3.10. State

3.10.1. Purpose

Encapsulate varying behavior for the same routine based on an object’s state. This can be a cleaner way for an object to change its behavior at runtime without resorting to large monolithic conditional statements.

3.10.2. UML Diagram

3.10.3. Code

You can also find this code on GitHub

ContextOrder.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\State;

class ContextOrder
{
    private StateOrder $state;

    public static function create(): ContextOrder
    {
        $order = new self();
        $order->state = new CreateOrder();

        return $order;
    }

    public function setState(StateOrder $state): void
    {
        $this->state = $state;
    }

    public function proceedToNext(): void
    {
        $this->state->proceedToNext($this);
    }

    public function toString(): string
    {
        return $this->state->toString();
    }
}

StateOrder.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\State;

interface StateOrder
{
    public function proceedToNext(ContextOrder $context): void;

    public function toString(): string;
}

CreateOrder.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\State;

class CreateOrder implements StateOrder
{
    public function proceedToNext(ContextOrder $context): void
    {
        $context->setState(new ShippingOrder());
    }

    public function toString(): string
    {
        return 'created';
    }
}

ShippingOrder.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\State;

class ShippingOrder implements StateOrder
{
    public function proceedToNext(ContextOrder $context): void
    {
        $context->setState(new OrderDone());
    }

    public function toString(): string
    {
        return 'shipped';
    }
}

OrderDone.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\State;

class OrderDone implements StateOrder
{
    public function proceedToNext(ContextOrder $context): void
    {
        // there is nothing more to do
    }

    public function toString(): string
    {
        return 'done';
    }
}

3.10.4. Test

Tests/StateTest.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\State\Tests;

use DesignPatterns\Behavioral\State\ContextOrder;
use PHPUnit\Framework\TestCase;

class StateTest extends TestCase
{
    public function testIsCreatedWithStateCreated(): void
    {
        $orderContext = ContextOrder::create();

        $this->assertSame('created', $orderContext->toString());
    }

    public function testCanProceedToStateShipped(): void
    {
        $contextOrder = ContextOrder::create();
        $contextOrder->proceedToNext();

        $this->assertSame('shipped', $contextOrder->toString());
    }

    public function testCanProceedToStateDone(): void
    {
        $contextOrder = ContextOrder::create();
        $contextOrder->proceedToNext();
        $contextOrder->proceedToNext();

        $this->assertSame('done', $contextOrder->toString());
    }

    public function testStateDoneIsTheLastPossibleState(): void
    {
        $contextOrder = ContextOrder::create();
        $contextOrder->proceedToNext();
        $contextOrder->proceedToNext();
        $contextOrder->proceedToNext();

        $this->assertSame('done', $contextOrder->toString());
    }
}