refactor: enhance NewClient to support environment variable fallback and add tests

cmd/miab/main.go

@@ -8,6 +8,7 @@ import (
 	miab "gitea.koszewscy.waw.pl/koszewscy/mailinabox-go"
 )
 
+
 func usage() {
 	fmt.Fprintf(os.Stderr, `Usage: miab <command> [options]
 
@@ -17,33 +18,21 @@ Commands:
   delete  Delete a DNS record
   add     Add a DNS record
 
-Credentials are read from environment variables:
-  MIAB_HOST      Mail-in-a-Box hostname (e.g. box.example.com)
-  MIAB_USERNAME  Admin email address
-  MIAB_PASSWORD  Admin password
+Credentials: any empty parameter falls back to environment variables.
+  MIAB_HOST / MAILINABOX_BASE_URL      Mail-in-a-Box hostname (MIAB_HOST takes precedence;
+                                       hostname is parsed from MAILINABOX_BASE_URL if set)
+  MIAB_USERNAME / MAILINABOX_EMAIL     Admin email address
+  MIAB_PASSWORD / MAILINABOX_PASSWORD  Admin password
 `)
 }
 
 func mustClient() *miab.Client {
-	host := os.Getenv("MIAB_HOST")
-	username := os.Getenv("MIAB_USERNAME")
-	password := os.Getenv("MIAB_PASSWORD")
-
-	var missing []string
-	if host == "" {
-		missing = append(missing, "MIAB_HOST")
-	}
-	if username == "" {
-		missing = append(missing, "MIAB_USERNAME")
-	}
-	if password == "" {
-		missing = append(missing, "MIAB_PASSWORD")
-	}
-	if len(missing) > 0 {
-		fmt.Fprintf(os.Stderr, "miab: missing required environment variables: %v\n", missing)
+	c, err := miab.NewClient("", "", "")
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
 		os.Exit(1)
 	}
-	return miab.NewClient(host, username, password)
+	return c
 }
 
 func main() {