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#region

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

 * <copyright file="DeleteAgent.cs" company="GRNet">

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 * Copyright 2011-2012 GRNET S.A. All rights reserved.

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#endregion

using System.Collections.Concurrent;

using System.ComponentModel.Composition;

using System.Diagnostics.Contracts;

using System.IO;

using System.Net;

using System.Threading.Tasks.Dataflow;

using Pithos.Interfaces;

using Pithos.Network;

using System;

using log4net;

namespace Pithos.Core.Agents

{

    /// <summary>

    /// The Delete Agent is used to delete files from the Pithos server with high priority, 

    /// blocking the network agent through the PauseEvent until all pending deletions complete

    /// </summary>    

    [Export]

    public class DeleteAgent

    {

        [Import]

        public IStatusKeeper StatusKeeper { get; set; }

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

        //A separate agent is used to execute delete actions immediatelly;

        private readonly ActionBlock<CloudDeleteAction> _deleteAgent;

        //The Pause event stops the network agent to give priority to the deletion agent

        //Initially the event is signalled because we don't need to pause

        private readonly AsyncManualResetEvent _pauseEvent = new AsyncManualResetEvent(true);

        public AsyncManualResetEvent PauseEvent

        {

            get { return _pauseEvent; }

        }

        //Deleted file names are stored in memory so we can check that a file has already been deleted.

        //and avoid sending duplicate delete commands

        readonly ConcurrentDictionary<string, DateTime> _deletedFiles = new ConcurrentDictionary<string, DateTime>();

        public DeleteAgent()

        {

            _deleteAgent = new ActionBlock<CloudDeleteAction>(message => ProcessDelete(message), new ExecutionDataflowBlockOptions { MaxDegreeOfParallelism = 4 });

        }

        /// <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 void 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 (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;

                        _pauseEvent.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)

                        _pauseEvent.Set();

                }

            }

        }

        //Returns true if an action concerns a file that was deleted

        public bool IsDeletedFile(CloudAction action)

        {

            //Doesn't work for actions targeting shared files

            if (action.IsShared)

                return false;

            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;

        }

        public void Post(CloudDeleteAction action)

        {

            _deleteAgent.Post(action);

        }

        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 (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);

            }

        }

        private static string GetFileKey(ObjectInfo info)

        {

            var key = String.Format("{0}/{1}/{2}", info.Account, info.Container, info.Name);

            return key;

        }

        private static FileAgent GetFileAgent(AccountInfo accountInfo)

        {

            return AgentLocator<FileAgent>.Get(accountInfo.AccountPath);

        }

    }

}