Created default delegate that returns a JSON response when accepted type is json

module/Core/src/Response/NotFoundDelegate.php

@@ -0,0 +1,54 @@
+<?php
+declare(strict_types=1);
+
+namespace Shlinkio\Shlink\Core\Response;
+
+use Fig\Http\Message\StatusCodeInterface;
+use Interop\Http\ServerMiddleware\DelegateInterface;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Zend\Diactoros\Response;
+use Zend\Expressive\Template\TemplateRendererInterface;
+
+class NotFoundDelegate implements DelegateInterface
+{
+    /**
+     * @var TemplateRendererInterface
+     */
+    private $renderer;
+    /**
+     * @var string
+     */
+    private $template;
+
+    public function __construct(TemplateRendererInterface $renderer, string $template = 'ShlinkCore::error/404')
+    {
+        $this->renderer = $renderer;
+        $this->template = $template;
+    }
+
+    /**
+     * Dispatch the next available middleware and return the response.
+     *
+     * @param ServerRequestInterface $request
+     *
+     * @return ResponseInterface
+     * @throws \InvalidArgumentException
+     */
+    public function process(ServerRequestInterface $request): ResponseInterface
+    {
+        $accepts = explode(',', $request->getHeaderLine('Accept'));
+        $accept = array_shift($accepts);
+        $status = StatusCodeInterface::STATUS_NOT_FOUND;
+
+        // If the first accepted type is json, return a json response
+        if (in_array($accept, ['application/json', 'text/json', 'application/x-json'], true)) {
+            return new Response\JsonResponse([
+                'error' => 'NOT_FOUND',
+                'message' => 'Not found',
+            ], $status);
+        }
+
+        return new Response\HtmlResponse($this->renderer->render($this->template, ['request' => $request]), $status);
+    }
+}