implement transform and validate validator

Author: ArturAssisComp

lib/new_api_prototype/core_validators/check_list_remaining_core_validators.md

@@ -6,4 +6,5 @@
 - [X] validate with default value validator
 - [X] Required/optional validators
 - [X] Add tests to override error msg validator
-- [ ] Transform validator
+- [ ] Type validators
+- [X] Transform validator

lib/new_api_prototype/core_validators/transform_validator.dart

@@ -0,0 +1,54 @@
+import '../constants.dart';
+
+String errorTransformAndValidateTemporary<T>(
+    T userInput, String? transformedResultTypeDescription) {
+  if (transformedResultTypeDescription != null) {
+    // An example, it will print the error message: "Hello" is not a valid integer.
+    return '"${userInput.toString()}" is not a valid $transformedResultTypeDescription';
+  }
+
+  return '"${userInput.toString()}" is not able to be transformed.';
+}
+
+/// This function returns a validator which transforms the user input.
+/// If the transformation fails, it returns a transformation error message.
+/// Otherwise, it passes the input to the `next` validator, if it was provided,
+/// or, if `next` was not provided, it returns `null`.
+///
+/// # Parameters
+/// - `String?` `transformedResultTypeDescription`: This parameter helps improving
+/// the readability of the error message. If provided, the error message can
+/// specify what is the expected type/result of the transformation. For example,
+/// if 'positive integer' is provided, it can return a message like:
+/// '"hello" is not a valid positive integer'. Otherwise, if this parameter is
+/// not provided, the default error message will be more generic.
+/// - `String` `Function(IN)?` `transformAndValidateMsg`: this is the custom message
+/// for the validation error message. It is a function that receives the user
+/// input as argument and returns a String, the error message.
+///
+/// # Transformation
+/// This process transforms the user input from the type `IN` to the type `OUT`.
+/// Its failure is considered a validation failure, and, when it happens, a
+/// validation failure message is returned.
+///
+/// # Example
+/// ```dart
+///
+/// ```
+Validator<IN> transformAndValidate<IN extends Object?, OUT extends Object?>(
+  OUT Function(IN) transformFunction, {
+  Validator<OUT>? next,
+  String Function(IN)? transformAndValidateMsg,
+  String? transformedResultTypeDescription,
+}) {
+  return (IN input) {
+    try {
+      final OUT transformedValue = transformFunction(input);
+      return next?.call(transformedValue);
+    } catch (_) {
+      return transformAndValidateMsg?.call(input) ??
+          errorTransformAndValidateTemporary(
+              input.toString(), transformedResultTypeDescription);
+    }
+  };
+}

test/new_api_testing/core_validators/transform_validator_test.dart

@@ -0,0 +1,62 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:form_builder_validators/new_api_prototype/constants.dart';
+import 'package:form_builder_validators/new_api_prototype/core_validators/transform_validator.dart';
+
+void main() {
+  const String defaultMsg = 'default error msg';
+  String? isEvenGreaterThan56(int input) {
+    return input > 56 && (input % 2 == 0) ? null : defaultMsg;
+  }
+
+  group('Validator: transformAndValidate', () {
+    test('Should check if the String input is integer, transforming it', () {
+      final Validator<String> v = transformAndValidate(int.parse);
+
+      expect(v('12'), isNull);
+      expect(v('not integer'),
+          errorTransformAndValidateTemporary('not integer', null));
+    });
+    test('Should transform and apply a next validator', () {
+      final Validator<String> v =
+          transformAndValidate(int.parse, next: isEvenGreaterThan56);
+
+      expect(v('12'), defaultMsg);
+      expect(v('56'), defaultMsg);
+      expect(v('59'), defaultMsg);
+      expect(v('60'), isNull);
+      expect(v('not integer'),
+          errorTransformAndValidateTemporary('not integer', null));
+    });
+    test('Should return a custom transformation error message', () {
+      const String customErrorMsg = 'custom error msg';
+      final Validator<String> v = transformAndValidate(
+        int.parse,
+        next: isEvenGreaterThan56,
+        transformAndValidateMsg: (_) => customErrorMsg,
+      );
+
+      expect(v('12'), defaultMsg);
+      expect(v('56'), defaultMsg);
+      expect(v('59'), defaultMsg);
+      expect(v('60'), isNull);
+      expect(v('not integer'), customErrorMsg);
+    });
+    test(
+        'Should return an error message with transformed result type description',
+        () {
+      const String t = 'integer';
+      final Validator<String> v = transformAndValidate(
+        int.parse,
+        next: isEvenGreaterThan56,
+        transformedResultTypeDescription: t,
+      );
+
+      expect(v('12'), defaultMsg);
+      expect(v('56'), defaultMsg);
+      expect(v('59'), defaultMsg);
+      expect(v('60'), isNull);
+      expect(v('not integer'),
+          errorTransformAndValidateTemporary('not integer', t));
+    });
+  });
+}