diff --git a/interval/hub/doc.go b/interval/hub/doc.go
new file mode 100644
index 0000000..c207cf1
--- /dev/null
+++ b/interval/hub/doc.go
@@ -0,0 +1,2 @@
+// Package hub implements the message distribution core of the push service.
+package hub
diff --git a/interval/hub/hub.go b/interval/hub/hub.go
new file mode 100644
index 0000000..4376a28
--- /dev/null
+++ b/interval/hub/hub.go
@@ -0,0 +1,177 @@
+package hub
+
+import (
+	"context"
+	"log"
+
+	"git.jinshen.cn/remilia/push-server/interval/model"
+	"github.com/coder/websocket"
+)
+
+// Client represents a connected client in the hub.
+type Client struct {
+	ID       string
+	Conn     *websocket.Conn
+	SendChan chan []byte
+}
+
+// Hub is the central message distribution hub.
+type Hub struct {
+	// ClientID -> *Client
+	clientsByID map[string]*Client
+	// topic -> clientID -> *Client
+	//
+	// Invariant:
+	// - clientsByTopic contains only topics with at least one active subscriber.
+	// - A topic key must not exist if it has zero clients.
+	clientsByTopic map[model.Topic]map[string]*Client
+	// clientID -> topic -> struct{}
+	topicsByClients map[string]map[model.Topic]struct{}
+
+	register    chan *Client
+	unregister  chan *Client
+	subscribe   chan model.Subscription
+	unsubscribe chan model.Subscription
+	broadcast   chan model.Message
+}
+
+func NewHub() *Hub {
+	return &Hub{
+		clientsByID:     make(map[string]*Client),
+		clientsByTopic:  make(map[model.Topic]map[string]*Client),
+		topicsByClients: make(map[string]map[model.Topic]struct{}),
+
+		register:    make(chan *Client),
+		unregister:  make(chan *Client),
+		subscribe:   make(chan model.Subscription),
+		unsubscribe: make(chan model.Subscription),
+		broadcast:   make(chan model.Message),
+	}
+}
+
+func (h *Hub) RegisterClient(client *Client) {
+	h.register <- client
+}
+
+func (h *Hub) UnregisterClient(client *Client) {
+	h.unregister <- client
+}
+
+func (h *Hub) Subscribe(sub model.Subscription) {
+	h.subscribe <- sub
+}
+
+func (h *Hub) Unsubscribe(sub model.Subscription) {
+	h.unsubscribe <- sub
+}
+
+func (h *Hub) BroadcastMessage(message model.Message) {
+	h.broadcast <- message
+}
+
+func (h *Hub) Run(ctx context.Context) {
+	for {
+		select {
+		case c := <-h.register:
+			h.onRegister(c)
+
+		case c := <-h.unregister:
+			h.onUnregister(c)
+
+		case c := <-h.subscribe:
+			h.onSubscribe(c)
+
+		case s := <-h.unsubscribe:
+			h.onUnsubscribe(s)
+
+		case msg := <-h.broadcast:
+			h.onBroadcast(msg)
+
+		case <-ctx.Done():
+			h.shutdown()
+			return
+		}
+	}
+}
+
+// Get a client by its ClientID
+func (h *Hub) getClient(id string) (*Client, bool) {
+	c, ok := h.clientsByID[id]
+	return c, ok
+}
+
+// Create a new entry for the client in topicsByClients map when it registers.
+func (h *Hub) onRegister(c *Client) {
+	h.clientsByID[c.ID] = c
+	h.topicsByClients[c.ID] = make(map[model.Topic]struct{})
+}
+
+// Delete all topic subscriptions for the client when it unregisters.
+func (h *Hub) onUnregister(c *Client) {
+	topics := h.topicsByClients[c.ID]
+	for t := range topics {
+		if clients, ok := h.clientsByTopic[t]; ok {
+			delete(clients, c.ID)
+			if len(clients) == 0 {
+				delete(h.clientsByTopic, t)
+			}
+		}
+
+	}
+	delete(h.topicsByClients, c.ID)
+	delete(h.clientsByID, c.ID)
+}
+
+func (h *Hub) onSubscribe(s model.Subscription) {
+	c, ok := h.getClient(s.ClientID)
+	if !ok {
+		// If the client does not exist, log an error and return.
+		log.Printf("Subscribe failed: client %s not found", s.ClientID)
+		return
+	}
+	if h.clientsByTopic[s.Topic] == nil {
+		h.clientsByTopic[s.Topic] = make(map[string]*Client)
+	}
+
+	h.clientsByTopic[s.Topic][s.ClientID] = c
+	h.topicsByClients[s.ClientID][s.Topic] = struct{}{}
+}
+
+func (h *Hub) onUnsubscribe(s model.Subscription) {
+	if clients, ok := h.clientsByTopic[s.Topic]; ok {
+		delete(clients, s.ClientID)
+		if len(clients) == 0 {
+			delete(h.clientsByTopic, s.Topic)
+		}
+	}
+
+	if topics, ok := h.topicsByClients[s.ClientID]; ok {
+		delete(topics, s.Topic)
+	}
+}
+
+func (h *Hub) onBroadcast(msg model.Message) {
+	if !msg.Topic.Valid() {
+		log.Printf("Broadcast failed: invalid topic")
+		return
+	}
+	for _, c := range h.clientsByTopic[msg.Topic] {
+		select {
+		case c.SendChan <- msg.Content:
+		default:
+			h.UnregisterClient(c)
+			if c.Conn != nil {
+				_ = c.Conn.Close(websocket.StatusPolicyViolation, "Slow consumer")
+			}
+		}
+	}
+}
+
+func (h *Hub) shutdown() {
+	for _, c := range h.clientsByID {
+		close(c.SendChan)
+		if c.Conn != nil {
+			_ = c.Conn.Close(websocket.StatusNormalClosure, "Server shutdown")
+		}
+	}
+}