Agent-Status und Inaktivitaets-Erkennung implementiert

- Status wird aus last_heartbeat berechnet (online/stale/offline/unknown)
- GET /agents und GET /agents/{id} liefern status Feld
- agent_events Tabelle fuer Event-Tracking (Migration automatisch)
- Inaktivitaets-Monitor als Goroutine (prueft alle 60s, schreibt Events bei Statuswechsel)
- WebSocket Connect/Disconnect Events werden automatisch geschrieben
- API-Endpoints: GET /agents/events und GET /agents/{id}/events (?limit=N&type=X)
- DB-Methoden: InsertAgentEvent, GetAgentEvents, GetAllAgentEvents, GetAgentStatus
- README aktualisiert (Status-Doku, Events API, Dateistruktur)

backend/db/postgres.go

@@ -88,6 +88,15 @@ func (d *Database) migrate() error {
 
 	CREATE INDEX IF NOT EXISTS idx_config_backups_agent ON config_backups(agent_id, created_at DESC);
 	CREATE INDEX IF NOT EXISTS idx_config_backups_hash ON config_backups(agent_id, hash);
+
+	CREATE TABLE IF NOT EXISTS agent_events (
+		id SERIAL PRIMARY KEY,
+		agent_id TEXT NOT NULL REFERENCES agents(id) ON DELETE CASCADE,
+		event_type TEXT NOT NULL,
+		message TEXT,
+		created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+	);
+	CREATE INDEX IF NOT EXISTS idx_agent_events_agent ON agent_events(agent_id, created_at DESC);
 	`
 
 	if _, err := d.db.Exec(schema); err != nil {
@@ -631,3 +640,101 @@ func (d *Database) GetMetricsSummary(agentID, metric, bucket string, from, to ti
 	}
 	return results, rows.Err()
 }
+
+// --- Agent Events Methoden ---
+
+// InsertAgentEvent schreibt ein Event in die agent_events Tabelle
+func (d *Database) InsertAgentEvent(agentID, eventType, message string) error {
+	_, err := d.db.Exec(
+		"INSERT INTO agent_events (agent_id, event_type, message) VALUES ($1, $2, $3)",
+		agentID, eventType, message,
+	)
+	if err != nil {
+		log.Printf("Event schreiben fehlgeschlagen: %v", err)
+	}
+	return err
+}
+
+// GetAgentEvents holt Events fuer einen bestimmten Agent
+func (d *Database) GetAgentEvents(agentID string, eventType string, limit int) ([]models.AgentEvent, error) {
+	if limit <= 0 {
+		limit = 100
+	}
+
+	query := "SELECT id, agent_id, event_type, COALESCE(message, ''), created_at FROM agent_events WHERE agent_id = $1"
+	args := []interface{}{agentID}
+
+	if eventType != "" {
+		query += " AND event_type = $2"
+		args = append(args, eventType)
+	}
+
+	query += fmt.Sprintf(" ORDER BY created_at DESC LIMIT $%d", len(args)+1)
+	args = append(args, limit)
+
+	rows, err := d.db.Query(query, args...)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var events []models.AgentEvent
+	for rows.Next() {
+		var e models.AgentEvent
+		if err := rows.Scan(&e.ID, &e.AgentID, &e.EventType, &e.Message, &e.CreatedAt); err != nil {
+			return nil, err
+		}
+		events = append(events, e)
+	}
+	if events == nil {
+		events = []models.AgentEvent{}
+	}
+	return events, rows.Err()
+}
+
+// GetAllAgentEvents holt Events fuer alle Agents
+func (d *Database) GetAllAgentEvents(eventType string, limit int) ([]models.AgentEvent, error) {
+	if limit <= 0 {
+		limit = 100
+	}
+
+	query := "SELECT id, agent_id, event_type, COALESCE(message, ''), created_at FROM agent_events"
+	args := []interface{}{}
+
+	if eventType != "" {
+		query += " WHERE event_type = $1"
+		args = append(args, eventType)
+	}
+
+	query += fmt.Sprintf(" ORDER BY created_at DESC LIMIT $%d", len(args)+1)
+	args = append(args, limit)
+
+	rows, err := d.db.Query(query, args...)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var events []models.AgentEvent
+	for rows.Next() {
+		var e models.AgentEvent
+		if err := rows.Scan(&e.ID, &e.AgentID, &e.EventType, &e.Message, &e.CreatedAt); err != nil {
+			return nil, err
+		}
+		events = append(events, e)
+	}
+	if events == nil {
+		events = []models.AgentEvent{}
+	}
+	return events, rows.Err()
+}
+
+// GetAgentStatus berechnet den Status eines Agents aus last_heartbeat
+func (d *Database) GetAgentStatus(agentID string) string {
+	var lastHB sql.NullTime
+	err := d.db.QueryRow("SELECT last_heartbeat FROM agents WHERE id = $1", agentID).Scan(&lastHB)
+	if err != nil || !lastHB.Valid {
+		return "unknown"
+	}
+	return models.CalculateAgentStatus(&lastHB.Time)
+}