deserialize CPA kafka deviceData messages into a types.Blood

Previously a glucose.Glucose was used, which was fine in that we only
look at the UserID and UploadID fields, but there are other
incompatible fields that can "spoil" the deserialization.

BACK-2559

Author: ewollesen

data/events/alerts.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/tidepool-org/platform/alerts"
 	"github.com/tidepool-org/platform/auth"
+	"github.com/tidepool-org/platform/data/types"
 	"github.com/tidepool-org/platform/data/types/blood/glucose"
 	"github.com/tidepool-org/platform/data/types/dosingdecision"
 	"github.com/tidepool-org/platform/devicetokens"
@@ -115,7 +116,10 @@ func isActivityAndActivityOnly(updatedFields []string) bool {
 func (c *Consumer) consumeDeviceData(ctx context.Context,
 	session sarama.ConsumerGroupSession, msg *sarama.ConsumerMessage) error {
 
-	datum := &Glucose{}
+	// The actual type should be either a glucose.Glucose or a
+	// dosingdecision.DosingDecision, but they both use types.Base, and that's where the
+	// only fields we need are defined.
+	datum := &types.Base{}
 	if _, err := unmarshalMessageValue(msg.Value, datum); err != nil {
 		return err
 	}