package prometheusmetrics

import (
	"context"
	"time"

	"github.com/google/uuid"
	"github.com/prometheus/client_golang/prometheus"

	"github.com/coder/coder/coderd/database"
)

// ActiveUsers tracks the number of users that have authenticated within the past hour.
func ActiveUsers(ctx context.Context, registerer prometheus.Registerer, db database.Store, duration time.Duration) (context.CancelFunc, error) {
	if duration == 0 {
		duration = 5 * time.Minute
	}

	gauge := prometheus.NewGauge(prometheus.GaugeOpts{
		Namespace: "coderd",
		Subsystem: "api",
		Name:      "active_users_duration_hour",
		Help:      "The number of users that have been active within the last hour.",
	})
	err := registerer.Register(gauge)
	if err != nil {
		return nil, err
	}

	ctx, cancelFunc := context.WithCancel(ctx)
	ticker := time.NewTicker(duration)
	go func() {
		defer ticker.Stop()
		for {
			select {
			case <-ctx.Done():
				return
			case <-ticker.C:
			}
			apiKeys, err := db.GetAPIKeysLastUsedAfter(ctx, database.Now().Add(-1*time.Hour))
			if err != nil {
				continue
			}
			distinctUsers := map[uuid.UUID]struct{}{}
			for _, apiKey := range apiKeys {
				distinctUsers[apiKey.UserID] = struct{}{}
			}
			gauge.Set(float64(len(distinctUsers)))
		}
	}()
	return cancelFunc, nil
}