using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using CommonIO;
using MediaBrowser.Common.Events;
using MediaBrowser.Common.ScheduledTasks;
using MediaBrowser.Controller.Configuration;
using MediaBrowser.Controller.Entities;
using MediaBrowser.Controller.Library;
using MediaBrowser.Model.Logging;
using MediaBrowser.Server.Implementations.ScheduledTasks;

namespace MediaBrowser.Server.Implementations.IO
{
    public class FileRefresher : IDisposable
    {
        private ILogger Logger { get; set; }
        private ITaskManager TaskManager { get; set; }
        private ILibraryManager LibraryManager { get; set; }
        private IServerConfigurationManager ConfigurationManager { get; set; }
        private readonly IFileSystem _fileSystem;
        private readonly List<string> _affectedPaths = new List<string>();
        private Timer _timer;
        private readonly object _timerLock = new object();
        public string Path { get; private set; }

        public event EventHandler<EventArgs> Completed;

        public FileRefresher(string path, IFileSystem fileSystem, IServerConfigurationManager configurationManager, ILibraryManager libraryManager, ITaskManager taskManager, ILogger logger)
        {
            logger.Debug("New file refresher created for {0}", path);
            Path = path;

            _fileSystem = fileSystem;
            ConfigurationManager = configurationManager;
            LibraryManager = libraryManager;
            TaskManager = taskManager;
            Logger = logger;
            AddPath(path);
        }

        private void AddAffectedPath(string path)
        {
            if (!_affectedPaths.Contains(path, StringComparer.Ordinal))
            {
                _affectedPaths.Add(path);
            }
        }

        public void AddPath(string path)
        {
            lock (_timerLock)
            {
                AddAffectedPath(path);
            }
            RestartTimer();
        }

        public void RestartTimer()
        {
            if (_disposed)
            {
                return;
            }

            lock (_timerLock)
            {
                if (_timer == null)
                {
                    _timer = new Timer(OnTimerCallback, null, TimeSpan.FromSeconds(ConfigurationManager.Configuration.LibraryMonitorDelay), TimeSpan.FromMilliseconds(-1));
                }
                else
                {
                    _timer.Change(TimeSpan.FromSeconds(ConfigurationManager.Configuration.LibraryMonitorDelay), TimeSpan.FromMilliseconds(-1));
                }
            }
        }

        public void ResetPath(string path, string affectedFile)
        {
            lock (_timerLock)
            {
                Logger.Debug("Resetting file refresher from {0} to {1}", Path, path);

                Path = path;
                AddAffectedPath(path);

                if (!string.IsNullOrWhiteSpace(affectedFile))
                {
                    AddAffectedPath(affectedFile);
                }
            }
            RestartTimer();
        }

        private async void OnTimerCallback(object state)
        {
            List<string> paths;

            lock (_timerLock)
            {
                paths = _affectedPaths.ToList();
            }

            // Extend the timer as long as any of the paths are still being written to.
            if (paths.Any(IsFileLocked))
            {
                Logger.Info("Timer extended.");
                RestartTimer();
                return;
            }

            Logger.Debug("Timer stopped.");

            DisposeTimer();
            EventHelper.FireEventIfNotNull(Completed, this, EventArgs.Empty, Logger);

            try
            {
                await ProcessPathChanges(paths.ToList()).ConfigureAwait(false);
            }
            catch (Exception ex)
            {
                Logger.ErrorException("Error processing directory changes", ex);
            }
        }

        private async Task ProcessPathChanges(List<string> paths)
        {
            var itemsToRefresh = paths
                .Select(GetAffectedBaseItem)
                .Where(item => item != null)
                .Distinct()
                .ToList();

            foreach (var p in paths)
            {
                Logger.Info(p + " reports change.");
            }

            // If the root folder changed, run the library task so the user can see it
            if (itemsToRefresh.Any(i => i is AggregateFolder))
            {
                TaskManager.CancelIfRunningAndQueue<RefreshMediaLibraryTask>();
                return;
            }

            foreach (var item in itemsToRefresh)
            {
                Logger.Info(item.Name + " (" + item.Path + ") will be refreshed.");

                try
                {
                    await item.ChangedExternally().ConfigureAwait(false);
                }
                catch (IOException ex)
                {
                    // For now swallow and log. 
                    // Research item: If an IOException occurs, the item may be in a disconnected state (media unavailable)
                    // Should we remove it from it's parent?
                    Logger.ErrorException("Error refreshing {0}", ex, item.Name);
                }
                catch (Exception ex)
                {
                    Logger.ErrorException("Error refreshing {0}", ex, item.Name);
                }
            }
        }

        /// <summary>
        /// Gets the affected base item.
        /// </summary>
        /// <param name="path">The path.</param>
        /// <returns>BaseItem.</returns>
        private BaseItem GetAffectedBaseItem(string path)
        {
            BaseItem item = null;

            while (item == null && !string.IsNullOrEmpty(path))
            {
                item = LibraryManager.FindByPath(path, null);

                path = System.IO.Path.GetDirectoryName(path);
            }

            if (item != null)
            {
                // If the item has been deleted find the first valid parent that still exists
                while (!_fileSystem.DirectoryExists(item.Path) && !_fileSystem.FileExists(item.Path))
                {
                    item = item.GetParent();

                    if (item == null)
                    {
                        break;
                    }
                }
            }

            return item;
        }

        private bool IsFileLocked(string path)
        {
            if (Environment.OSVersion.Platform != PlatformID.Win32NT)
            {
                // Causing lockups on linux
                return false;
            }

            try
            {
                var data = _fileSystem.GetFileSystemInfo(path);

                if (!data.Exists
                    || data.IsDirectory

                    // Opening a writable stream will fail with readonly files
                    || data.Attributes.HasFlag(FileAttributes.ReadOnly))
                {
                    return false;
                }
            }
            catch (IOException)
            {
                return false;
            }
            catch (Exception ex)
            {
                Logger.ErrorException("Error getting file system info for: {0}", ex, path);
                return false;
            }

            // In order to determine if the file is being written to, we have to request write access
            // But if the server only has readonly access, this is going to cause this entire algorithm to fail
            // So we'll take a best guess about our access level
            var requestedFileAccess = ConfigurationManager.Configuration.SaveLocalMeta
                ? FileAccess.ReadWrite
                : FileAccess.Read;

            try
            {
                using (_fileSystem.GetFileStream(path, FileMode.Open, requestedFileAccess, FileShare.ReadWrite))
                {
                    //file is not locked
                    return false;
                }
            }
            catch (DirectoryNotFoundException)
            {
                // File may have been deleted
                return false;
            }
            catch (FileNotFoundException)
            {
                // File may have been deleted
                return false;
            }
            catch (UnauthorizedAccessException)
            {
                Logger.Debug("No write permission for: {0}.", path);
                return false;
            }
            catch (IOException)
            {
                //the file is unavailable because it is:
                //still being written to
                //or being processed by another thread
                //or does not exist (has already been processed)
                Logger.Debug("{0} is locked.", path);
                return true;
            }
            catch (Exception ex)
            {
                Logger.ErrorException("Error determining if file is locked: {0}", ex, path);
                return false;
            }
        }

        private void DisposeTimer()
        {
            lock (_timerLock)
            {
                if (_timer != null)
                {
                    _timer.Dispose();
                }
            }
        }

        private bool _disposed;
        public void Dispose()
        {
            _disposed = true;
            DisposeTimer();
        }
    }
}
