using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

namespace ArchestrAServices.Common;

public sealed class ConfigFileWatcher : IDisposable
{
	private static readonly ConfigFileWatcher theInstance = new ConfigFileWatcher();

	private readonly List<FileSystemEventHandler> eventHandlers = new List<FileSystemEventHandler>();

	private bool disposed;

	private FileSystemWatcher watcher;

	private ConfigFileWatcher()
	{
		string directoryName = Path.GetDirectoryName(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);
		string fileName = Path.GetFileName(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);
		if (string.IsNullOrWhiteSpace(directoryName) || string.IsNullOrWhiteSpace(fileName))
		{
			throw new ArgumentException("Invalid configuration file path.");
		}
		watcher = new FileSystemWatcher(directoryName, fileName);
		AppDomain.CurrentDomain.ProcessExit += delegate
		{
			Dispose();
		};
	}

	public static void AddHandler(FileSystemEventHandler eventHandler)
	{
		theInstance.RegisterHandler(eventHandler);
	}

	public static void RemoveHandler(FileSystemEventHandler eventHandler)
	{
		theInstance.UnRegisterHandler(eventHandler);
	}

	public void Dispose()
	{
		Dispose(disposing: true);
	}

	private void RegisterHandler(FileSystemEventHandler eventHandler)
	{
		if (watcher != null)
		{
			watcher.Changed += eventHandler;
			eventHandlers.Add(eventHandler);
			watcher.EnableRaisingEvents = true;
		}
	}

	private void UnRegisterHandler(FileSystemEventHandler eventHandler)
	{
		if (watcher != null)
		{
			watcher.Changed -= eventHandler;
			eventHandlers.Remove(eventHandler);
			if (!eventHandlers.Any())
			{
				watcher.EnableRaisingEvents = false;
			}
		}
	}

	private void Dispose(bool disposing)
	{
		if (disposed)
		{
			return;
		}
		if (disposing && watcher != null)
		{
			foreach (FileSystemEventHandler eventHandler in eventHandlers)
			{
				watcher.Changed -= eventHandler;
			}
			watcher.EnableRaisingEvents = false;
			watcher.Dispose();
			watcher = null;
			eventHandlers.Clear();
		}
		disposed = true;
	}
}