explain implementation of ad-hoc depencency container

09-dependency-injector.md

@@ -10,12 +10,201 @@ to explain the problem and work on a solution.
 #### Adding a clock service
 
 Lets assume that we want to show the current time in our Hello action. We could easily just call use one of the many
-ways to get the current time directly in the handle-method, but maybe we want to make that configurable and 
+ways to get the current time directly in the handle-method, but lets create a separate class and interface for that so
+we can later configure and switch our implementation.
+
+We need a new 'Service\Time' namespace, so lets first create the folder in our 'src' directory 'src/Service/Time'.
+There we place a Clock.php interface and a SystemClock.php implementation:
+
+
+The Clock.php interface:
+```php
+<?php declare(strict_types=1);
+
+namespace Lubian\NoFramework\Service\Time;
+
+interface Clock
+{
+    public function now(): \DateTimeImmutable;
+}
+```
+
+The SystemClock.php implementation:
+```php
+<?php declare(strict_types=1);
+
+namespace Lubian\NoFramework\Service\Time;
+
+final class SystemClock implements Clock
+{
+    public function now(): \DateTimeImmutable
+    {
+        return new \DateTimeImmutable();
+    }
+
+}
+```
+
+Now we can require the Clockinterface as a depencency in our controller and use it to display the current time.
+```php
+<?php declare(strict_types=1);
+
+namespace Lubian\NoFramework\Action;
+
+
+use Lubian\NoFramework\Service\Time\Clock;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Psr\Http\Server\RequestHandlerInterface;
+
+final class Hello implements RequestHandlerInterface
+{
+    public function __construct(
+        private readonly ResponseInterface $response,
+        private readonly Clock $clock
+    )
+    {
+    }
+
+    public function handle(ServerRequestInterface $request): ResponseInterface
+    {
+        $name = $request->getAttribute('name', 'Stranger');
+        $body = $this->response->getBody();
+
+        $time = $this->clock->now()->format('H:i:s');
+
+        $body->write('Hello ' . $name . '!<br />');
+        $body->write('The Time is: ' . $time);
+
+        return $this->response->withBody($body)
+            ->withStatus(200);
+    }
+}
+```
+
+But if we try to access the corresponding route in the webbrowser we get an error:
+> Too few arguments to function Lubian\NoFramework\Action\Hello::__construct(), 1 passed in /home/lubiana/PhpstormProjects/no-framework/app/src/Bootstrap.php on line 62 and exactly 2 expected
+
+Our current problem is, that we have two Actions defined, which both have different constructor requirements. That means,
+that we need to have some code in our Application, that creates our Action Objects and takes care of injection all the
+needed dependencies.
+
+This code is called a Dependency Injector. If you want you can read [this](https://afilina.com/learn/design/dependency-injection)
+great blogpost about that topic, which I highly recommend.
+
+Lets build our own Dependency Injector to make our application work again.
+
+As a starting point we are going to take a look at the [Container Interface])(https://www.php-fig.org/psr/psr-11/) that
+is widely adopted in the PHP-World.
+
+#### Building a dependency container
+
+**Short Disclaimer:** *Although it would be fun to write our own great implementation of this interface with everything that
+is needed for modern php development I will take a shortcut here and implement very reduced version to show you the
+basic concept.*
+
+The `Pst\Container\ContainerIterface` defines two methods:
+
+* has($id): bool
+    returns true if the container can provide a value for a given ID
+* get($id): mixed
+    returns some kind of value that is registered in the container for the given ID
+
+I mostly define an Interface or a fully qualified classname as an ID. That way I can query the container for
+the Clock interface or an Action class and get an object of that class or an object implementing the given Interface.
+
+For the sake of this tutorial we will put a new file in our config folder that returns an anonymous class implementing
+the containerinterface.
+
+In this class we will configure all services required for our application and make them accessible via the get($id)
+method.
+
+`config/container.php`:
+```php
+<?php declare(strict_types=1);
+
+return new class () implements \Psr\Container\ContainerInterface {
+
+    private readonly array $services;
+
+    public function __construct()
+    {
+        $this->services = [
+            \Psr\Http\Message\ServerRequestInterface::class => fn () => \Laminas\Diactoros\ServerRequestFactory::fromGlobals(),
+            \Psr\Http\Message\ResponseInterface::class => fn () => new \Laminas\Diactoros\Response(),
+            \FastRoute\Dispatcher::class => fn () => \FastRoute\simpleDispatcher(require __DIR__ . '/routes.php'),
+            \Lubian\NoFramework\Service\Time\Clock::class => fn () => new \Lubian\NoFramework\Service\Time\SystemClock(),
+            \Lubian\NoFramework\Action\Hello::class => fn () => new \Lubian\NoFramework\Action\Hello(
+                $this->get(\Psr\Http\Message\ResponseInterface::class),
+                $this->get(\Lubian\NoFramework\Service\Time\Clock::class)
+            ),
+            \Lubian\NoFramework\Action\Other::class => fn () => new \Lubian\NoFramework\Action\Other(
+                $this->get(\Psr\Http\Message\ResponseInterface::class)
+            ),
+        ];
+    }
+
+    public function get(string $id)
+    {
+        if (! $this->has($id)) {
+            throw new class () extends \Exception implements \Psr\Container\NotFoundExceptionInterface {
+            };
+        }
+        return $this->services[$id]();
+    }
+
+    public function has(string $id): bool
+    {
+        return array_key_exists($id, $this->services);
+    }
+};
+```
+
+Here I have declared a services array, that has a class- or interfacename as the keys, and the values are short
+closures that return an Object of the defined class or interface. The `has` method simply checks if the given id is
+defined in our services array, and the `get` method calls the closure defined in the array for the given id key and then
+returns the result of that closure.
+
+To use the container we need to update our Bootstrap.php. Firstly we need to get an instance of our container, and then
+use that to create our Request-Object as well as the Dispatcher. So remove the manual instantion of those objects and
+replace that with the following code:
+
+```php
+$container = require __DIR__ . '/../config/container.php';
+assert($container instanceof \Psr\Container\ContainerInterface);
+
+$request = $container->get(\Psr\Http\Message\ServerRequestInterface::class);
+assert($request instanceof \Psr\Http\Message\ServerRequestInterface);
+
+$dispatcher = $container->get(FastRoute\Dispatcher::class);
+assert($dispatcher instanceof \FastRoute\Dispatcher);
+```
+
+In the Dispatcher switch block we manually build our handler object with this two lines:
+
+
+```php
+$handler = new $className($response);
+assert($handler instanceof RequestHandlerInterface);
+```
+
+Instead of manually creating the Handler-Instance we are going to kindly ask the Container to build it for us:
+
+```php
+$handler = $container->get($className);
+assert($handler instanceof RequestHandlerInterface);
+```
+
+If you now open the `/hello` route in your browser everything should work again!
+
+#### Using Autowiring
+
+
 
 A dependency injector resolves the dependencies of your class and makes sure that the correct objects are injected when
 the class is instantiated.
 
-Again the psr has defined an [interface](https://www.php-fig.org/psr/psr-11/) for dependency injection that we can work
+Again the FIG has defined an [interface](https://www.php-fig.org/psr/psr-11/) for dependency injection that we can work
 with. Almost all common dependency injection containers implement this interface, so it is a good starting point to look
 for a [suitable solution on packagist](https://packagist.org/providers/psr/container-implementation).
 

app/src/Action/Hello.php

@@ -2,6 +2,7 @@
 
 namespace Lubian\NoFramework\Action;
 
+
 use Lubian\NoFramework\Service\Time\Clock;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\ServerRequestInterface;
@@ -9,7 +10,10 @@ use Psr\Http\Server\RequestHandlerInterface;
 
 final class Hello implements RequestHandlerInterface
 {
-    public function __construct(private readonly ResponseInterface $response, private readonly Clock $clock)
+    public function __construct(
+        private readonly ResponseInterface $response,
+        private readonly Clock $clock
+    )
     {
     }
 

app/src/Bootstrap.php

@@ -59,7 +59,7 @@ try {
     switch ($routeInfo[0]) {
         case Dispatcher::FOUND:
             $className = $routeInfo[1];
-            $handler = $container->get($className);
+            $handler = new $className($response);
             assert($handler instanceof RequestHandlerInterface);
             foreach ($routeInfo[2] as $attributeName => $attributeValue) {
                 $request = $request->withAttribute($attributeName, $attributeValue);