refactor:

- Updated the class name callback to allow null values.
- Enhanced the toString method to include className in GenerateOptions.
- Added validation for className to ensure it is a valid Dart identifier.
- Trimmed whitespace from className before use.

Author: Mustafa Ali Dikçinar

bin/generate.dart

@@ -85,8 +85,8 @@ ArgParser _generateArgParser(GenerateOptions? generateOptions) {
     'class-name',
     abbr: 'c',
     defaultsTo: 'LocaleKeys',
-    callback: (String? x) => generateOptions!.className = x!,
-    help: 'Custom class name for generated file',
+    callback: (String? x) => generateOptions!.className = x,
+    help: 'Custom class name for generated keys class (keys format)',
   );
 
   return parser;
@@ -104,7 +104,13 @@ class GenerateOptions {
 
   @override
   String toString() {
-    return 'format: $format sourceDir: $sourceDir sourceFile: $sourceFile outputDir: $outputDir outputFile: $outputFile skipUnnecessaryKeys: $skipUnnecessaryKeys';
+    return 'format: $format '
+        'sourceDir: $sourceDir '
+        'sourceFile: $sourceFile '
+        'outputDir: $outputDir '
+        'outputFile: $outputFile '
+        'skipUnnecessaryKeys: $skipUnnecessaryKeys '
+        'className: $className';
   }
 }
 
@@ -154,7 +160,15 @@ void generateFile(
   Directory outputPath,
   GenerateOptions options,
 ) async {
-  final className = options.className ?? 'LocaleKeys';
+  final className = (options.className?.trim().isNotEmpty ?? false)
+      ? options.className!.trim()
+      : 'LocaleKeys';
+  if (options.format == 'keys' &&
+      !RegExp(r'^[A-Za-z_$][A-Za-z0-9_$]*$').hasMatch(className)) {
+    stderr.writeln(
+        "Invalid --class-name '$className'. It must be a valid Dart identifier (start with a letter or _; only letters, digits, _ or \$).");
+    return;
+  }
   var generatedFile = File(outputPath.path);
   if (!generatedFile.existsSync()) {
     generatedFile.createSync(recursive: true);
@@ -194,7 +208,7 @@ Future _writeKeys(
 
 // ignore_for_file: constant_identifier_names
 
-abstract class  $className {
+abstract class $className {
 ''';
 
   final fileData = File(files.first.path);