Fill in property set identifiers when updating. (#82)

This is a bit of a cludge, the frontend keeps property set identifiers
the same when updating them, as it knows the indicies as they are being
written.

We can't really do that here, but we do have some chance. If the
property set name stays the same, then we can align the identifier by comparing
the old values. This should cover most use cases, but one can also use
an explicit id as well.

client/resource_cluster.go

@@ -370,6 +370,7 @@ func resourceClusterCreate(d *schema.ResourceData, m interface{}) error {
 	}
 
 	d.SetId(strconv.Itoa(e.ID))
+	resourceClusterRead(d, m)
 	return err
 }
 
@@ -386,6 +387,7 @@ func resourceClusterUpdate(d *schema.ResourceData, m interface{}) error {
 		return err
 	}
 
+	resourceClusterRead(d, m)
 	return nil
 }
 
@@ -594,25 +596,44 @@ func composeSparkConfig(d map[string]interface{}) SparkConfig {
 }
 
 func expandPropertySet(d *schema.ResourceData) []PropertySet {
-	drs := d.Get("property_set").(*schema.Set).List()
+	prev, new := d.GetChange("property_set")
+	prevX := prev.(*schema.Set).List()
+	drs := new.(*schema.Set).List()
 	res := make([]PropertySet, 0, len(drs))
 	for _, dr := range drs {
-		val, _ := dr.(map[string]interface{})
-		source := val["additional_spark_properties"].(map[string]interface{})
+		vals := dr.(map[string]interface{})
+		source := vals["additional_spark_properties"].(map[string]interface{})
 		additionalSparkProperties := make(map[string]string)
 
 		for k, v := range source {
 			additionalSparkProperties[k] = v.(string)
 		}
 
-		if val["name"].(string) != "" {
-			parsed := PropertySet{
-				Name:                      val["name"].(string),
-				AdditionalSparkProperties: additionalSparkProperties,
+		if vals["name"].(string) != "" {
+			var identifier *int
+			name := vals["name"].(string)
+			explicit, hasId := vals["id"].(int)
+
+			if hasId && explicit != 0 {
+				identifier = &explicit
+			} else {
+				// No identifier was explicitly specified.
+				// Try to find a property set from the last read
+				// with the same name, we'll use its ID.
+				for _, drX := range prevX {
+					oldVals, _ := drX.(map[string]interface{})
+					implicit, hasOld := oldVals["id"].(int)
+					oldName := oldVals["name"].(string)
+					if oldName == name && hasOld && implicit != 0 {
+						identifier = &implicit
+					}
+				}
 			}
 
-			if id, ok := val["id"].(int); ok && id != 0 {
-				parsed.ID = &id
+			parsed := PropertySet{
+				ID:                        identifier,
+				Name:                      name,
+				AdditionalSparkProperties: additionalSparkProperties,
 			}
 
 			res = append(res, parsed)