merkle Hashing for Upload {0:p} of {1}", d, localInfo.Name))));

                                //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 (!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()
                                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)
        {
            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, Progress<double> 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}",
                                                  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 bool MoveForLocalMove(AccountInfo accountInfo, StateTuple tuple)
        {
            //Is the file a directory or previous path missing?
            if (tuple.FileInfo is DirectoryInfo)
                return false;
            //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);
                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}", tuple.FileInfo.Name))
                {
                    client.MoveObject(objectInfo.Account, objectInfo.Container, oldName.ToEscapedUri(),
                                                          objectInfo.Container, objectInfo.Name);
                }
                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}", 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 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, 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());
        }


        /*
         *                 //Use the queue to retry locked file hashing
                var fileQueue = new ConcurrentQueue<FileSystemInfo>(localInfos);
                

                var results = new List<Tuple<FileSystemInfo, string>>();
                var backoff = 0;
                while (fileQueue.Count > 0)
                {
                    FileSystemInfo file;
                    fileQueue.TryDequeue(out file);
                    using (ThreadContext.Stacks["File"].Push(file.FullName))
                    {
                        try
                        {
                            //Replace MD5 here, do the calc while syncing individual files
                            string hash ;
                            if (file is DirectoryInfo)
                                hash = MD5_EMPTY;
                            else
                            {
                                //Wait in case the FileAgent has requested a Pause
                                await _unPauseEvent.WaitAsync().ConfigureAwait(false);
                                
                                using (StatusNotification.GetNotifier("Hashing {0}", "", file.Name))
                                {
                                    hash = ((FileInfo)file).ComputeShortHash(StatusNotification);
                                    backoff = 0;
                                }
                            }                            
                            results.Add(Tuple.Create(file, hash));
                        }
                        catch (IOException exc)
                        {
                            Log.WarnFormat("[HASH] File in use, will retry [{0}]", exc);
                            fileQueue.Enqueue(file);
                            //If this is the only enqueued file                            
                            if (fileQueue.Count != 1) continue;
                            
                            
                            //Increase delay
                            if (backoff<60000)
                                backoff += 10000;
                            //Pause Polling for the specified time
                        }
                        if (backoff>0)
                            await PauseFor(backoff).ConfigureAwait(false);
                    }
                }

                return results;

         */
        private IEnumerable<StateTuple> MergeSources(IEnumerable<Tuple<string, ObjectInfo>> infos, IEnumerable<FileSystemInfo> files, List<FileState> states, ConcurrentDictionary<string, MovedEventArgs> moves)
        {
            var tuplesByPath = new Dictionary<string, StateTuple>();
            foreach (var info in files)
            {
                var tuple = new StateTuple(info);
                //Is this the target of a move event?
                var moveArg = moves.Values.FirstOrDefault(arg => info.FullName.Equals(arg.FullPath, StringComparison.InvariantCultureIgnoreCase) 
                    || info.FullName.IsAtOrBelow(arg.FullPath));
                if (moveArg != null)
                {
                    tuple.NewFullPath = info.FullName;
                    var relativePath = info.AsRelativeTo(moveArg.FullPath);                    
                    tuple.OldFullPath = Path.Combine(moveArg.OldFullPath, relativePath);
                    tuple.OldChecksum = states.FirstOrDefault(st => st.FilePath.Equals(tuple.OldFullPath, StringComparison.InvariantCultureIgnoreCase))
                                .NullSafe(st => st.Checksum);
                }

                tuplesByPath[tuple.FilePath] = tuple;
            }
            

            
            
            //For files that have state
            foreach (var state in states)
            {
                StateTuple hashTuple;

                
                if (tuplesByPath.TryGetValue(state.FilePath, out hashTuple))
                {
                    hashTuple.FileState = state;
                    UpdateHashes(hashTuple);
                }
                else if (moves.ContainsKey(state.FilePath) && tuplesByPath.TryGetValue(moves[state.FilePath].FullPath, out hashTuple))
                {
                    hashTuple.FileState = state;
                    UpdateHashes(hashTuple);
                }
                else
                {
                    var fsInfo = FileInfoExtensions.FromPath(state.FilePath);
                    hashTuple = new StateTuple {FileInfo = fsInfo, FileState = state};

                    //Is the source of a moved item?
                    var moveArg = moves.Values.FirstOrDefault(arg => state.FilePath.Equals(arg.OldFullPath,StringComparison.InvariantCultureIgnoreCase) 
                        || state.FilePath.IsAtOrBelow(arg.OldFullPath));
                    if (moveArg != null)
                    {
                        var relativePath = state.FilePath.AsRelativeTo(moveArg.OldFullPath);
                        hashTuple.NewFullPath = Path.Combine(moveArg.FullPath,relativePath);
                        hashTuple.OldFullPath = state.FilePath;
                        //Do we have the old MD5?
                        //hashTuple.OldMD5 = state.LastMD5;
                    }


                    tuplesByPath[state.FilePath] = hashTuple;
                }
            }
            //for files that don't have state
            foreach (var tuple in tuplesByPath.Values.Where(t => t.FileState == null))
            {
                UpdateHashes(tuple);
            }

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

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

                if (objectID != _emptyGuid &&  tuplesByID.TryGetValue(objectID, out hashTuple))
                {
                    hashTuple.ObjectInfo = objectInfo;                    
                }
                else if (tuplesByPath.TryGetValue(filePath, out hashTuple))
                {
                    hashTuple.ObjectInfo = objectInfo;
                }
                else
                {

                    
                    var fsInfo = FileInfoExtensions.FromPath(filePath);
                    hashTuple= new StateTuple {FileInfo = fsInfo, ObjectInfo = objectInfo};
                    tuplesByPath[filePath] = hashTuple;
                    
                    if (objectInfo.UUID!=_emptyGuid)
                        tuplesByID[objectInfo.UUID] = hashTuple;
                }
            }

            var tuples = tuplesByPath.Values;
            var brokenTuples = from tuple in tuples
                               where tuple.FileState != null && tuple.FileState.Checksum == null
                                    && tuple.ObjectInfo != null && (tuple.FileInfo==null || !tuple.FileInfo.Exists)
                               select tuple;
            var actualTuples = tuples.Except(brokenTuples);
            Debug.Assert(actualTuples.All(t => t.HashesValid()));

            foreach (var tuple in brokenTuples)
            {
                StatusKeeper.SetFileState(tuple.FileState.FilePath, 
                    FileStatus.Conflict, FileOverlayStatus.Conflict, "FileState without checksum encountered for server object missing from disk");    
            }
                                   
            return actualTuples;
        }

        
        /// <summary>
        /// Update the tuple with the file's hashes, avoiding calculation if the file is unchanged
        /// </summary>
        /// <param name="hashTuple"></param>
        /// <remarks>
        /// The function first checks the file's size and last write date to see if there are any changes. If there are none,
        /// the file's stored hashes are used.
        /// Otherwise, MD5 is calculated first to ensure there are no changes. If MD5 is different, the Merkle hash is calculated
        /// </remarks>
        private void  UpdateHashes(StateTuple hashTuple)
        {
            
            try
            {
                var state = hashTuple.NullSafe(s => s.FileState);
                var storedHash = state.NullSafe(s => s.Checksum);
                var storedHashes = state.NullSafe(s => s.Hashes);
                //var storedMD5 = state.NullSafe(s => s.LastMD5);
                var storedDate = state.NullSafe(s => s.LastWriteDate) ?? DateTime.MinValue;
                var storedLength = state.NullSafe(s => s.LastLength);

                //var md5Hash = Signature.MD5_EMPTY;                
                var merkle=TreeHash.Empty;

                if (hashTuple.FileInfo is FileInfo)
                {
                    var file = (FileInfo)hashTuple.FileInfo.WithProperCapitalization();
                    
                    //Attributes unchanged?
                    //LastWriteTime is only accurate to the second
                    var unchangedAttributes = file.LastWriteTime - storedDate < TimeSpan.FromSeconds(1) 
                        && storedLength == file.Length;
                    
                    //Attributes appear unchanged but the file length doesn't match the stored hash ?
                    var nonEmptyMismatch = unchangedAttributes && 
                        (file.Length == 0 ^ storedHash== Signature.MERKLE_EMPTY);

                    //Missing hashes for NON-EMPTY hash ?
                    var missingHashes = storedHash != Signature.MERKLE_EMPTY &&
                        String.IsNullOrWhiteSpace(storedHashes);

                    //Unchanged attributes but changed MD5 
                    //Short-circuiting ensures MD5 is computed only if the attributes are changed
                    
                    //var md5Mismatch = (!unchangedAttributes && file.ComputeShortHash(StatusNotification) != storedMD5);


                    //If the attributes are unchanged but the Merkle doesn't match the size,
                    //or the attributes and the MD5 hash have changed, 
                    //or the hashes are missing but the tophash is NOT empty, we need to recalculate
                    //
                    //Otherwise we load the hashes from state
                    if (!unchangedAttributes || nonEmptyMismatch || missingHashes)
                        merkle = RecalculateTreehash(file);
                    else
                    {
                        merkle=TreeHash.Parse(hashTuple.FileState.Hashes);
                        //merkle.MD5 = storedMD5;
                    }


                    //md5Hash = merkle.MD5;
                }
                //hashTuple.MD5 = md5Hash;
                //Setting Merkle also updates C
                hashTuple.Merkle = merkle;
            }
            catch (IOException)
            {
                hashTuple.Locked = true;
            }            
        }

        /// <summary>
        /// Recalculate a file's treehash and md5 and update the database
        /// </summary>
        /// <param name="file"></param>
        /// <returns></returns>
        private TreeHash RecalculateTreehash(FileInfo file)
        {
            var progress = new Progress<double>(d =>StatusNotification.Notify(
                                                    new StatusNotification(String.Format("Hashing {0} of {1}", d, file.Name))));
            var merkle = Signature.CalculateTreeHash(file, StatusKeeper.BlockSize, 
                StatusKeeper.BlockHash,CancellationToken, progress);
            
            StatusKeeper.UpdateFileHashes(file.FullName, merkle);
            return merkle;
        }

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

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

        readonly AccountsDifferencer _differencer = new AccountsDifferencer();
        private bool _pause;
        private readonly string _emptyGuid = Guid.Empty.ToString();



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

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

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

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