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#region

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

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

 * 

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

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 * 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.

 *

 *   2. Redistributions in binary form must reproduce the above

 *      copyright notice, this list of conditions and the following

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 * 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

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 * </copyright>

 * -----------------------------------------------------------------------

 */

#endregion

using System.Diagnostics.Contracts;

using System.IO;

using System.Reflection;

using System.Threading.Tasks;

using Pithos.Interfaces;

using log4net;

namespace Pithos.Core.Agents

{

    using System;

    /// <summary>

    /// Wraps a FileSystemWatcher and raises Move and child object events 

    /// </summary>

    public class FileSystemWatcherAdapter

    {

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

        public event FileSystemEventHandler Changed;

        public event FileSystemEventHandler Created;

        public event FileSystemEventHandler Deleted;

        //public event RenamedEventHandler Renamed;

        public event MovedEventHandler Moved;

        public FileSystemWatcherAdapter(FileSystemWatcher watcher)

        {

            if (watcher==null)

                throw new ArgumentNullException("watcher");

            Contract.EndContractBlock();

            watcher.Changed += OnChangeOrCreate;

            watcher.Created += OnChangeOrCreate;

            watcher.Deleted += OnDeleted;

            watcher.Renamed += OnRename;

            watcher.Error += OnError;

        }

        private void OnError(object sender, ErrorEventArgs e)

        {

            var error = e.GetException();

            Log.Error("FSW error",error);

        }

        private string _cachedDeletedFullPath;

        private const int PropagateDelay = 10;

        private void OnDeleted(object sender, FileSystemEventArgs e)

        {

            if (sender == null)

                throw new ArgumentNullException("sender");

            if (e.ChangeType != WatcherChangeTypes.Deleted)

                throw new ArgumentException("e");

            if (string.IsNullOrWhiteSpace(e.FullPath))

                throw new ArgumentException("e");

            Contract.Ensures(!String.IsNullOrWhiteSpace(_cachedDeletedFullPath));

            Contract.EndContractBlock();

            TaskEx.Run(() => InnerOnDeleted(sender, e));

        }

        private void InnerOnDeleted(object sender, FileSystemEventArgs e)

        {

//Handle any previously deleted event

            if (Log.IsDebugEnabled)

                Log.DebugFormat("[{0}] for [{1}]", Enum.GetName(typeof(WatcherChangeTypes), e.ChangeType), e.FullPath);

            PropagateCachedDeleted(sender);

            //A delete event may be an actual delete event or the first event in a move action.

            //To decide which action occured, we need to wait for the next action, so

            //we  store the file path and return .

            //A delete action will not be followed by any other event, so we need to add a watchdog 

            //that will declare a Delete action after a short amount of time

            //TODO: Moving a folder to the recycle bin results in a single delete event for the entire folder and its contents

            //      as this is actually a MOVE operation

            //Deleting by Shift+Delete results in a delete event for each file followed by the delete of the folder itself

            _cachedDeletedFullPath = e.FullPath;

            //TODO: This requires synchronization of the _cachedDeletedFullPath field

            //TODO: This creates a new task for each file even though we can cancel any existing tasks if a new event arrives

            //Maybe, use a timer instead of a task

            TaskEx.Delay(PropagateDelay).ContinueWith(t =>

                                                          {

                                                              var myPath = e.FullPath;

                                                              if (_cachedDeletedFullPath == myPath)

                                                                  PropagateCachedDeleted(sender);

                                                          });

        }

        private void OnRename(object sender, RenamedEventArgs e)

        {

            if (sender == null)

                throw new ArgumentNullException("sender");

            Contract.Ensures(_cachedDeletedFullPath == null);

            Contract.EndContractBlock();

            TaskEx.Run(() => InnerRename(sender, e));

        }

        private void InnerRename(object sender, RenamedEventArgs e)

        {

            try

            {

                if (Log.IsDebugEnabled)

                    Log.DebugFormat("[{0}] for [{1}]", Enum.GetName(typeof(WatcherChangeTypes), e.ChangeType), e.FullPath);

                //Propagate any previous cached delete event

                PropagateCachedDeleted(sender);

                if (Moved!= null)

                {

                    try

                    {

                        Moved(sender, new MovedEventArgs(e.FullPath,e.Name,e.OldFullPath,e.OldName));

                    }

                    catch (Exception exc)

                    {

                        Log.Error("Rename event error", exc);

                        throw;

                    }

                    var directory = new DirectoryInfo(e.FullPath);

                    if (directory.Exists)

                    {

                        var newDirectory = e.FullPath;

                        var oldDirectory = e.OldFullPath;

                        foreach (

                            var child in

                                directory.EnumerateFileSystemInfos("*", SearchOption.AllDirectories))

                        {

                            var newChildDirectory = Path.GetDirectoryName(child.FullName);

                            var relativePath = child.AsRelativeTo(newDirectory);

                            var relativeFolder = Path.GetDirectoryName(relativePath);

                            var oldChildDirectory = Path.Combine(oldDirectory, relativeFolder);

                            Moved(sender,

                                  new MovedEventArgs(newChildDirectory, child.Name, oldChildDirectory,

                                                     child.Name));

                        }

                    }

                }

            }

            finally

            {

                _cachedDeletedFullPath = null;

            }

        }

        private void OnChangeOrCreate(object sender, FileSystemEventArgs e)

        {

            if (sender == null)

                throw new ArgumentNullException("sender");

            if (!(e.ChangeType == WatcherChangeTypes.Created || e.ChangeType == WatcherChangeTypes.Changed))

                throw new ArgumentException("e");

            Contract.Ensures(_cachedDeletedFullPath == null);

            Contract.EndContractBlock();

            TaskEx.Run(() => InnerChangeOrCreated(sender, e));

        }

        private void InnerChangeOrCreated(object sender, FileSystemEventArgs e)

        {

            try

            {

                if (Log.IsDebugEnabled)

                    Log.DebugFormat("[{0}] for [{1}]",Enum.GetName(typeof(WatcherChangeTypes),e.ChangeType),e.FullPath);

                //A Move action results in a sequence of a Delete and a Create or Change event

                //If the actual action is a Move, raise a Move event instead of the actual event

                if (HandleMoved(sender, e))

                    return;

                //Otherwise, propagate the Delete event if it exists 

                PropagateCachedDeleted(sender);

                //and propagate the actual event

                var actualEvent = e.ChangeType == WatcherChangeTypes.Created ? Created : Changed;

                if (actualEvent != null)

                {

                    actualEvent(sender, e);

                    //For Folders, raise Created events for all children

                    RaiseCreatedForChildren(sender, e);

                }

            }

            finally

            {

                //Finally, make sure the cached path is cleared

                _cachedDeletedFullPath = null;

            }

        }

        private void RaiseCreatedForChildren(object sender, FileSystemEventArgs e)

        {

            Contract.Requires(sender!=null);

            Contract.Requires(e!=null);

            if (e.ChangeType != WatcherChangeTypes.Created)

                return;

            var dir= new DirectoryInfo(e.FullPath);

            //Skip if this is not a folder

            if (!dir.Exists)

                return;

            try

            {

                foreach (var info in dir.EnumerateFileSystemInfos("*",SearchOption.AllDirectories))

                {

                    var path = Path.GetDirectoryName(info.FullName);

                    Created(sender,new FileSystemEventArgs(WatcherChangeTypes.Created,path,info.Name));

                }

            }

            catch (IOException exc)

            {

                TaskEx.Delay(1000)

                    .ContinueWith(_=>RaiseCreatedForChildren(sender,e));

            }

        }

        private bool HandleMoved(object sender, FileSystemEventArgs e)

        {

            if (sender == null)

                throw new ArgumentNullException("sender");

            if (!(e.ChangeType == WatcherChangeTypes.Created ||

                                                  e.ChangeType == WatcherChangeTypes.Changed))

                throw new ArgumentException("e");

            Contract.EndContractBlock();

            //TODO: If a file is deleted and another file with the same name is created, it will be detected as a MOVE

            //instead of a sequence of independent actions

            //One way to detect this would be to request that the full paths are NOT the same

            var oldName = Path.GetFileName(_cachedDeletedFullPath);

            //NOTE: e.Name is a path relative to the watched path. We MUST call Path.GetFileName to get the actual path

            var newName = Path.GetFileName(e.Name);

            //If the last deleted filename is equal to the current and the action is create, we have a MOVE operation

            var hasMoved = (_cachedDeletedFullPath != e.FullPath && oldName == newName);

            if (!hasMoved)

                return false;

            try

            {

                if (Log.IsDebugEnabled)

                    Log.DebugFormat("Moved for [{0}]",  e.FullPath);

                //If the actual action is a Move, raise a Move event instead of the actual event

                var newDirectory = Path.GetDirectoryName(e.FullPath);

                var oldDirectory = Path.GetDirectoryName(_cachedDeletedFullPath);

                if (Moved != null)

                {

                    Moved(sender, new MovedEventArgs(newDirectory, newName, oldDirectory, oldName));

                    //If the moved item is a dictionary, we need to raise a change event for each child item

                    //When a directory is moved within the same volume, Windows raises events only for the directory object,

                    //not its children. This happens because the move actually changes a single directory entry. It doesn't

                    //affect the entries of the children.

                    var directory = new DirectoryInfo(e.FullPath);

                    if (directory.Exists)

                    {

                        foreach (var child in directory.EnumerateFileSystemInfos("*", SearchOption.AllDirectories))

                        {

                            var newChildDirectory = Path.GetDirectoryName(child.FullName);

                            var relativePath=child.AsRelativeTo(newDirectory);

                            var relativeFolder = Path.GetDirectoryName(relativePath);

                            var oldChildDirectory = Path.Combine(oldDirectory, relativeFolder);

                            Moved(sender,new MovedEventArgs(newChildDirectory,child.Name,oldChildDirectory,child.Name));

                        }

                    }

                }

            }

            finally

            {

                _cachedDeletedFullPath = null;

            }

            return true;

        }

        private void PropagateCachedDeleted(object sender)

        {

            if (sender == null)

                throw new ArgumentNullException("sender");

            Contract.Ensures(_cachedDeletedFullPath == null);

            Contract.EndContractBlock();

            //Nothing to handle if there is no cached deleted file

            if (String.IsNullOrWhiteSpace(_cachedDeletedFullPath))

                return;

            var deletedFileName = Path.GetFileName(_cachedDeletedFullPath);

            var deletedFileDirectory = Path.GetDirectoryName(_cachedDeletedFullPath);

            if (Log.IsDebugEnabled)

                Log.DebugFormat("Propagating delete for [{0}]", _cachedDeletedFullPath);

            //Only a single file Delete event is raised when moving a file to the Recycle Bin, as this is actually a MOVE operation

            //In this case we need to raise the proper events for all child objects of the deleted directory.

            //UNFORTUNATELY, this can't be detected here, eg. by retrieving the child objects, because they are already deleted

            //This should be done at a higher level, eg by checking the stored state

            if (Deleted != null)            

                Deleted(sender,new FileSystemEventArgs(WatcherChangeTypes.Deleted, deletedFileDirectory, deletedFileName));

            _cachedDeletedFullPath = null;

        }

    }

}