fix(entities): filter out read-only tag values

Without this change, all tags are included in the list operation which leads to
user surprise when modifications are attempted.  Here we modify the method
response to exclude those tags which are not modifiable by the user.

pkg/entities/tags.go

@@ -28,7 +28,36 @@ func (e *Entities) ListTags(guid string) ([]*Tag, error) {
 		return nil, err
 	}
 
-	return resp.Actor.Entity.Tags, nil
+	return filterMutable(resp)
+}
+
+// filterMutable removes tag values that are read-only from the received response.
+func filterMutable(resp listTagsResponse) ([]*Tag, error) {
+	var tags []*Tag
+
+	for _, responseTag := range resp.Actor.Entity.TagsWithMetadata {
+		if responseTag != nil {
+			tag := Tag{
+				Key: responseTag.Key,
+			}
+
+			mutable := 0
+			for _, responseTagValue := range responseTag.Values {
+				if responseTagValue.Mutable {
+					mutable++
+					tag.Values = append(tag.Values, responseTagValue.Value)
+				}
+			}
+
+			// All values were mutable
+			if len(responseTag.Values) == mutable {
+				tags = append(tags, &tag)
+			}
+
+		}
+	}
+
+	return tags, nil
 }
 
 // AddTags writes tags to the entity specified by the provided entity GUID.
@@ -121,6 +150,22 @@ func parseTagMutationErrors(errors []tagMutationError) string {
 	return strings.Join(messages, ", ")
 }
 
+// EntityTagValueWithMetadata - The value and metadata of a single entity tag.
+type EntityTagValueWithMetadata struct {
+	// Whether or not the tag can be mutated by the user.
+	Mutable bool `json:"mutable"`
+	// The tag value.
+	Value string `json:"value"`
+}
+
+// EntityTagWithMetadata - The tags with metadata of the entity.
+type EntityTagWithMetadata struct {
+	// The tag's key.
+	Key string `json:"key"`
+	// A list of tag values with metadata information.
+	Values []EntityTagValueWithMetadata `json:"values"`
+}
+
 var listTagsQuery = `
 	query($guid:EntityGuid!) { actor { entity(guid: $guid)  {` +
 	graphqlEntityStructTagsFields +
@@ -129,7 +174,8 @@ var listTagsQuery = `
 type listTagsResponse struct {
 	Actor struct {
 		Entity struct {
-			Tags []*Tag
+			Tags             []*Tag
+			TagsWithMetadata []*EntityTagWithMetadata
 		}
 	}
 }