# Validation Module

**Standalone Validation System for Fields, Forms, and Data**

The Validation Module provides a comprehensive validation system that can be used independently or integrated with form-handling and LiveComponents.

---

## Features

- **Schema-Based Validation** - Define validation rules in a schema
- **Field-Level Validation** - Validate individual fields
- **Async Validation** - Support for asynchronous validation (e.g., API checks)
- **Custom Validation Rules** - Register your own validation rules
- **Integration with form-handling** - Works seamlessly with form-handling module
- **Integration with LiveComponents** - Validate LiveComponent data
- **HTML5 Attribute Support** - Automatically reads validation rules from HTML attributes

---

## Quick Start

### Basic Usage

```javascript
import { Validator } from './modules/validation/index.js';

// Create validator with schema
const validator = Validator.create({
    email: ['required', 'email'],
    age: [
        'required',
        'number',
        { rule: 'min', options: { value: 18 } },
        { rule: 'max', options: { value: 100 } }
    ],
    password: [
        'required',
        { rule: 'minLength', options: { value: 8 } }
    ]
});

// Validate data
const result = await validator.validate({
    email: 'user@example.com',
    age: 25,
    password: 'secret123'
});

if (result.valid) {
    console.log('Validation passed');
} else {
    console.log('Validation errors:', result.errors);
}
```

### From HTML Form

```javascript
import { Validator } from './modules/validation/index.js';

// Create validator from form element
const form = document.querySelector('#my-form');
const validator = Validator.fromForm(form);

// Validate form data
const formData = new FormData(form);
const data = Object.fromEntries(formData);
const result = await validator.validate(data);
```

---

## API Reference

### Validator.create(schema)

Create a new Validator instance with a schema.

**Parameters**:
- `schema` - Validation schema object

**Example**:
```javascript
const validator = Validator.create({
    email: 'email',
    age: ['required', 'number', { rule: 'min', options: { value: 18 } }]
});
```

### Validator.fromForm(form)

Create a validator from an HTML form element, reading validation rules from HTML attributes.

**Parameters**:
- `form` - HTMLFormElement

**Example**:
```html
<form id="my-form">
    <input type="email" name="email" required />
    <input type="number" name="age" min="18" max="100" required />
    <input type="password" name="password" minlength="8" required />
</form>
```

```javascript
const form = document.querySelector('#my-form');
const validator = Validator.fromForm(form);
```

### validator.validate(data)

Validate entire data object against schema.

**Parameters**:
- `data` - Data object to validate

**Returns**: `Promise<ValidationResults>`

**Example**:
```javascript
const result = await validator.validate({
    email: 'user@example.com',
    age: 25
});

console.log(result.valid); // true or false
console.log(result.errors); // { email: ['...'], age: ['...'] }
```

### validator.validateField(fieldName, value)

Validate a single field.

**Parameters**:
- `fieldName` - Field name
- `value` - Field value

**Returns**: `Promise<ValidationResult>`

**Example**:
```javascript
const result = await validator.validateField('email', 'user@example.com');
console.log(result.valid); // true or false
console.log(result.errors); // ['error message']
```

### validator.validateFields(data, fieldNames)

Validate specific fields.

**Parameters**:
- `data` - Data object
- `fieldNames` - Array of field names to validate

**Returns**: `Promise<ValidationResults>`

### validator.registerRule(name, rule)

Register a custom validation rule.

**Parameters**:
- `name` - Rule name
- `rule` - Validation function: `(value, options) => boolean | string`

**Example**:
```javascript
validator.registerRule('customRule', (value, options) => {
    if (value === options.expected) {
        return true;
    }
    return options.message || 'Validation failed';
});

// Use custom rule
const validator = Validator.create({
    field: { rule: 'customRule', options: { expected: 'test', message: 'Must be "test"' } }
});
```

---

## Built-in Validation Rules

### required

Field must have a value.

```javascript
email: 'required'
// or
email: { rule: 'required', options: { message: 'Email is required' } }
```

### email

Valid email address format.

```javascript
email: 'email'
```

### url

Valid URL format.

```javascript
website: 'url'
```

### min / max

Minimum/maximum numeric value.

```javascript
age: [
    { rule: 'min', options: { value: 18 } },
    { rule: 'max', options: { value: 100 } }
]
```

### minLength / maxLength

Minimum/maximum string length.

```javascript
password: [
    { rule: 'minLength', options: { value: 8 } },
    { rule: 'maxLength', options: { value: 128 } }
]
```

### pattern

Regex pattern validation.

```javascript
username: {
    rule: 'pattern',
    options: {
        value: '^[a-zA-Z0-9_]+$',
        message: 'Username can only contain letters, numbers, and underscores'
    }
}
```

### number

Must be a valid number.

```javascript
price: 'number'
```

### integer

Must be an integer.

```javascript
quantity: 'integer'
```

### phone

Valid phone number format.

```javascript
phone: 'phone'
```

### postalCode

Valid postal code (supports DE, US, UK, FR).

```javascript
postalCode: {
    rule: 'postalCode',
    options: { country: 'DE' }
}
```

### custom

Custom validation function.

```javascript
field: {
    rule: 'custom',
    options: {
        validator: (value, options) => {
            // Custom validation logic
            return value === options.expected ? true : 'Value must be ' + options.expected;
        },
        expected: 'test'
    }
}
```

---

## Async Validation

```javascript
const validator = Validator.create({
    email: {
        rule: 'custom',
        async: true,
        validator: async (value, options) => {
            // Check if email exists via API
            const response = await fetch(`/api/check-email?email=${value}`);
            const data = await response.json();
            
            if (data.exists) {
                return 'Email already exists';
            }
            return true;
        }
    }
});

const result = await validator.validate({ email: 'user@example.com' });
```

---

## Integration with form-handling

```javascript
import { Validator } from './modules/validation/index.js';
import { FormHandler } from './modules/form-handling/index.js';

const form = document.querySelector('#my-form');
const validator = Validator.fromForm(form);
const formHandler = FormHandler.create(form);

// Use validator with form handler
formHandler.validator = validator;
```

---

## Integration with LiveComponents

```javascript
import { Validator } from './modules/validation/index.js';
import { LiveComponentManager } from './modules/livecomponent/index.js';

const validator = Validator.create({
    email: ['required', 'email'],
    name: ['required', { rule: 'minLength', options: { value: 2 } }]
});

// Validate before action
const lcManager = LiveComponentManager.getInstance();
lcManager.on('action:before-execute', async (componentId, actionName, params) => {
    if (actionName === 'submitForm') {
        const result = await validator.validate(params);
        if (!result.valid) {
            // Handle validation errors
            return false; // Prevent action
        }
    }
});
```

---

## Use Cases

### Form Validation

```javascript
const validator = Validator.create({
    email: ['required', 'email'],
    password: [
        'required',
        { rule: 'minLength', options: { value: 8 } }
    ],
    confirmPassword: [
        'required',
        {
            rule: 'custom',
            validator: (value, options) => {
                const password = options.password;
                return value === password ? true : 'Passwords do not match';
            },
            options: { password: formData.password }
        }
    ]
});
```

### API Response Validation

```javascript
const validator = Validator.create({
    id: ['required', 'integer'],
    name: ['required', { rule: 'minLength', options: { value: 1 } }],
    email: ['required', 'email']
});

// Validate API response
const response = await fetch('/api/user');
const data = await response.json();
const result = await validator.validate(data);

if (!result.valid) {
    console.error('Invalid API response:', result.errors);
}
```

### User Input Validation

```javascript
// Validate on input
const validator = Validator.create({
    search: {
        rule: 'minLength',
        options: { value: 3, message: 'Search must be at least 3 characters' }
    }
});

const input = document.querySelector('#search');
input.addEventListener('input', async (e) => {
    const result = await validator.validateField('search', e.target.value);
    if (!result.valid) {
        showError(result.errors[0]);
    } else {
        hideError();
    }
});
```

---

## Best Practices

1. **Use Schema-Based Validation** - Define validation rules in a schema for reusability
2. **Register Custom Rules** - Create reusable custom validation rules
3. **Validate Early** - Validate on blur or input for better UX
4. **Show Clear Errors** - Display validation errors clearly to users
5. **Use Async Validation Sparingly** - Only for necessary checks (e.g., email uniqueness)

---

## Browser Support

- **Chrome/Edge**: 90+
- **Firefox**: 88+
- **Safari**: 14+
- **Mobile**: iOS 14+, Android Chrome 90+

**Required Features**:
- ES2020 JavaScript
- Promise support
- Async/await support

---

**Next**: [Error Tracking Module](error-tracking.md) →