Monitoring client connections (#941)

## Description:
Disconnected client detection :
If a client haven't send a ping to the server since more than 30 seconds
They will then be marked disconnected with a dedicated icon.
No action are yet taken, this allows for extensive in-game test before
adding the *consequences* of the player leaving the game.
I also added extensive unit tests, lessening the risk of regression for
the future.


![image](https://github.com/user-attachments/assets/884e5e99-15e8-4544-bd52-7524542cc82a)



## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:
theodoreleon.aetarax

---------

Co-authored-by: evanpelle <evanpelle@gmail.com>

src/server/Client.ts

@@ -4,7 +4,8 @@ import { Tick } from "../core/game/Game";
 import { ClientID } from "../core/Schemas";
 
 export class Client {
-  public lastPing: number;
+  public lastPing: number = Date.now();
+  public isDisconnected: boolean = false;
 
   public hashes: Map<Tick, number> = new Map();
 

src/server/GameServer.ts

@@ -35,6 +35,8 @@ export class GameServer {
 
   private maxGameDuration = 3 * 60 * 60 * 1000; // 3 hours
 
+  private disconnectedTimeout = 1 * 30 * 1000; // 30 seconds
+
   private turns: Turn[] = [];
   private intents: Intent[] = [];
   public activeClients: Client[] = [];
@@ -164,6 +166,10 @@ export class GameServer {
         });
         return;
       }
+
+      client.isDisconnected = existing.isDisconnected;
+      client.lastPing = existing.lastPing;
+
       existing.ws.removeAllListeners("message");
       this.activeClients = this.activeClients.filter((c) => c !== existing);
     }
@@ -195,6 +201,12 @@ export class GameServer {
               );
               return;
             }
+            if (clientMsg.intent.type === "mark_disconnected") {
+              this.log.warn(
+                `Should not receive mark_disconnected intent from client`,
+              );
+              return;
+            }
             this.addIntent(clientMsg.intent);
           }
           if (clientMsg.type === "ping") {
@@ -357,6 +369,7 @@ export class GameServer {
     this.intents = [];
 
     this.handleSynchronization();
+    this.checkDisconnectedStatus();
 
     let msg = "";
     try {
@@ -537,6 +550,36 @@ export class GameServer {
     }
   }
 
+  private checkDisconnectedStatus() {
+    if (this.turns.length % 5 !== 0) {
+      return;
+    }
+
+    const now = Date.now();
+    for (const [clientID, client] of this.allClients) {
+      if (
+        client.isDisconnected === false &&
+        now - client.lastPing > this.disconnectedTimeout
+      ) {
+        this.markClientDisconnected(client, true);
+      } else if (
+        client.isDisconnected &&
+        now - client.lastPing < this.disconnectedTimeout
+      ) {
+        this.markClientDisconnected(client, false);
+      }
+    }
+  }
+
+  private markClientDisconnected(client: Client, isDisconnected: boolean) {
+    client.isDisconnected = isDisconnected;
+    this.addIntent({
+      type: "mark_disconnected",
+      clientID: client.clientID,
+      isDisconnected: isDisconnected,
+    });
+  }
+
   private archiveGame() {
     this.log.info("archiving game", {
       gameID: this.id,