feat(game): Combinations engine for use X on Y

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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

@@ -0,0 +1,67 @@
+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);
+        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.";
+    }
+}