Add support for Twig as template engine

README.md

@@ -153,6 +153,7 @@ We provide some basic formatters by default:
 * `StringCast`
 * `JmsSerializer` (requires you to also install and configure [`jms/serializer`](https://jmsyst.com/libs/serializer))
 * `Plates` (requires you to also install and configure [`league/plates`](http://platesphp.com))
+* `Twig` (requires you to also install and configure [`twig/twig`](https://twig.symfony.com))
 
 If you want to create a customised formatter the only thing needed is to
 implement the `Formatter` interface:

composer.json

@@ -34,12 +34,14 @@
         "phpstan/phpstan-strict-rules": "^0.10@dev",
         "phpunit/phpunit": "^7.0",
         "squizlabs/php_codesniffer": "^3.2",
+        "twig/twig": "^2.0",
         "zendframework/zend-diactoros": "^1.7"
     },
     "suggest": {
         "jms/serializer": "For content formatting using a more flexible serializer",
         "league/plates": "For content formatting using Plates as template engine",
         "middlewares/negotiation": "For acceptable format identification",
+        "twig/twig": "For content formatting using Twig as template engine",
         "zendframework/zend-diactoros": "For concrete implementation of PSR-7"
     },
     "autoload": {

src/Formatter/Twig.php

@@ -0,0 +1,61 @@
+<?php
+declare(strict_types=1);
+
+namespace Lcobucci\ContentNegotiation\Formatter;
+
+use Lcobucci\ContentNegotiation\ContentCouldNotBeFormatted;
+use Lcobucci\ContentNegotiation\Formatter;
+use Throwable;
+use Twig_Environment;
+
+final class Twig implements Formatter
+{
+    private const DEFAULT_ATTRIBUTE = 'template';
+
+    /**
+     * @var Twig_Environment
+     */
+    private $environment;
+
+    /**
+     * @var string
+     */
+    private $attributeName;
+
+    public function __construct(
+        Twig_Environment $environment,
+        string $attributeName = self::DEFAULT_ATTRIBUTE
+    ) {
+        $this->environment   = $environment;
+        $this->attributeName = $attributeName;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function format($content, array $attributes = []): string
+    {
+        try {
+            return $this->render($content, $attributes);
+        } catch (Throwable $exception) {
+            throw new ContentCouldNotBeFormatted(
+                'An error occurred while formatting using twig',
+                $exception->getCode(),
+                $exception
+            );
+        }
+    }
+
+    /**
+     * @param mixed   $content
+     * @param mixed[] $attributes
+     *
+     * @throws Throwable
+     */
+    private function render($content, array $attributes = []): string
+    {
+        $template = $attributes[$this->attributeName] ?? '';
+
+        return $this->environment->render($template, ['content' => $content]);
+    }
+}

templates/twig/person.twig

@@ -0,0 +1,8 @@
+<section>
+    <dl>
+        <dt>Identifier</dt>
+        <dd>{{ content.id }}</dd>
+        <dt>Name</dt>
+        <dd>{{ content.name }}</dd>
+    </dl>
+</section>

tests/Formatter/TwigTest.php

@@ -0,0 +1,82 @@
+<?php
+declare(strict_types=1);
+
+namespace Lcobucci\ContentNegotiation\Tests\Formatter;
+
+use Lcobucci\ContentNegotiation\ContentCouldNotBeFormatted;
+use Lcobucci\ContentNegotiation\Formatter\Twig;
+use Lcobucci\ContentNegotiation\Tests\PersonDto;
+use PHPUnit\Framework\TestCase;
+use Twig_Environment;
+use Twig_Loader_Filesystem;
+use function dirname;
+
+/**
+ * @coversDefaultClass \Lcobucci\ContentNegotiation\Formatter\Twig
+ */
+final class TwigTest extends TestCase
+{
+    /**
+     * @var Twig_Environment
+     */
+    private $environment;
+
+    /**
+     * @before
+     */
+    public function configureEngine(): void
+    {
+        $this->environment = new Twig_Environment(
+            new Twig_Loader_Filesystem('templates/twig', dirname(__DIR__, 2) . '/')
+        );
+    }
+
+    /**
+     * @test
+     *
+     * @covers ::__construct()
+     * @covers ::format()
+     * @covers ::render()
+     */
+    public function formatShouldReturnContentFormattedByPlates(): void
+    {
+        $formatter = new Twig($this->environment);
+        $content   = $formatter->format(new PersonDto(1, 'Testing'), ['template' => 'person.twig']);
+
+        self::assertContains('<dd>1</dd>', $content);
+        self::assertContains('<dd>Testing</dd>', $content);
+    }
+
+    /**
+     * @test
+     *
+     * @covers ::__construct()
+     * @covers ::format()
+     * @covers ::render()
+     */
+    public function formatShouldReadTemplateNameFromCustomAttribute(): void
+    {
+        $formatter = new Twig($this->environment, 'fancy!');
+        $content   = $formatter->format(new PersonDto(1, 'Testing'), ['fancy!' => 'person.twig']);
+
+        self::assertContains('<dd>1</dd>', $content);
+        self::assertContains('<dd>Testing</dd>', $content);
+    }
+
+    /**
+     * @test
+     *
+     * @covers ::__construct()
+     * @covers ::format()
+     * @covers ::render()
+     */
+    public function formatShouldConvertAnyTwigException(): void
+    {
+        $formatter = new Twig($this->environment);
+
+        $this->expectException(ContentCouldNotBeFormatted::class);
+        $this->expectExceptionMessage('An error occurred while formatting using twig');
+
+        $formatter->format(new PersonDto(1, 'Testing'), ['template' => 'no-template-at-all']);
+    }
+}