Add code, unit test and autoloader

Author: timoschinkel

composer.json

@@ -8,11 +8,20 @@
         "psr/http-client": "^1.0",
         "psr/http-message": "^1.0"
     },
+    "require-dev": {
+        "phpunit/phpunit": "^8.0",
+        "squizlabs/php_codesniffer": "^3.5"
+    },
     "autoload": {
         "psr-4": {
             "Coolblue\\Http\\Client\\": "src/"
         }
     },
+    "autoload-dev": {
+        "psr-4": {
+            "Coolblue\\Tests\\Http\\Client\\": "tests/"
+        }
+    },
     "config": {
         "sort-packages": true
     }

src/MiddlewareClient.php

@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Coolblue\Http\Client;
+
+use Psr\Http\Client\ClientInterface;
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
+
+final class MiddlewareClient implements ClientInterface
+{
+    /** @var ClientInterface */
+    private $client;
+
+    /** @var MiddlewareInterface[] */
+    private $middleware;
+
+    public function __construct(ClientInterface $client, MiddlewareInterface ...$middleware)
+    {
+        $this->client = $client;
+        $this->middleware = $middleware;
+    }
+
+    public function sendRequest(RequestInterface $request): ResponseInterface
+    {
+        $middleware = reset($this->middleware);
+        if ($middleware instanceof MiddlewareInterface) {
+            $new = new self($this->client, ...array_slice($this->middleware, 1));
+            return $middleware->process($request, $new);
+        }
+
+        return $this->client->sendRequest($request);
+    }
+}

src/MiddlewareInterface.php

@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Coolblue\Http\Client;
+
+use Psr\Http\Client\ClientInterface;
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
+
+interface MiddlewareInterface
+{
+    public function process(RequestInterface $request, ClientInterface $client): ResponseInterface;
+}

tests/MiddlewareClientTest.php

@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Coolblue\Tests\Http\Client;
+
+use Coolblue\Http\Client\MiddlewareClient;
+use Coolblue\Http\Client\MiddlewareInterface;
+use PHPUnit\Framework\TestCase;
+use Prophecy\Argument;
+use Psr\Http\Client\ClientInterface;
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
+
+final class MiddlewareClientTest extends TestCase
+{
+    public function testHandlingOfMiddlewareInCorrectOrder(): void
+    {
+        $order = [];
+
+        $request = $this->prophesize(RequestInterface::class);
+        $response = $this->prophesize(ResponseInterface::class);
+
+        $middlewareOne = $this->prophesize(MiddlewareInterface::class);
+        $middlewareOne->process(Argument::type(RequestInterface::class), Argument::type(ClientInterface::class))
+            ->shouldBeCalled()
+            ->will(function (array $arguments) use (&$order) {
+                [$request, $client] = $arguments;
+                $order[] = 'before one';
+                $response = $client->sendRequest($request);
+                $order[] = 'after one';
+                return $response;
+            });
+
+        $middlewareTwo = $this->prophesize(MiddlewareInterface::class);
+        $middlewareTwo->process(Argument::type(RequestInterface::class), Argument::type(ClientInterface::class))
+            ->shouldBeCalled()
+            ->will(function (array $arguments) use (&$order) {
+                [$request, $client] = $arguments;
+                $order[] = 'before two';
+                $response = $client->sendRequest($request);
+                $order[] = 'after two';
+
+                return $response;
+            });
+
+        $client = $this->prophesize(ClientInterface::class);
+        $client->sendRequest(Argument::type(RequestInterface::class))
+            ->shouldBeCalledOnce()
+            ->will(function () use (&$order, $response) {
+                $order[] = 'client';
+                return $response->reveal();
+            });
+
+        $middlewareClient = new MiddlewareClient(
+            $client->reveal(),
+            $middlewareOne->reveal(),
+            $middlewareTwo->reveal()
+        );
+
+        $response = $middlewareClient->sendRequest($request->reveal());
+
+        self::assertInstanceOf(ResponseInterface::class, $response);
+        self::assertEquals( // json_encode is used to also test the order of elements in the array
+            json_encode(['before one', 'before two', 'client', 'after two', 'after one']),
+            json_encode($order)
+        );
+    }
+}