func tagReferenceToTagEvent(stream *api.ImageStream, tagRef api.TagReference, tagOrID string) (*api.TagEvent, error) {
	var (
		event *api.TagEvent
		err   error
	)
	switch tagRef.From.Kind {
	case "DockerImage":
		event = &api.TagEvent{
			Created:              unversioned.Now(),
			DockerImageReference: tagRef.From.Name,
		}

	case "ImageStreamImage":
		event, err = api.ResolveImageID(stream, tagOrID)
	case "ImageStreamTag":
		event, err = api.LatestTaggedImage(stream, tagOrID), nil
	default:
		err = fmt.Errorf("invalid from.kind %q: it must be DockerImage, ImageStreamImage or ImageStreamTag", tagRef.From.Kind)
	}
	if err != nil {
		return nil, err
	}
	if event != nil && tagRef.Generation != nil {
		event.Generation = *tagRef.Generation
	}
	return event, nil
}

func autoConvert_v1_TagEvent_To_api_TagEvent(in *TagEvent, out *api.TagEvent, s conversion.Scope) error {
	out.Created = in.Created
	out.DockerImageReference = in.DockerImageReference
	out.Image = in.Image
	out.Generation = in.Generation
	return nil
}

func autoConvert_v1_TagEvent_To_api_TagEvent(in *TagEvent, out *api.TagEvent, s conversion.Scope) error {
	if err := pkg_api.Convert_unversioned_Time_To_unversioned_Time(&in.Created, &out.Created, s); err != nil {
		return err
	}
	out.DockerImageReference = in.DockerImageReference
	out.Image = in.Image
	out.Generation = in.Generation
	return nil
}

func autoConvert_v1_TagEvent_To_api_TagEvent(in *TagEvent, out *image_api.TagEvent, s conversion.Scope) error {
	if defaulting, found := s.DefaultingInterface(reflect.TypeOf(*in)); found {
		defaulting.(func(*TagEvent))(in)
	}
	if err := api.Convert_unversioned_Time_To_unversioned_Time(&in.Created, &out.Created, s); err != nil {
		return err
	}
	out.DockerImageReference = in.DockerImageReference
	out.Image = in.Image
	out.Generation = in.Generation
	return nil
}

// Create registers a new image (if it doesn't exist) and updates the
// specified ImageStream's tags. If attempts to update the ImageStream fail
// with a resource conflict, the update will be retried if the newer
// ImageStream has no tag diffs from the previous state. If tag diffs are
// detected, the conflict error is returned.
func (s *REST) Create(ctx kapi.Context, obj runtime.Object) (runtime.Object, error) {
	if err := rest.BeforeCreate(Strategy, ctx, obj); err != nil {
		return nil, err
	}

	mapping := obj.(*api.ImageStreamMapping)

	stream, err := s.findStreamForMapping(ctx, mapping)
	if err != nil {
		return nil, err
	}

	image := mapping.Image
	tag := mapping.Tag
	if len(tag) == 0 {
		tag = api.DefaultImageTag
	}

	if err := s.imageRegistry.CreateImage(ctx, &image); err != nil && !errors.IsAlreadyExists(err) {
		return nil, err
	}

	next := api.TagEvent{
		Created:              unversioned.Now(),
		DockerImageReference: image.DockerImageReference,
		Image:                image.Name,
	}

	err = wait.ExponentialBackoff(wait.Backoff{Steps: maxRetriesOnConflict}, func() (bool, error) {
		lastEvent := api.LatestTaggedImage(stream, tag)

		next.Generation = stream.Generation

		if !api.AddTagEventToImageStream(stream, tag, next) {
			// nothing actually changed
			return true, nil
		}
		api.UpdateTrackingTags(stream, tag, next)
		_, err := s.imageStreamRegistry.UpdateImageStreamStatus(ctx, stream)
		if err == nil {
			return true, nil
		}
		if !errors.IsConflict(err) {
			return false, err
		}
		// If the update conflicts, get the latest stream and check for tag
		// updates. If the latest tag hasn't changed, retry.
		latestStream, findLatestErr := s.findStreamForMapping(ctx, mapping)
		if findLatestErr != nil {
			return false, findLatestErr
		}

		// no previous tag
		if lastEvent == nil {
			// The tag hasn't changed, so try again with the updated stream.
			stream = latestStream
			return false, nil
		}

		// check for tag change
		newerEvent := api.LatestTaggedImage(latestStream, tag)
		// generation and creation time differences are ignored
		lastEvent.Generation = newerEvent.Generation
		lastEvent.Created = newerEvent.Created
		if kapi.Semantic.DeepEqual(lastEvent, newerEvent) {
			// The tag hasn't changed, so try again with the updated stream.
			stream = latestStream
			return false, nil
		}

		// The tag changed, so return the conflict error back to the client.
		return false, err
	})
	if err != nil {
		return nil, err
	}
	return &unversioned.Status{Status: unversioned.StatusSuccess}, nil
}