feat(board): add shared physical quest boards

src/main/java/games/dmg/spigotquestboard/BoardRegistry.java

@@ -0,0 +1,47 @@
+package games.dmg.spigotquestboard;
+
+import java.io.IOException;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+
+final class BoardRegistry {
+    private final BoardRepository repository;
+    private Map<BoardId, RegisteredBoard> boards;
+
+    BoardRegistry(BoardRepository repository) throws IOException {
+        this.repository = Objects.requireNonNull(repository, "repository");
+        boards = index(repository.load());
+    }
+
+    synchronized BoardRegistrationResult register(RegisteredBoard board) throws IOException {
+        Objects.requireNonNull(board, "board");
+        if (boards.containsKey(board.id())) {
+            return BoardRegistrationResult.ALREADY_REGISTERED;
+        }
+        Map<BoardId, RegisteredBoard> candidate = new LinkedHashMap<>(boards);
+        candidate.put(board.id(), board);
+        repository.save(new BoardState(Set.copyOf(candidate.values())));
+        boards = Map.copyOf(candidate);
+        return BoardRegistrationResult.CREATED;
+    }
+
+    synchronized boolean contains(BoardId id) {
+        return boards.containsKey(id);
+    }
+
+    synchronized int size() {
+        return boards.size();
+    }
+
+    private static Map<BoardId, RegisteredBoard> index(BoardState state) throws IOException {
+        Map<BoardId, RegisteredBoard> indexed = new LinkedHashMap<>();
+        for (RegisteredBoard board : state.boards()) {
+            if (indexed.put(board.id(), board) != null) {
+                throw new IOException("Duplicate quest board location: " + board.id());
+            }
+        }
+        return Map.copyOf(indexed);
+    }
+}