#region
/* -----------------------------------------------------------------------
 * <copyright file="PollAgent.cs" company="GRNet">
 * 
 * Copyright 2011-2012 GRNET S.A. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *
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 *      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
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 * </copyright>
 * -----------------------------------------------------------------------
 */
#endregion

using System.Collections.Concurrent;
using System.ComponentModel.Composition;
using System.Diagnostics;
using System.Diagnostics.Contracts;
using System.IO;
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
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;

    /// <summary>
    /// PollAgent periodically polls the server to detect object changes. The agent retrieves a listing of all
    /// objects and compares it with a previously cached version to detect differences. 
    /// New files are downloaded, missing files are deleted from the local file system and common files are compared
    /// to determine the appropriate action
    /// </summary>
    [Export]
    public class PollAgent
    {
        private static readonly ILog Log = LogManager.GetLogger("PollAgent");

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

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

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

        public IStatusNotification StatusNotification { get; set; }

        private bool _firstPoll = true;

        //The Sync Event signals a manual synchronisation
        private readonly AsyncManualResetEvent _syncEvent = new AsyncManualResetEvent();

        private ConcurrentDictionary<string, DateTime> _lastSeen = new ConcurrentDictionary<string, DateTime>();
        private readonly ConcurrentBag<AccountInfo> _accounts = new ConcurrentBag<AccountInfo>();


        /// <summary>
        /// Start a manual synchronization
        /// </summary>
        public void SynchNow()
        {            
            _syncEvent.Set();
        }

        /// <summary>
        /// Remote files are polled periodically. Any changes are processed
        /// </summary>
        /// <param name="since"></param>
        /// <returns></returns>
        public async Task PollRemoteFiles(DateTime? since = null)
        {
            Debug.Assert(Thread.CurrentThread.IsBackground, "Polling Ended up in the main thread!");

            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
                    var 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
                    nextSince = current;
                }
                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);
                //The multiple try blocks are required because we can't have an await call
                //inside a finally block
                //TODO: Find a more elegant solution for reschedulling in the event of an exception
                try
                {
                    //Wait for the polling interval to pass or the Sync event to be signalled
                    nextSince = await WaitForScheduledOrManualPoll(nextSince);
                }
                finally
                {
                    //Ensure polling is scheduled even in case of error
                    TaskEx.Run(() => PollRemoteFiles(nextSince));                        
                }
            }
        }

        /// <summary>
        /// Wait for the polling period to expire or a manual sync request
        /// </summary>
        /// <param name="since"></param>
        /// <returns></returns>
        private async Task<DateTime?> WaitForScheduledOrManualPoll(DateTime? since)
        {
            var sync = _syncEvent.WaitAsync();
            var wait = TaskEx.Delay(TimeSpan.FromSeconds(Settings.PollingInterval), NetworkAgent.CancellationToken);
            var signaledTask = await TaskEx.WhenAny(sync, wait);

            //Wait for network processing to finish before polling
            var pauseTask=NetworkAgent.ProceedEvent.WaitAsync();
            await TaskEx.WhenAll(signaledTask, pauseTask);

            //If polling is signalled by SynchNow, ignore the since tag
            if (sync.IsCompleted)
            {
                //TODO: Must convert to AutoReset
                _syncEvent.Reset();
                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))
            {
                await NetworkAgent.GetDeleteAwaiter();

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

                //We don't need to check the trash container
                var containers = client.ListContainers(accountInfo.UserName).Where(c=>c.Name!="trash");


                CreateContainerFolders(accountInfo, containers);

                try
                {
                    //Wait for any deletions to finish
                    await NetworkAgent.GetDeleteAwaiter();
                    //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();
                    //BUG: Can't detect difference between no changes or no objects
                    //ListObjects returns nothing if there are no changes since the last check time (since value)                    
                    //TODO: Must detect the difference between no server objects and no change

                    //NOTE: One option is to "mark" all result lists with their container name, or 
                    //rather the url of the container
                    //Another option 

                    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;

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

                        //DON'T process trashed files
                        //If some files are deleted and added again to a folder, they will be deleted
                        //even though they are new.
                        //We would have to check file dates and hashes to ensure that a trashed file
                        //can be deleted safely from the local hard drive.
                        /*
                        //Items with the same name, hash may be both in the container and the trash
                        //Don't delete items that exist in the container
                        var realTrash = from trash in trashObjects
                                        where
                                            !remoteObjects.Any(
                                                info => info.Name == trash.Name && info.Hash == trash.Hash)
                                        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();

                        var differencer = _differencer.PostSnapshot(accountInfo, cleanRemotes);

                        ProcessDeletedFiles(accountInfo, differencer.Deleted.FilterDirectlyBelow(SelectiveUris), pollTime);

                        // @@@ NEED To add previous state here as well, To compare with previous hash

                        

                        //Create a list of actions from the remote files
                        var allActions = ChangesToActions(accountInfo, differencer.Changed.FilterDirectlyBelow(SelectiveUris))
                                        .Union(
                                        CreatesToActions(accountInfo, differencer.Created.FilterDirectlyBelow(SelectiveUris)));

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

                        //Queue all the actions
                        foreach (var message in distinctActions)
                        {
                            NetworkAgent.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");

            }
        }

        AccountsDifferencer _differencer = new AccountsDifferencer();
        private List<Uri> _selectiveUris=new List<Uri>();

        /// <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();

            //On the first run
            if (_firstPoll)
            {
                //Only consider files that are not being modified, ie they are in the Unchanged state            
                var deleteCandidates = FileState.Queryable.Where(state =>
                    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)
                                     where
                                         !cloudFiles.Any(r => r.RelativeUrlToFilePath(accountInfo.UserName) == relativeFilePath)
                                     select localFile).ToList();



                //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));
                StatusNotification.NotifyForFiles(filesToDelete, String.Format("{0} files were deleted", filesToDelete.Count), TraceLevel.Info);
            }
            else
            {
                var deletedFiles = new List<FileSystemInfo>();
                foreach (var objectInfo in cloudFiles)
                {
                    var relativePath = objectInfo.RelativeUrlToFilePath(accountInfo.UserName);
                    var item = FileAgent.GetFileAgent(accountInfo).GetFileSystemInfo(relativePath);
                    if (item.Exists)
                    {
                        if ((item.Attributes & FileAttributes.ReadOnly) == FileAttributes.ReadOnly)
                        {
                            item.Attributes = item.Attributes & ~FileAttributes.ReadOnly;

                        }
                        item.Delete();
                        DateTime lastDate;
                        _lastSeen.TryRemove(item.FullName, out lastDate);
                        deletedFiles.Add(item);
                    }
                    StatusKeeper.SetFileState(item.FullName, FileStatus.Deleted, FileOverlayStatus.Deleted);
                }
                StatusNotification.NotifyForFiles(deletedFiles, String.Format("{0} files were deleted", deletedFiles.Count), TraceLevel.Info);
            }

        }

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

            //In order to avoid multiple iterations over the files, we iterate only once
            //over the remote files
            foreach (var objectInfo in changes)
            {
                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;
                        //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
                {
                    //Remote files should be downloaded
                    yield return new CloudDownloadAction(accountInfo, objectInfo);
                }
            }
        }

        private IEnumerable<CloudAction> CreatesToActions(AccountInfo accountInfo, IEnumerable<ObjectInfo> creates)
        {
            if (creates == null)
                throw new ArgumentNullException();
            Contract.EndContractBlock();
            var fileAgent = FileAgent.GetFileAgent(accountInfo);

            //In order to avoid multiple iterations over the files, we iterate only once
            //over the remote files
            foreach (var objectInfo in creates)
            {
                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 the object already exists, we probably have a conflict
                    //If a directory object already exists, we don't need to perform any other action                    
                    var localFile = fileAgent.GetFileSystemInfo(relativePath);
                    StatusKeeper.SetFileState(localFile.FullName, FileStatus.Conflict, FileOverlayStatus.Conflict);
                }
                else
                {
                    //Remote files should be downloaded
                    yield return new CloudDownloadAction(accountInfo, objectInfo);
                }
            }
        }

        private void ProcessTrashedFiles(AccountInfo accountInfo, IEnumerable<ObjectInfo> trashObjects)
        {
            var fileAgent = 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);
            }
        }

        /// <summary>
        /// Notify the UI to update the visual status
        /// </summary>
        /// <param name="status"></param>
        private void UpdateStatus(PithosStatus status)
        {
            try
            {
                StatusKeeper.SetPithosStatus(status);
                StatusNotification.Notify(new Notification());
            }
            catch (Exception exc)
            {
                //Failure is not critical, just log it
                Log.Warn("Error while updating status", exc);
            }
        }

        private static void CreateContainerFolders(AccountInfo accountInfo, IEnumerable<ContainerInfo> containers)
        {
            var containerPaths = from container in containers
                                 let containerPath = Path.Combine(accountInfo.AccountPath, container.Name)
                                 where container.Name != FolderConstants.TrashContainer && !Directory.Exists(containerPath)
                                 select containerPath;

            foreach (var path in containerPaths)
            {
                Directory.CreateDirectory(path);
            }
        }

        public void SetSyncUris(Uri[] uris)
        {            
            SelectiveUris=uris.ToList();
        }

        protected List<Uri> SelectiveUris
        {
            get { return _selectiveUris;}
            set { _selectiveUris = value; }
        }

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