[pithos-ms-client] / trunk / Pithos.Core / Agents / NetworkAgent.cs

// -----------------------------------------------------------------------
// <copyright file="NetworkAgent.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
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// 
//   1. Redistributions of source code must retain the above
//      copyright notice, this list of conditions and the following
//      disclaimer.
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//      copyright notice, this list of conditions and the following
//      disclaimer in the documentation and/or other materials
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using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.ComponentModel.Composition;
using System.Diagnostics;
using System.Diagnostics.Contracts;
using System.IO;
using System.Linq;
using System.Net;
using System.Threading;
using System.Threading.Tasks;
using System.Threading.Tasks.Dataflow;
using Castle.ActiveRecord;
using Pithos.Interfaces;
using Pithos.Network;
using log4net;

namespace Pithos.Core.Agents
{
    //TODO: Ensure all network operations use exact casing. Pithos is case sensitive
    [Export]
    public class NetworkAgent
    {
        private Agent<CloudAction> _agent;

        //A separate agent is used to execute delete actions immediatelly;
        private ActionBlock<CloudDeleteAction> _deleteAgent;
        readonly ConcurrentDictionary<string,DateTime> _deletedFiles=new ConcurrentDictionary<string, DateTime>();


        private readonly ManualResetEventSlim _pauseAgent = new ManualResetEventSlim(true);

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

        private static readonly ILog Log = LogManager.GetLogger("NetworkAgent");

        private readonly ConcurrentBag<AccountInfo> _accounts = new ConcurrentBag<AccountInfo>();

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

        private bool _firstPoll = true;
        private TaskCompletionSource<bool> _tcs;
        private ConcurrentDictionary<string,DateTime> _lastSeen=new ConcurrentDictionary<string, DateTime>();

        public void Start()
        {
            _firstPoll = true;
            _agent = Agent<CloudAction>.Start(inbox =>
            {
                Action loop = null;
                loop = () =>
                {
                    _pauseAgent.Wait();
                    var message = inbox.Receive();
                    var process=message.Then(Process,inbox.CancellationToken);
                    inbox.LoopAsync(process, loop);
                };
                loop();
            });

            _deleteAgent = new ActionBlock<CloudDeleteAction>(message =>ProcessDelete(message),new ExecutionDataflowBlockOptions{MaxDegreeOfParallelism=4});
            /*
                Action loop = null;
                loop = () =>
                            {
                                var message = inbox.Receive();
                                var process = message.Then(ProcessDelete,inbox.CancellationToken);
                                inbox.LoopAsync(process, loop);
                            };
                loop();
*/

        }

        private async Task Process(CloudAction action)
        {
            if (action == null)
                throw new ArgumentNullException("action");
            if (action.AccountInfo==null)
                throw new ArgumentException("The action.AccountInfo is empty","action");
            Contract.EndContractBlock();

            UpdateStatus(PithosStatus.Syncing);
            var accountInfo = action.AccountInfo;

            using (log4net.ThreadContext.Stacks["NETWORK"].Push("PROCESS"))
            {                
                Log.InfoFormat("[ACTION] Start Processing {0}", action);

                var cloudFile = action.CloudFile;
                var downloadPath = action.GetDownloadPath();

                try
                {                    
                    if (action.Action == CloudActionType.DeleteCloud)
                    {                        
                        //Redirect deletes to the delete agent 
                        _deleteAgent.Post((CloudDeleteAction)action);
                    }
                    if (IsDeletedFile(action))
                    {
                        //Clear the status of already deleted files to avoid reprocessing
                        if (action.LocalFile != null)
                            this.StatusKeeper.ClearFileStatus(action.LocalFile.FullName);
                    }
                    else
                    {
                        switch (action.Action)
                        {
                            case CloudActionType.UploadUnconditional:
                                //Abort if the file was deleted before we reached this point
                                await UploadCloudFile(action);
                                break;
                            case CloudActionType.DownloadUnconditional:
                                await DownloadCloudFile(accountInfo, cloudFile, downloadPath);
                                break;
                            case CloudActionType.RenameCloud:
                                var moveAction = (CloudMoveAction)action;
                                RenameCloudFile(accountInfo, moveAction);
                                break;
                            case CloudActionType.MustSynch:
                                if (!File.Exists(downloadPath) && !Directory.Exists(downloadPath))
                                {
                                    await DownloadCloudFile(accountInfo, cloudFile, downloadPath);
                                }
                                else
                                {
                                    await SyncFiles(accountInfo, action);
                                }
                                break;
                        }
                    }
                    Log.InfoFormat("[ACTION] End Processing {0}:{1}->{2}", action.Action, action.LocalFile,
                                           action.CloudFile.Name);
                }
                catch (WebException exc)
                {
                    Log.ErrorFormat("[WEB ERROR] {0} : {1} -> {2} due to exception\r\n{3}", action.Action, action.LocalFile, action.CloudFile, exc);
                }
                catch (OperationCanceledException)
                {
                    throw;
                }
                catch (DirectoryNotFoundException)
                {
                    Log.ErrorFormat("{0} : {1} -> {2}  failed because the directory was not found.\n Rescheduling a delete",
                        action.Action, action.LocalFile, action.CloudFile);
                    //Post a delete action for the missing file
                    Post(new CloudDeleteAction(action));
                }
                catch (FileNotFoundException)
                {
                    Log.ErrorFormat("{0} : {1} -> {2}  failed because the file was not found.\n Rescheduling a delete",
                        action.Action, action.LocalFile, action.CloudFile);
                    //Post a delete action for the missing file
                    Post(new CloudDeleteAction(action));
                }
                catch (Exception exc)
                {
                    Log.ErrorFormat("[REQUEUE] {0} : {1} -> {2} due to exception\r\n{3}",
                                     action.Action, action.LocalFile, action.CloudFile, exc);

                    _agent.Post(action);
                }
                finally
                {
                    UpdateStatus(PithosStatus.InSynch);                    
                }
            }
        }

        private void UpdateStatus(PithosStatus status)
        {
            StatusKeeper.SetPithosStatus(status);
            StatusNotification.Notify(new Notification());
        }

        /// <summary>
        /// Processes cloud delete actions
        /// </summary>
        /// <param name="action">The delete action to execute</param>
        /// <returns></returns>
        /// <remarks>
        /// When a file/folder is deleted locally, we must delete it ASAP from the server and block any download
        /// operations that may be in progress.
        /// <para>
        /// A separate agent is used to process deletes because the main agent may be busy with a long operation.
        /// </para>
        /// </remarks>
        private async Task ProcessDelete(CloudDeleteAction action)
        {
            if (action == null)
                throw new ArgumentNullException("action");
            if (action.AccountInfo==null)
                throw new ArgumentException("The action.AccountInfo is empty","action");
            Contract.EndContractBlock();

            var accountInfo = action.AccountInfo;

            using (log4net.ThreadContext.Stacks["NETWORK"].Push("PROCESS"))
            {                
                Log.InfoFormat("[ACTION] Start Processing {0}", action);

                var cloudFile = action.CloudFile;

                try
                {
                    //Acquire a lock on the deleted file to prevent uploading/downloading operations from the normal
                    //agent
                    using (var gate = NetworkGate.Acquire(action.LocalFile.FullName, NetworkOperation.Deleting))
                    {

                        //Add the file URL to the deleted files list
                        var key = GetFileKey(action.CloudFile);
                        _deletedFiles[key] = DateTime.Now;

                        _pauseAgent.Reset();
                        // and then delete the file from the server
                                DeleteCloudFile(accountInfo, cloudFile);

                        Log.InfoFormat("[ACTION] End Delete {0}:{1}->{2}", action.Action, action.LocalFile,
                                       action.CloudFile.Name);
                    }
                }
                catch (WebException exc)
                {
                    Log.ErrorFormat("[WEB ERROR] {0} : {1} -> {2} due to exception\r\n{3}", action.Action, action.LocalFile, action.CloudFile, exc);
                }
                catch (OperationCanceledException)
                {
                    throw;
                }
                catch (DirectoryNotFoundException)
                {
                    Log.ErrorFormat("{0} : {1} -> {2}  failed because the directory was not found.\n Rescheduling a delete",
                        action.Action, action.LocalFile, action.CloudFile);
                    //Repost a delete action for the missing file
                    _deleteAgent.Post(action);
                }
                catch (FileNotFoundException)
                {
                    Log.ErrorFormat("{0} : {1} -> {2}  failed because the file was not found.\n Rescheduling a delete",
                        action.Action, action.LocalFile, action.CloudFile);
                    //Post a delete action for the missing file
                    _deleteAgent.Post(action);
                }
                catch (Exception exc)
                {
                    Log.ErrorFormat("[REQUEUE] {0} : {1} -> {2} due to exception\r\n{3}",
                                     action.Action, action.LocalFile, action.CloudFile, exc);

                    _deleteAgent.Post(action);
                }
                finally
                {
                    //Set the event when all delete actions are processed
                    if (_deleteAgent.InputCount == 0)
                        _pauseAgent.Set();

                }
            }
        }

        private static string GetFileKey(ObjectInfo info)
        {
            var key = String.Format("{0}/{1}/{2}", info.Account, info.Container,info.Name);
            return key;
        }

        private async Task SyncFiles(AccountInfo accountInfo,CloudAction action)
        {
            if (accountInfo == null)
                throw new ArgumentNullException("accountInfo");
            if (action==null)
                throw new ArgumentNullException("action");
            if (action.LocalFile==null)
                throw new ArgumentException("The action's local file is not specified","action");
            if (!Path.IsPathRooted(action.LocalFile.FullName))
                throw new ArgumentException("The action's local file path must be absolute","action");
            if (action.CloudFile== null)
                throw new ArgumentException("The action's cloud file is not specified", "action");
            Contract.EndContractBlock();

            var localFile = action.LocalFile;
            var cloudFile = action.CloudFile;
            var downloadPath=action.LocalFile.GetProperCapitalization();

            var cloudHash = cloudFile.Hash.ToLower();
            var localHash = action.LocalHash.Value.ToLower();
            var topHash = action.TopHash.Value.ToLower();

            //Not enough to compare only the local hashes, also have to compare the tophashes
            
            //If any of the hashes match, we are done
            if ((cloudHash == localHash || cloudHash == topHash))
            {
                Log.InfoFormat("Skipping {0}, hashes match",downloadPath);
                return;
            }

            //The hashes DON'T match. We need to sync
            var lastLocalTime = localFile.LastWriteTime;
            var lastUpTime = cloudFile.Last_Modified;
            
            //If the local file is newer upload it
            if (lastUpTime <= lastLocalTime)
            {
                //It probably means it was changed while the app was down                        
                UploadCloudFile(action);
            }
            else
            {
                //It the cloud file has a later date, it was modified by another user or computer.
                //We need to check the local file's status                
                var status = StatusKeeper.GetFileStatus(downloadPath);
                switch (status)
                {
                    case FileStatus.Unchanged:                        
                        //If the local file's status is Unchanged, we can go on and download the newer cloud file
                        await DownloadCloudFile(accountInfo,cloudFile,downloadPath);
                        break;
                    case FileStatus.Modified:
                        //If the local file is Modified, we may have a conflict. In this case we should mark the file as Conflict
                        //We can't ensure that a file modified online since the last time will appear as Modified, unless we 
                        //index all files before we start listening.                       
                    case FileStatus.Created:
                        //If the local file is Created, it means that the local and cloud files aren't related,
                        // yet they have the same name.

                        //In both cases we must mark the file as in conflict
                        ReportConflict(downloadPath);
                        break;
                    default:
                        //Other cases should never occur. Mark them as Conflict as well but log a warning
                        ReportConflict(downloadPath);
                        Log.WarnFormat("Unexcepted status {0} for file {1}->{2}", status,
                                       downloadPath, action.CloudFile.Name);
                        break;
                }
            }
        }

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

            StatusKeeper.SetFileOverlayStatus(downloadPath, FileOverlayStatus.Conflict);
            UpdateStatus(PithosStatus.HasConflicts);
            var message = String.Format("Conflict detected for file {0}", downloadPath);
            Log.Warn(message);
            StatusNotification.NotifyChange(message, TraceLevel.Warning);
        }

        public void Post(CloudAction cloudAction)
        {
            if (cloudAction == null)
                throw new ArgumentNullException("cloudAction");
            if (cloudAction.AccountInfo==null)
                throw new ArgumentException("The CloudAction.AccountInfo is empty","cloudAction");
            Contract.EndContractBlock();

            _pauseAgent.Wait();

            //If the action targets a local file, add a treehash calculation
            if (!(cloudAction is CloudDeleteAction) && cloudAction.LocalFile as FileInfo != null)
            {
                var accountInfo = cloudAction.AccountInfo;
                var localFile = (FileInfo) cloudAction.LocalFile;
                if (localFile.Length > accountInfo.BlockSize)
                    cloudAction.TopHash =
                        new Lazy<string>(() => Signature.CalculateTreeHashAsync(localFile,
                                                                                accountInfo.BlockSize,
                                                                                accountInfo.BlockHash).Result
                                                    .TopHash.ToHashString());
                else
                {
                    cloudAction.TopHash = new Lazy<string>(() => cloudAction.LocalHash.Value);
                }
            }
            else
            {
                //The hash for a directory is the empty string
                cloudAction.TopHash = new Lazy<string>(() => String.Empty);
            }
            
            if (cloudAction is CloudDeleteAction)
                _deleteAgent.Post((CloudDeleteAction)cloudAction);
            else
                _agent.Post(cloudAction);
        }

       /* class ObjectInfoByNameComparer:IEqualityComparer<ObjectInfo>
        {
            public bool Equals(ObjectInfo x, ObjectInfo y)
            {
                return x.Name.Equals(y.Name,StringComparison.InvariantCultureIgnoreCase);
            }

            public int GetHashCode(ObjectInfo obj)
            {
                return obj.Name.ToLower().GetHashCode();
            }
        }*/

        public void SynchNow()
        {             
            if (_tcs!=null)
                _tcs.TrySetResult(true);
            else
            {
                //TODO: This may be OK for testing purposes, but we have no guarantee that it will
                //work properly in production
                PollRemoteFiles(repeat:false);
            }
        }

        //Remote files are polled periodically. Any changes are processed
        public async Task PollRemoteFiles(DateTime? since = null,bool repeat=true)
        {
            UpdateStatus(PithosStatus.Syncing);
            StatusNotification.Notify(new PollNotification());

            using (log4net.ThreadContext.Stacks["Retrieve Remote"].Push("All accounts"))
            {
                //If this poll fails, we will retry with the same since value
                var nextSince = since;
                try
                {
                    //Next time we will check for all changes since the current check minus 1 second
                    //This is done to ensure there are no discrepancies due to clock differences
                    DateTime current = DateTime.Now.AddSeconds(-1);

                    var tasks = from accountInfo in _accounts
                                select ProcessAccountFiles(accountInfo, since);

                    await TaskEx.WhenAll(tasks.ToList());
                                        
                    _firstPoll = false;
                    //Reschedule the poll with the current timestamp as a "since" value
                    if (repeat)
                        nextSince = current;
                    else
                        return;
                }
                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.InSynch);
                //Wait for the polling interval to pass or the Manual flat to be toggled
                nextSince = await WaitForScheduledOrManualPoll(nextSince);

                PollRemoteFiles(nextSince);

            }
        }

        private async Task<DateTime?> WaitForScheduledOrManualPoll(DateTime? since)
        {            
            _tcs = new TaskCompletionSource<bool>();
            var wait = TaskEx.Delay(TimeSpan.FromSeconds(Settings.PollingInterval), _agent.CancellationToken);
            var signaledTask = await TaskEx.WhenAny(_tcs.Task, wait);
            //If polling is signalled by SynchNow, ignore the since tag
            if (signaledTask is Task<bool>)
                return null;
            return since;
        }

        public async Task ProcessAccountFiles(AccountInfo accountInfo,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 (log4net.ThreadContext.Stacks["Retrieve Remote"].Push(accountInfo.UserName))
            {
                _pauseAgent.Wait();

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

                var containers = client.ListContainers(accountInfo.UserName);


                CreateContainerFolders(accountInfo, containers);

                try
                {
                    _pauseAgent.Wait();
                    //Get the poll time now. We may miss some deletions but it's better to keep a file that was deleted
                    //than delete a file that was created while we were executing the poll                    
                    var pollTime = DateTime.Now;
                    
                    //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 (log4net.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
                                            select obj;

                        //TODO: Change the way deleted objects are detected.
                        //The list operation returns all existing objects so we could detect deleted remote objects
                        //by detecting objects that exist only locally. There are several cases where this is NOT the case:
                        //1.    The first time the application runs, as there may be files that were added while 
                        //      the application was down.
                        //2.    An object that is currently being uploaded will not appear in the remote list
                        //      until the upload finishes.
                        //      SOLUTION 1: Check the upload/download queue for the file
                        //      SOLUTION 2: Check the SQLite states for the file's entry. If it is being uploaded, 
                        //          or its last modification was after the current poll, don't delete it. This way we don't
                        //          delete objects whose upload finished too late to be included in the list.
                        //We need to detect and protect against such situations
                        //TODO: Does FileState have a LastModification field?
                        //TODO: How do we update the LastModification field? Do we need to add SQLite triggers?
                        //      Do we need to use a proper SQLite schema?
                        //      We can create a trigger with 
                        // CREATE TRIGGER IF NOT EXISTS update_last_modified UPDATE ON FileState FOR EACH ROW
                        //  BEGIN
                        //      UPDATE FileState SET LastModification=datetime('now')  WHERE Id=old.Id;
                        //  END;
                        //
                        //NOTE: Some files may have been deleted remotely while the application was down. 
                        //  We DO have to delete those files. Checking the trash makes it easy to detect them,
                        //  Otherwise, we can't be really sure whether we need to upload or delete 
                        //  the local-only files.
                        //  SOLUTION 1: Ask the user when such a local-only file is detected during the first poll.
                        //  SOLUTION 2: Mark conflict and ask the user as in #1

                        var trashObjects = dict["trash"].Result;
                        var sharedObjects = dict["shared"].Result;

                        //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)
                                        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();



                        ProcessDeletedFiles(accountInfo, cleanRemotes, pollTime);

                        //Create a list of actions from the remote files
                        var allActions = ObjectsToActions(accountInfo, cleanRemotes);

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

                        //And remove those that are already being processed by the agent
                        var distinctActions = allActions
                            .Except(_agent.GetEnumerable(), new PithosMonitor.LocalFileComparer())
                            .ToList();

                        //Queue all the actions
                        foreach (var message in distinctActions)
                        {
                            Post(message);
                        }

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

                Log.Info("[LISTENER] Finished");

            }
        }

        /// <summary>
        /// Deletes local files that are not found in the list of cloud files
        /// </summary>
        /// <param name="accountInfo"></param>
        /// <param name="cloudFiles"></param>
        /// <param name="pollTime"></param>
        private void ProcessDeletedFiles(AccountInfo accountInfo, IEnumerable<ObjectInfo> cloudFiles, DateTime pollTime)
        {
            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();

            //Check the Modified date to ensure that were just created and haven't been uploaded yet
            //NOTE: The NHibernate LINQ provider doesn't support custom functions so we need to break the query 
            //in two steps
            //NOTE: DON'T return files that are already in conflict. The first poll would mark them as 
            //"In Conflict" but subsequent polls would delete them
/*            var t=FileState.Find(new Guid("{cd664c9a-5f17-47c9-b27f-3bcbcb0595ff}"));

            var d0 = FileState.Queryable
                .Where(state => 
                            state.FilePath.StartsWith(accountInfo.AccountPath)).ToList();
            
            var d1 = FileState.Queryable
                .Where(state => state.Modified <= pollTime).ToList();
            var d2= FileState.Queryable
                .Where(state => state.Modified <= pollTime
                            &&
                            state.FilePath.StartsWith(accountInfo.AccountPath)).ToList();*/

            //Consider for deleteion only files modified before the PREVIOUS poll
            //A user may perform a file creation or rename at roughly the same time as a poll. In such a case
            //the new file will appear as deleted
            var previousPollTime = pollTime.Subtract(TimeSpan.FromMilliseconds(Settings.PollingInterval));                       

            //Only consider files that are not being modified, ie they are in the Unchanged state            
            var deleteCandidates = FileState.Queryable.Where(state => 
                state.Modified <= previousPollTime
                && 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) 
                         let agentActions = _agent.GetEnumerable()
                         where 
                                 !_lastSeen.ContainsKey(localFile.FullName)
                         && !cloudFiles.Any(r => r.RelativeUrlToFilePath(accountInfo.UserName) == relativeFilePath ) 
                         //Exclude files enqueued for uploading
                         //Large files will not appear on the server for multiple polls. They must not be marked as deleted
                         && !agentActions.Any(action => action.LocalFile.WithProperCapitalization().FullName == localFile.FullName)
                         //Do NOT delete files modified since the previous poll
                                && localFile.LastAccessTime < previousPollTime
                         select localFile).ToList();
            

            //On the first run
            if (_firstPoll)
            {
                //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);
                    }
                }
                UpdateStatus(PithosStatus.HasConflicts);
                StatusNotification.NotifyConflicts(filesToDelete, String.Format("{0} local files are missing from Pithos, possibly because they were deleted",filesToDelete.Count));
            }
            else
            {
                foreach (var item in filesToDelete)
                {
                    if (item.Exists)
                    {
                        //Try to acquire a gate on the file, to take into account files that have been dequeued
                        //and are being processed
                        //TODO: The gate is not enough. Perhaps we need to keep a journal of processed files and check against
                        //that as well.
                        using (var gate = NetworkGate.Acquire(item.FullName, NetworkOperation.Deleting))
                        {
                            if (gate.Failed)
                                continue;
                            if ((item.Attributes & FileAttributes.ReadOnly) == FileAttributes.ReadOnly)
                            {
                                item.Attributes = item.Attributes & ~FileAttributes.ReadOnly;

                            }
                            item.Delete();
                        }
                    }
                    StatusKeeper.ClearFileStatus(item.FullName);
                }
                StatusNotification.NotifyForFiles(filesToDelete, String.Format("{0} files were deleted",filesToDelete.Count),TraceLevel.Info);
            }

        }

        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);
            }
        }

        //Creates an appropriate action for each server file
        private IEnumerable<CloudAction> ObjectsToActions(AccountInfo accountInfo,IEnumerable<ObjectInfo> remote)
        {
            if (remote==null)
                throw new ArgumentNullException();
            Contract.EndContractBlock();
            var fileAgent = GetFileAgent(accountInfo);

            //In order to avoid multiple iterations over the files, we iterate only once
            //over the remote files
            foreach (var objectInfo in remote)
            {
                var relativePath = objectInfo.RelativeUrlToFilePath(accountInfo.UserName);
                //and remove any matching objects from the list, adding them to the commonObjects list
                
                if (fileAgent.Exists(relativePath))
                {
                    //If a directory object already exists, we don't need to perform any other action                    
                    var localFile = fileAgent.GetFileSystemInfo(relativePath);
                    if (objectInfo.Content_Type == @"application/directory" && localFile is DirectoryInfo)
                        continue;
                    using (new SessionScope(FlushAction.Never))
                    {
                        var state =  StatusKeeper.GetStateByFilePath(localFile.FullName);
                        _lastSeen[localFile.FullName] = DateTime.Now;
                        //FileState.FindByFilePath(localFile.FullName);
                        //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);
                    }
                }
                else
                {
                    //If there is no match we add them to the localFiles list
                    //but only if the file is not marked for deletion
                    var targetFile = Path.Combine(accountInfo.AccountPath, relativePath);
                    var fileStatus = StatusKeeper.GetFileStatus(targetFile);
                    if (fileStatus != FileStatus.Deleted)
                    {
                        //Remote files should be downloaded
                        yield return new CloudDownloadAction(accountInfo,objectInfo);
                    }
                }
            }            
        }

        private static FileAgent GetFileAgent(AccountInfo accountInfo)
        {
            return AgentLocator<FileAgent>.Get(accountInfo.AccountPath);
        }

        private void ProcessTrashedFiles(AccountInfo accountInfo,IEnumerable<ObjectInfo> trashObjects)
        {
            var fileAgent = GetFileAgent(accountInfo);
            foreach (var trashObject in trashObjects)
            {
                var barePath = trashObject.RelativeUrlToFilePath(accountInfo.UserName);
                //HACK: Assume only the "pithos" container is used. Must find out what happens when
                //deleting a file from a different container
                var relativePath = Path.Combine("pithos", barePath);
                fileAgent.Delete(relativePath);                                
            }
        }


        private void RenameCloudFile(AccountInfo accountInfo,CloudMoveAction action)
        {
            if (accountInfo==null)
                throw new ArgumentNullException("accountInfo");
            if (action==null)
                throw new ArgumentNullException("action");
            if (action.CloudFile==null)
                throw new ArgumentException("CloudFile","action");
            if (action.LocalFile==null)
                throw new ArgumentException("LocalFile","action");
            if (action.OldLocalFile==null)
                throw new ArgumentException("OldLocalFile","action");
            if (action.OldCloudFile==null)
                throw new ArgumentException("OldCloudFile","action");
            Contract.EndContractBlock();
            
            
            var newFilePath = action.LocalFile.FullName;
            
            //How do we handle concurrent renames and deletes/uploads/downloads?
            //* A conflicting upload means that a file was renamed before it had a chance to finish uploading
            //  This should never happen as the network agent executes only one action at a time
            //* A conflicting download means that the file was modified on the cloud. While we can go on and complete
            //  the rename, there may be a problem if the file is downloaded in blocks, as subsequent block requests for the 
            //  same name will fail.
            //  This should never happen as the network agent executes only one action at a time.
            //* A conflicting delete can happen if the rename was followed by a delete action that didn't have the chance
            //  to remove the rename from the queue.
            //  We can probably ignore this case. It will result in an error which should be ignored            

            
            //The local file is already renamed
            StatusKeeper.SetFileOverlayStatus(newFilePath, FileOverlayStatus.Modified);


            var account = action.CloudFile.Account ?? accountInfo.UserName;
            var container = action.CloudFile.Container;
            
            var client = new CloudFilesClient(accountInfo);
            //TODO: What code is returned when the source file doesn't exist?
            client.MoveObject(account, container, action.OldCloudFile.Name, container, action.CloudFile.Name);

            StatusKeeper.SetFileStatus(newFilePath, FileStatus.Unchanged);
            StatusKeeper.SetFileOverlayStatus(newFilePath, FileOverlayStatus.Normal);
            NativeMethods.RaiseChangeNotification(newFilePath);
        }

        private void DeleteCloudFile(AccountInfo accountInfo, ObjectInfo cloudFile)
        {
            if (accountInfo == null)
                throw new ArgumentNullException("accountInfo");
            if (cloudFile==null)
                throw new ArgumentNullException("cloudFile");

            if (String.IsNullOrWhiteSpace(cloudFile.Container))
                throw new ArgumentException("Invalid container", "cloudFile");
            Contract.EndContractBlock();
            
            var fileAgent = GetFileAgent(accountInfo);

            using ( log4net.ThreadContext.Stacks["DeleteCloudFile"].Push("Delete"))
            {
                var fileName= cloudFile.RelativeUrlToFilePath(accountInfo.UserName);
                var info = fileAgent.GetFileSystemInfo(fileName);                
                var fullPath = info.FullName.ToLower();

                StatusKeeper.SetFileOverlayStatus(fullPath, FileOverlayStatus.Modified);

                var account = cloudFile.Account ?? accountInfo.UserName;
                var container = cloudFile.Container ;//?? FolderConstants.PithosContainer;

                var client = new CloudFilesClient(accountInfo);
                client.DeleteObject(account, container, cloudFile.Name);

                StatusKeeper.ClearFileStatus(fullPath);
            }
        }

        //Download a file.
        private async Task DownloadCloudFile(AccountInfo accountInfo, ObjectInfo cloudFile , string filePath)
        {
            if (accountInfo == null)
                throw new ArgumentNullException("accountInfo");
            if (cloudFile == null)
                throw new ArgumentNullException("cloudFile");
            if (String.IsNullOrWhiteSpace(cloudFile.Account))
                throw new ArgumentNullException("cloudFile");
            if (String.IsNullOrWhiteSpace(cloudFile.Container))
                throw new ArgumentNullException("cloudFile");
            if (String.IsNullOrWhiteSpace(filePath))
                throw new ArgumentNullException("filePath");
            if (!Path.IsPathRooted(filePath))
                throw new ArgumentException("The filePath must be rooted", "filePath");
            Contract.EndContractBlock();
            

            var localPath = Interfaces.FileInfoExtensions.GetProperFilePathCapitalization(filePath);
            var relativeUrl = new Uri(cloudFile.Name, UriKind.Relative);

            var url = relativeUrl.ToString();
            if (cloudFile.Name.EndsWith(".ignore", StringComparison.InvariantCultureIgnoreCase))
                return;


            //Are we already downloading or uploading the file? 
            using (var gate=NetworkGate.Acquire(localPath, NetworkOperation.Downloading))
            {
                if (gate.Failed)
                    return;
                //The file's hashmap will be stored in the same location with the extension .hashmap
                //var hashPath = Path.Combine(FileAgent.CachePath, relativePath + ".hashmap");
                
                var client = new CloudFilesClient(accountInfo);
                var account = cloudFile.Account;
                var container = cloudFile.Container;

                if (cloudFile.Content_Type == @"application/directory")
                {
                    if (!Directory.Exists(localPath))
                        Directory.CreateDirectory(localPath);
                }
                else
                {                    
                    //Retrieve the hashmap from the server
                    var serverHash = await client.GetHashMap(account, container, url);
                    //If it's a small file
                    if (serverHash.Hashes.Count == 1)
                        //Download it in one go
                        await
                            DownloadEntireFileAsync(accountInfo, client, cloudFile, relativeUrl, localPath, serverHash);
                        //Otherwise download it block by block
                    else
                        await DownloadWithBlocks(accountInfo, client, cloudFile, relativeUrl, localPath, serverHash);

                    if (cloudFile.AllowedTo == "read")
                    {
                        var attributes = File.GetAttributes(localPath);
                        File.SetAttributes(localPath, attributes | FileAttributes.ReadOnly);                        
                    }
                }

                //Now we can store the object's metadata without worrying about ghost status entries
                StatusKeeper.StoreInfo(localPath, cloudFile);
                
            }
        }

        //Download a small file with a single GET operation
        private async Task DownloadEntireFileAsync(AccountInfo accountInfo, CloudFilesClient client, ObjectInfo cloudFile, Uri relativeUrl, string filePath,TreeHash serverHash)
        {
            if (client == null)
                throw new ArgumentNullException("client");
            if (cloudFile==null)
                throw new ArgumentNullException("cloudFile");
            if (relativeUrl == null)
                throw new ArgumentNullException("relativeUrl");
            if (String.IsNullOrWhiteSpace(filePath))
                throw new ArgumentNullException("filePath");
            if (!Path.IsPathRooted(filePath))
                throw new ArgumentException("The localPath must be rooted", "filePath");
            Contract.EndContractBlock();

            var localPath = Pithos.Interfaces.FileInfoExtensions.GetProperFilePathCapitalization(filePath);
            //If the file already exists
            if (File.Exists(localPath))
            {
                //First check with MD5 as this is a small file
                var localMD5 = Signature.CalculateMD5(localPath);
                var cloudHash=serverHash.TopHash.ToHashString();
                if (localMD5==cloudHash)
                    return;
                //Then check with a treehash
                var localTreeHash = Signature.CalculateTreeHash(localPath, serverHash.BlockSize, serverHash.BlockHash);
                var localHash = localTreeHash.TopHash.ToHashString();
                if (localHash==cloudHash)
                    return;
            }
            StatusNotification.Notify(new CloudNotification { Data = cloudFile });

            var fileAgent = GetFileAgent(accountInfo);
            //Calculate the relative file path for the new file
            var relativePath = relativeUrl.RelativeUriToFilePath();
            //The file will be stored in a temporary location while downloading with an extension .download
            var tempPath = Path.Combine(fileAgent.CachePath, relativePath + ".download");
            //Make sure the target folder exists. DownloadFileTask will not create the folder
            var tempFolder = Path.GetDirectoryName(tempPath);
            if (!Directory.Exists(tempFolder))
                Directory.CreateDirectory(tempFolder);

            //Download the object to the temporary location
            await client.GetObject(cloudFile.Account, cloudFile.Container, relativeUrl.ToString(), tempPath);

            //Create the local folder if it doesn't exist (necessary for shared objects)
            var localFolder = Path.GetDirectoryName(localPath);
            if (!Directory.Exists(localFolder))
                Directory.CreateDirectory(localFolder);            
            //And move it to its actual location once downloading is finished
            if (File.Exists(localPath))
                File.Replace(tempPath,localPath,null,true);
            else
                File.Move(tempPath,localPath);
            //Notify listeners that a local file has changed
            StatusNotification.NotifyChangedFile(localPath);

                       
        }

        //Download a file asynchronously using blocks
        public async Task DownloadWithBlocks(AccountInfo accountInfo, CloudFilesClient client, ObjectInfo cloudFile, Uri relativeUrl, string filePath, TreeHash serverHash)
        {
            if (client == null)
                throw new ArgumentNullException("client");
            if (cloudFile == null)
                throw new ArgumentNullException("cloudFile");
            if (relativeUrl == null)
                throw new ArgumentNullException("relativeUrl");
            if (String.IsNullOrWhiteSpace(filePath))
                throw new ArgumentNullException("filePath");
            if (!Path.IsPathRooted(filePath))
                throw new ArgumentException("The filePath must be rooted", "filePath");
            if (serverHash == null)
                throw new ArgumentNullException("serverHash");
            Contract.EndContractBlock();
            
           var fileAgent = GetFileAgent(accountInfo);
            var localPath = Interfaces.FileInfoExtensions.GetProperFilePathCapitalization(filePath);
            
            //Calculate the relative file path for the new file
            var relativePath = relativeUrl.RelativeUriToFilePath();
            var blockUpdater = new BlockUpdater(fileAgent.CachePath, localPath, relativePath, serverHash);

            
                        
            //Calculate the file's treehash
            var treeHash = await Signature.CalculateTreeHashAsync(localPath, serverHash.BlockSize, serverHash.BlockHash);
                
            //And compare it with the server's hash
            var upHashes = serverHash.GetHashesAsStrings();
            var localHashes = treeHash.HashDictionary;
            for (int i = 0; i < upHashes.Length; i++)
            {
                //For every non-matching hash
                var upHash = upHashes[i];
                if (!localHashes.ContainsKey(upHash))
                {
                    StatusNotification.Notify(new CloudNotification { Data = cloudFile });

                    if (blockUpdater.UseOrphan(i, upHash))
                    {
                        Log.InfoFormat("[BLOCK GET] ORPHAN FOUND for {0} of {1} for {2}", i, upHashes.Length, localPath);
                        continue;
                    }
                    Log.InfoFormat("[BLOCK GET] START {0} of {1} for {2}", i, upHashes.Length, localPath);
                    var start = i*serverHash.BlockSize;
                    //To download the last block just pass a null for the end of the range
                    long? end = null;
                    if (i < upHashes.Length - 1 )
                        end= ((i + 1)*serverHash.BlockSize) ;
                            
                    //Download the missing block
                    var block = await client.GetBlock(cloudFile.Account, cloudFile.Container, relativeUrl, start, end);

                    //and store it
                    blockUpdater.StoreBlock(i, block);


                    Log.InfoFormat("[BLOCK GET] FINISH {0} of {1} for {2}", i, upHashes.Length, localPath);
                }
            }

            //Want to avoid notifications if no changes were made
            var hasChanges = blockUpdater.HasBlocks;
            blockUpdater.Commit();
            
            if (hasChanges)
                //Notify listeners that a local file has changed
                StatusNotification.NotifyChangedFile(localPath);

            Log.InfoFormat("[BLOCK GET] COMPLETE {0}", localPath);            
        }


        private async Task UploadCloudFile(CloudAction action)
        {
            if (action == null)
                throw new ArgumentNullException("action");           
            Contract.EndContractBlock();

            try
            {                
                var accountInfo = action.AccountInfo;

                var fileInfo = action.LocalFile;

                if (fileInfo.Extension.Equals("ignore", StringComparison.InvariantCultureIgnoreCase))
                    return;
                
                var relativePath = fileInfo.AsRelativeTo(accountInfo.AccountPath);
                if (relativePath.StartsWith(FolderConstants.OthersFolder))
                {
                    var parts = relativePath.Split('\\');
                    var accountName = parts[1];
                    var oldName = accountInfo.UserName;
                    var absoluteUri = accountInfo.StorageUri.AbsoluteUri;
                    var nameIndex = absoluteUri.IndexOf(oldName);
                    var root = absoluteUri.Substring(0, nameIndex);

                    accountInfo = new AccountInfo
                    {
                        UserName = accountName,
                        AccountPath = Path.Combine(accountInfo.AccountPath, parts[0], parts[1]),
                        StorageUri = new Uri(root + accountName),
                        BlockHash = accountInfo.BlockHash,
                        BlockSize = accountInfo.BlockSize,
                        Token = accountInfo.Token
                    };
                }


                var fullFileName = fileInfo.GetProperCapitalization();
                using (var gate = NetworkGate.Acquire(fullFileName, NetworkOperation.Uploading))
                {
                    //Abort if the file is already being uploaded or downloaded
                    if (gate.Failed)
                        return;

                    var cloudFile = action.CloudFile;
                    var account = cloudFile.Account ?? accountInfo.UserName;

                    var client = new CloudFilesClient(accountInfo);                    
                    //Even if GetObjectInfo times out, we can proceed with the upload            
                    var info = client.GetObjectInfo(account, cloudFile.Container, cloudFile.Name);

                    //If this is a read-only file, do not upload changes
                    if (info.AllowedTo == "read")
                        return;
                    
                    //TODO: Check how a directory hash is calculated -> All dirs seem to have the same hash
                    if (fileInfo is DirectoryInfo)
                    {
                        //If the directory doesn't exist the Hash property will be empty
                        if (String.IsNullOrWhiteSpace(info.Hash))
                            //Go on and create the directory
                            await client.PutObject(account, cloudFile.Container, cloudFile.Name, fullFileName, String.Empty, "application/directory");
                    }
                    else
                    {

                        var cloudHash = info.Hash.ToLower();

                        var hash = action.LocalHash.Value;
                        var topHash = action.TopHash.Value;

                        //If the file hashes match, abort the upload
                        if (hash == cloudHash || topHash == cloudHash)
                        {
                            //but store any metadata changes 
                            StatusKeeper.StoreInfo(fullFileName, info);
                            Log.InfoFormat("Skip upload of {0}, hashes match", fullFileName);
                            return;
                        }


                        //Mark the file as modified while we upload it
                        StatusKeeper.SetFileOverlayStatus(fullFileName, FileOverlayStatus.Modified);
                        //And then upload it

                        //Upload even small files using the Hashmap. The server may already contain
                        //the relevant block

                        //First, calculate the tree hash
                        var treeHash = await Signature.CalculateTreeHashAsync(fullFileName, accountInfo.BlockSize,
                                                                              accountInfo.BlockHash);

                        await UploadWithHashMap(accountInfo, cloudFile, fileInfo as FileInfo, cloudFile.Name, treeHash);
                    }
                    //If everything succeeds, change the file and overlay status to normal
                    StatusKeeper.SetFileState(fullFileName, FileStatus.Unchanged, FileOverlayStatus.Normal);
                }
                //Notify the Shell to update the overlays
                NativeMethods.RaiseChangeNotification(fullFileName);
                StatusNotification.NotifyChangedFile(fullFileName);
            }
            catch (AggregateException ex)
            {
                var exc = ex.InnerException as WebException;
                if (exc == null)
                    throw ex.InnerException;
                if (HandleUploadWebException(action, exc)) 
                    return;
                throw;
            }
            catch (WebException ex)
            {
                if (HandleUploadWebException(action, ex))
                    return;
                throw;
            }
            catch (Exception ex)
            {
                Log.Error("Unexpected error while uploading file", ex);
                throw;
            }

        }

        private bool IsDeletedFile(CloudAction action)
        {            
            var key = GetFileKey(action.CloudFile);
            DateTime entryDate;
            if (_deletedFiles.TryGetValue(key, out entryDate))
            {
                //If the delete entry was created after this action, abort the action
                if (entryDate > action.Created)
                    return true;
                //Otherwise, remove the stale entry 
                _deletedFiles.TryRemove(key, out entryDate);
            }
            return false;
        }

        private bool HandleUploadWebException(CloudAction action, WebException exc)
        {
            var response = exc.Response as HttpWebResponse;
            if (response == null)
                throw exc;
            if (response.StatusCode == HttpStatusCode.Unauthorized)
            {
                Log.Error("Not allowed to upload file", exc);
                var message = String.Format("Not allowed to uplad file {0}", action.LocalFile.FullName);
                StatusKeeper.SetFileState(action.LocalFile.FullName, FileStatus.Unchanged, FileOverlayStatus.Normal);
                StatusNotification.NotifyChange(message, TraceLevel.Warning);
                return true;
            }
            return false;
        }

        public async Task UploadWithHashMap(AccountInfo accountInfo,ObjectInfo cloudFile,FileInfo fileInfo,string url,TreeHash treeHash)
        {
            if (accountInfo == null)
                throw new ArgumentNullException("accountInfo");
            if (cloudFile==null)
                throw new ArgumentNullException("cloudFile");
            if (fileInfo == null)
                throw new ArgumentNullException("fileInfo");
            if (String.IsNullOrWhiteSpace(url))
                throw new ArgumentNullException(url);
            if (treeHash==null)
                throw new ArgumentNullException("treeHash");
            if (String.IsNullOrWhiteSpace(cloudFile.Container) )
                throw new ArgumentException("Invalid container","cloudFile");
            Contract.EndContractBlock();

            var fullFileName = fileInfo.GetProperCapitalization();

            var account = cloudFile.Account ?? accountInfo.UserName;
            var container = cloudFile.Container ;

            var client = new CloudFilesClient(accountInfo);
            //Send the hashmap to the server            
            var missingHashes =  await client.PutHashMap(account, container, url, treeHash);
            //If the server returns no missing hashes, we are done
            while (missingHashes.Count > 0)
            {

                var buffer = new byte[accountInfo.BlockSize];
                foreach (var missingHash in missingHashes)
                {
                    //Find the proper block
                    var blockIndex = treeHash.HashDictionary[missingHash];
                    var offset = blockIndex*accountInfo.BlockSize;

                    var read = fileInfo.Read(buffer, offset, accountInfo.BlockSize);

                    try
                    {
                        //And upload the block                
                        await client.PostBlock(account, container, buffer, 0, read);
                        Log.InfoFormat("[BLOCK] Block {0} of {1} uploaded", blockIndex, fullFileName);
                    }
                    catch (Exception exc)
                    {
                        Log.ErrorFormat("[ERROR] uploading block {0} of {1}\n{2}", blockIndex, fullFileName, exc);
                    }

                }

                //Repeat until there are no more missing hashes                
                missingHashes = await client.PutHashMap(account, container, url, treeHash);
            }
        }


        public void AddAccount(AccountInfo accountInfo)
        {            
            if (!_accounts.Contains(accountInfo))
                _accounts.Add(accountInfo);
        }
    }

   


}