Refactor sorting a bit

parser/parser.go

@@ -67,8 +67,31 @@ func NewSortConfig() qEntrySortConfig {
 	return qEntrySortConfig{}
 }
 
-func (c qEntrySortConfig) By(field string, order string) qEntrySortConfig {
+func isQEntryAttribute(attributeName string) bool {
-	newAttributeConfig := qEntryAttributeSortConfig{attribute: field, order: order}
+	var isValidAttribute bool
+	switch attributeName {
+	case "Id":
+	case "Status":
+	case "Date":
+	case "Size":
+	case "Sender":
+	case "Recipients":
+	case "Reason":
+		isValidAttribute = true
+	default:
+		isValidAttribute = false
+	}
+	return isValidAttribute
+}
+
+func (c qEntrySortConfig) By(attributeName string, order string) qEntrySortConfig {
+	if !isQEntryAttribute(attributeName) {
+		panic(fmt.Sprintf("Invalid sort attribute: '%s' given!", attributeName))
+	}
+    if order != "ASC" && order != "DESC" {
+        panic(fmt.Sprintf("Invalid sort order '%s' given!", order))
+    }
+	newAttributeConfig := qEntryAttributeSortConfig{attribute: attributeName, order: order}
 	c.attributes = append(c.attributes, newAttributeConfig)
 	return c
 }
@@ -77,6 +100,7 @@ func (queue MailQ) Sort(config qEntrySortConfig) {
 	if len(config.attributes) == 0 {
 		return
 	}
+	fmt.Printf("SortConfig: %q\n", config)
 	sort.Slice(queue.Entries, func(a int, b int) bool {
 		for _, sortBy := range config.attributes {
 			var cmp bool