feat: add last active time per user

backend/db/metrics.go

@@ -6,8 +6,10 @@ import (
 
 	"codeberg.org/u1f320/pronouns.cc/backend/log"
 	"emperror.dev/errors"
+	"github.com/jackc/pgx/v5/pgconn"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promauto"
+	"github.com/rs/xid"
 )
 
 func (db *DB) initMetrics() (err error) {
@@ -39,6 +41,20 @@ func (db *DB) initMetrics() (err error) {
 		return errors.Wrap(err, "registering member count gauge")
 	}
 
+	err = prometheus.Register(prometheus.NewGaugeFunc(prometheus.GaugeOpts{
+		Name: "pronouns_users_active",
+		Help: "The number of users active in the past 30 days",
+	}, func() float64 {
+		count, err := db.ActiveUsers(context.Background())
+		if err != nil {
+			log.Errorf("getting active user count for metrics: %v", err)
+		}
+		return float64(count)
+	}))
+	if err != nil {
+		return errors.Wrap(err, "registering active user count gauge")
+	}
+
 	err = prometheus.Register(prometheus.NewGaugeFunc(prometheus.GaugeOpts{
 		Name: "pronouns_database_latency",
 		Help: "The latency to the database in nanoseconds",
@@ -51,6 +67,9 @@ func (db *DB) initMetrics() (err error) {
 		}
 		return float64(time.Since(start))
 	}))
+	if err != nil {
+		return errors.Wrap(err, "registering database latency gauge")
+	}
 
 	db.TotalRequests = promauto.NewCounter(prometheus.CounterOpts{
 		Name: "pronouns_api_requests_total",
@@ -75,3 +94,32 @@ func (db *DB) TotalMemberCount(ctx context.Context) (numMembers int64, err error
 	}
 	return numMembers, nil
 }
+
+const activeTime = 30 * 24 * time.Hour
+
+func (db *DB) ActiveUsers(ctx context.Context) (numUsers int64, err error) {
+	t := time.Now().Add(-activeTime)
+	err = db.QueryRow(ctx, "SELECT COUNT(*) FROM users WHERE deleted_at IS NULL AND last_active > $1", t).Scan(&numUsers)
+	if err != nil {
+		return 0, errors.Wrap(err, "querying active user count")
+	}
+	return numUsers, nil
+}
+
+type connOrTx interface {
+	Exec(ctx context.Context, sql string, arguments ...any) (commandTag pgconn.CommandTag, err error)
+}
+
+// UpdateActiveTime is called on create and update endpoints (PATCH /users/@me, POST/PATCH/DELETE /members)
+func (db *DB) UpdateActiveTime(ctx context.Context, tx connOrTx, userID xid.ID) (err error) {
+	sql, args, err := sq.Update("users").Set("last_active", time.Now().UTC()).Where("id = ?", userID).ToSql()
+	if err != nil {
+		return errors.Wrap(err, "building sql")
+	}
+
+	_, err = tx.Exec(ctx, sql, args...)
+	if err != nil {
+		return errors.Wrap(err, "executing query")
+	}
+	return nil
+}

backend/db/user.go

@@ -24,6 +24,7 @@ type User struct {
 	DisplayName *string
 	Bio         *string
 	MemberTitle *string
+	LastActive  time.Time
 
 	Avatar *string
 	Links  []string