Decent work on config reload ability

It was always annoying to restart whole ASF process just to issue a small config update for one of the bots, with this commit - auto reload has been implemented. ASF will automatically restart given bot instance if it's config file gets changed. With introduction of this commit, we also ditch StartOnLaunch property (because it no longer means sense, any disabled bot can be started through config edit), and we also ditch auto-shutdown of ASF process, because it's possible to edit bot config file to start it.
Some further work might be needed, this is pretty much work in progress. It would be super if ASF was also able to automatically decent new bot configs, and create new bots for them, but this is initial step.

ArchiSteamFarm/BotConfig.cs

@@ -28,13 +28,22 @@ using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
+using System.Threading.Tasks;
 
 namespace ArchiSteamFarm {
 	[SuppressMessage("ReSharper", "ClassCannotBeInstantiated")]
 	[SuppressMessage("ReSharper", "ClassNeverInstantiated.Global")]
 	[SuppressMessage("ReSharper", "ConvertToConstant.Local")]
 	[SuppressMessage("ReSharper", "ConvertToConstant.Global")]
-	internal sealed class BotConfig {
+	internal sealed class BotConfig : IDisposable {
+		internal sealed class BotConfigEventArgs : EventArgs {
+			internal readonly BotConfig BotConfig;
+
+			internal BotConfigEventArgs(BotConfig botConfig = null) {
+				BotConfig = botConfig;
+			}
+		}
+
 		internal enum EFarmingOrder : byte {
 			Unordered,
 			AppIDsAscending,
@@ -53,9 +62,6 @@ namespace ArchiSteamFarm {
 		[JsonProperty(Required = Required.DisallowNull)]
 		internal readonly bool Paused = false;
 
-		[JsonProperty(Required = Required.DisallowNull)]
-		internal readonly bool StartOnLaunch = true;
-
 		[JsonProperty]
 		internal string SteamLogin { get; set; }
 
@@ -131,6 +137,12 @@ namespace ArchiSteamFarm {
 		[JsonProperty(Required = Required.DisallowNull)]
 		private readonly CryptoHelper.ECryptoMethod PasswordFormat = CryptoHelper.ECryptoMethod.PlainText;
 
+		internal event EventHandler<BotConfigEventArgs> NewConfigLoaded;
+
+		private string FilePath;
+		private FileSystemWatcher FileSystemWatcher;
+		private DateTime LastWriteTime = DateTime.MinValue;
+
 		internal static BotConfig Load(string filePath) {
 			if (string.IsNullOrEmpty(filePath)) {
 				Logging.LogNullError(nameof(filePath));
@@ -155,6 +167,8 @@ namespace ArchiSteamFarm {
 				return null;
 			}
 
+			botConfig.FilePath = filePath;
+
 			// Support encrypted passwords
 			if ((botConfig.PasswordFormat != CryptoHelper.ECryptoMethod.PlainText) && !string.IsNullOrEmpty(botConfig.SteamPassword)) {
 				// In worst case password will result in null, which will have to be corrected by user during runtime
@@ -178,5 +192,78 @@ namespace ArchiSteamFarm {
 
 		// This constructor is used only by deserializer
 		private BotConfig() { }
+
+		internal void InitializeWatcher() {
+			if (FileSystemWatcher != null) {
+				return;
+			}
+
+			if (string.IsNullOrEmpty(FilePath)) {
+				Logging.LogNullError(nameof(FilePath));
+				return;
+			}
+
+			string fileDirectory = Path.GetDirectoryName(FilePath);
+			if (string.IsNullOrEmpty(fileDirectory)) {
+				Logging.LogNullError(nameof(fileDirectory));
+				return;
+			}
+
+			string fileName = Path.GetFileName(FilePath);
+			if (string.IsNullOrEmpty(fileName)) {
+				Logging.LogNullError(nameof(fileName));
+				return;
+			}
+
+			FileSystemWatcher = new FileSystemWatcher(fileDirectory, fileName) {
+				NotifyFilter = NotifyFilters.FileName | NotifyFilters.LastWrite
+			};
+
+			FileSystemWatcher.Changed += OnChanged;
+			FileSystemWatcher.Deleted += OnDeleted;
+			FileSystemWatcher.Renamed += OnRenamed;
+
+			FileSystemWatcher.EnableRaisingEvents = true;
+		}
+
+		private async void OnChanged(object sender, FileSystemEventArgs e) {
+			if (NewConfigLoaded == null) {
+				return;
+			}
+
+			DateTime lastWriteTime;
+
+			lock (FileSystemWatcher) {
+				lastWriteTime = File.GetLastWriteTime(FilePath);
+				if (LastWriteTime == lastWriteTime) {
+					return;
+				}
+
+				LastWriteTime = lastWriteTime;
+			}
+
+			// It's entirely possible that some process is still accessing our file, allow at least a second before trying to read it
+			await Task.Delay(1000).ConfigureAwait(false);
+
+			// It's also possible that we got some other event in the meantime
+			if (lastWriteTime != LastWriteTime) {
+				return;
+			}
+
+			NewConfigLoaded?.Invoke(this, new BotConfigEventArgs(Load(FilePath)));
+		}
+		private void OnDeleted(object sender, FileSystemEventArgs e) => NewConfigLoaded?.Invoke(this, new BotConfigEventArgs());
+		private void OnRenamed(object sender, RenamedEventArgs e) => NewConfigLoaded?.Invoke(this, new BotConfigEventArgs());
+
+		public void Dispose() {
+			if (FileSystemWatcher == null) {
+				return;
+			}
+
+			FileSystemWatcher.Changed -= OnChanged;
+			FileSystemWatcher.Deleted -= OnDeleted;
+			FileSystemWatcher.Renamed -= OnRenamed;
+			FileSystemWatcher.Dispose();
+		}
 	}
 }