feat(game): Pathfinder BFS over visited rooms (locks + light aware)

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

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

@@ -0,0 +1,76 @@
+package thb.jeanluc.adventure.game;
+
+import thb.jeanluc.adventure.model.Direction;
+import thb.jeanluc.adventure.model.ExitLock;
+import thb.jeanluc.adventure.model.Room;
+
+import java.util.ArrayDeque;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.Queue;
+import java.util.Set;
+
+/**
+ * Breadth-first shortest-path search over the rooms the player has already
+ * visited, honouring the same gates as a manual move: locked exits and
+ * darkness. Stateless utility, alongside {@link Conditions}/{@link Effects}/
+ * {@link Light}.
+ */
+public final class Pathfinder {
+
+    private Pathfinder() {
+    }
+
+    /**
+     * Finds the shortest path from the player's current room to {@code target}.
+     *
+     * @param ctx    active game context
+     * @param target destination room (expected to be a visited room)
+     * @return the rooms to step through, excluding the start and ending at
+     *         {@code target}; empty if there is no currently-passable path
+     *         (or {@code target} is the current room)
+     */
+    public static List<Room> findPath(GameContext ctx, Room target) {
+        Room start = ctx.getPlayer().getCurrentRoom();
+        Set<String> visited = ctx.getPlayer().getVisitedRoomIds();
+
+        Queue<Room> queue = new ArrayDeque<>();
+        Map<Room, Room> cameFrom = new HashMap<>();
+        queue.add(start);
+        cameFrom.put(start, null);
+
+        while (!queue.isEmpty()) {
+            Room current = queue.poll();
+            if (current == target) {
+                return reconstruct(cameFrom, target);
+            }
+            for (Map.Entry<Direction, Room> exit : current.getExits().entrySet()) {
+                Room next = exit.getValue();
+                if (cameFrom.containsKey(next) || !visited.contains(next.getId())) {
+                    continue;
+                }
+                ExitLock lock = current.getExitLocks().get(exit.getKey());
+                if (lock != null && !Conditions.all(lock.requires(), ctx)) {
+                    continue;
+                }
+                if (!Light.isLit(ctx, next)) {
+                    continue;
+                }
+                cameFrom.put(next, current);
+                queue.add(next);
+            }
+        }
+        return List.of();
+    }
+
+    /** Walks predecessors back from target to start; returns steps after start. */
+    private static List<Room> reconstruct(Map<Room, Room> cameFrom, Room target) {
+        LinkedList<Room> path = new LinkedList<>();
+        for (Room r = target; r != null && cameFrom.get(r) != null; r = cameFrom.get(r)) {
+            path.addFirst(r);
+        }
+        return path;
+    }
+}