3.2. Command

3.2.1. Rôle

Encapsuler l’invocation et le découplage.

Nous avons un Invoker (exécuteur) et un Receiver (récepteur). Ce modèle utilise une « commande » pour déléguer l’exécution d’une méthode à un récepteur et fournir une méthode « execute » unifiée. De cette façon, l’exécuteur ne connaît que la méthode « execute » pour exécuter la commande. Le récepteur est donc découplé de l’appelant.

Le deuxième aspect de ce modèle est la méthode undo(), qui permet d’annuler l’exécution de la méthode execute(). Les commandes peuvent également être agrégées pour créer des commandes complexes avec une surcharge minimale et par composition (plutôt que par héritage).

3.2.2. Exemples

  • A text editor : all events are commands which can be undone, stacked and saved.

  • Les outils complexes de la console sont composés de sous-commandes afin de mieux modulariser les tâches. Chacune de ces commandes peut être implémentée comme un modèle de commande (par exemple vagrant).

3.2.3. Diagramme UML

Alt Command UML Diagram

3.2.4. Code

Vous pouvez également trouver ce code sur GitHub

Command.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command;

interface Command
{
    /**
     * this is the most important method in the Command pattern,
     * The Receiver goes in the constructor.
     */
    public function execute();
}

UndoableCommand.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command;

interface UndoableCommand extends Command
{
    /**
     * This method is used to undo change made by command execution
     */
    public function undo();
}

HelloCommand.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command;

/**
 * This concrete command calls "print" on the Receiver, but an external
 * invoker just knows that it can call "execute"
 */
class HelloCommand implements Command
{
    private Receiver $output;

    /**
     * Each concrete command is built with different receivers.
     * There can be one, many or completely no receivers, but there can be other commands in the parameters
     */
    public function __construct(Receiver $console)
    {
        $this->output = $console;
    }

    /**
     * execute and output "Hello World".
     */
    public function execute()
    {
        // sometimes, there is no receiver and this is the command which does all the work
        $this->output->write('Hello World');
    }
}

AddMessageDateCommand.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command;

/**
 * This concrete command tweaks receiver to add current date to messages
 * invoker just knows that it can call "execute"
 */
class AddMessageDateCommand implements UndoableCommand
{
    private Receiver $output;

    /**
     * Each concrete command is built with different receivers.
     * There can be one, many or completely no receivers, but there can be other commands in the parameters.
     */
    public function __construct(Receiver $console)
    {
        $this->output = $console;
    }

    /**
     * Execute and make receiver to enable displaying messages date.
     */
    public function execute()
    {
        // sometimes, there is no receiver and this is the command which
        // does all the work
        $this->output->enableDate();
    }

    /**
     * Undo the command and make receiver to disable displaying messages date.
     */
    public function undo()
    {
        // sometimes, there is no receiver and this is the command which
        // does all the work
        $this->output->disableDate();
    }
}

Receiver.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command;

/**
 * Receiver is a specific service with its own contract and can be only concrete.
 */
class Receiver
{
    private bool $enableDate = false;

    /**
     * @var string[]
     */
    private array $output = [];

    public function write(string $str)
    {
        if ($this->enableDate) {
            $str .= ' ['.date('Y-m-d').']';
        }

        $this->output[] = $str;
    }

    public function getOutput(): string
    {
        return join("\n", $this->output);
    }

    /**
     * Enable receiver to display message date
     */
    public function enableDate()
    {
        $this->enableDate = true;
    }

    /**
     * Disable receiver to display message date
     */
    public function disableDate()
    {
        $this->enableDate = false;
    }
}

Invoker.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command;

/**
 * Invoker is using the command given to it.
 * Example : an Application in SF2.
 */
class Invoker
{
    private Command $command;

    /**
     * in the invoker we find this kind of method for subscribing the command
     * There can be also a stack, a list, a fixed set ...
     */
    public function setCommand(Command $cmd)
    {
        $this->command = $cmd;
    }

    /**
     * executes the command; the invoker is the same whatever is the command
     */
    public function run()
    {
        $this->command->execute();
    }
}

3.2.5. Test

Tests/CommandTest.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command\Tests;

use DesignPatterns\Behavioral\Command\HelloCommand;
use DesignPatterns\Behavioral\Command\Invoker;
use DesignPatterns\Behavioral\Command\Receiver;
use PHPUnit\Framework\TestCase;

class CommandTest extends TestCase
{
    public function testInvocation()
    {
        $invoker = new Invoker();
        $receiver = new Receiver();

        $invoker->setCommand(new HelloCommand($receiver));
        $invoker->run();
        $this->assertSame('Hello World', $receiver->getOutput());
    }
}

Tests/UndoableCommandTest.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command\Tests;

use DesignPatterns\Behavioral\Command\AddMessageDateCommand;
use DesignPatterns\Behavioral\Command\HelloCommand;
use DesignPatterns\Behavioral\Command\Invoker;
use DesignPatterns\Behavioral\Command\Receiver;
use PHPUnit\Framework\TestCase;

class UndoableCommandTest extends TestCase
{
    public function testInvocation()
    {
        $invoker = new Invoker();
        $receiver = new Receiver();

        $invoker->setCommand(new HelloCommand($receiver));
        $invoker->run();
        $this->assertSame('Hello World', $receiver->getOutput());

        $messageDateCommand = new AddMessageDateCommand($receiver);
        $messageDateCommand->execute();

        $invoker->run();
        $this->assertSame("Hello World\nHello World [".date('Y-m-d').']', $receiver->getOutput());

        $messageDateCommand->undo();

        $invoker->run();
        $this->assertSame("Hello World\nHello World [".date('Y-m-d')."]\nHello World", $receiver->getOutput());
    }
}