Chain of Responsibility Pattern Generator

Creates Chain of Responsibility pattern infrastructure for sequential request processing.

When to Use

Scenario	Example
Multiple processors	Validation, discounts, approvals
Unknown handlers	Plugin systems
Priority processing	First match wins
Middleware	HTTP pipeline, logging

Component Characteristics

HandlerInterface

• Defines handle method
• Optional setNext for linking
• Returns result or delegates

AbstractHandler

• Implements chain linking
• Provides base handle logic
• Simplifies concrete handlers

Concrete Handlers

• Process specific requests
• Decide to handle or pass
• Can terminate or continue chain

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Generation Process

Step 1: Generate Handler Interface

Path: src/Domain/{BoundedContext}/Handler/

1. {Name}HandlerInterface.php — Handler contract with setNext and handle methods

Step 2: Generate Abstract Handler

Path: src/Domain/{BoundedContext}/Handler/

1. Abstract{Name}Handler.php — Base class with chain linking logic

Step 3: Generate Concrete Handlers

Path: src/Domain/{BoundedContext}/Handler/

1. {Specific}{Name}Handler.php — Specific handler implementations

Step 4: Generate Chain Builder (Optional)

Path: src/Domain/{BoundedContext}/Handler/

1. {Name}ChainBuilder.php — Fluent builder for chain construction

Step 5: Generate Tests

1. {Handler}Test.php — Individual handler tests
2. {Name}ChainTest.php — Chain integration tests

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File Placement

Component	Path
Handler Interface	src/Domain/{BoundedContext}/Handler/
Abstract Handler	src/Domain/{BoundedContext}/Handler/
Concrete Handlers	src/Domain/{BoundedContext}/Handler/
Chain Builder	src/Domain/{BoundedContext}/Handler/
Pipeline	src/Application/Pipeline/
Unit Tests	tests/Unit/Domain/{BoundedContext}/Handler/

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Naming Conventions

Component	Pattern	Example
Interface	{Name}HandlerInterface	ValidationHandlerInterface
Abstract	Abstract{Name}Handler	AbstractValidationHandler
Concrete	{Specific}{Name}Handler	EmailValidationHandler
Builder	{Name}ChainBuilder	ValidationChainBuilder
Test	{ClassName}Test	EmailValidationHandlerTest

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Quick Template Reference

Handler Interface

interface {Name}HandlerInterface
{
    public function setNext(self $handler): self;
    public function handle({RequestType} $request): {ResultType};
}

Abstract Handler

abstract class Abstract{Name}Handler implements {Name}HandlerInterface
{
    private ?{Name}HandlerInterface $next = null;

    public function setNext({Name}HandlerInterface $handler): {Name}HandlerInterface
    {
        $this->next = $handler;
        return $handler;
    }

    public function handle({RequestType} $request): {ResultType}
    {
        if ($this->next !== null) {
            return $this->next->handle($request);
        }
        return $this->getDefaultResult();
    }

    abstract protected function getDefaultResult(): {ResultType};
}

Concrete Handler

final class {Specific}Handler extends Abstract{Name}Handler
{
    public function handle({RequestType} $request): {ResultType}
    {
        if ($this->canHandle($request)) {
            return $this->process($request);
        }
        return parent::handle($request);
    }

    private function canHandle({RequestType} $request): bool
    {
        return {condition};
    }
}

Chain Builder

final class {Name}ChainBuilder
{
    private array $handlers = [];

    public function add({Name}HandlerInterface $handler): self
    {
        $this->handlers[] = $handler;
        return $this;
    }

    public function build(): {Name}HandlerInterface
    {
        $first = $this->handlers[0];
        $current = $first;
        for ($i = 1; $i < count($this->handlers); $i++) {
            $current = $current->setNext($this->handlers[$i]);
        }
        return $first;
    }
}

---

Usage Examples

Validation Chain

$chain = (new ValidationChainBuilder())
    ->add(new NotEmptyValidationHandler('email'))
    ->add(new EmailValidationHandler('email'))
    ->add(new MinLengthValidationHandler('password', 8))
    ->build();

$result = $chain->validate($request);

if ($result->hasErrors()) {
    throw new ValidationException($result->getMessage());
}

Discount Chain

$vipHandler = new VipDiscountHandler();
$promoHandler = new PromoCodeDiscountHandler($promoCodes);
$bulkHandler = new BulkDiscountHandler();

$vipHandler->setNext($promoHandler);
$promoHandler->setNext($bulkHandler);

$result = $vipHandler->apply($discountRequest);

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Anti-patterns to Avoid

Anti-pattern	Problem	Solution
Circular Chain	Infinite loop	Validate chain structure
No Default	Unhandled requests	Provide fallback handler
Coupled Handlers	Hard to reorder	Use interface properly
Missing Builder	Manual chain assembly	Create ChainBuilder
State in Handler	Non-reentrant	Make handlers stateless

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References

For complete PHP templates and examples, see:

• references/templates.md — Handler Interface, Abstract Handler, Concrete Handler, Chain Builder, Pipeline templates
• references/examples.md — Validation Chain, Discount Chain examples and tests