Agent skill

acc-create-domain-service

Generates DDD Domain Services for PHP 8.5. Creates stateless services for business logic that doesn't belong to entities or value objects. Includes unit tests.

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SKILL.md

Domain Service Generator

Generate DDD-compliant Domain Services for business operations spanning multiple aggregates or requiring external coordination.

Domain Service Characteristics

  • Stateless: No internal state, operates on passed arguments
  • Domain Logic: Contains business rules that don't fit in entities
  • Cross-Aggregate: Coordinates multiple aggregates
  • Named by Domain Operation: Verb-based naming (e.g., TransferMoney, CalculateShipping)
  • No Infrastructure: Pure domain logic, no DB/HTTP calls
  • Immutable Dependencies: Uses repository interfaces, not implementations

When to Use Domain Service

Scenario Example
Operation spans multiple aggregates MoneyTransfer between accounts
Complex business calculation PricingCalculator, TaxCalculator
Domain policy enforcement PasswordPolicy, OrderPolicy
Stateless transformation CurrencyConverter
Aggregate coordination OrderFulfillmentService

Template

php
<?php

declare(strict_types=1);

namespace Domain\{BoundedContext}\Service;

use Domain\{BoundedContext}\Entity\{Entity};
use Domain\{BoundedContext}\ValueObject\{ValueObjects};
use Domain\{BoundedContext}\Repository\{RepositoryInterfaces};
use Domain\{BoundedContext}\Exception\{DomainExceptions};

final readonly class {Name}Service
{
    public function __construct(
        {repositoryDependencies}
    ) {}

    /**
     * @throws {DomainException}
     */
    public function {operation}({parameters}): {ReturnType}
    {
        {domainLogic}
    }

    {privateMethods}
}

Examples

Money Transfer Service

php
<?php

declare(strict_types=1);

namespace Domain\Banking\Service;

use Domain\Banking\Entity\Account;
use Domain\Banking\ValueObject\Money;
use Domain\Banking\Repository\AccountRepositoryInterface;
use Domain\Banking\Exception\InsufficientFundsException;
use Domain\Banking\Exception\SameAccountTransferException;

final readonly class MoneyTransferService
{
    public function __construct(
        private AccountRepositoryInterface $accounts
    ) {}

    /**
     * @throws InsufficientFundsException
     * @throws SameAccountTransferException
     */
    public function transfer(
        Account $source,
        Account $destination,
        Money $amount
    ): void {
        if ($source->id()->equals($destination->id())) {
            throw new SameAccountTransferException();
        }

        if (!$source->canWithdraw($amount)) {
            throw new InsufficientFundsException($source->id(), $amount);
        }

        $source->withdraw($amount);
        $destination->deposit($amount);
    }
}

Pricing Calculator Service

php
<?php

declare(strict_types=1);

namespace Domain\Pricing\Service;

use Domain\Pricing\ValueObject\Money;
use Domain\Pricing\ValueObject\Discount;
use Domain\Pricing\ValueObject\TaxRate;
use Domain\Order\Entity\Order;
use Domain\Customer\Entity\Customer;

final readonly class PricingCalculatorService
{
    public function calculateTotal(
        Order $order,
        Customer $customer,
        ?Discount $discount = null
    ): Money {
        $subtotal = $this->calculateSubtotal($order);
        $discounted = $this->applyDiscount($subtotal, $discount, $customer);
        $taxed = $this->applyTax($discounted, $order->shippingAddress());

        return $taxed;
    }

    private function calculateSubtotal(Order $order): Money
    {
        return $order->items()->reduce(
            fn(Money $total, OrderItem $item) => $total->add(
                $item->price()->multiply($item->quantity())
            ),
            Money::zero($order->currency())
        );
    }

    private function applyDiscount(
        Money $amount,
        ?Discount $discount,
        Customer $customer
    ): Money {
        if ($discount === null) {
            return $amount;
        }

        if (!$discount->isApplicableTo($customer)) {
            return $amount;
        }

        return $discount->apply($amount);
    }

    private function applyTax(Money $amount, Address $address): Money
    {
        $taxRate = TaxRate::forRegion($address->region());
        return $amount->add($amount->multiply($taxRate->value()));
    }
}

Password Policy Service

php
<?php

declare(strict_types=1);

namespace Domain\User\Service;

use Domain\User\ValueObject\Password;
use Domain\User\ValueObject\PasswordStrength;
use Domain\User\Exception\WeakPasswordException;

final readonly class PasswordPolicyService
{
    private const MIN_LENGTH = 8;
    private const REQUIRED_STRENGTH = PasswordStrength::Strong;

    public function validate(Password $password): void
    {
        $violations = [];

        if ($password->length() < self::MIN_LENGTH) {
            $violations[] = "Password must be at least " . self::MIN_LENGTH . " characters";
        }

        if (!$password->hasUppercase()) {
            $violations[] = "Password must contain uppercase letters";
        }

        if (!$password->hasLowercase()) {
            $violations[] = "Password must contain lowercase letters";
        }

        if (!$password->hasDigit()) {
            $violations[] = "Password must contain digits";
        }

        if (!$password->hasSpecialChar()) {
            $violations[] = "Password must contain special characters";
        }

        if ($password->strength()->isWeakerThan(self::REQUIRED_STRENGTH)) {
            $violations[] = "Password strength must be at least " . self::REQUIRED_STRENGTH->value;
        }

        if ($violations !== []) {
            throw new WeakPasswordException($violations);
        }
    }

    public function calculateStrength(Password $password): PasswordStrength
    {
        $score = 0;

        if ($password->length() >= 12) $score += 2;
        elseif ($password->length() >= 8) $score += 1;

        if ($password->hasUppercase()) $score += 1;
        if ($password->hasLowercase()) $score += 1;
        if ($password->hasDigit()) $score += 1;
        if ($password->hasSpecialChar()) $score += 2;

        return match (true) {
            $score >= 6 => PasswordStrength::Strong,
            $score >= 4 => PasswordStrength::Medium,
            default => PasswordStrength::Weak,
        };
    }
}

Test Template

php
<?php

declare(strict_types=1);

namespace Tests\Unit\Domain\{BoundedContext}\Service;

use Domain\{BoundedContext}\Service\{Name}Service;
use Domain\{BoundedContext}\Entity\{Entity};
use Domain\{BoundedContext}\ValueObject\{ValueObject};
use Domain\{BoundedContext}\Exception\{DomainException};
use PHPUnit\Framework\Attributes\CoversClass;
use PHPUnit\Framework\Attributes\Group;
use PHPUnit\Framework\TestCase;

#[Group('unit')]
#[CoversClass({Name}Service::class)]
final class {Name}ServiceTest extends TestCase
{
    private {Name}Service $service;

    protected function setUp(): void
    {
        $this->service = new {Name}Service(
            {mockDependencies}
        );
    }

    public function test{Operation}Successfully(): void
    {
        {arrange}

        $result = $this->service->{operation}({parameters});

        {assert}
    }

    public function test{Operation}ThrowsOn{Condition}(): void
    {
        {arrange}

        $this->expectException({DomainException}::class);

        $this->service->{operation}({invalidParameters});
    }

    {additionalTests}
}

Example Test

php
<?php

declare(strict_types=1);

namespace Tests\Unit\Domain\Banking\Service;

use Domain\Banking\Service\MoneyTransferService;
use Domain\Banking\Entity\Account;
use Domain\Banking\ValueObject\AccountId;
use Domain\Banking\ValueObject\Money;
use Domain\Banking\Exception\InsufficientFundsException;
use Domain\Banking\Exception\SameAccountTransferException;
use PHPUnit\Framework\Attributes\CoversClass;
use PHPUnit\Framework\Attributes\Group;
use PHPUnit\Framework\TestCase;

#[Group('unit')]
#[CoversClass(MoneyTransferService::class)]
final class MoneyTransferServiceTest extends TestCase
{
    private MoneyTransferService $service;

    protected function setUp(): void
    {
        $this->service = new MoneyTransferService(
            $this->createMock(AccountRepositoryInterface::class)
        );
    }

    public function testTransfersMoneyBetweenAccounts(): void
    {
        $source = $this->createAccountWithBalance(Money::USD(1000));
        $destination = $this->createAccountWithBalance(Money::USD(500));
        $amount = Money::USD(300);

        $this->service->transfer($source, $destination, $amount);

        self::assertTrue($source->balance()->equals(Money::USD(700)));
        self::assertTrue($destination->balance()->equals(Money::USD(800)));
    }

    public function testThrowsOnInsufficientFunds(): void
    {
        $source = $this->createAccountWithBalance(Money::USD(100));
        $destination = $this->createAccountWithBalance(Money::USD(500));
        $amount = Money::USD(300);

        $this->expectException(InsufficientFundsException::class);

        $this->service->transfer($source, $destination, $amount);
    }

    public function testThrowsOnSameAccountTransfer(): void
    {
        $account = $this->createAccountWithBalance(Money::USD(1000));

        $this->expectException(SameAccountTransferException::class);

        $this->service->transfer($account, $account, Money::USD(100));
    }

    private function createAccountWithBalance(Money $balance): Account
    {
        $account = new Account(AccountId::generate());
        $account->deposit($balance);
        return $account;
    }
}

Naming Conventions

Pattern Example
Service {Operation}Service
Method {verb}{noun}
Exception {Condition}Exception
Test {ServiceName}Test

File Placement

Component Path
Domain Service src/Domain/{BoundedContext}/Service/
Exceptions src/Domain/{BoundedContext}/Exception/
Unit Tests tests/Unit/Domain/{BoundedContext}/Service/

Anti-patterns to Avoid

Anti-pattern Problem Solution
Anemic Service Just delegates to entities Move logic to entities
Infrastructure in Service DB/HTTP calls Use repository interfaces
Stateful Service Maintains internal state Make stateless
God Service Too many responsibilities Split into focused services
Business Logic in Constructors Complex setup Keep constructors simple

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