feat(model): Combination recipe record + order-independent key

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);
+    }
+}