Merge light & darkness mechanic into develop

Room.dark + Item.light flags and a Light helper (isLit/carryingLight). Model B
gating: you can't enter a dark room without a lit light source; look/take/examine
are obscured in the dark; the HUD light field is wired. Entry-gate prevents
soft-locks. Demo: the dark dungeon needs the lit lamp to reach the generator.
127 tests green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Semesterprojekt/docs/enhancement-ideas.md

@@ -122,6 +122,10 @@ des Bogens; einzelne Teilziele schalten je den nächsten Bereich frei.
    Hebel/Ventile setzen Flags und öffnen Bereiche.
 3. **Licht & Dunkelheit** – dunkle Räume brauchen eine brennende Lichtquelle,
    sonst keine Sicht auf Exits/Items (Atmosphäre, einfach umzusetzen).
+   > ✅ Umgesetzt (Branch `feature/light-darkness`): `Room.dark` + `Item.light`,
+   > `Light`-Helper, Gating in go/look/take/examine (Modell B: kein Eintritt ohne
+   > Licht), HUD-Licht verdrahtet. Demo: dunkler Dungeon braucht die brennende
+   > Lampe für den Generator.
 4. **Item-Kombination** – z.B. `match + candle → lit candle`. Achtung: v1.0 hat
    bewusst argloses `use X` ohne Targets gewählt → Command-Grammatik muss erweitert
    werden (jetzt erlaubt, da über MVP hinaus).

Semesterprojekt/src/main/java/thb/jeanluc/adventure/command/impl/ExamineCommand.java

@@ -2,6 +2,7 @@ package thb.jeanluc.adventure.command.impl;
 
 import thb.jeanluc.adventure.command.Command;
 import thb.jeanluc.adventure.game.GameContext;
+import thb.jeanluc.adventure.game.Light;
 import thb.jeanluc.adventure.model.Npc;
 import thb.jeanluc.adventure.model.item.Item;
 
@@ -20,6 +21,10 @@ public class ExamineCommand implements Command {
             ctx.getIo().write("Examine what?");
             return;
         }
+        if (!Light.isLit(ctx, ctx.getPlayer().getCurrentRoom())) {
+            ctx.getIo().write("It's too dark to see that.");
+            return;
+        }
         String id = args.getFirst();
         Optional<Item> item = ctx.getPlayer().findItem(id);
         if (item.isEmpty()) {

Semesterprojekt/src/main/java/thb/jeanluc/adventure/command/impl/GoCommand.java

@@ -3,6 +3,7 @@ package thb.jeanluc.adventure.command.impl;
 import thb.jeanluc.adventure.command.Command;
 import thb.jeanluc.adventure.game.Conditions;
 import thb.jeanluc.adventure.game.GameContext;
+import thb.jeanluc.adventure.game.Light;
 import thb.jeanluc.adventure.model.Direction;
 import thb.jeanluc.adventure.model.ExitLock;
 import thb.jeanluc.adventure.model.Room;
@@ -39,6 +40,11 @@ public class GoCommand implements Command {
             ctx.getIo().write(lock.blocked());
             return;
         }
+        if (!Light.isLit(ctx, next.get())) {
+            ctx.getIo().write("It's pitch black beyond the doorway — you need a lit light source "
+                    + "(try lighting your lamp with 'use lamp').");
+            return;
+        }
         ctx.getPlayer().setCurrentRoom(next.get());
         new LookCommand().execute(ctx, List.of());
     }

Semesterprojekt/src/main/java/thb/jeanluc/adventure/command/impl/LookCommand.java

@@ -3,6 +3,7 @@ package thb.jeanluc.adventure.command.impl;
 import thb.jeanluc.adventure.command.Command;
 import thb.jeanluc.adventure.game.Conditions;
 import thb.jeanluc.adventure.game.GameContext;
+import thb.jeanluc.adventure.game.Light;
 import thb.jeanluc.adventure.io.text.RoomView;
 import thb.jeanluc.adventure.model.DescriptionState;
 import thb.jeanluc.adventure.model.Direction;
@@ -21,6 +22,10 @@ public class LookCommand implements Command {
     @Override
     public void execute(GameContext ctx, List<String> args) {
         Room room = ctx.getPlayer().getCurrentRoom();
+        if (!Light.isLit(ctx, room)) {
+            ctx.getIo().write("It's pitch black; you can't make anything out. You need a light source.");
+            return;
+        }
         List<String> items = room.getItems().values().stream().map(Item::getName).toList();
         List<String> npcs = room.getNpcs().values().stream().map(Npc::getName).toList();
         List<String> exits = room.getExits().keySet().stream().map(Direction::getLabel).toList();

Semesterprojekt/src/main/java/thb/jeanluc/adventure/command/impl/TakeCommand.java

@@ -2,6 +2,7 @@ package thb.jeanluc.adventure.command.impl;
 
 import thb.jeanluc.adventure.command.Command;
 import thb.jeanluc.adventure.game.GameContext;
+import thb.jeanluc.adventure.game.Light;
 import thb.jeanluc.adventure.model.Room;
 import thb.jeanluc.adventure.model.item.Item;
 
@@ -20,6 +21,10 @@ public class TakeCommand implements Command {
             ctx.getIo().write("Take what?");
             return;
         }
+        if (!Light.isLit(ctx, ctx.getPlayer().getCurrentRoom())) {
+            ctx.getIo().write("It's too dark to see that.");
+            return;
+        }
         String itemId = args.getFirst();
         Room room = ctx.getPlayer().getCurrentRoom();
         Optional<Item> taken = room.removeItem(itemId);

Semesterprojekt/src/main/java/thb/jeanluc/adventure/game/Game.java

@@ -77,7 +77,7 @@ public class Game {
                 ctx.getPlayer().getCurrentRoom().getName(),
                 ctx.getPlayer().getGold(),
                 turn,
-                false));
+                Light.carryingLight(ctx)));
         MapView map = MapLayout.compute(
                 ctx.getWorld(),
                 ctx.getPlayer().getVisitedRoomIds(),

Semesterprojekt/src/main/java/thb/jeanluc/adventure/game/Light.java

@@ -0,0 +1,44 @@
+package thb.jeanluc.adventure.game;
+
+import thb.jeanluc.adventure.model.Room;
+import thb.jeanluc.adventure.model.item.Item;
+import thb.jeanluc.adventure.model.item.SwitchableItem;
+
+import java.util.Collection;
+
+/** Decides whether a room is lit, given dark rooms and active light sources. */
+public final class Light {
+
+    private Light() {
+    }
+
+    /** A room is lit if it is not dark, or an active light source is carried or present. */
+    public static boolean isLit(GameContext ctx, Room room) {
+        if (!room.isDark()) {
+            return true;
+        }
+        return hasActiveLight(ctx.getPlayer().getInventory().values())
+                || hasActiveLight(room.getItems().values());
+    }
+
+    /** True if the player carries an active light source (for the HUD). */
+    public static boolean carryingLight(GameContext ctx) {
+        return hasActiveLight(ctx.getPlayer().getInventory().values());
+    }
+
+    private static boolean hasActiveLight(Collection<Item> items) {
+        for (Item it : items) {
+            if (isActiveLight(it)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private static boolean isActiveLight(Item it) {
+        if (!it.isLight()) {
+            return false;
+        }
+        return !(it instanceof SwitchableItem s) || s.isOn();
+    }
+}

Semesterprojekt/src/main/java/thb/jeanluc/adventure/loader/ItemFactory.java

@@ -30,12 +30,14 @@ public final class ItemFactory {
                     .id(dto.id())
                     .name(dto.name())
                     .description(dto.description())
+                    .light(Boolean.TRUE.equals(dto.light()))
                     .build();
             case "readable" -> ReadableItem.builder()
                     .id(dto.id())
                     .name(dto.name())
                     .description(dto.description())
                     .readText(dto.readText())
+                    .light(Boolean.TRUE.equals(dto.light()))
                     .build();
             case "switchable" -> SwitchableItem.builder()
                     .id(dto.id())
@@ -45,6 +47,7 @@ public final class ItemFactory {
                     .onText(dto.onText())
                     .offText(dto.offText())
                     .effects(thb.jeanluc.adventure.loader.dto.EffectDto.toModelList(dto.effects()))
+                    .light(Boolean.TRUE.equals(dto.light()))
                     .build();
             default -> throw new WorldLoadException(
                     "Unknown item type '" + dto.type() + "' on item '" + dto.id() + "'");

Semesterprojekt/src/main/java/thb/jeanluc/adventure/loader/RoomFactory.java

@@ -19,6 +19,8 @@ public final class RoomFactory {
      * @return the freshly built room shell
      */
     public static Room shellFromDto(RoomDto dto) {
-        return new Room(dto.id(), dto.name(), dto.description());
+        Room room = new Room(dto.id(), dto.name(), dto.description());
+        room.setDark(Boolean.TRUE.equals(dto.dark()));
+        return room;
     }
 }

Semesterprojekt/src/main/java/thb/jeanluc/adventure/loader/dto/ItemDto.java

@@ -15,6 +15,7 @@ import java.util.List;
  * @param onText       message printed when a switchable transitions to on
  * @param offText      message printed when a switchable transitions to off
  * @param effects      effects applied when a switchable transitions to on; nullable
+ * @param light        whether this item is a light source; nullable
  */
 public record ItemDto(
         String type,
@@ -25,11 +26,12 @@ public record ItemDto(
         Boolean initialState,
         String onText,
         String offText,
-        List<EffectDto> effects
+        List<EffectDto> effects,
+        Boolean light
 ) {
-    /** Backward-compatible constructor without effects. */
+    /** Backward-compatible constructor without effects/light. */
     public ItemDto(String type, String id, String name, String description,
                    String readText, Boolean initialState, String onText, String offText) {
-        this(type, id, name, description, readText, initialState, onText, offText, null);
+        this(type, id, name, description, readText, initialState, onText, offText, null, null);
     }
 }

Semesterprojekt/src/main/java/thb/jeanluc/adventure/loader/dto/RoomDto.java

@@ -14,6 +14,7 @@ import java.util.Map;
  * @param npcs        ids of NPCs initially in this room
  * @param exitLocks   optional condition-gates per exit direction
  * @param descriptionStates optional condition-gated description variants
+ * @param dark        whether this room is dark; nullable
  */
 public record RoomDto(
         String id,
@@ -23,11 +24,12 @@ public record RoomDto(
         List<String> items,
         List<String> npcs,
         List<ExitLockDto> exitLocks,
-        List<DescriptionStateDto> descriptionStates
+        List<DescriptionStateDto> descriptionStates,
+        Boolean dark
 ) {
     /** Backward-compatible constructor without the optional state fields. */
     public RoomDto(String id, String name, String description,
                    Map<String, String> exits, List<String> items, List<String> npcs) {
-        this(id, name, description, exits, items, npcs, null, null);
+        this(id, name, description, exits, items, npcs, null, null, null);
     }
 }

Semesterprojekt/src/main/java/thb/jeanluc/adventure/model/Room.java

@@ -2,6 +2,7 @@ package thb.jeanluc.adventure.model;
 
 import lombok.Getter;
 import lombok.RequiredArgsConstructor;
+import lombok.Setter;
 import thb.jeanluc.adventure.model.item.Item;
 
 import java.util.ArrayList;
@@ -50,6 +51,10 @@ public class Room {
     /** Optional condition-gated description variants, first match wins. */
     private final List<DescriptionState> descriptionStates = new ArrayList<>();
 
+    /** Whether this room is dark (needs a light source to enter/see). */
+    @Setter
+    private boolean dark;
+
     /**
      * Connects this room to another in the given direction. Does not
      * create the reverse connection — callers must set that up

Semesterprojekt/src/main/java/thb/jeanluc/adventure/model/item/Item.java

@@ -33,6 +33,9 @@ public abstract class Item {
     /** Long description shown by the {@code examine} command. */
     protected final String description;
 
+    /** Whether this item can serve as a light source (when on, for switchables). */
+    protected final boolean light;
+
     /**
      * Executes the item's primary action. Side effects (text output,
      * mutation of player state) flow through the given context.

Semesterprojekt/src/main/resources/world/items.yaml

@@ -10,6 +10,7 @@
   name: Oil Lamp
   description: An old oil lamp, heavy with fuel.
   initialState: false
+  light: true
   onText: The lamp flares to life, casting a warm glow.
   offText: You snuff out the lamp.
 

Semesterprojekt/src/main/resources/world/rooms.yaml

@@ -54,7 +54,8 @@
 - id: dungeon
   name: Dungeon
   description: |
-    A dark, damp room. A rusty generator squats in the corner.
+    A cramped stone room, black as pitch. A rusty generator squats in the corner.
+  dark: true
   exits:
     north: kitchen
   items: [generator]

Semesterprojekt/src/test/java/thb/jeanluc/adventure/command/impl/DarknessTest.java

@@ -0,0 +1,64 @@
+package thb.jeanluc.adventure.command.impl;
+
+import org.junit.jupiter.api.Test;
+import thb.jeanluc.adventure.game.GameContext;
+import thb.jeanluc.adventure.io.TestIO;
+import thb.jeanluc.adventure.model.Direction;
+import thb.jeanluc.adventure.model.Player;
+import thb.jeanluc.adventure.model.Room;
+import thb.jeanluc.adventure.model.item.SwitchableItem;
+
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class DarknessTest {
+    private SwitchableItem lamp(boolean on) {
+        return SwitchableItem.builder().id("lamp").name("Lamp").description("d")
+                .state(on).onText("on").offText("off").light(true).build();
+    }
+
+    @Test
+    void cannotEnterDarkRoomWithoutLight() {
+        Room hall = new Room("hall", "Hall", "d");
+        Room cave = new Room("cave", "Cave", "d");
+        cave.setDark(true);
+        hall.addExit(Direction.NORTH, cave);
+        Player p = new Player(hall, 0);
+        GameContext ctx = new GameContext(null, p, new TestIO());
+
+        new GoCommand().execute(ctx, List.of("north"));
+        assertThat(p.getCurrentRoom()).isEqualTo(hall);
+        assertThat(((TestIO) ctx.getIo()).allOutput()).containsIgnoringCase("pitch black");
+    }
+
+    @Test
+    void canEnterDarkRoomWithLitLamp() {
+        Room hall = new Room("hall", "Hall", "d");
+        Room cave = new Room("cave", "Cave", "d");
+        cave.setDark(true);
+        hall.addExit(Direction.NORTH, cave);
+        Player p = new Player(hall, 0);
+        p.addItem(lamp(true));
+        GameContext ctx = new GameContext(null, p, new TestIO());
+
+        new GoCommand().execute(ctx, List.of("north"));
+        assertThat(p.getCurrentRoom()).isEqualTo(cave);
+    }
+
+    @Test
+    void lookAndTakeAreBlockedInTheDark() {
+        Room cave = new Room("cave", "Cave", "d");
+        cave.setDark(true);
+        Player p = new Player(cave, 0);
+        TestIO io = new TestIO();
+        GameContext ctx = new GameContext(null, p, io);
+
+        new LookCommand().execute(ctx, List.of());
+        assertThat(io.allOutput()).containsIgnoringCase("pitch black");
+
+        io.outputs().clear();
+        new TakeCommand().execute(ctx, List.of("anything"));
+        assertThat(io.allOutput()).containsIgnoringCase("too dark");
+    }
+}

Semesterprojekt/src/test/java/thb/jeanluc/adventure/game/LightTest.java

@@ -0,0 +1,63 @@
+package thb.jeanluc.adventure.game;
+
+import org.junit.jupiter.api.Test;
+import thb.jeanluc.adventure.io.TestIO;
+import thb.jeanluc.adventure.model.Player;
+import thb.jeanluc.adventure.model.Room;
+import thb.jeanluc.adventure.model.item.PlainItem;
+import thb.jeanluc.adventure.model.item.SwitchableItem;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class LightTest {
+    private GameContext ctx(Player p) {
+        return new GameContext(null, p, new TestIO());
+    }
+
+    private SwitchableItem lamp(boolean on) {
+        return SwitchableItem.builder().id("lamp").name("Lamp").description("d")
+                .state(on).onText("on").offText("off").light(true).build();
+    }
+
+    @Test
+    void litRoomIsAlwaysLit() {
+        Room bright = new Room("r", "R", "d"); // dark defaults to false
+        assertThat(Light.isLit(ctx(new Player(bright, 0)), bright)).isTrue();
+    }
+
+    @Test
+    void darkRoomNeedsActiveLight() {
+        Room dark = new Room("r", "R", "d");
+        dark.setDark(true);
+        Player p = new Player(dark, 0);
+        GameContext ctx = ctx(p);
+        assertThat(Light.isLit(ctx, dark)).isFalse();
+
+        p.addItem(lamp(false));
+        assertThat(Light.isLit(ctx, dark)).isFalse();   // lamp off
+
+        p.removeItem("lamp");
+        p.addItem(lamp(true));
+        assertThat(Light.isLit(ctx, dark)).isTrue();    // lamp on, carried
+        assertThat(Light.carryingLight(ctx)).isTrue();
+    }
+
+    @Test
+    void litLampLyingInRoomLightsIt() {
+        Room dark = new Room("r", "R", "d");
+        dark.setDark(true);
+        dark.addItem(lamp(true));
+        Player p = new Player(dark, 0);
+        assertThat(Light.isLit(ctx(p), dark)).isTrue();
+        assertThat(Light.carryingLight(ctx(p))).isFalse(); // not carried
+    }
+
+    @Test
+    void nonLightItemDoesNotLight() {
+        Room dark = new Room("r", "R", "d");
+        dark.setDark(true);
+        Player p = new Player(dark, 0);
+        p.addItem(PlainItem.builder().id("rock").name("Rock").description("d").build());
+        assertThat(Light.isLit(ctx(p), dark)).isFalse();
+    }
+}