zero: refactor telemetry and controller (#5135)

* zero: refactor controller

* refactor zero telemetry and controller

* wire with connect handler

* cr

internal/zero/telemetry/sessions/sessions.go

@@ -0,0 +1,51 @@
+package sessions
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/pomerium/pomerium/internal/sets"
+	"github.com/pomerium/pomerium/pkg/grpc/databroker"
+	"github.com/pomerium/pomerium/pkg/grpc/session"
+	"github.com/pomerium/pomerium/pkg/protoutil"
+)
+
+var sessionTypeURL = protoutil.GetTypeURL(new(session.Session))
+
+// CurrentUsers returns a list of users active within the current UTC day
+func CurrentUsers(
+	ctx context.Context,
+	client databroker.DataBrokerServiceClient,
+) ([]string, error) {
+	records, _, _, err := databroker.InitialSync(ctx, client, &databroker.SyncLatestRequest{
+		Type: sessionTypeURL,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("fetching sessions: %w", err)
+	}
+
+	users := sets.NewHash[string]()
+	utcNow := time.Now().UTC()
+	threshold := time.Date(utcNow.Year(), utcNow.Month(), utcNow.Day(), 0, 0, 0, 0, time.UTC)
+
+	for _, record := range records {
+		var s session.Session
+		err := record.GetData().UnmarshalTo(&s)
+		if err != nil {
+			return nil, fmt.Errorf("unmarshaling session: %w", err)
+		}
+		if s.UserId == "" { // session creation is in progress
+			continue
+		}
+		if s.AccessedAt == nil {
+			continue
+		}
+		if s.AccessedAt.AsTime().Before(threshold) {
+			continue
+		}
+		users.Add(s.UserId)
+	}
+
+	return users.Items(), nil
+}