Synnefo » Pithos MS Client

#region

/* -----------------------------------------------------------------------

 * <copyright file="StatusAgent.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;

using System.Collections.Generic;

using System.ComponentModel.Composition;

using System.Data.SQLite;

using System.Diagnostics;

using System.Diagnostics.Contracts;

using System.IO;

using System.Linq;

using System.Reflection;

using System.Security.Cryptography;

using System.Text;

using System.Threading;

using System.Threading.Tasks;

using Castle.ActiveRecord;

using Castle.ActiveRecord.Framework;

using Castle.ActiveRecord.Framework.Config;

using NHibernate.ByteCode.Castle;

using NHibernate.Cfg;

using NHibernate.Cfg.Loquacious;

using NHibernate.Dialect;

using Pithos.Interfaces;

using Pithos.Network;

using log4net;

using Environment = System.Environment;

namespace Pithos.Core.Agents

{

    [Export(typeof(IStatusChecker)),Export(typeof(IStatusKeeper))]

    public class StatusAgent:IStatusChecker,IStatusKeeper

    {

        private static readonly ILog Log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);

        [System.ComponentModel.Composition.Import]

        public IPithosSettings Settings { get; set; }

        private Agent<Action> _persistenceAgent;

        public StatusAgent()

        {            

            var appDataPath = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);

            _pithosDataPath = Path.Combine(appDataPath , "GRNET\\PITHOS");

            if (!Directory.Exists(_pithosDataPath))

                Directory.CreateDirectory(_pithosDataPath);

            var dbPath = Path.Combine(_pithosDataPath, "pithos.db");

            MigrateOldDb(dbPath, appDataPath);

            var source = GetConfiguration(_pithosDataPath);

            ActiveRecordStarter.Initialize(source,typeof(FileState),typeof(FileTag));

            ActiveRecordStarter.UpdateSchema();

            if (!File.Exists(dbPath))

                ActiveRecordStarter.CreateSchema();

            CreateTrigger();

        }

        private static void MigrateOldDb(string dbPath, string appDataPath)

        {

            if(String.IsNullOrWhiteSpace(dbPath))

                throw new ArgumentNullException("dbPath");

            if(String.IsNullOrWhiteSpace(appDataPath))

                throw new ArgumentNullException("appDataPath");

            Contract.EndContractBlock();

            var oldDbPath = Path.Combine(appDataPath, "Pithos", "pithos.db");

            var oldDbInfo = new FileInfo(oldDbPath);

            if (oldDbInfo.Exists && !File.Exists(dbPath))

            {

                Log.InfoFormat("Moving database from {0} to {1}",oldDbInfo.FullName,dbPath);

                var oldDirectory = oldDbInfo.Directory;

                oldDbInfo.MoveTo(dbPath);

                if (Log.IsDebugEnabled)

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

                oldDirectory.Delete(true);

            }

        }

        private void CreateTrigger()

        {

            using (var connection = GetConnection())

            using (var triggerCommand = connection.CreateCommand())

            {

                var cmdText = new StringBuilder()

                    .AppendLine("CREATE TRIGGER IF NOT EXISTS update_last_modified UPDATE ON FileState FOR EACH ROW")

                    .AppendLine("BEGIN")

                    .AppendLine("UPDATE FileState SET Modified=datetime('now')  WHERE Id=old.Id;")

                    .AppendLine("END;")

                    .AppendLine("CREATE TRIGGER IF NOT EXISTS insert_last_modified INSERT ON FileState FOR EACH ROW")

                    .AppendLine("BEGIN")

                    .AppendLine("UPDATE FileState SET Modified=datetime('now')  WHERE Id=new.Id;")

                    .AppendLine("END;")

                    .ToString();

                triggerCommand.CommandText = cmdText;                

                triggerCommand.ExecuteNonQuery();

            }

        }

        private static InPlaceConfigurationSource GetConfiguration(string pithosDbPath)

        {

            if (String.IsNullOrWhiteSpace(pithosDbPath))

                throw new ArgumentNullException("pithosDbPath");

            if (!Path.IsPathRooted(pithosDbPath))

                throw new ArgumentException("path must be a rooted path", "pithosDbPath");

            Contract.EndContractBlock();

            var properties = new Dictionary<string, string>

                                 {

                                     {"connection.driver_class", "NHibernate.Driver.SQLite20Driver"},

                                     {"dialect", "NHibernate.Dialect.SQLiteDialect"},

                                     {"connection.provider", "NHibernate.Connection.DriverConnectionProvider"},

                                     {

                                         "proxyfactory.factory_class",

                                         "NHibernate.ByteCode.Castle.ProxyFactoryFactory, NHibernate.ByteCode.Castle"

                                         },

                                 };

            var connectionString = String.Format(@"Data Source={0}\pithos.db;Version=3;Enlist=N", pithosDbPath);

            properties.Add("connection.connection_string", connectionString);

            var source = new InPlaceConfigurationSource();                        

            source.Add(typeof (ActiveRecordBase), properties);

            source.SetDebugFlag(false);            

            return source;

        }

        public void StartProcessing(CancellationToken token)

        {

            _persistenceAgent = Agent<Action>.Start(queue =>

            {

                Action loop = null;

                loop = () =>

                {

                    var job = queue.Receive();

                    job.ContinueWith(t =>

                    {

                        var action = job.Result;

                        try

                        {

                            action();

                        }

                        catch (SQLiteException ex)

                        {

                            Log.ErrorFormat("[ERROR] SQL \n{0}", ex);

                        }

                        catch (Exception ex)

                        {

                            Log.ErrorFormat("[ERROR] STATE \n{0}", ex);

                        }

                        queue.NotifyComplete(action);

// ReSharper disable AccessToModifiedClosure

                        queue.DoAsync(loop);

// ReSharper restore AccessToModifiedClosure

                    });

                };

                loop();

            });

        }

        public void Stop()

        {

            _persistenceAgent.Stop();            

        }

        public void ProcessExistingFiles(IEnumerable<FileInfo> existingFiles)

        {

            if(existingFiles  ==null)

                throw new ArgumentNullException("existingFiles");

            Contract.EndContractBlock();

            //Find new or matching files with a left join to the stored states

            var fileStates = FileState.Queryable;

            var currentFiles=from file in existingFiles

                      join state in fileStates on file.FullName.ToLower() equals state.FilePath.ToLower() into gs

                      from substate in gs.DefaultIfEmpty()

                               select new {File = file, State = substate};

            //To get the deleted files we must get the states that have no corresponding

            //files. 

            //We can't use the File.Exists method inside a query, so we get all file paths from the states

            var statePaths = (from state in fileStates

                             select new {state.Id, state.FilePath}).ToList();

            //and check each one

            var missingStates= (from path in statePaths

                                where !File.Exists(path.FilePath) && !Directory.Exists(path.FilePath)

                               select path.Id).ToList();

            //Finally, retrieve the states that correspond to the deleted files            

            var deletedFiles = from state in fileStates 

                        where missingStates.Contains(state.Id)

                        select new { File = default(FileInfo), State = state };

            var pairs = currentFiles.Union(deletedFiles).ToList();

            using (var shortHasher = HashAlgorithm.Create("sha1"))

            {

                foreach (var pair in pairs)

                {

                    var fileState = pair.State;

                    var file = pair.File;

                    if (fileState == null)

                    {

                        //This is a new file                        

                        var createState = FileState.CreateFor(file);

                        _persistenceAgent.Post(createState.Create);                        

                    }

                    else if (file == null)

                    {

                        //This file was deleted while we were down. We should mark it as deleted

                        //We have to go through UpdateStatus here because the state object we are using

                        //was created by a different ORM session.

                        _persistenceAgent.Post(() => UpdateStatusDirect(fileState.Id, FileStatus.Deleted));

                    }

                    else

                    {

                        //This file has a matching state. Need to check for possible changes

                        //To check for changes, we use the cheap (in CPU terms) SHA1 algorithm

                        //on the entire file.

                        var hashString = file.ComputeShortHash(shortHasher);                        

                        //TODO: Need a way to attach the hashes to the filestate so we don't

                        //recalculate them each time a call to calculate has is made

                        //We can either store them to the filestate or add them to a 

                        //dictionary

                        //If the hashes don't match the file was changed

                        if (fileState.ShortHash != hashString)

                        {

                            _persistenceAgent.Post(() => UpdateStatusDirect(fileState.Id, FileStatus.Modified));

                        }

                    }

                }

            }

        }

        private int UpdateStatusDirect(Guid id, FileStatus status)

        {

            using (log4net.ThreadContext.Stacks["StatusAgent"].Push("UpdateStatusDirect"))

            {

                try

                {

                    using (var connection = GetConnection())

                    using (

                        var command = new SQLiteCommand("update FileState set FileStatus= :fileStatus where Id = :id  ",

                                                        connection))

                    {                                                

                        command.Parameters.AddWithValue("fileStatus", status);

                        command.Parameters.AddWithValue("id", id);

                        var affected = command.ExecuteNonQuery();

                        return affected;

                    }

                }

                catch (Exception exc)

                {

                    Log.Error(exc.ToString());

                    throw;

                }

            }

        }

        private int UpdateStatusDirect(string path, FileStatus status)

        {

            using (log4net.ThreadContext.Stacks["StatusAgent"].Push("UpdateStatusDirect"))

            {

                try

                {

                    using (var connection = GetConnection())

                    using (

                        var command =

                            new SQLiteCommand("update FileState set FileStatus= :fileStatus where FilePath = :path COLLATE NOCASE",

                                              connection))

                    {

                        command.Parameters.AddWithValue("fileStatus", status);

                        command.Parameters.AddWithValue("path", path);

                        var affected = command.ExecuteNonQuery();

                        return affected;

                    }

                }

                catch (Exception exc)

                {

                    Log.Error(exc.ToString());

                    throw;

                }

            }

        }

        private int UpdateStatusDirect(string absolutePath, FileStatus fileStatus, FileOverlayStatus overlayStatus)

        {

            using (log4net.ThreadContext.Stacks["StatusAgent"].Push("UpdateStatusDirect"))

            {

                try

                {

                    using (var connection = GetConnection())

                    using (

                        var command =

                            new SQLiteCommand(

                                "update FileState set OverlayStatus= :overlayStatus, FileStatus= :fileStatus where FilePath = :path COLLATE NOCASE ",

                                connection))

                    {

                        command.Parameters.AddWithValue("path", absolutePath);

                        command.Parameters.AddWithValue("fileStatus", fileStatus);

                        command.Parameters.AddWithValue("overlayStatus", overlayStatus);

                        var affected = command.ExecuteNonQuery();

                        return affected;

                    }

                }

                catch (Exception exc)

                {

                    Log.Error(exc.ToString());

                    throw;

                }

            }

        }

        public string BlockHash { get; set; }

        public int BlockSize { get; set; }

        public void ChangeRoots(string oldPath, string newPath)

        {

            if (String.IsNullOrWhiteSpace(oldPath))

                throw new ArgumentNullException("oldPath");

            if (!Path.IsPathRooted(oldPath))

                throw new ArgumentException("oldPath must be an absolute path", "oldPath");

            if (string.IsNullOrWhiteSpace(newPath))

                throw new ArgumentNullException("newPath");

            if (!Path.IsPathRooted(newPath))

                throw new ArgumentException("newPath must be an absolute path", "newPath");

            Contract.EndContractBlock();

            FileState.ChangeRootPath(oldPath,newPath);

        }

        private readonly string _pithosDataPath;

        public FileState GetStateByFilePath(string path)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("The path must be rooted", "path");

            Contract.EndContractBlock();

            try

            {

                using (var connection = GetConnection())

                using (var command = new SQLiteCommand("select Id, FilePath, OverlayStatus,FileStatus ,Checksum ,ShortHash,Version    ,VersionTimeStamp,IsShared   ,SharedBy   ,ShareWrite  from FileState where FilePath=:path COLLATE NOCASE", connection))

                {

                    command.Parameters.AddWithValue("path", path);

                    using (var reader = command.ExecuteReader())

                    {

                        if (reader.Read())

                        {

                            //var values = new object[reader.FieldCount];

                            //reader.GetValues(values);

                            var state = new FileState

                                            {

                                                Id = reader.GetGuid(0),

                                                FilePath = reader.IsDBNull(1)?"":reader.GetString(1),

                                                OverlayStatus =reader.IsDBNull(2)?FileOverlayStatus.Unversioned: (FileOverlayStatus) reader.GetInt64(2),

                                                FileStatus = reader.IsDBNull(3)?FileStatus.Missing:(FileStatus) reader.GetInt64(3),

                                                Checksum = reader.IsDBNull(4)?"":reader.GetString(4),

                                                ShortHash= reader.IsDBNull(5)?"":reader.GetString(5),

                                                Version = reader.IsDBNull(6)?default(long):reader.GetInt64(6),

                                                VersionTimeStamp = reader.IsDBNull(7)?default(DateTime):reader.GetDateTime(7),

                                                IsShared = !reader.IsDBNull(8) && reader.GetBoolean(8),

                                                SharedBy = reader.IsDBNull(9)?"":reader.GetString(9),

                                                ShareWrite = !reader.IsDBNull(10) && reader.GetBoolean(10)

                                            };

/*

                            var state = new FileState

                                            {

                                                Id = (Guid) values[0],

                                                FilePath = (string) values[1],

                                                OverlayStatus = (FileOverlayStatus) (long)values[2],

                                                FileStatus = (FileStatus) (long)values[3],

                                                Checksum = (string) values[4],

                                                Version = (long?) values[5],

                                                VersionTimeStamp = (DateTime?) values[6],

                                                IsShared = (long)values[7] == 1,

                                                SharedBy = (string) values[8],

                                                ShareWrite = (long)values[9] == 1

                                            };

*/

                            return state;

                        }

                        else

                        {

                            return null;

                        }

                    }                    

                }

            }

            catch (Exception exc)

            {

                Log.ErrorFormat(exc.ToString());

                throw;

            }            

        }

        public FileOverlayStatus GetFileOverlayStatus(string path)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("The path must be rooted", "path");

            Contract.EndContractBlock();

            try

            {

                using (var connection = GetConnection())

                using (var command = new SQLiteCommand("select OverlayStatus from FileState where FilePath=:path  COLLATE NOCASE", connection))

                {

                    command.Parameters.AddWithValue("path", path);

                    var s = command.ExecuteScalar();

                    return (FileOverlayStatus) Convert.ToInt32(s);

                }

            }

            catch (Exception exc)

            {

                Log.ErrorFormat(exc.ToString());

                return FileOverlayStatus.Unversioned;

            }

        }

        private string GetConnectionString()

        {

            var connectionString = String.Format(@"Data Source={0}\pithos.db;Version=3;Enlist=N;Pooling=True", _pithosDataPath);

            return connectionString;

        }

        private SQLiteConnection GetConnection()

        {

            var connectionString = GetConnectionString();

            var connection = new SQLiteConnection(connectionString);

            connection.Open();

            using(var cmd =connection.CreateCommand())

            {

                cmd.CommandText = "PRAGMA journal_mode=WAL";

                cmd.ExecuteNonQuery();

            }

            return connection;

        }

       /* public void SetFileOverlayStatus(string path, FileOverlayStatus overlayStatus)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("The path must be rooted","path");

            Contract.EndContractBlock();

            _persistenceAgent.Post(() => FileState.StoreOverlayStatus(path,overlayStatus));

        }*/

        public Task SetFileOverlayStatus(string path, FileOverlayStatus overlayStatus, string shortHash = null)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("The path must be rooted","path");

            Contract.EndContractBlock();

            return _persistenceAgent.PostAndAwait(() => FileState.StoreOverlayStatus(path,overlayStatus,shortHash));

        }

       /* public void RenameFileOverlayStatus(string oldPath, string newPath)

        {

            if (String.IsNullOrWhiteSpace(oldPath))

                throw new ArgumentNullException("oldPath");

            if (!Path.IsPathRooted(oldPath))

                throw new ArgumentException("The oldPath must be rooted", "oldPath");

            if (String.IsNullOrWhiteSpace(newPath))

                throw new ArgumentNullException("newPath");

            if (!Path.IsPathRooted(newPath))

                throw new ArgumentException("The newPath must be rooted", "newPath");

            Contract.EndContractBlock();

            _persistenceAgent.Post(() =>FileState.RenameState(oldPath, newPath));

        }*/

        public void SetFileState(string path, FileStatus fileStatus, FileOverlayStatus overlayStatus)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("The path must be rooted", "path");

            Contract.EndContractBlock();

            Debug.Assert(!path.Contains(FolderConstants.CacheFolder));

            Debug.Assert(!path.EndsWith(".ignore"));

            _persistenceAgent.Post(() => UpdateStatusDirect(path, fileStatus, overlayStatus));

        }

/*

        public void StoreInfo(string path,ObjectInfo objectInfo)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("The path must be rooted", "path");            

            if (objectInfo == null)

                throw new ArgumentNullException("objectInfo", "objectInfo can't be empty");

            Contract.EndContractBlock();

            _persistenceAgent.Post(() =>

            {

                var filePath = path.ToLower();

                //Load the existing files state and set its properties in one session            

                using (new SessionScope())

                {

                    //Forgetting to use a sessionscope results in two sessions being created, one by 

                    //FirstOrDefault and one by Save()

                    var state =FileState.FindByFilePath(filePath);

                    //Create a new empty state object if this is a new file

                    state = state ?? new FileState();

                    state.FilePath = filePath;

                    state.Checksum = objectInfo.Hash;

                    state.Version = objectInfo.Version;

                    state.VersionTimeStamp = objectInfo.VersionTimestamp;

                    state.FileStatus = FileStatus.Unchanged;

                    state.OverlayStatus = FileOverlayStatus.Normal;

                    //Do the save

                    state.Save();

                }

            });

        }

*/

        public void StoreInfo(string path, ObjectInfo objectInfo)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("The path must be rooted", "path");

            if (objectInfo == null)

                throw new ArgumentNullException("objectInfo", "objectInfo can't be empty");

            Contract.EndContractBlock();

            _persistenceAgent.Post(() => StoreInfoDirect(path, objectInfo));

        }

        private void StoreInfoDirect(string path, ObjectInfo objectInfo)

        {

            try

            {

                using (var connection = GetConnection())

                using (var command = new SQLiteCommand(connection))

                {

                    if (StateExists(path, connection))

                        command.CommandText =

                            "update FileState set FileStatus= :fileStatus where FilePath = :path  COLLATE NOCASE ";

                    else

                    {

                        command.CommandText =

                            "INSERT INTO FileState (Id,FilePath,Checksum,Version,VersionTimeStamp,ShortHash,FileStatus,OverlayStatus) VALUES (:id,:path,:checksum,:version,:versionTimeStamp,:shortHash,:fileStatus,:overlayStatus)";

                        command.Parameters.AddWithValue("id", Guid.NewGuid());

                    }

                    command.Parameters.AddWithValue("path", path);

                    command.Parameters.AddWithValue("checksum", objectInfo.Hash);

                    command.Parameters.AddWithValue("shortHash", "");

                    command.Parameters.AddWithValue("version", objectInfo.Version);

                    command.Parameters.AddWithValue("versionTimeStamp",

                                                    objectInfo.VersionTimestamp);

                    command.Parameters.AddWithValue("fileStatus", FileStatus.Unchanged);

                    command.Parameters.AddWithValue("overlayStatus",

                                                    FileOverlayStatus.Normal);

                    var affected = command.ExecuteNonQuery();

                    return;

                }

            }

            catch (Exception exc)

            {

                Log.Error(exc.ToString());

                throw;

            }

        }

        private bool StateExists(string filePath,SQLiteConnection connection)

        {

            using (var command = new SQLiteCommand("Select count(*) from FileState where FilePath=:path  COLLATE NOCASE", connection))

            {

                command.Parameters.AddWithValue("path", filePath);

                var result = command.ExecuteScalar();

                return ((long)result >= 1);

            }

        }

        public void SetFileStatus(string path, FileStatus status)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("The path must be rooted", "path");

            Contract.EndContractBlock();

            _persistenceAgent.Post(() => UpdateStatusDirect(path, status));

        }

        public FileStatus GetFileStatus(string path)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("The path must be rooted", "path");

            Contract.EndContractBlock();

            using (var connection = GetConnection())

            {

                var command = new SQLiteCommand("select FileStatus from FileState where FilePath=:path  COLLATE NOCASE", connection);

                command.Parameters.AddWithValue("path", path);

                var statusValue = command.ExecuteScalar();

                if (statusValue==null)

                    return FileStatus.Missing;

                return (FileStatus)Convert.ToInt32(statusValue);

            }

        }

        /// <summary>

        /// Deletes the status of the specified file

        /// </summary>

        /// <param name="path"></param>

        public void ClearFileStatus(string path)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("The path must be rooted", "path");

            Contract.EndContractBlock();

            _persistenceAgent.Post(() => DeleteDirect(path));   

        }

        /// <summary>

        /// Deletes the status of the specified folder and all its contents

        /// </summary>

        /// <param name="path"></param>

        public void ClearFolderStatus(string path)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("The path must be rooted", "path");

            Contract.EndContractBlock();

            _persistenceAgent.Post(() => DeleteFolderDirect(path));   

        }

        public IEnumerable<FileState> GetChildren(FileState fileState)

        {

            if (fileState == null)

                throw new ArgumentNullException("fileState");

            Contract.EndContractBlock();

            var children = from state in FileState.Queryable

                           where state.FilePath.StartsWith(fileState.FilePath + "\\")

                           select state;

            return children;

        }

        public void EnsureFileState(string path)

        {

            var existingState = GetStateByFilePath(path);

            if (existingState != null)

                return;

            var fileInfo = FileInfoExtensions.FromPath(path);

            using (new SessionScope())

            {

                var newState = FileState.CreateFor(fileInfo);

                newState.FileStatus=FileStatus.Missing;

                _persistenceAgent.PostAndAwait(newState.CreateAndFlush).Wait();

            }

        }

        private int DeleteDirect(string filePath)

        {

            using (log4net.ThreadContext.Stacks["StatusAgent"].Push("DeleteDirect"))

            {

                try

                {

                    using (var connection = GetConnection())

                    {

                        var command = new SQLiteCommand("delete from FileState where FilePath = :path  COLLATE NOCASE",

                                                        connection);

                        command.Parameters.AddWithValue("path", filePath);

                        var affected = command.ExecuteNonQuery();

                        return affected;

                    }

                }

                catch (Exception exc)

                {

                    Log.Error(exc.ToString());

                    throw;

                }

            }

        }

        private int DeleteFolderDirect(string filePath)

        {

            using (log4net.ThreadContext.Stacks["StatusAgent"].Push("DeleteDirect"))

            {

                try

                {

                    using (var connection = GetConnection())

                    {

                        var command = new SQLiteCommand(@"delete from FileState where FilePath = :path or FilePath like :path || '\%'  COLLATE NOCASE",

                                                        connection);

                        command.Parameters.AddWithValue("path", filePath);

                        var affected = command.ExecuteNonQuery();

                        return affected;

                    }

                }

                catch (Exception exc)

                {

                    Log.Error(exc.ToString());

                    throw;

                }

            }

        }

        public void UpdateFileChecksum(string path, string shortHash, string checksum)

        {

            if (String.IsNullOrWhiteSpace(path))

                throw new ArgumentNullException("path");

            if (!Path.IsPathRooted(path))

                throw new ArgumentException("The path must be rooted", "path");            

            Contract.EndContractBlock();

            _persistenceAgent.Post(() => FileState.UpdateChecksum(path, shortHash,checksum));

        }

    }

}