feat(call): enhance call handling with user connection events and active call management

- Updated CallService to handle user connection and disconnection events, allowing for automatic management of active calls based on user status.
- Introduced methods to retrieve active calls for users and send pending call invites when users reconnect.
- Modified the Invite method to return the callee's online status, improving user experience during call invitations.
- Enhanced WSHandler to support connection and disconnection event handlers, ensuring accurate call state management.

internal/pkg/ws/hub.go

@@ -61,22 +61,36 @@ type subscriber struct {
 	quit chan struct{}
 }
 
+// DisconnectHandler 用户断开连接时的回调函数
+// userID: 断开的用户ID
+// remainingCount: 该用户剩余的连接数（0表示用户完全离线）
+type DisconnectHandler func(userID string, remainingCount int)
+
+// ConnectHandler 用户连接时的回调函数
+// userID: 连接的用户ID
+// isFirstConnection: 是否是该用户的第一个连接（之前完全离线）
+type ConnectHandler func(userID string, isFirstConnection bool)
+
 // Hub WebSocket连接管理器
 type Hub struct {
 	seq uint64
 
-	mu          sync.RWMutex
-	clients     map[string]map[uint64]*Client // userID -> clientID -> Client
-	history     map[string][]Event            // userID -> []Event (用于断线重连历史回放)
-	subscribers map[string]map[uint64]*subscriber // userID -> subscriberID -> subscriber
+	mu                 sync.RWMutex
+	clients            map[string]map[uint64]*Client // userID -> clientID -> Client
+	history            map[string][]Event            // userID -> []Event (用于断线重连历史回放)
+	subscribers        map[string]map[uint64]*subscriber // userID -> subscriberID -> subscriber
+	disconnectHandlers []DisconnectHandler           // 断开连接事件处理器列表
+	connectHandlers    []ConnectHandler              // 连接事件处理器列表
 }
 
 // NewHub 创建WebSocket Hub
 func NewHub() *Hub {
 	return &Hub{
-		clients:     make(map[string]map[uint64]*Client),
-		history:     make(map[string][]Event),
-		subscribers: make(map[string]map[uint64]*subscriber),
+		clients:            make(map[string]map[uint64]*Client),
+		history:            make(map[string][]Event),
+		subscribers:        make(map[string]map[uint64]*subscriber),
+		disconnectHandlers: make([]DisconnectHandler, 0),
+		connectHandlers:    make([]ConnectHandler, 0),
 	}
 }
 
@@ -88,9 +102,12 @@ func (h *Hub) NextID() uint64 {
 // Register 注册客户端连接
 func (h *Hub) Register(client *Client) []Event {
 	h.mu.Lock()
-	defer h.mu.Unlock()
 
-	if _, ok := h.clients[client.UserID]; !ok {
+	// 检查是否是该用户的第一个连接（之前完全离线）
+	_, existed := h.clients[client.UserID]
+	isFirstConnection := !existed
+
+	if !existed {
 		h.clients[client.UserID] = make(map[uint64]*Client)
 	}
 	h.clients[client.UserID][client.ID] = client
@@ -105,31 +122,62 @@ func (h *Hub) Register(client *Client) []Event {
 		zap.String("user_id", client.UserID),
 		zap.Uint64("client_id", client.ID),
 		zap.Int("total_clients", len(h.clients[client.UserID])),
+		zap.Bool("is_first_connection", isFirstConnection),
 	)
 
+	// 复制处理器列表避免锁竞争
+	handlers := make([]ConnectHandler, len(h.connectHandlers))
+	copy(handlers, h.connectHandlers)
+	h.mu.Unlock()
+
+	// 异步调用连接处理器，避免阻塞 Register
+	if len(handlers) > 0 {
+		go func() {
+			for _, handler := range handlers {
+				handler(client.UserID, isFirstConnection)
+			}
+		}()
+	}
+
 	return replay
 }
 
 // Unregister 注销客户端连接
 func (h *Hub) Unregister(client *Client) {
 	h.mu.Lock()
-	defer h.mu.Unlock()
 
+	var remainingCount int
 	if userClients, ok := h.clients[client.UserID]; ok {
 		if _, exists := userClients[client.ID]; exists {
 			delete(userClients, client.ID)
 			close(client.Quit)
+			remainingCount = len(userClients)
 
-			if len(userClients) == 0 {
+			if remainingCount == 0 {
 				delete(h.clients, client.UserID)
 			}
 
 			zap.L().Debug("WebSocket client unregistered",
 				zap.String("user_id", client.UserID),
 				zap.Uint64("client_id", client.ID),
+				zap.Int("remaining_connections", remainingCount),
 			)
 		}
 	}
+
+	// 复制处理器列表避免锁竞争
+	handlers := make([]DisconnectHandler, len(h.disconnectHandlers))
+	copy(handlers, h.disconnectHandlers)
+	h.mu.Unlock()
+
+	// 异步调用断开处理器，避免阻塞 Unregister
+	if len(handlers) > 0 {
+		go func() {
+			for _, handler := range handlers {
+				handler(client.UserID, remainingCount)
+			}
+		}()
+	}
 }
 
 // HasClients 检查用户是否有活跃连接
@@ -139,6 +187,24 @@ func (h *Hub) HasClients(userID string) bool {
 	return len(h.clients[userID]) > 0
 }
 
+// OnDisconnect 注册断开连接事件处理器
+// 当用户断开 WebSocket 连接时，会调用所有注册的处理器
+// 处理器会收到用户ID和该用户剩余的连接数
+func (h *Hub) OnDisconnect(handler DisconnectHandler) {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	h.disconnectHandlers = append(h.disconnectHandlers, handler)
+}
+
+// OnConnect 注册连接事件处理器
+// 当用户建立 WebSocket 连接时，会调用所有注册的处理器
+// 处理器会收到用户ID和是否是该用户的第一个连接
+func (h *Hub) OnConnect(handler ConnectHandler) {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	h.connectHandlers = append(h.connectHandlers, handler)
+}
+
 // GetClientCount 获取用户的连接数
 func (h *Hub) GetClientCount(userID string) int {
 	h.mu.RLock()