Support turning citizens into specialists and changing their type

This doesn't yet implement the benefits of specialists, but it does allow us to force certain tiles to not be worked. This is important when passing tiles between cities, for example.

#541

C7/Game.cs

@@ -132,6 +132,7 @@ public override void _Ready() {
 				// are visible and map UI locations back to map locations.
 				cityScreen.tileAssignmentLayer = mapView.tileAssignmentLayer;
 				cityScreen.mapView = mapView;
+				cityScreen.citizenTypes = gameDataAccess.gameData.citizenTypes;
 			}
 
 			//TODO: What was this supposed to do?  It throws errors and occasinally causes crashes now, because _OnViewportSizeChanged doesn't exist

C7/UIElements/CityScreen/CityScreen.cs

@@ -14,6 +14,7 @@ public partial class CityScreen : CenterContainer {
 	private ILogger log = LogManager.ForContext<CityScreen>();
 	public TileAssignmentLayer tileAssignmentLayer;
 	public MapView mapView;
+	public List<CitizenType> citizenTypes;
 	private TextureRect background;
 	private List<TextureButton> popHeads = new();
 
@@ -50,7 +51,7 @@ public override void _UnhandledInput(InputEvent @event) {
 					using (UIGameDataAccess gameDataAccess = new()) {
 						Tile tile = mapView.tileOnScreenAt(gameDataAccess.gameData.map, eventMouseButton.Position);
 						if (tile != null) {
-							HandleReassignment(tile, gameDataAccess.gameData.citizenTypes);
+							HandleReassignment(tile);
 							RenderPopHeads(tileAssignmentLayer.city);
 						}
 					}
@@ -59,7 +60,14 @@ public override void _UnhandledInput(InputEvent @event) {
 		}
 	}
 
-	private void HandleReassignment(Tile tile, List<CitizenType> citizenTypes) {
+	// Returns a list of specialists that this player can use.
+	private List<CitizenType> GetKnownSpecialists(Player player) {
+		return citizenTypes.FindAll(x => {
+			return !x.IsDefaultCitizen && (x.PrerequisiteTech == null || player.knownTechs.Contains(x.PrerequisiteTech));
+		});
+	}
+
+	private void HandleReassignment(Tile tile) {
 		City city = tileAssignmentLayer.city;
 
 		// We can't assign citizens to other cities.
@@ -73,9 +81,15 @@ private void HandleReassignment(Tile tile, List<CitizenType> citizenTypes) {
 		}
 
 		// If we're already working a tile and click on it, turn the citizen
-		// into an entertainer.
+		// into a specialist.
 		if (tile.personWorkingTile != null && tile.personWorkingTile.city == city) {
-			// TODO: implement entertainers.
+			foreach (CitizenType citizenType in GetKnownSpecialists(city.owner)) {
+				CityResident resident = tile.personWorkingTile;
+				tile.personWorkingTile = null;
+				resident.tileWorked = Tile.NONE;
+				resident.citizenType = citizenType;
+				return;
+			}
 			return;
 		}
 
@@ -202,9 +216,6 @@ private void RenderPopHeads(City city) {
 
 		// Add each of the specialists.
 		//
-		// TODO: When clicking a specialist, have it iterate through the types
-		// of specialists known to the player.
-		//
 		// TODO: Render the specialist effect (like a smiley for entertainers)
 		// in the corner of the head.
 		foreach (CityResident cr in specialists) {
@@ -215,6 +226,16 @@ private void RenderPopHeads(City city) {
 			tb.TextureNormal = Util.LoadTextureFromPCX("Art/SmallHeads/popHeads.pcx",
 														textX + 1, textY + 1, 48, 48);
 			tb.SetPosition(new Vector2(xPos, 440));
+
+			List<CitizenType> specialistTypes = GetKnownSpecialists(city.owner);
+			int index = specialistTypes.FindIndex(x => x.Id == cr.citizenType.Id);
+			tb.Pressed += () => {
+				cr.citizenType = specialistTypes[(index + 1) % specialistTypes.Count];
+				++index;
+				RenderPopHeads(city);
+			};
+
+
 			background.AddChild(tb);
 			popHeads.Add(tb);
 			xPos += 48;