feat(save): SaveCodec capture/apply over a fresh world; tolerate null collections

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

Semesterprojekt/src/main/java/thb/jeanluc/adventure/save/SaveCodec.java

@@ -0,0 +1,126 @@
+package thb.jeanluc.adventure.save;
+
+import thb.jeanluc.adventure.game.GameSession;
+import thb.jeanluc.adventure.game.QuestLog;
+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.SwitchableItem;
+
+import java.util.ArrayList;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Converts between a live {@link GameSession} and a {@link SaveData} snapshot.
+ * Pure (no disk): {@link #capture} reads a session; {@link #apply} overlays a
+ * snapshot onto a session built from a freshly loaded world.
+ */
+public final class SaveCodec {
+
+    private SaveCodec() {
+    }
+
+    /** Reads the mutable state of {@code session} into a {@link SaveData}. */
+    public static SaveData capture(GameSession session) {
+        World w = session.getWorld();
+        Player p = session.getPlayer();
+
+        Map<String, List<String>> roomItems = new LinkedHashMap<>();
+        for (Room room : w.getRooms().values()) {
+            if (!room.getItems().isEmpty()) {
+                roomItems.put(room.getId(), new ArrayList<>(room.getItems().keySet()));
+            }
+        }
+        Map<String, Boolean> switches = new LinkedHashMap<>();
+        for (Item item : w.getItems().values()) {
+            if (item instanceof SwitchableItem sw) {
+                switches.put(sw.getId(), sw.isOn());
+            }
+        }
+        Map<String, Integer> stages = new LinkedHashMap<>();
+        QuestLog log = session.getQuestLog();
+        for (String id : log.active()) {
+            stages.put(id, log.stageIndex(id));
+        }
+
+        return new SaveData(
+                SaveData.CURRENT_VERSION,
+                w.getTitle(),
+                session.getSlotName(),
+                System.currentTimeMillis(),
+                session.getTurn(),
+                p.getCurrentRoom().getId(),
+                new ArrayList<>(p.getVisitedRoomIds()),
+                p.getGold(),
+                new ArrayList<>(p.getInventory().keySet()),
+                new ArrayList<>(session.getState().all()),
+                stages,
+                new ArrayList<>(log.completed()),
+                roomItems,
+                switches);
+    }
+
+    /**
+     * Overlays {@code data} onto {@code session} (whose world was just loaded
+     * from YAML). Throws {@link SaveException} if the save references ids that
+     * no longer exist in the current world.
+     */
+    public static void apply(SaveData data, GameSession session) {
+        World w = session.getWorld();
+        Player p = session.getPlayer();
+
+        // 1. Clear all item placements, then redistribute from the save.
+        for (Room room : w.getRooms().values()) {
+            room.getItems().clear();
+        }
+        p.getInventory().clear();
+        for (Map.Entry<String, List<String>> e : data.roomItemIds().entrySet()) {
+            Room room = requireRoom(w, e.getKey());
+            for (String itemId : e.getValue()) {
+                room.addItem(requireItem(w, itemId));
+            }
+        }
+        for (String itemId : data.inventoryItemIds()) {
+            p.addItem(requireItem(w, itemId));
+        }
+
+        // 2. Switch states.
+        for (Map.Entry<String, Boolean> e : data.switchStates().entrySet()) {
+            if (requireItem(w, e.getKey()) instanceof SwitchableItem sw) {
+                sw.setState(e.getValue());
+            }
+        }
+
+        // 3. Player position + visited + gold.
+        p.setCurrentRoom(requireRoom(w, data.currentRoomId()));
+        p.getVisitedRoomIds().clear();
+        p.getVisitedRoomIds().addAll(data.visitedRoomIds());
+        p.setGold(data.gold());
+
+        // 4. Flags, quests, turn.
+        session.getState().restore(data.flags());
+        session.getQuestLog().restore(data.questStages(), data.questCompleted());
+        session.setTurn(data.turn());
+    }
+
+    private static Room requireRoom(World w, String id) {
+        Room r = w.getRooms().get(id);
+        if (r == null) {
+            throw new SaveException("Save refers to unknown room '" + id
+                    + "'. The game content may have changed.");
+        }
+        return r;
+    }
+
+    private static Item requireItem(World w, String id) {
+        Item i = w.getItems().get(id);
+        if (i == null) {
+            throw new SaveException("Save refers to unknown item '" + id
+                    + "'. The game content may have changed.");
+        }
+        return i;
+    }
+}

Semesterprojekt/src/main/java/thb/jeanluc/adventure/save/SaveData.java

@@ -26,4 +26,19 @@ public record SaveData(
 ) {
     /** Current on-disk schema version. */
     public static final int CURRENT_VERSION = 1;
+
+    /**
+     * Compact canonical constructor: normalizes any null collection component
+     * to an empty immutable collection so a truncated/hand-edited save JSON
+     * degrades gracefully instead of NPE-ing in {@link SaveCodec#apply}.
+     */
+    public SaveData {
+        if (visitedRoomIds == null)   visitedRoomIds   = List.of();
+        if (inventoryItemIds == null) inventoryItemIds = List.of();
+        if (flags == null)            flags            = List.of();
+        if (questStages == null)      questStages      = Map.of();
+        if (questCompleted == null)   questCompleted   = List.of();
+        if (roomItemIds == null)      roomItemIds      = Map.of();
+        if (switchStates == null)     switchStates     = Map.of();
+    }
 }