TMP 4

lib/core/validator.dart

@@ -0,0 +1,39 @@
+import 'package:flutter/foundation.dart';
+
+abstract class Validator<T> {
+  Validator({@required this.errorMessage});
+
+  final String errorMessage;
+
+  bool isValid(T value);
+
+  String call(T value) => !isValid(value) ? errorMessage : null;
+}
+
+class TextValidator extends Validator<String> {
+  TextValidator(
+      {this.minLength, this.maxLength, this.pattern, String errorMessage})
+      : super(errorMessage: errorMessage);
+
+  final int minLength;
+  final int maxLength;
+  String pattern;
+
+  @override
+  bool isValid(String value) {
+    if (value == null || value.isEmpty) {
+      return true;
+    }
+
+    return value.length > minLength &&
+        (maxLength > 0 ? (value.length <= maxLength) : true) &&
+        (pattern != null ? match(value) : true);
+  }
+
+  bool match(String value) => RegExp(pattern).hasMatch(value);
+}
+
+class WalletNameValidator extends TextValidator {
+  WalletNameValidator()
+      : super(minLength: 1, maxLength: 15, pattern: '^[a-zA-Z0-9_]\$');
+}