Prometheus: Refactor exemplar sampler (#60278)

pkg/tsdb/prometheus/querydata/exemplar/sampler.go

@@ -0,0 +1,46 @@
+package exemplar
+
+import (
+	"sort"
+	"time"
+
+	"github.com/grafana/grafana/pkg/tsdb/prometheus/models"
+)
+
+type Sampler interface {
+	Add(models.Exemplar)
+	SetStep(time.Duration)
+	Sample() []models.Exemplar
+	Reset()
+}
+
+var _ Sampler = (*NoOpSampler)(nil)
+
+type NoOpSampler struct {
+	exemplars []models.Exemplar
+}
+
+func NewNoOpSampler() Sampler {
+	return &NoOpSampler{
+		exemplars: []models.Exemplar{},
+	}
+}
+
+func (e *NoOpSampler) Add(ex models.Exemplar) {
+	e.exemplars = append(e.exemplars, ex)
+}
+
+func (e *NoOpSampler) SetStep(time.Duration) {
+	// noop
+}
+
+func (e *NoOpSampler) Sample() []models.Exemplar {
+	sort.SliceStable(e.exemplars, func(i, j int) bool {
+		return e.exemplars[i].Timestamp.Before(e.exemplars[j].Timestamp)
+	})
+	return e.exemplars
+}
+
+func (e *NoOpSampler) Reset() {
+	e.exemplars = []models.Exemplar{}
+}