dns: SortRegions() by ISO3166

Signed-off-by: Alejandro Mery <amery@jpi.io>

pkg/dns/record.go

@@ -34,6 +34,32 @@ func SortAddrRecords(s []AddrRecord) []AddrRecord {
 	return s
 }
 
+// SortRegions sorts regions. first by length those 3-character
+// or shorter, and then by length. It's mostly aimed at
+// supporting ISO-3166 order
+func SortRegions(regions []string) []string {
+	sort.Slice(regions, func(i, j int) bool {
+		r1, r2 := regions[i], regions[j]
+
+		switch {
+		case len(r1) < 4:
+			switch {
+			case len(r1) < len(r2):
+				return true
+			case len(r1) > len(r2):
+				return false
+			default:
+				return r1 < r2
+			}
+		case len(r2) < 4:
+			return false
+		default:
+			return r1 < r2
+		}
+	})
+	return regions
+}
+
 // AddrRecord represents an A or AAAA record
 type AddrRecord struct {
 	Name string