Session: add reference price and CO2 (#28712)

tariff/tariffs.go

@@ -44,6 +44,32 @@ func Rates(t api.Tariff) api.Rates {
 	return rr
 }
 
+// AverageRate returns the arithmetic mean of rates in [now, now+d), or nil if unavailable.
+func AverageRate(t api.Tariff, d time.Duration) *float64 {
+	rr := Rates(t)
+	if rr == nil {
+		return nil
+	}
+
+	now := time.Now()
+	end := now.Add(d)
+
+	var sum float64
+	var count int
+	for _, r := range rr {
+		if r.Start.Before(end) && r.End.After(now) {
+			sum += r.Value
+			count++
+		}
+	}
+
+	if count == 0 {
+		return nil
+	}
+
+	return new(sum / float64(count))
+}
+
 func (t *Tariffs) Get(u api.TariffUsage) api.Tariff {
 	// ensure tariff is not a wrapper
 	exists := func(t api.Tariff) bool {