feat: notify document updates over websocket

apps/server/internal/realtime/hub.go

@@ -0,0 +1,70 @@
+package realtime
+
+import (
+	"encoding/json"
+	"log/slog"
+	"sync"
+)
+
+type Event struct {
+	Type string `json:"type"`
+	Data any    `json:"data"`
+}
+
+type Client struct {
+	send chan []byte
+}
+
+type Hub struct {
+	logger  *slog.Logger
+	mu      sync.RWMutex
+	clients map[*Client]struct{}
+}
+
+func NewHub(logger *slog.Logger) *Hub {
+	return &Hub{
+		logger:  logger,
+		clients: make(map[*Client]struct{}),
+	}
+}
+
+func (h *Hub) NewClient(buffer int) *Client {
+	return &Client{send: make(chan []byte, buffer)}
+}
+
+func (h *Hub) Register(client *Client) {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	h.clients[client] = struct{}{}
+}
+
+func (h *Hub) Unregister(client *Client) {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	if _, ok := h.clients[client]; ok {
+		delete(h.clients, client)
+		close(client.send)
+	}
+}
+
+func (h *Hub) Broadcast(event Event) {
+	payload, err := json.Marshal(event)
+	if err != nil {
+		h.logger.Error("marshal realtime event", "error", err)
+		return
+	}
+
+	h.mu.RLock()
+	defer h.mu.RUnlock()
+	for client := range h.clients {
+		select {
+		case client.send <- payload:
+		default:
+			h.logger.Warn("dropping realtime event for slow client")
+		}
+	}
+}
+
+func (c *Client) Send() <-chan []byte {
+	return c.send
+}