refactor: modularize chat backend, update docs for .m4s segments

backend/chat/src/metrics/metrics.go

@@ -0,0 +1,128 @@
+package metrics
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+
+	"gorm.io/gorm"
+
+	"chat/src/auth"
+	"chat/src/db"
+	"chat/src/ws"
+)
+
+// HandleMetrics returns Prometheus-format metrics for the chat service.
+func HandleMetrics(gormDB *gorm.DB, redis db.RedisClient, hub *ws.Hub, sessionStore *auth.SessionStore, dbDriver, instanceID string) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodGet {
+			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+			return
+		}
+
+		var storedMessages int64
+		if gormDB != nil {
+			_ = gormDB.Model(&db.Message{}).Count(&storedMessages).Error
+		}
+
+		var moderationActions int64
+		if gormDB != nil {
+			_ = gormDB.Model(&db.ModerationLog{}).Count(&moderationActions).Error
+		}
+
+		redisEnabled := 0
+		redisUp := 0
+		redisClients := 0
+		if redis != nil {
+			redisEnabled = 1
+			if err := redis.Ping(context.Background()); err == nil {
+				redisUp = 1
+				if info, err := redis.Info(context.Background(), "clients"); err == nil {
+					for _, line := range strings.Split(info, "\n") {
+						if strings.HasPrefix(line, "connected_clients:") {
+							if value, err := strconv.Atoi(strings.TrimSpace(strings.TrimPrefix(line, "connected_clients:"))); err == nil {
+								redisClients = value
+							}
+							break
+						}
+					}
+				}
+			}
+		}
+
+		connectedClients := 0
+		dmsSent := int64(0)
+		if hub != nil {
+			connectedClients = hub.ConnectedClients()
+			dmsSent = hub.DMsSent
+		}
+
+		activeSessions := 0
+		if sessionStore != nil {
+			activeSessions = sessionStore.CountActive()
+		}
+
+		w.Header().Set("Content-Type", "text/plain; version=0.0.4; charset=utf-8")
+
+		writeLine := func(name string, value any) {
+			fmt.Fprintf(w, "%s %v\n", name, value)
+		}
+
+		fmt.Fprintln(w, "# HELP linearvoid_chat_connected_clients Current connected WebSocket clients.")
+		fmt.Fprintln(w, "# TYPE linearvoid_chat_connected_clients gauge")
+		writeLine("linearvoid_chat_connected_clients", connectedClients)
+
+		fmt.Fprintln(w, "# HELP linearvoid_chat_messages_total Total stored chat messages.")
+		fmt.Fprintln(w, "# TYPE linearvoid_chat_messages_total gauge")
+		writeLine("linearvoid_chat_messages_total", storedMessages)
+
+		fmt.Fprintln(w, "# HELP linearvoid_chat_dms_total Total private messages sent.")
+		fmt.Fprintln(w, "# TYPE linearvoid_chat_dms_total counter")
+		writeLine("linearvoid_chat_dms_total", dmsSent)
+
+		fmt.Fprintln(w, "# HELP linearvoid_chat_moderation_actions_total Total moderation log entries.")
+		fmt.Fprintln(w, "# TYPE linearvoid_chat_moderation_actions_total gauge")
+		writeLine("linearvoid_chat_moderation_actions_total", moderationActions)
+
+		fmt.Fprintln(w, "# HELP linearvoid_chat_redis_enabled Redis configured for chat service.")
+		fmt.Fprintln(w, "# TYPE linearvoid_chat_redis_enabled gauge")
+		writeLine("linearvoid_chat_redis_enabled", redisEnabled)
+
+		fmt.Fprintln(w, "# HELP linearvoid_chat_redis_up Redis reachable from chat service.")
+		fmt.Fprintln(w, "# TYPE linearvoid_chat_redis_up gauge")
+		writeLine("linearvoid_chat_redis_up", redisUp)
+
+		fmt.Fprintln(w, "# HELP linearvoid_chat_redis_connected_clients Redis connected client count seen by chat service.")
+		fmt.Fprintln(w, "# TYPE linearvoid_chat_redis_connected_clients gauge")
+		writeLine("linearvoid_chat_redis_connected_clients", redisClients)
+
+		fmt.Fprintln(w, "# HELP linearvoid_chat_admin_sessions_active Active unexpired admin sessions.")
+		fmt.Fprintln(w, "# TYPE linearvoid_chat_admin_sessions_active gauge")
+		writeLine("linearvoid_chat_admin_sessions_active", activeSessions)
+
+		fmt.Fprintln(w, "# HELP linearvoid_chat_build_info Static build info for chat service.")
+		fmt.Fprintln(w, "# TYPE linearvoid_chat_build_info gauge")
+		fmt.Fprintf(w, "linearvoid_chat_build_info{service=\"chat\",database_driver=\"%s\",instance_id=\"%s\"} 1\n", dbDriver, instanceID)
+	}
+}
+
+// HandleHealth returns a simple health check endpoint.
+func HandleHealth() http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusOK)
+		fmt.Fprint(w, `{"status":"healthy","service":"chat","timestamp":"`+time.Now().UTC().Format(time.RFC3339)+`"}`)
+	}
+}
+
+// HandleNotFound returns a 404 JSON response for all unhandled paths.
+func HandleNotFound() http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusNotFound)
+		fmt.Fprint(w, `{"error":"not found"}`)
+	}
+}