Imported from Flutterando/lucid_validation (SKILL.md). Install upstream with npx skills add Flutterando/lucid_validation. Copyright stays with the author.

LucidValidation AI Developer Guide

This guide contains everything an AI assistant or human developer needs to know to work with the LucidValidation package. Use it as a reference for syntax, API surface, architectural patterns, and extension methodologies.

1. Core Architecture

LucidValidation is inspired by FluentValidation (C#). It evaluates validation rules against models s s.

Key Classes

1. LucidValidator<E>: The base abstract class. Subclasses extend this with their target entity type E (e.g. UserValidator extends LucidValidator<User>).
   • Registers validation builders in the constructor.
   • Triggers validations via validate or validateAsync.
2. LucidValidationBuilder<TProp, Entity>: Extends the validator to define rules for a specific property of type TProp extracted from the parent Entity.
3. SimpleValidationBuilder<T>: Alias of LucidValidationBuilder<T, T>, used when validating primitive values or when writing extensions that don't depend on the parent entity.
4. ValidationException: Holds validation details (message, code, key, entity, index).
5. ValidationResult: Wraps the execution result (isValid, exceptions, errorsByKey, firstErrorFor).

Sync vs. Async Rule Engine

[!IMPORTANT]

• Sync validations: Registered using must, use, or useValidation. Executed via validate(entity).
• Async validations: Registered using mustAsync, useAsync, or useValidationAsync. Executed via validateAsync(entity).
• Critical Pitfall: If a validator contains any async rules, calling validate() will throw an AsyncValidationException. You must use validateAsync() in this case.

2. Built-In Validators

All built-in validation rules are implemented as extensions on SimpleValidationBuilder<T> or LucidValidationBuilder<T, E>.

Common & Core

• must(bool Function(T value) predicate, String message, String code): Custom check.
• mustWith(bool Function(T value, E entity) predicate, String message, String code): Custom check with entity context.
• mustAsync(Future<bool> Function(T value) predicate, ...): Async custom check.
• mustWithAsync(Future<bool> Function(T value, E entity) predicate, ...): Async custom check with entity context.
• isNull(), isNotNull(): Check for nullability.
• equalTo(T Function(E) comparison): Check equality to another field.
• notEqualTo(T Function(E) comparison): Check inequality to another field.
• isInEnum(List<T> values): Check value is in allowed list (e.g. MyEnum.values).

String Checks

• isEmpty(), notEmpty(): Checks if string is empty / not empty.
• minLength(int), maxLength(int), length(min, max): Length constraints.
• isAlphanumeric(), isNumeric(): Character set validations.
• isUppercase(), isLowercase(): Casing constraints.
• contains(String), startsWith(String), endsWith(String): Substring checks.
• matchesPattern(Pattern): Regular expression validation.
• mustHaveLowercase(), mustHaveUppercase(): Character type presence.
• mustHaveNumber(), mustHaveSpecialCharacter(): Character type presence (note: mustHaveNumber is singular).
• hasNoSequentialRepeatedCharacters(int length): Rejects sequences like "aaa".
• hasNoSequentialCharacters(int length): Rejects sequences like "123" or "abc".

Numeric & Boolean Checks

• min(num), max(num): Value bounds.
• range(min, max), inclusiveBetween(min, max), exclusiveBetween(min, max): Range bounds.
• isPositive(), isNegative(), isNonNegative(), isNonZero(): Sign checks.
• isEven(), isOdd(): Modulo checks.
• multipleOf(num factor): Divisibility check.
• precisionScale(int precision, int scale): Digits and decimal bounds.
• isTrue(), isFalse(): Strictly boolean checks.

DateTime Checks

• greaterThan(DateTime), greaterThanOrEqualTo(DateTime): Min date checks.
• lessThan(DateTime), lessThanOrEqualTo(DateTime): Max date checks.
• inclusiveBetween(DateTime, DateTime), exclusiveBetween(DateTime, DateTime): Date range checks.
• inPast(), inFuture(): Time-relative checks.
• afterField(DateTime Function(E) other): Asserts date is after another property.
• beforeField(DateTime Function(E) other): Asserts date is before another property.

Collections & Lists

• minItems(int), maxItems(int): Iterable length bounds.
• listContains(T item): Item presence in list.

Web, Network, & Identification

• validEmail(): Valid email format.
• validUrl(), httpUrl(): Valid URL / HTTP(S) URL.
• validUuid(): Valid UUID format (note: validUuid is camelCased).
• validIpv4(), validIpv6(): IPv4 / IPv6 addresses (note: lowercase pv).
• validCreditCard(): Luhn algorithm check.

Brazilian Formats

• validCPF(), validCNPJ(), validCPFOrCNPJ(), validCEP(): Brazilian national identifiers.
• validPhoneBR(), validPhoneWithCountryCodeBR(): Brazilian telephone numbers.

3. Composition & Complex Nesting

Validator Composition (include)

To combine multiple validators for the same entity class:

class FullUserValidator extends LucidValidator<UserModel> {
  FullUserValidator() {
    include(ContactValidator());
    include(BillingValidator());
  }
}

Nesting Single Objects (setValidator)

Use setValidator to delegate validation of a sub-property to a dedicated validator:

class CustomerValidator extends LucidValidator<Customer> {
  CustomerValidator() {
    ruleFor((c) => c.address, key: 'address').setValidator(AddressValidator());
  }
}

Nesting Iterables (setEach)

Use setEach to apply a validator to every item inside a collection, which automatically tracks item index:

ruleFor((c) => c.students, key: 'students').setEach(StudentValidator());

Inline Iterable Validation (ruleForEach)

Use ruleForEach when validating lists of primitive values or inline rules:

ruleForEach((order) => order.tags, key: 'tags').notEmpty().maxLength(10);

4. Localization & Custom Languages

Global language setting is managed via the Culture object:

LucidValidation.global.culture = Culture('en', 'US');

Overriding Translations Globally

Override individual translations s s dynamically using LanguageManager:

class CustomLanguageManager extends LanguageManager {
  CustomLanguageManager() {
    // Override a specific translation code
    addTranslation(Culture('pt', 'BR'), Language.code.equalTo, 'O valor deve ser idêntico a {ComparisonValue}.');
  }
}

// Assign it globally
LucidValidation.global.languageManager = CustomLanguageManager();

Implementing a New Language

To add a new language, subclass Language from lib/src/localization/language.dart and pass a map of s s translation keys in the call to super():

import 'package:lucid_validation/src/localization/language.dart';

class SpanishLanguage extends Language {
  SpanishLanguage()
      : super({
          Language.code.notEmpty: "'{PropertyName}' no puede estar vacío.",
          Language.code.validEmail: "'{PropertyName}' no es un correo electrónico válido.",
          // Add translations for all Language.code.* keys
        });
}

5. Creating Custom Validation Rules

Custom rules are declared as Dart extensions on SimpleValidationBuilder<T> (for entity-agnostic rules) or LucidValidationBuilder<T, E> (for entity-aware rules).

Method 1: Composing Existing Rules

extension StrongPasswordValidation on SimpleValidationBuilder<String> {
  SimpleValidationBuilder<String> strongPassword() {
    return notEmpty()
        .minLength(8)
        .mustHaveLowercase()
        .mustHaveUppercase()
        .mustHaveNumber()
        .mustHaveSpecialCharacter();
  }
}

Method 2: Synchronous Rules using useValidation (Simple Predicate)

Use this when you want the validation engine to handle formatting and ValidationException creation:

extension CustomMinWords on SimpleValidationBuilder<String> {
  SimpleValidationBuilder<String> minWords(int min, {String? message, String? code}) {
    return useValidation(
      (value, entity) => value.trim().split(RegExp(r'\s+')).length >= min,
      code: code ?? 'minWords',
      message: message ?? "'{PropertyName}' must have at least {Min} words.",
      parameters: (value, entity) => {'Min': '$min'},
    );
  }
}

Method 3: Asynchronous Rules using useValidationAsync

For database lookups or HTTP calls, s:

extension UniqueUsername on SimpleValidationBuilder<String> {
  SimpleValidationBuilder<String> uniqueUsername(
    Future<bool> Function(String username) isUnique, {
    String? message,
    String? code,
  }) {
    return useValidationAsync(
      (value, entity) => isUnique(value),
      code: code ?? 'usernameTaken',
      message: message ?? "'{PropertyName}' is already taken.",
    );
  }
}

Method 4: S/Async Rules with Full Exception Control (use / useAsync)

Use use (sync) or useAsync (async) when you want to construct the ValidationException manually (e.g. dynamic keys, nested properties, customized entity names):

extension CustomPrefixCheck on SimpleValidationBuilder<String> {
  SimpleValidationBuilder<String> checkPrefix(String prefix) {
    return use((value, entity) {
      if (!value.startsWith(prefix)) {
        return ValidationException(
          key: key,
          message: "'{PropertyName}' must start with '$prefix'.",
          code: 'invalid_prefix',
          entity: 'CustomEntity',
        );
      }
      return null; // Return null if validation passes
    });
  }
}

6. Advanced Practical Examples

Example A: Flutter Form Integration

You can integrate validations in your Flutter forms by defining a dedicated validator class (recommended for clean architecture / Domain Layer validations) or inline directly within your Widget (recommended for rapid prototyping or purely UI-focused validation).

Option A1: Class-Based Validator (Recommended for Domain Layer)

First, create a dedicated validation class:

import 'package:lucid_validation/lucid_validation.dart';

class UserRegisterForm {
  String email = '';
  String username = '';
}

class UserRegisterValidator extends LucidValidator<UserRegisterForm> {
  UserRegisterValidator() {
    ruleFor((c) => c.email, key: 'email')
        .notEmpty()
        .validEmail();

    ruleFor((c) => c.username, key: 'username')
        .notEmpty()
        .minLength(3);
  }
}

Then, use it in your Widget:

import 'package:flutter/material.dart';
import 'package:lucid_validation/lucid_validation.dart';

class RegisterFormWidget extends StatelessWidget {
  final credentials = UserRegisterForm();
  final validator = UserRegisterValidator();

  RegisterFormWidget({super.key});

  @override
  Widget build(BuildContext context) {
    return Form(
      child: Column(
        children: [
          TextFormField(
            decoration: const InputDecoration(hintText: 'Email'),
            onChanged: (val) => credentials.email = val,
            validator: validator.byField(credentials, 'email'),
          ),
          TextFormField(
            decoration: const InputDecoration(hintText: 'Username'),
            onChanged: (val) => credentials.username = val,
            validator: validator.byField(credentials, 'username'),
          ),
        ],
      ),
    );
  }
}

Option A2: Inline Validator (LucidValidator.inline)

Define the validator directly within your Widget to keep validations local to the UI file:

import 'package:flutter/material.dart';
import 'package:lucid_validation/lucid_validation.dart';

class RegisterFormWidgetInline extends StatelessWidget {
  final credentials = UserRegisterForm();

  // Define the validator inline on the class
  final validator = LucidValidator<UserRegisterForm>.inline((v) {
    v.ruleFor((c) => c.email, key: 'email')
        .notEmpty()
        .validEmail();

    v.ruleFor((c) => c.username, key: 'username')
        .notEmpty()
        .minLength(3);
  });

  RegisterFormWidgetInline({super.key});

  @override
  Widget build(BuildContext context) {
    return Form(
      child: Column(
        children: [
          TextFormField(
            decoration: const InputDecoration(hintText: 'Email'),
            onChanged: (val) => credentials.email = val,
            validator: validator.byField(credentials, 'email'),
          ),
          TextFormField(
            decoration: const InputDecoration(hintText: 'Username'),
            onChanged: (val) => credentials.username = val,
            validator: validator.byField(credentials, 'username'),
          ),
        ],
      ),
    );
  }
}

Example B: Real-Time Password Strength Checklist

This example demonstrates how to use rulesForField to drive a checklist UI indicating to the user in real-time which password criteria are met as they type.

import 'package:flutter/material.dart';
import 'package:lucid_validation/lucid_validation.dart';

class PasswordChecklistWidget extends StatefulWidget {
  const PasswordChecklistWidget({super.key});

  @override
  State<PasswordChecklistWidget> createState() => _PasswordChecklistWidgetState();
}

class _PasswordChecklistWidgetState extends State<PasswordChecklistWidget> {
  String _password = '';

  final validator = LucidValidator<String>.inline((v) {
    v.ruleFor((p) => p, key: 'password')
        .notEmpty().withErrorCode('required')
        .minLength(8).withErrorCode('length')
        .mustHaveUppercase().withErrorCode('uppercase')
        .mustHaveNumber().withErrorCode('number')
        .mustHaveSpecialCharacter().withErrorCode('special');
  });

  @override
  Widget build(BuildContext context) {
    // Evaluate all rules for the password field against the current string state
    final rules = validator.rulesForField(_password, 'password');

    return Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        TextField(
          onChanged: (value) => setState(() => _password = value),
          obscureText: true,
          decoration: const InputDecoration(
            labelText: 'Password',
            border: OutlineInputBorder(),
          ),
        ),
        const SizedBox(height: 12),
        ...rules.map((rule) {
          return Padding(
            padding: const EdgeInsets.symmetric(vertical: 4.0),
            child: Row(
              children: [
                Icon(
                  rule.isValid ? Icons.check_circle : Icons.cancel,
                  color: rule.isValid ? Colors.green : Colors.red,
                  size: 20,
                ),
                const SizedBox(width: 8),
                Text(
                  rule.message,
                  style: TextStyle(
                    color: rule.isValid ? Colors.green[800] : Colors.red[800],
                  ),
                ),
              ],
            ),
          );
        }),
      ],
    );
  }
}

Example C: Complex Nested Entity Graph Validation

This example showcases a full order-placement schema with:

• Nested object validation (setValidator).
• List validation with item index tracking (setEach and minItems).
• Polymorphic branching of nested objects based on a discriminator (switchOn).

import 'package:lucid_validation/lucid_validation.dart';

// Domain Models
class Order {
  final Customer customer;
  final List<OrderItem> items;
  final PaymentDetails payment;
  final String status;

  Order({
    required this.customer,
    required this.items,
    required this.payment,
    required this.status,
  });
}

class Customer {
  final String name;
  final String email;

  Customer({required this.name, required this.email});
}

class OrderItem {
  final String sku;
  final int quantity;
  final double price;

  OrderItem({required this.sku, required this.quantity, required this.price});
}

class PaymentDetails {
  final String type; // 'credit', 'pix', 'bank_transfer'
  final String? cardNumber;
  final String? pixKey;

  PaymentDetails({required this.type, this.cardNumber, this.pixKey});
}

// Validator
class OrderValidator extends LucidValidator<Order> {
  OrderValidator() {
    // Flat field check
    ruleFor((o) => o.status, key: 'status').notEmpty();

    // Nested object validator
    ruleFor((o) => o.customer, key: 'customer').setValidator(
      LucidValidator<Customer>.inline((v) {
        v.ruleFor((c) => c.name, key: 'name').notEmpty();
        v.ruleFor((c) => c.email, key: 'email').notEmpty().validEmail();
      }),
    );

    // List validation with item index tracking
    ruleFor((o) => o.items, key: 'items')
        .minItems(1, message: 'Your order must contain at least one item.')
        .setEach(
          LucidValidator<OrderItem>.inline((v) {
            v.ruleFor((i) => i.sku, key: 'sku').notEmpty().maxLength(10);
            v.ruleFor((i) => i.quantity, key: 'quantity').min(1);
            v.ruleFor((i) => i.price, key: 'price').isPositive();
          }),
        );

    // Nested object with polymorphic validation using switchOn
    ruleFor((o) => o.payment, key: 'payment').setValidator(
      LucidValidator<PaymentDetails>.inline((v) {
        v.ruleFor((p) => p.type, key: 'type').notEmpty();

        v.switchOn((p) => p.type, cases: {
          'credit': (inner) {
            inner.ruleFor((p) => p.cardNumber!, key: 'cardNumber').notEmpty().validCreditCard();
          },
          'pix': (inner) {
            inner.ruleFor((p) => p.pixKey!, key: 'pixKey').notEmpty();
          },
        });
      }),
    );
  }
}

// Executing Validation
void main() {
  final order = Order(
    status: 'pending',
    customer: Customer(name: 'Alice', email: 'invalid-email'),
    items: [
      OrderItem(sku: 'SKU123', quantity: 0, price: -5.0), // invalid quantity/price
    ],
    payment: PaymentDetails(type: 'credit', cardNumber: ''), // missing credit card number
  );

  final result = OrderValidator().validate(order);
  
  print(result.isValid); // false
  print(result.errorsByKey);
  // Output maps errors to nested paths & indices:
  // {
  //   "customer.email": ["'email' is not a valid email address."],
  //   "items.quantity": ["'quantity' must be greater than or equal to 1. You entered 0."],
  //   "items.price": ["'price' must be a positive number."],
  //   "payment.cardNumber": ["'cardNumber' must not be empty."]
  // }
}