#352: Add custom map directory file watcher

- Add a file watcher that will detect when a map is added or deleted, then update the game mode dropdown according to the new map list
- Add and use `CustomMapsDirectory` field to `MapLoader` to avoid hard coded strings.
- Add `GetLoadedMapBySha1` to remove some duplicate `GameModeMaps.Find()`.
- Add a function `RefreshGameModeDropdown` to modify the dropdown after client is loaded. The function is a bit complicated due to doing inline modifications to the items and keeping the selected mode.

Issue: #352
PR: #358

DXMainClient/DXGUI/Generic/LoadingScreen.cs

@@ -81,6 +81,7 @@ private void LoadMaps()
         {
             mapLoader = new MapLoader();
             mapLoader.LoadMaps();
+            mapLoader.StartCustomMapFileWatcher();
         }
 
         private void Finish()

DXMainClient/DXGUI/Multiplayer/GameLobby/CnCNetGameLobby.cs

@@ -1594,14 +1594,14 @@ private void MapSharer_HandleMapDownloadComplete(SHA1EventArgs e)
         {
             string mapFileName = MapSharer.GetMapFileName(e.SHA1, e.MapName);
             Logger.Log("Map " + mapFileName + " downloaded, parsing.");
-            string mapPath = "Maps/Custom/" + mapFileName;
+            string mapPath = MapLoader.CustomMapsDirectory + mapFileName;
             Map map = MapLoader.LoadCustomMap(mapPath, out string returnMessage);
             if (map != null)
             {
                 AddNotice(returnMessage);
                 if (lastMapSHA1 == e.SHA1)
                 {
-                    GameModeMap = GameModeMaps.Find(gmm => gmm.Map.SHA1 == lastMapSHA1);
+                    GameModeMap = MapLoader.GetLoadedMapBySha1(lastMapSHA1);
                     ChangeMap(GameModeMap);
                 }
             }
@@ -1803,7 +1803,7 @@ private void DownloadMapByIdCommand(string parameters)
             sha1 = sha1.Replace("?", "");
 
             // See if the user already has this map, with any filename, before attempting to download it.
-            GameModeMap loadedMap = GameModeMaps.Find(gmm => gmm.Map.SHA1 == sha1);
+            GameModeMap loadedMap = MapLoader.GetLoadedMapBySha1(sha1);
 
             if (loadedMap != null)
             {

DXMainClient/DXGUI/Multiplayer/GameLobby/GameLobbyBase.cs

@@ -59,7 +59,10 @@ DiscordHandler discordHandler
         ) : base(windowManager)
         {
             _iniSectionName = iniName;
+
             MapLoader = mapLoader;
+            MapLoader.GameModeMapsUpdated += MapLoader_GameModeMapsUpdated;
+
             this.isMultiplayer = isMultiplayer;
             this.discordHandler = discordHandler;
         }
@@ -2315,5 +2318,63 @@ public bool LoadGameOptionPreset(string name)
         }
 
         protected abstract bool AllowPlayerOptionsChange();
+
+        /// <summary>
+        /// Handle the GameModeMapsUpdated event from the MapLoader.
+        ///
+        /// Updates the gamemode dropdown for new maps being added while the client is running
+        /// </summary>
+        /// <param name="sender"></param>
+        /// <param name="e"></param>
+        private void MapLoader_GameModeMapsUpdated(object sender, MapLoaderEventArgs e)
+        {
+            RefreshGameModeDropdown();
+        }
+
+        /// <summary>
+        /// Update the gamemode dropdown.
+        ///
+        /// Allows us to show gamemodes for maps that were loaded after the client was started.
+        /// This function will do in-place modifications to `ddGameModeMapFilter.Items`.
+        /// </summary>
+        public void RefreshGameModeDropdown()
+        {
+            // Use a hashset to store the existing gamemodes in the dropdown for instant lookups.
+            // This is the set of existing dropdown items. Add anything from GameModeMaps, that isn't in this set, to the dropdown.
+            HashSet<string> existingDdGameModes = new HashSet<string>(ddGameModeMapFilter.Items.Select(ddItem => ddItem.Text));
+            // This is the updated list of game modes. Anything not in this set, that is in existingDdGameModes, should be removed from the dropdown.
+            HashSet<string> gameModeUpdated = new HashSet<string>(GameModeMaps.GameModes.Select(gm => gm.UIName));
+            // Don't accidentally remove favorite maps item.
+            gameModeUpdated.Add(FavoriteMapsLabel);
+
+            XNADropDownItem currentItem = ddGameModeMapFilter.SelectedItem;
+
+            Logger.Log($"Updating game modes dropdown display: lobbyType={this.GetType().Name}");
+
+            // Add any new game modes.
+            foreach (GameMode gm in GameModeMaps.GameModes)
+            {
+                //skip the game mode if it is already in the dropdown.
+                if (existingDdGameModes.Contains(gm.UIName))
+                    continue;
+
+                // If the gamemode was not present, then add it.
+                ddGameModeMapFilter.AddItem(CreateGameFilterItem(gm.UIName, new GameModeMapFilter(GetGameModeMaps(gm))));
+            }
+
+            // Now remove game modes that should no longer be displayed.
+            ddGameModeMapFilter.Items.RemoveAll(ddItem => !gameModeUpdated.Contains(ddItem.Text));
+
+            // Make sure we keep the same game mode selected after adding or removing game modes.
+            // If the game mode is no longer available then switch to 0, aka, favorite maps.
+            int newIndex = 0;
+            for (int i = 0; i < ddGameModeMapFilter.Items.Count; i++)
+            {
+                if (ddGameModeMapFilter.Items[i].Text == currentItem.Text)
+                    newIndex = i;
+            }
+
+            ddGameModeMapFilter.SelectedIndex = newIndex;
+        }
     }
 }

DXMainClient/DXGUI/Multiplayer/GameLobby/MultiplayerGameLobby.cs

@@ -44,7 +44,7 @@ public MultiplayerGameLobby(WindowManager windowManager, string iniName,
                     s => SetMaxAhead(s)),
                 new ChatBoxCommand("PROTOCOLVERSION", "Change ProtocolVersion (default 2) (game host only)".L10N("UI:Main:ChatboxCommandProtocolVersionHelp"), true,
                     s => SetProtocolVersion(s)),
-                new ChatBoxCommand("LOADMAP", "Load a custom map with given filename from /Maps/Custom/ folder.".L10N("UI:Main:ChatboxCommandLoadMapHelp"), true, LoadCustomMap),
+                new ChatBoxCommand("LOADMAP", $"Load a custom map with given filename from {MapLoader.CustomMapsDirectory} folder.".L10N("UI:Main:ChatboxCommandLoadMapHelp"), true, LoadCustomMap),
                 new ChatBoxCommand("RANDOMSTARTS", "Enables completely random starting locations (Tiberian Sun based games only).".L10N("UI:Main:ChatboxCommandRandomStartsHelp"), true,
                     s => SetStartingLocationClearance(s)),
                 new ChatBoxCommand("ROLL", "Roll dice, for example /roll 3d6".L10N("UI:Main:ChatboxCommandRollHelp"), false, RollDiceCommand),
@@ -487,7 +487,7 @@ private void RollDiceCommand(string dieType)
         /// <param name="mapName">Name of the map given as a parameter, without file extension.</param>
         private void LoadCustomMap(string mapName)
         {
-            Map map = MapLoader.LoadCustomMap($"Maps/Custom/{mapName}", out string resultMessage);
+            Map map = MapLoader.LoadCustomMap($"{MapLoader.CustomMapsDirectory}{mapName}", out string resultMessage);
             if (map != null)
             {
                 AddNotice(resultMessage);

DXMainClient/DXMainClient.csproj

@@ -432,6 +432,7 @@
     <Compile Include="Domain\Multiplayer\CnCNet\MapSharer.cs" />
     <Compile Include="Domain\Multiplayer\GameModeMap.cs" />
     <Compile Include="Domain\Multiplayer\GameModeMapCollection.cs" />
+    <Compile Include="Domain\Multiplayer\MapLoaderEventArgs.cs" />
     <Compile Include="Domain\Multiplayer\GameOptionPresets.cs" />
     <Compile Include="Domain\Multiplayer\LAN\ClientIntCommandHandler.cs" />
     <Compile Include="Domain\Multiplayer\LAN\LANLobbyUser.cs" />

DXMainClient/Domain/Multiplayer/CnCNet/MapSharer.cs

@@ -121,7 +121,7 @@ private static string MapUpload(string _URL, Map map, string gameName, out bool
         {
             ServicePointManager.Expect100Continue = false;
 
-            string zipFile = ProgramConstants.GamePath + "Maps/Custom/" + map.SHA1 + ".zip";
+            string zipFile = ProgramConstants.GamePath + MapLoader.CustomMapsDirectory + map.SHA1 + ".zip";
 
             if (File.Exists(zipFile)) File.Delete(zipFile);
 
@@ -380,7 +380,7 @@ public static string GetMapFileName(string sha1, string mapName)
 
         private static string DownloadMain(string sha1, string myGame, string mapName, out bool success)
         {
-            string customMapsDirectory = ProgramConstants.GamePath + "Maps/Custom/";
+            string customMapsDirectory = ProgramConstants.GamePath + MapLoader.CustomMapsDirectory;
 
             string mapFileName = GetMapFileName(sha1, mapName);