Added a default error handler to handle all uncaught exceptions

app/src/Bootstrap/AppManager.php

@@ -51,6 +51,9 @@ class AppManager
             'text/json' => '+1 hour',
         ]));
 
+        $errorMiddleware = $app->addErrorMiddleware(true, true, true);
+        $errorMiddleware->setDefaultErrorHandler(ErrorHandler::class);
+
         return $app;
     }
 

app/src/Bootstrap/ErrorHandler.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace App\Bootstrap;
+
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Slim\Interfaces\ErrorHandlerInterface;
+use Slim\Psr7\Response;
+use Slim\Views\Twig;
+use Throwable;
+
+class ErrorHandler implements ErrorHandlerInterface
+{
+    /** @const The default error message string */
+    protected const DEFAULT_ERROR_MESSAGE = 'An unexpected error occured';
+
+    /** @var Twig Twig templating component */
+    protected $view;
+
+    /**
+     * Create a new ErrorHandler object.
+     *
+     * @param \Slim\Views\Twig $view
+     */
+    public function __construct(Twig $view)
+    {
+        $this->view = $view;
+    }
+
+    /**
+     * Invoke the ErrorHandler class.
+     *
+     * @param \Psr\Http\Message\ServerRequestInterface $request
+     * @param \Throwable                               $exception
+     * @param bool                                     $displayErrorDetails
+     * @param bool                                     $logErrors
+     * @param bool                                     $logErrorDetails
+     *
+     * @return \Psr\Http\Message\ResponseInterface
+     */
+    public function __invoke(
+        ServerRequestInterface $request,
+        Throwable $exception,
+        bool $displayErrorDetails,
+        bool $logErrors,
+        bool $logErrorDetails
+    ): ResponseInterface {
+        $response = (new Response)->withStatus(500);
+
+        if (in_array('application/json', explode(',', $request->getHeaderLine('Accept')))) {
+            $response->getBody()->write(json_encode([
+                'error' => ['message' => self::DEFAULT_ERROR_MESSAGE]
+            ]));
+
+            return $response->withHeader('Content-Type', 'application/json');
+        }
+
+        return $this->view->render($response, 'error.twig', [
+            'message' => self::DEFAULT_ERROR_MESSAGE,
+            'subtext' => 'Enable debugging for additional information',
+        ]);
+    }
+}

app/views/error.twig

@@ -4,10 +4,14 @@
 {% block content %}
     {% include 'components/header.twig' %}
 
-    <div id="content" class="flex-grow container flex justify-center items-center mx-auto px-4">
+    <div id="content" class="flex-grow container flex flex-col justify-center items-center mx-auto px-4">
         <p class="font-thin text-4xl text-gray-600">
             {{ message | default('An unexpected error occured') }}
         </p>
+
+        <p class="text-lg text-gray-400">
+            {{ subtext }}
+        </p>
     </div>
 
     {% include 'components/footer.twig' %}

tests/Bootstrap/ErrorHandlerTest.php

@@ -0,0 +1,57 @@
+<?php
+
+namespace Tests\Bootstrap;
+
+use App\Bootstrap\ErrorHandler;
+use App\Providers\TwigProvider;
+use Exception;
+use Slim\Psr7\Request;
+use Slim\Views\Twig;
+use Tests\TestCase;
+
+class ErrorHandlerTest extends TestCase
+{
+    public function test_it_returns_an_error(): void
+    {
+        $this->container->call(TwigProvider::class);
+        $errorHandler = new ErrorHandler($this->container->get(Twig::class));
+
+        $response = $errorHandler(
+            $this->createMock(Request::class),
+            new Exception('Test exception; please ignore'),
+            true,
+            true,
+            true
+        );
+
+        $this->assertEquals(500, $response->getStatusCode());
+        $this->assertEquals('text/html', finfo_buffer(
+            finfo_open(), (string) $response->getBody(), FILEINFO_MIME_TYPE
+        ));
+    }
+
+    public function test_it_returns_an_error_for_a_json_request(): void
+    {
+        $this->container->call(TwigProvider::class);
+        $errorHandler = new ErrorHandler($this->container->get(Twig::class));
+
+        $request = $this->createMock(Request::class);
+        $request->expects($this->once())->method('getHeaderLine')->willReturn(
+            'application/json'
+        );
+
+        $response = $errorHandler(
+            $request,
+            new Exception('Test exception; please ignore'),
+            true,
+            true,
+            true
+        );
+
+        $this->assertEquals(500, $response->getStatusCode());
+        $this->assertEquals('application/json', $response->getHeaderLine('Content-Type'));
+        $this->assertEquals('An unexpected error occured', json_decode(
+            (string) $response->getBody()
+        )->error->message);
+    }
+}