Merge use X on Y item combinations into develop

Data-driven combination recipes (combinations.yaml: requires/consume/produce/
effects/response/failText), operands resolved from inventory or current room,
order-independent canonical pair key. UseCommand routes 2+ args to a new
Combinations engine; no parser change (on/with/to already fillers). Loader
validates ids + rejects self-combination/duplicate pairs at load. Demo:
matches + torch -> lit_torch (a working light source).

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

Semesterprojekt/docs/enhancement-ideas.md

@@ -129,6 +129,12 @@ des Bogens; einzelne Teilziele schalten je den nächsten Bereich frei.
 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).
+   > ✅ umgesetzt (Branch `feature/use-x-on-y`): `use X on Y` als datengetriebene
+   > Rezepte (`combinations.yaml`: requires/consume/produce/effects/response/failText),
+   > Operanden aus Inventar oder Raum, reihenfolge-unabhängiger Paar-Key. Kein
+   > Parser-Eingriff (`on`/`with`/`to` sind bereits Filler). Selbst-Kombination
+   > (a==b) wird beim Laden abgelehnt. Demo: `matches` + `torch` → `lit_torch`
+   > (dauerhafte Lichtquelle).
 5. **Quest-Ketten + mehrere Enden** – Teilziele referenzieren Flags; Kette
    abschließen = Win; *welche* Flags gesetzt sind, entscheidet das Ende.
 

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

@@ -1,6 +1,7 @@
 package thb.jeanluc.adventure.command.impl;
 
 import thb.jeanluc.adventure.command.Command;
+import thb.jeanluc.adventure.game.Combinations;
 import thb.jeanluc.adventure.game.GameContext;
 import thb.jeanluc.adventure.model.item.Item;
 
@@ -8,9 +9,10 @@ import java.util.List;
 import java.util.Optional;
 
 /**
- * Invokes the item-specific {@link Item#use(GameContext)} action. The
+ * With one argument, invokes the item-specific {@link Item#use(GameContext)}
- * item must either be in the player's inventory or in the current room.
+ * action; the item must be in the player's inventory or the current room.
- * Usage: {@code use <item-id>}.
+ * With two arguments ({@code use <item> on <item>}), delegates to the
+ * combination engine. Usage: {@code use <item>} or {@code use <item> on <item>}.
  */
 public class UseCommand implements Command {
 
@@ -20,6 +22,10 @@ public class UseCommand implements Command {
             ctx.getIo().write("Use what?");
             return;
         }
+        if (args.size() >= 2) {
+            Combinations.tryUse(ctx, args.get(0), args.get(1));
+            return;
+        }
         String itemId = args.getFirst();
         Optional<Item> item = ctx.getPlayer().findItem(itemId);
         if (item.isEmpty()) {
@@ -34,6 +40,6 @@ public class UseCommand implements Command {
 
     @Override
     public String help() {
-        return "use <item>  -  use an item (read it, switch it on/off, ...)";
+        return "use <item>  -  use an item; or  use <item> on <item>  to combine them";
     }
 }

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

@@ -0,0 +1,69 @@
+package thb.jeanluc.adventure.game;
+
+import thb.jeanluc.adventure.model.Combination;
+import thb.jeanluc.adventure.model.item.Item;
+
+/**
+ * Applies {@code use X on Y} item combinations. Stateless utility, mirroring
+ * {@link Conditions}/{@link Effects}/{@link Light}. Operands resolve from the
+ * player's inventory or the current room.
+ */
+public final class Combinations {
+
+    private Combinations() {
+    }
+
+    /**
+     * Attempts to combine the two named items. Prints a resolution error if an
+     * operand is absent, the recipe's {@code failText} (or a generic line) if a
+     * recipe's requirements are unmet, "Nothing happens." if there is no recipe,
+     * or applies consume/produce/effects + the response on success.
+     */
+    public static void tryUse(GameContext ctx, String idX, String idY) {
+        if (!present(ctx, idX)) {
+            ctx.getIo().write(noSuch(idX));
+            return;
+        }
+        if (!present(ctx, idY)) {
+            ctx.getIo().write(noSuch(idY));
+            return;
+        }
+        Combination c = ctx.getWorld().getCombinations().get(Combination.key(idX, idY));
+        if (c == null) {
+            ctx.getIo().write("Nothing happens.");
+            return;
+        }
+        if (!Conditions.all(c.requires(), ctx)) {
+            ctx.getIo().write(c.failText() != null ? c.failText() : "Nothing happens.");
+            return;
+        }
+        for (String id : c.consume()) {
+            removeFromAnywhere(ctx, id);
+        }
+        if (c.produce() != null) {
+            Item produced = ctx.getWorld().getItems().get(c.produce());
+            if (produced != null) {
+                ctx.getPlayer().addItem(produced);
+            }
+        }
+        Effects.applyAll(c.effects(), ctx);
+        if (c.response() != null && !c.response().isBlank()) {
+            ctx.getIo().write(c.response());
+        }
+    }
+
+    private static boolean present(GameContext ctx, String id) {
+        return ctx.getPlayer().hasItem(id)
+                || ctx.getPlayer().getCurrentRoom().findItem(id).isPresent();
+    }
+
+    private static void removeFromAnywhere(GameContext ctx, String id) {
+        if (ctx.getPlayer().removeItem(id).isEmpty()) {
+            ctx.getPlayer().getCurrentRoom().removeItem(id);
+        }
+    }
+
+    private static String noSuch(String id) {
+        return "There is no '" + id + "' here or in your inventory.";
+    }
+}

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

@@ -0,0 +1,53 @@
+package thb.jeanluc.adventure.loader;
+
+import thb.jeanluc.adventure.loader.dto.CombinationDto;
+import thb.jeanluc.adventure.loader.dto.ConditionDto;
+import thb.jeanluc.adventure.loader.dto.EffectDto;
+import thb.jeanluc.adventure.model.Combination;
+import thb.jeanluc.adventure.model.item.Item;
+
+import java.util.List;
+import java.util.Map;
+
+/** Builds {@link Combination}s from {@link CombinationDto}s, validating item ids. */
+public final class CombinationFactory {
+
+    private CombinationFactory() {
+    }
+
+    public static Combination fromDto(CombinationDto dto, Map<String, Item> items) {
+        requireItem(items, dto.a(), "a");
+        requireItem(items, dto.b(), "b");
+        if (dto.a().equals(dto.b())) {
+            throw new WorldLoadException(
+                    "Combination cannot combine an item with itself: '" + dto.a() + "'");
+        }
+        if (dto.consume() != null) {
+            for (String id : dto.consume()) {
+                requireItem(items, id, "consume");
+            }
+        }
+        if (dto.produce() != null) {
+            requireItem(items, dto.produce(), "produce");
+        }
+        return new Combination(
+                dto.a(),
+                dto.b(),
+                ConditionDto.toModelList(dto.requires()),
+                dto.consume() == null ? List.of() : List.copyOf(dto.consume()),
+                dto.produce(),
+                EffectDto.toModelList(dto.effects()),
+                dto.response(),
+                dto.failText());
+    }
+
+    private static void requireItem(Map<String, Item> items, String id, String field) {
+        if (id == null) {
+            throw new WorldLoadException("Combination '" + field + "' is missing an item id");
+        }
+        if (!items.containsKey(id)) {
+            throw new WorldLoadException(
+                    "Combination references unknown item '" + id + "' (field '" + field + "')");
+        }
+    }
+}

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

@@ -5,12 +5,14 @@ import com.fasterxml.jackson.databind.type.CollectionType;
 import com.fasterxml.jackson.dataformat.yaml.YAMLFactory;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
+import thb.jeanluc.adventure.loader.dto.CombinationDto;
 import thb.jeanluc.adventure.loader.dto.EndingDto;
 import thb.jeanluc.adventure.loader.dto.GameDto;
 import thb.jeanluc.adventure.loader.dto.ItemDto;
 import thb.jeanluc.adventure.loader.dto.NpcDto;
 import thb.jeanluc.adventure.loader.dto.QuestDto;
 import thb.jeanluc.adventure.loader.dto.RoomDto;
+import thb.jeanluc.adventure.model.Combination;
 import thb.jeanluc.adventure.model.Ending;
 import thb.jeanluc.adventure.model.Npc;
 import thb.jeanluc.adventure.model.Player;
@@ -75,6 +77,8 @@ public class WorldLoader {
         List<RoomDto> roomDtos = readList(basePath + "/rooms.yaml", RoomDto.class);
         List<QuestDto> questDtos = readListOptional(basePath + "/quests.yaml", QuestDto.class);
         List<EndingDto> endingDtos = readListOptional(basePath + "/endings.yaml", EndingDto.class);
+        List<CombinationDto> combinationDtos =
+                readListOptional(basePath + "/combinations.yaml", CombinationDto.class);
         GameDto gameDto = readSingle(basePath + "/game.yaml", GameDto.class);
 
         requireUniqueIds("item", itemDtos.stream().map(ItemDto::id).toList());
@@ -104,6 +108,16 @@ public class WorldLoader {
             endings.add(EndingFactory.fromDto(dto));
         }
 
+        Map<String, Combination> combinations = new HashMap<>();
+        for (CombinationDto dto : combinationDtos) {
+            Combination c = CombinationFactory.fromDto(dto, items);
+            String key = c.key();
+            if (combinations.containsKey(key)) {
+                throw new WorldLoadException("Duplicate combination for pair '" + key + "'");
+            }
+            combinations.put(key, c);
+        }
+
         ReferenceResolver resolver = new ReferenceResolver(items, npcs, rooms);
         resolver.resolveRooms(roomDtos);
         resolver.resolveNpcs(npcDtos);
@@ -115,7 +129,7 @@ public class WorldLoader {
         Player player = new Player(start, gold);
 
         World world = new World(rooms, items, npcs,
-                gameDto.title(), gameDto.welcomeMessage(), quests, endings);
+                gameDto.title(), gameDto.welcomeMessage(), quests, endings, combinations);
         log.info("World '{}' loaded: {} rooms, {} items, {} npcs",
                 gameDto.title(), rooms.size(), items.size(), npcs.size());
         return new LoadResult(world, player);

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

@@ -0,0 +1,16 @@
+package thb.jeanluc.adventure.loader.dto;
+
+import java.util.List;
+
+/** YAML representation of an item-combination recipe. */
+public record CombinationDto(
+        String a,
+        String b,
+        List<ConditionDto> requires,
+        List<String> consume,
+        String produce,
+        List<EffectDto> effects,
+        String response,
+        String failText
+) {
+}

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

@@ -0,0 +1,35 @@
+package thb.jeanluc.adventure.model;
+
+import java.util.List;
+
+/**
+ * A data-driven item-combination recipe. Identified by an unordered pair of
+ * item ids ({@code a}, {@code b}). When applied it may require conditions,
+ * consume items, produce an item, apply effects, and print a response.
+ */
+public record Combination(
+        String a,
+        String b,
+        List<Condition> requires,
+        List<String> consume,
+        String produce,
+        List<Effect> effects,
+        String response,
+        String failText
+) {
+    public Combination {
+        requires = requires == null ? List.of() : List.copyOf(requires);
+        consume = consume == null ? List.of() : List.copyOf(consume);
+        effects = effects == null ? List.of() : List.copyOf(effects);
+    }
+
+    /** Order-independent key for an item pair (sorted, '|'-joined). */
+    public static String key(String x, String y) {
+        return x.compareTo(y) <= 0 ? x + "|" + y : y + "|" + x;
+    }
+
+    /** This recipe's canonical pair key. */
+    public String key() {
+        return key(a, b);
+    }
+}

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

@@ -37,15 +37,24 @@ public class World {
     /** Ordered list of endings (first matching one wins). */
     private final List<Ending> endings;
 
-    /** Backward-compatible constructor for worlds without quests or endings. */
+    /** Global lookup of combination recipes by canonical pair key. */
+    private final Map<String, Combination> combinations;
+
+    /** Backward-compatible constructor for worlds without quests, endings, or combinations. */
     public World(Map<String, Room> rooms, Map<String, Item> items, Map<String, Npc> npcs,
                  String title, String welcomeMessage) {
-        this(rooms, items, npcs, title, welcomeMessage, Map.of(), List.of());
+        this(rooms, items, npcs, title, welcomeMessage, Map.of(), List.of(), Map.of());
     }
 
-    /** Backward-compatible constructor for worlds with quests but no endings. */
+    /** Backward-compatible constructor for worlds with quests but no endings/combinations. */
     public World(Map<String, Room> rooms, Map<String, Item> items, Map<String, Npc> npcs,
                  String title, String welcomeMessage, Map<String, Quest> quests) {
-        this(rooms, items, npcs, title, welcomeMessage, quests, List.of());
+        this(rooms, items, npcs, title, welcomeMessage, quests, List.of(), Map.of());
+    }
+
+    /** Backward-compatible constructor for worlds with quests + endings but no combinations. */
+    public World(Map<String, Room> rooms, Map<String, Item> items, Map<String, Npc> npcs,
+                 String title, String welcomeMessage, Map<String, Quest> quests, List<Ending> endings) {
+        this(rooms, items, npcs, title, welcomeMessage, quests, endings, Map.of());
     }
 }

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

@@ -0,0 +1,7 @@
+- a: matches
+  b: torch
+  consume: [matches, torch]
+  produce: lit_torch
+  response: |
+    You strike a match and touch it to the torch; it catches with a low hiss
+    and burns steady. You now hold a lit torch.

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

@@ -47,3 +47,19 @@
     You ease the door shut again.
   effects:
     - { setFlag: fled }
+
+- type: plain
+  id: matches
+  name: Box of Matches
+  description: A small box of dry matches. They rattle when you shake it.
+
+- type: plain
+  id: torch
+  name: Unlit Torch
+  description: A pitch-soaked torch, waiting for a flame.
+
+- type: plain
+  id: lit_torch
+  name: Lit Torch
+  description: A burning torch, throwing back the dark.
+  light: true

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

@@ -23,7 +23,7 @@
   exits:
     south: kitchen
     west: library
-  items: []
+  items: [torch]
   npcs: []
 
 - id: library
@@ -33,7 +33,7 @@
     An old chest stands in the corner.
   exits:
     east: hallway
-  items: [shovel]
+  items: [shovel, matches]
   npcs: []
 
 - id: cellar

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

@@ -0,0 +1,65 @@
+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.Combination;
+import thb.jeanluc.adventure.model.Player;
+import thb.jeanluc.adventure.model.Room;
+import thb.jeanluc.adventure.model.World;
+import thb.jeanluc.adventure.model.item.Item;
+import thb.jeanluc.adventure.model.item.PlainItem;
+import thb.jeanluc.adventure.model.item.SwitchableItem;
+
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class UseCommandComboTest {
+
+    private GameContext ctx() {
+        Map<String, Item> items = new LinkedHashMap<>();
+        items.put("matches", PlainItem.builder().id("matches").name("Matches").description("d").light(false).build());
+        items.put("torch", PlainItem.builder().id("torch").name("Torch").description("d").light(false).build());
+        items.put("lit_torch", PlainItem.builder().id("lit_torch").name("Lit Torch").description("d").light(true).build());
+        SwitchableItem lamp = SwitchableItem.builder()
+                .id("lamp").name("Lamp").description("d").light(true)
+                .onText("The lamp glows.").offText("off").state(false).effects(List.of()).build();
+        items.put("lamp", lamp);
+        Combination recipe = new Combination("matches", "torch", List.of(),
+                List.of("matches", "torch"), "lit_torch", List.of(), "You light the torch.", null);
+        Room start = new Room("start", "Start", "d");
+        World w = new World(Map.of("start", start), items, Map.of(), "t", "w",
+                Map.of(), List.of(), Map.of(recipe.key(), recipe));
+        GameContext ctx = new GameContext(w, new Player(start, 0), new TestIO());
+        ctx.getPlayer().addItem(items.get("matches"));
+        ctx.getPlayer().addItem(items.get("torch"));
+        ctx.getPlayer().addItem(lamp);
+        return ctx;
+    }
+
+    @Test
+    void emptyArgsAsksWhat() {
+        GameContext ctx = ctx();
+        new UseCommand().execute(ctx, List.of());
+        assertThat(((TestIO) ctx.getIo()).allOutput()).contains("Use what?");
+    }
+
+    @Test
+    void twoArgsRoutesToCombination() {
+        GameContext ctx = ctx();
+        new UseCommand().execute(ctx, List.of("matches", "torch"));
+        assertThat(ctx.getPlayer().hasItem("lit_torch")).isTrue();
+        assertThat(((TestIO) ctx.getIo()).allOutput()).contains("light the torch");
+    }
+
+    @Test
+    void oneArgUsesItemDirectly() {
+        GameContext ctx = ctx();
+        new UseCommand().execute(ctx, List.of("lamp"));
+        assertThat(((SwitchableItem) ctx.getWorld().getItems().get("lamp")).isOn()).isTrue();
+        assertThat(((TestIO) ctx.getIo()).allOutput()).contains("lamp glows");
+    }
+}

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

@@ -0,0 +1,155 @@
+package thb.jeanluc.adventure.game;
+
+import org.junit.jupiter.api.Test;
+import thb.jeanluc.adventure.io.TestIO;
+import thb.jeanluc.adventure.model.Combination;
+import thb.jeanluc.adventure.model.Condition;
+import thb.jeanluc.adventure.model.Effect;
+import thb.jeanluc.adventure.model.Player;
+import thb.jeanluc.adventure.model.Room;
+import thb.jeanluc.adventure.model.World;
+import thb.jeanluc.adventure.model.item.Item;
+import thb.jeanluc.adventure.model.item.PlainItem;
+
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class CombinationsTest {
+
+    private Item plain(String id, boolean light) {
+        return PlainItem.builder().id(id).name(id).description("d").light(light).build();
+    }
+
+    /** World with matches/torch/lit_torch/shovel and the given recipes; player in an empty room. */
+    private GameContext ctx(Combination... recipes) {
+        Map<String, Item> items = new LinkedHashMap<>();
+        items.put("matches", plain("matches", false));
+        items.put("torch", plain("torch", false));
+        items.put("lit_torch", plain("lit_torch", true));
+        items.put("shovel", plain("shovel", false));
+        Map<String, Combination> combos = new HashMap<>();
+        for (Combination c : recipes) {
+            combos.put(c.key(), c);
+        }
+        Room start = new Room("start", "Start", "d");
+        World w = new World(Map.of("start", start), items, Map.of(), "t", "w",
+                Map.of(), List.of(), combos);
+        return new GameContext(w, new Player(start, 0), new TestIO());
+    }
+
+    private void give(GameContext ctx, String id) {
+        ctx.getPlayer().addItem(ctx.getWorld().getItems().get(id));
+    }
+
+    private void putInRoom(GameContext ctx, String id) {
+        ctx.getPlayer().getCurrentRoom().addItem(ctx.getWorld().getItems().get(id));
+    }
+
+    private String out(GameContext ctx) {
+        return ((TestIO) ctx.getIo()).allOutput();
+    }
+
+    private Combination torchRecipe() {
+        return new Combination("matches", "torch", List.of(),
+                List.of("matches", "torch"), "lit_torch", List.of(),
+                "You light the torch.", null);
+    }
+
+    @Test
+    void combinesFromInventory() {
+        GameContext ctx = ctx(torchRecipe());
+        give(ctx, "matches");
+        give(ctx, "torch");
+        Combinations.tryUse(ctx, "matches", "torch");
+        assertThat(ctx.getPlayer().hasItem("lit_torch")).isTrue();
+        assertThat(ctx.getPlayer().hasItem("matches")).isFalse();
+        assertThat(ctx.getPlayer().hasItem("torch")).isFalse();
+        assertThat(out(ctx)).contains("light the torch");
+    }
+
+    @Test
+    void matchIsOrderIndependent() {
+        GameContext ctx = ctx(torchRecipe());
+        give(ctx, "matches");
+        give(ctx, "torch");
+        Combinations.tryUse(ctx, "torch", "matches");
+        assertThat(ctx.getPlayer().hasItem("lit_torch")).isTrue();
+    }
+
+    @Test
+    void consumesOperandFromCurrentRoom() {
+        GameContext ctx = ctx(torchRecipe());
+        give(ctx, "matches");
+        putInRoom(ctx, "torch");
+        Combinations.tryUse(ctx, "matches", "torch");
+        assertThat(ctx.getPlayer().hasItem("lit_torch")).isTrue();
+        assertThat(ctx.getPlayer().getCurrentRoom().findItem("torch")).isEmpty();
+    }
+
+    @Test
+    void missingOperandReportsNoSuch() {
+        GameContext ctx = ctx(torchRecipe());
+        give(ctx, "matches"); // torch absent
+        Combinations.tryUse(ctx, "matches", "torch");
+        assertThat(out(ctx)).contains("no 'torch'");
+        assertThat(ctx.getPlayer().hasItem("lit_torch")).isFalse();
+    }
+
+    @Test
+    void noRecipeForPairSaysNothingHappens() {
+        GameContext ctx = ctx(torchRecipe());
+        give(ctx, "shovel");
+        give(ctx, "torch");
+        Combinations.tryUse(ctx, "shovel", "torch");
+        assertThat(out(ctx)).contains("Nothing happens.");
+    }
+
+    @Test
+    void unmetRequiresShowsFailTextAndDoesNotProduce() {
+        Combination gated = new Combination("matches", "torch",
+                List.of(new Condition(Condition.Type.FLAG, "dry")),
+                List.of("matches", "torch"), "lit_torch", List.of(),
+                "It catches.", "The torch is too damp to light.");
+        GameContext ctx = ctx(gated);
+        give(ctx, "matches");
+        give(ctx, "torch");
+        Combinations.tryUse(ctx, "matches", "torch");
+        assertThat(out(ctx)).contains("too damp");
+        assertThat(ctx.getPlayer().hasItem("lit_torch")).isFalse();
+        assertThat(ctx.getPlayer().hasItem("matches")).isTrue(); // not consumed
+    }
+
+    @Test
+    void effectsOnlyRecipeAppliesEffectsWithoutProduceOrResponse() {
+        Combination effectsOnly = new Combination("matches", "shovel",
+                java.util.List.of(), java.util.List.of(), null,
+                java.util.List.of(new Effect(Effect.Type.SET_FLAG, "rite_done")),
+                null, null);
+        GameContext ctx = ctx(effectsOnly);
+        give(ctx, "matches");
+        give(ctx, "shovel");
+        Combinations.tryUse(ctx, "matches", "shovel");
+        assertThat(ctx.getState().isSet("rite_done")).isTrue();
+        assertThat(out(ctx)).doesNotContain("null");
+    }
+
+    @Test
+    void metRequiresAppliesEffectsAndProduces() {
+        Combination gated = new Combination("matches", "torch",
+                List.of(new Condition(Condition.Type.FLAG, "dry")),
+                List.of("matches", "torch"), "lit_torch",
+                List.of(new Effect(Effect.Type.SET_FLAG, "torch_lit")),
+                "It catches.", "too damp");
+        GameContext ctx = ctx(gated);
+        ctx.getState().set("dry");
+        give(ctx, "matches");
+        give(ctx, "torch");
+        Combinations.tryUse(ctx, "matches", "torch");
+        assertThat(ctx.getPlayer().hasItem("lit_torch")).isTrue();
+        assertThat(ctx.getState().isSet("torch_lit")).isTrue();
+    }
+}

Semesterprojekt/src/test/java/thb/jeanluc/adventure/loader/CombinationFactoryTest.java

@@ -0,0 +1,69 @@
+package thb.jeanluc.adventure.loader;
+
+import org.junit.jupiter.api.Test;
+import thb.jeanluc.adventure.loader.dto.CombinationDto;
+import thb.jeanluc.adventure.model.Combination;
+import thb.jeanluc.adventure.model.item.Item;
+import thb.jeanluc.adventure.model.item.PlainItem;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class CombinationFactoryTest {
+
+    private Map<String, Item> items() {
+        Map<String, Item> m = new HashMap<>();
+        for (String id : List.of("matches", "torch", "lit_torch")) {
+            m.put(id, PlainItem.builder().id(id).name(id).description("d").light(false).build());
+        }
+        return m;
+    }
+
+    @Test
+    void buildsCombinationFromDto() {
+        CombinationDto dto = new CombinationDto("matches", "torch", null,
+                List.of("matches", "torch"), "lit_torch", null, "You light it.", null);
+        Combination c = CombinationFactory.fromDto(dto, items());
+        assertThat(c.key()).isEqualTo("matches|torch");
+        assertThat(c.consume()).containsExactly("matches", "torch");
+        assertThat(c.produce()).isEqualTo("lit_torch");
+        assertThat(c.response()).isEqualTo("You light it.");
+    }
+
+    @Test
+    void rejectsUnknownOperandId() {
+        CombinationDto dto = new CombinationDto("matches", "ghost", null, null, null, null, "x", null);
+        assertThatThrownBy(() -> CombinationFactory.fromDto(dto, items()))
+                .isInstanceOf(WorldLoadException.class)
+                .hasMessageContaining("ghost");
+    }
+
+    @Test
+    void rejectsUnknownProduceId() {
+        CombinationDto dto = new CombinationDto("matches", "torch", null, null, "phantom", null, "x", null);
+        assertThatThrownBy(() -> CombinationFactory.fromDto(dto, items()))
+                .isInstanceOf(WorldLoadException.class)
+                .hasMessageContaining("phantom");
+    }
+
+    @Test
+    void rejectsUnknownConsumeId() {
+        CombinationDto dto = new CombinationDto("matches", "torch", null,
+                List.of("matches", "wraith"), null, null, "x", null);
+        assertThatThrownBy(() -> CombinationFactory.fromDto(dto, items()))
+                .isInstanceOf(WorldLoadException.class)
+                .hasMessageContaining("wraith");
+    }
+
+    @Test
+    void rejectsSelfCombination() {
+        CombinationDto dto = new CombinationDto("torch", "torch", null, null, null, null, "x", null);
+        assertThatThrownBy(() -> CombinationFactory.fromDto(dto, items()))
+                .isInstanceOf(WorldLoadException.class)
+                .hasMessageContaining("itself");
+    }
+}

Semesterprojekt/src/test/java/thb/jeanluc/adventure/loader/CombinationLoadingTest.java

@@ -0,0 +1,33 @@
+package thb.jeanluc.adventure.loader;
+
+import org.junit.jupiter.api.Test;
+import thb.jeanluc.adventure.game.Combinations;
+import thb.jeanluc.adventure.game.GameContext;
+import thb.jeanluc.adventure.game.GameSession;
+import thb.jeanluc.adventure.io.TestIO;
+import thb.jeanluc.adventure.model.Combination;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class CombinationLoadingTest {
+
+    @Test
+    void realWorldLoadsTheTorchRecipe() {
+        WorldLoader.LoadResult loaded = new WorldLoader().load();
+        assertThat(loaded.world().getCombinations())
+                .containsKey(Combination.key("matches", "torch"));
+        assertThat(loaded.world().getItems()).containsKeys("matches", "torch", "lit_torch");
+    }
+
+    @Test
+    void torchRecipeWorksEndToEnd() {
+        WorldLoader.LoadResult loaded = new WorldLoader().load();
+        GameContext ctx = new GameContext(
+                new GameSession(loaded.world(), loaded.player(), "test"), new TestIO());
+        // grab the demo items straight from the registry, regardless of room
+        ctx.getPlayer().addItem(ctx.getWorld().getItems().get("matches"));
+        ctx.getPlayer().addItem(ctx.getWorld().getItems().get("torch"));
+        Combinations.tryUse(ctx, "matches", "torch");
+        assertThat(ctx.getPlayer().hasItem("lit_torch")).isTrue();
+    }
+}

Semesterprojekt/src/test/java/thb/jeanluc/adventure/loader/WorldLoaderTest.java

@@ -14,7 +14,8 @@ class WorldLoaderTest {
 
         assertThat(result.world().getTitle()).isEqualTo("Test Manor");
         assertThat(result.world().getRooms().keySet()).containsExactlyInAnyOrder("kitchen", "hallway");
-        assertThat(result.world().getItems().keySet()).containsExactlyInAnyOrder("letter", "lamp", "key");
+        assertThat(result.world().getItems().keySet())
+                .containsExactlyInAnyOrder("letter", "lamp", "key", "matches", "torch", "lit_torch");
         assertThat(result.world().getNpcs().keySet()).containsExactly("old_man");
 
         assertThat(result.player().getCurrentRoom().getId()).isEqualTo("kitchen");

Semesterprojekt/src/test/java/thb/jeanluc/adventure/model/CombinationTest.java

@@ -0,0 +1,26 @@
+package thb.jeanluc.adventure.model;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class CombinationTest {
+
+    @Test
+    void keyIsOrderIndependentAndSorted() {
+        assertThat(Combination.key("matches", "torch"))
+                .isEqualTo(Combination.key("torch", "matches"))
+                .isEqualTo("matches|torch");
+        assertThat(Combination.key("b", "a")).isEqualTo("a|b");
+    }
+
+    @Test
+    void nullCollectionComponentsBecomeEmpty() {
+        Combination c = new Combination("a", "b", null, null, null, null, "ok", null);
+        assertThat(c.requires()).isEmpty();
+        assertThat(c.consume()).isEmpty();
+        assertThat(c.effects()).isEmpty();
+        assertThat(c.produce()).isNull();
+        assertThat(c.key()).isEqualTo("a|b");
+    }
+}

Semesterprojekt/src/test/java/thb/jeanluc/adventure/model/WorldCombinationsTest.java

@@ -0,0 +1,29 @@
+package thb.jeanluc.adventure.model;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class WorldCombinationsTest {
+
+    @Test
+    void legacyConstructorsDefaultToEmptyCombinations() {
+        World w5 = new World(Map.of(), Map.of(), Map.of(), "t", "w");
+        World w6 = new World(Map.of(), Map.of(), Map.of(), "t", "w", Map.of());
+        World w7 = new World(Map.of(), Map.of(), Map.of(), "t", "w", Map.of(), List.of());
+        assertThat(w5.getCombinations()).isEmpty();
+        assertThat(w6.getCombinations()).isEmpty();
+        assertThat(w7.getCombinations()).isEmpty();
+    }
+
+    @Test
+    void fullConstructorStoresCombinations() {
+        Combination c = new Combination("a", "b", List.of(), List.of(), null, List.of(), "r", null);
+        World w = new World(Map.of(), Map.of(), Map.of(), "t", "w",
+                Map.of(), List.of(), Map.of(c.key(), c));
+        assertThat(w.getCombinations()).containsKey("a|b");
+    }
+}

Semesterprojekt/src/test/resources/world/combinations.yaml

@@ -0,0 +1,7 @@
+- a: matches
+  b: torch
+  consume: [matches, torch]
+  produce: lit_torch
+  response: |
+    You strike a match and touch it to the torch; it catches with a low hiss
+    and burns steady. You now hold a lit torch.

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

@@ -17,3 +17,19 @@
   id: key
   name: Key
   description: A key.
+
+- type: plain
+  id: matches
+  name: Box of Matches
+  description: A small box of dry matches.
+
+- type: plain
+  id: torch
+  name: Unlit Torch
+  description: A pitch-soaked torch.
+
+- type: plain
+  id: lit_torch
+  name: Lit Torch
+  description: A burning torch.
+  light: true