Add client leaving host notification

tests/hooks/useGame.kickLeave.test.tsx

@@ -909,5 +909,150 @@ describe('Kick and Leave Feature Logic', () => {
       expect(isValidPlayerLeftMessage({ type: 'PLAYER_LEFT', payload: {} })).toBe(false);
       expect(isValidPlayerLeftMessage({ type: 'PLAYER_LEFT' })).toBe(false);
     });
+
+    it('validates LEAVE message structure', () => {
+      const isValidLeaveMessage = (message: unknown): boolean => {
+        if (typeof message !== 'object' || message === null) return false;
+        const msg = message as { type?: string; payload?: object };
+        return msg.type === 'LEAVE' && typeof msg.payload === 'object';
+      };
+      
+      expect(isValidLeaveMessage({ type: 'LEAVE', payload: {} })).toBe(true);
+      expect(isValidLeaveMessage({ type: 'LEAVE' })).toBe(false);
+      expect(isValidLeaveMessage({ type: 'OTHER', payload: {} })).toBe(false);
+      expect(isValidLeaveMessage(null)).toBe(false);
+    });
+  });
+
+  describe('host handling LEAVE message', () => {
+    const processLeaveMessage = (
+      leavingPlayerId: string,
+      players: Player[],
+      presenterId: string | null
+    ): {
+      updatedPlayers: Player[];
+      newPresenterId: string | null;
+      shouldBroadcastPlayerLeft: boolean;
+      shouldBroadcastPresenterChanged: boolean;
+    } => {
+      const updatedPlayers = players.filter(p => p.id !== leavingPlayerId);
+      const wasPresenter = presenterId === leavingPlayerId;
+      
+      let newPresenterId = presenterId;
+      if (wasPresenter) {
+        const realPlayers = updatedPlayers.filter(p => p.id !== 'host');
+        newPresenterId = realPlayers.length > 0 ? realPlayers[0].id : null;
+      }
+      
+      return {
+        updatedPlayers,
+        newPresenterId,
+        shouldBroadcastPlayerLeft: true,
+        shouldBroadcastPresenterChanged: wasPresenter,
+      };
+    };
+
+    it('removes leaving player from players list', () => {
+      const players = [
+        createPlayer({ id: 'player-1', name: 'Alice' }),
+        createPlayer({ id: 'player-2', name: 'Bob' }),
+      ];
+      
+      const result = processLeaveMessage('player-1', players, null);
+      
+      expect(result.updatedPlayers).toHaveLength(1);
+      expect(result.updatedPlayers[0].id).toBe('player-2');
+    });
+
+    it('broadcasts PLAYER_LEFT to remaining players', () => {
+      const players = [
+        createPlayer({ id: 'player-1', name: 'Alice' }),
+        createPlayer({ id: 'player-2', name: 'Bob' }),
+      ];
+      
+      const result = processLeaveMessage('player-1', players, null);
+      
+      expect(result.shouldBroadcastPlayerLeft).toBe(true);
+    });
+
+    it('reassigns presenter when leaving player was presenter', () => {
+      const players = [
+        createPlayer({ id: 'player-1', name: 'Alice' }),
+        createPlayer({ id: 'player-2', name: 'Bob' }),
+      ];
+      
+      const result = processLeaveMessage('player-1', players, 'player-1');
+      
+      expect(result.newPresenterId).toBe('player-2');
+      expect(result.shouldBroadcastPresenterChanged).toBe(true);
+    });
+
+    it('preserves presenter when non-presenter leaves', () => {
+      const players = [
+        createPlayer({ id: 'player-1', name: 'Alice' }),
+        createPlayer({ id: 'player-2', name: 'Bob' }),
+      ];
+      
+      const result = processLeaveMessage('player-2', players, 'player-1');
+      
+      expect(result.newPresenterId).toBe('player-1');
+      expect(result.shouldBroadcastPresenterChanged).toBe(false);
+    });
+
+    it('sets presenter to null when last non-host player leaves', () => {
+      const players = [
+        createPlayer({ id: 'host', name: 'Host' }),
+        createPlayer({ id: 'player-1', name: 'Alice' }),
+      ];
+      
+      const result = processLeaveMessage('player-1', players, 'player-1');
+      
+      expect(result.newPresenterId).toBeNull();
+      expect(result.shouldBroadcastPresenterChanged).toBe(true);
+    });
+
+    it('handles leave when player does not exist', () => {
+      const players = [
+        createPlayer({ id: 'player-1', name: 'Alice' }),
+      ];
+      
+      const result = processLeaveMessage('player-999', players, null);
+      
+      expect(result.updatedPlayers).toHaveLength(1);
+      expect(result.shouldBroadcastPlayerLeft).toBe(true);
+    });
+
+    it('does not modify original players array', () => {
+      const players = [
+        createPlayer({ id: 'player-1', name: 'Alice' }),
+        createPlayer({ id: 'player-2', name: 'Bob' }),
+      ];
+      const originalLength = players.length;
+      
+      processLeaveMessage('player-1', players, null);
+      
+      expect(players).toHaveLength(originalLength);
+    });
+
+    it('handles multiple sequential leaves', () => {
+      let players = [
+        createPlayer({ id: 'player-1', name: 'Alice' }),
+        createPlayer({ id: 'player-2', name: 'Bob' }),
+        createPlayer({ id: 'player-3', name: 'Charlie' }),
+      ];
+      let presenterId: string | null = 'player-1';
+      
+      const result1 = processLeaveMessage('player-1', players, presenterId);
+      players = result1.updatedPlayers;
+      presenterId = result1.newPresenterId;
+      
+      const result2 = processLeaveMessage('player-2', players, presenterId);
+      players = result2.updatedPlayers;
+      presenterId = result2.newPresenterId;
+      
+      expect(players).toHaveLength(1);
+      expect(players[0].id).toBe('player-3');
+      expect(presenterId).toBe('player-3');
+    });
   });
 });