/*
* Copyright (c) 2023 Vaughn Nugent
* 
* Library: VNLib
* Package: VNLib.Plugins.Runtime
* File: AsmFileWatcher.cs 
*
* AsmFileWatcher.cs is part of VNLib.Plugins.Runtime which is part of the larger 
* VNLib collection of libraries and utilities.
*
* VNLib.Plugins.Runtime is free software: you can redistribute it and/or modify 
* it under the terms of the GNU General Public License as published
* by the Free Software Foundation, either version 2 of the License,
* or (at your option) any later version.
*
* VNLib.Plugins.Runtime is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License 
* along with VNLib.Plugins.Runtime. If not, see http://www.gnu.org/licenses/.
*/

using System.IO;
using System.Threading;

using VNLib.Utils;
using VNLib.Utils.Extensions;

namespace VNLib.Plugins.Runtime
{
    internal sealed class AsmFileWatcher : VnDisposeable
    {
        public IPluginReloadEventHandler Handler { get; }

        private readonly IPluginAssemblyLoader _loaderSource;
        private readonly Timer _delayTimer;
        private readonly FileSystemWatcher _watcher;

        private bool _pause;

        public AsmFileWatcher(IPluginAssemblyLoader LoaderSource, IPluginReloadEventHandler handler)
        {
            Handler = handler;
            _loaderSource = LoaderSource;

            string dir = Path.GetDirectoryName(LoaderSource.Config.AssemblyFile)!;

            //Configure watcher to notify only when the assembly file changes
            _watcher = new FileSystemWatcher(dir)
            {
                Filter = "*.dll",
                EnableRaisingEvents = false,
                IncludeSubdirectories = true,
                NotifyFilter = NotifyFilters.LastWrite,
            };

            //Configure listener
            _watcher.Changed += OnFileChanged;
            _watcher.Created += OnFileChanged;

            _watcher.EnableRaisingEvents = true;

            //setup delay timer to wait on the config
            _delayTimer = new(OnTimeout, this, Timeout.InfiniteTimeSpan, Timeout.InfiniteTimeSpan);
        }

        void OnFileChanged(object sender, FileSystemEventArgs e)
        {
            //if were already waiting to process an event, we dont need to stage another
            if (_pause)
            {
                return;
            }

            //Set pause flag
            _pause = true;

            //Restart the timer to trigger reload event on elapsed
            _delayTimer.Restart(_loaderSource.Config.ReloadDelay);
        }

        private void OnTimeout(object? state)
        {
            _delayTimer.Stop();

            //Fire event, let exception crash app
            Handler.OnPluginUnloaded(_loaderSource);

            //Clear pause flag
            _pause = false;
        }

        protected override void Free()
        {
            _delayTimer.Dispose();

            //Detach event handler and dispose watcher
            _watcher.Changed -= OnFileChanged;
            _watcher.Dispose();
        }
    }
}