add validation service

Frontend/lib/mih_apis/mih_validation_services.dart

@@ -0,0 +1,67 @@
+class MihValidationServices {
+  String? validateEmail(String? email) {
+    if (email == null || email.isEmpty) {
+      return "Email is required";
+    }
+    final emailRegex =
+        RegExp(r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$');
+    if (!emailRegex.hasMatch(email)) {
+      return "Invalid Email Format";
+    }
+    return null;
+  }
+
+  String? validateUsername(String? username) {
+    String? errorMessage = "";
+    if (username == null || username.isEmpty) {
+      errorMessage += "Username is required";
+      return errorMessage;
+    }
+    if (!RegExp(r'^[a-zA-Z]').hasMatch(username)) {
+      errorMessage += "\n• Your username should start with a letter.";
+    }
+    if (!RegExp(r'^[a-zA-Z0-9_]+$').hasMatch(username)) {
+      errorMessage +=
+          "\n• You can use letters, numbers, and/or underscores only.";
+    }
+    if (username.length < 6 || username.length > 30) {
+      errorMessage += "\n• Keep it between 6 and 30 characters.";
+    }
+    if (RegExp(r'[@#\$]').hasMatch(username)) {
+      errorMessage += "\n• Avoid special characters like @, #, or \$.";
+    }
+
+    if (errorMessage.isEmpty) {
+      return null; // No errors, username is valid
+    }
+    return "Let's create a great username for you!$errorMessage";
+  }
+
+  String? validatePassword(String? password) {
+    String? errorMessage = "";
+    if (password == null || password.isEmpty) {
+      errorMessage += "Password is required";
+      return errorMessage;
+    }
+    if (password.length < 8) {
+      errorMessage += "\n• Contains at least 8 characters long";
+    }
+    if (!RegExp(r'[A-Z]').hasMatch(password)) {
+      errorMessage += "\n• Contains at least 1 uppercase letter";
+    }
+    if (!RegExp(r'[a-z]').hasMatch(password)) {
+      errorMessage += "\n• Contains at least 1 lowercase letter";
+    }
+    if (!RegExp(r'[0-9]').hasMatch(password)) {
+      errorMessage += "\n• Contains at least 1 digit";
+    }
+    if (!RegExp(r'[!@#$%^&*]').hasMatch(password)) {
+      errorMessage += "\n• Contains at least 1 special character (!@#\$%^&*)";
+    }
+    if (errorMessage.isEmpty) {
+      return null; // No errors, password is valid
+    }
+    errorMessage = "Let's create a great password for you!$errorMessage";
+    return errorMessage;
+  }
+}