Organize & sort the KCP system

src/main/java/emu/grasscutter/server/game/session/GameSessionManager.java

@@ -0,0 +1,91 @@
+package emu.grasscutter.server.game.session;
+
+import emu.grasscutter.Grasscutter;
+import emu.grasscutter.server.game.*;
+import emu.grasscutter.utils.Utils;
+import io.netty.buffer.ByteBuf;
+import kcp.highway.*;
+import lombok.Getter;
+
+import java.util.Map;
+import java.util.concurrent.*;
+
+public final class GameSessionManager implements KcpListener {
+    @Getter private static final GameSessionManager instance
+        = new GameSessionManager();
+    @Getter private static final ExecutorService executor
+        = Executors.newFixedThreadPool(4);
+    @Getter private static final Map<Ukcp, GameSession> sessions
+        = new ConcurrentHashMap<>();
+
+    /**
+     * Waits for the game server to be ready.
+     *
+     * @return The game server.
+     */
+    private GameServer waitForServer() {
+        var server = Grasscutter.getGameServer();
+        var times = 0; while (server == null || !server.isStarted()) {
+            Utils.sleep(1000); // Wait 1s for the server to start.
+            if (times++ > 5) {
+                Grasscutter.getLogger().error("Game server has not started in a reasonable time.");
+                return null;
+            }
+
+            server = Grasscutter.getGameServer();
+        }
+
+        return server;
+    }
+
+    @Override
+    public void onConnected(Ukcp ukcp) {
+        // Fetch the game server.
+        var server = this.waitForServer();
+        if (server == null) {
+            ukcp.close();
+            return;
+        }
+
+        // Create a new session.
+        var session = sessions.compute(ukcp, (k, existing) -> {
+            // Close an existing session.
+            if (existing != null) {
+                existing.close();
+            }
+
+            return new GameSession(server);
+        });
+
+        // Connect the session.
+        session.onConnected(new GameSessionHandler(ukcp));
+    }
+
+    @Override
+    public void handleReceive(ByteBuf byteBuf, Ukcp ukcp) {
+        // Get the session.
+        var session = sessions.get(ukcp);
+        if (session == null) {
+            ukcp.close(); return;
+        }
+
+        // Handle the message in a separate thread.
+        executor.submit(() -> {
+            var bytes = Utils.byteBufToArray(byteBuf);
+            session.onMessage(bytes);
+        });
+    }
+
+    @Override
+    public void handleException(Throwable throwable, Ukcp ukcp) {
+        Grasscutter.getLogger().error("Exception in game session.", throwable);
+    }
+
+    @Override
+    public void handleClose(Ukcp ukcp) {
+        var session = sessions.remove(ukcp);
+        if (session != null) {
+            session.close();
+        }
+    }
+}