Introduce a DecoratableTypeResolver base class

src/GraphQL/DecoratableTypeResolver.php

@@ -0,0 +1,73 @@
+<?php
+
+namespace Drupal\graphql\GraphQL;
+
+/**
+ * A base class for decoratable type resolvers.
+ *
+ * @package Drupal\graphql\GraphQL
+ * @see \Drupal\graphql\GraphQL\DecoratableTypeResolverInterface
+ */
+abstract class DecoratableTypeResolver implements DecoratableTypeResolverInterface {
+
+  /**
+   * The previous type resolver that was set in the chain.
+   *
+   * @var \Drupal\graphql\GraphQL\DecoratableTypeResolverInterface|null
+   */
+  private ?DecoratableTypeResolverInterface $decorated;
+
+  /**
+   * Create a new decoratable type resolver.
+   *
+   * @param \Drupal\graphql\GraphQL\DecoratableTypeResolverInterface|null $resolver
+   *   The previous type resolver if any.
+   */
+  public function __construct(?DecoratableTypeResolverInterface $resolver) {
+    $this->decorated = $resolver;
+  }
+
+  /**
+   * Resolve the type for the provided object.
+   *
+   * @param mixed $object
+   *   The object to resolve to a concrete type.
+   *
+   * @return string|null
+   *   The GraphQL type name or NULL if this resolver could not determine it.
+   */
+  abstract protected function resolve($object) : ?string;
+
+  /**
+   * Allows this type resolver to be called by the GraphQL library.
+   *
+   * Takes care of chaining the various type resolvers together and invokes the
+   * `resolve` method for each concrete implementation in the chain.
+   *
+   * @param mixed $object
+   *   The object to resolve to a concrete type.
+   *
+   * @return string
+   *   The resolved GraphQL type name.
+   *
+   * @throws \RuntimeException
+   *   When a type was passed for which no type resolver exists in the chain.
+   */
+  public function __invoke($object) : string {
+    $type = $this->resolve($object);
+    if ($type !== NULL) {
+      return $type;
+    }
+
+    if ($this->decorated !== NULL) {
+      $type = $this->decorated->__invoke($object);
+      if ($type !== NULL) {
+        return $type;
+      }
+    }
+
+    $klass = get_class($object);
+    throw new \RuntimeException("Can not map instance of '${klass}' to concrete GraphQL Type.");
+  }
+
+}

src/GraphQL/DecoratableTypeResolverInterface.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace Drupal\graphql\GraphQL;
+
+/**
+ * A decoratable type resolver to resolve GraphQL interfaces to concrete types.
+ *
+ * Type resolvers should extend this class so that they can be chained in
+ * schema extensions plugins.
+ *
+ * For example with the following class defined.
+ * ```php
+ * class ConcreteTypeResolver extends DecoratableTypeResolver {
+ *
+ *   protected function resolve($object) : ?string {
+ *     return $object instanceof MyType ? 'MyType' : NULL;
+ *   }
+ * }
+ * ```
+ *
+ * A schema extension would call:
+ * ```php
+ * $registry->addTypeResolver(
+ *   'InterfaceType',
+ *   new ConcreteTypeResolver($registry->getTypeResolver('InterfaceType'))
+ * );
+ * ```
+ *
+ * TypeResolvers should not extend other type resolvers but always extend this
+ * class directly. Classes will be called in the reverse order of being added
+ * (classes added last will be called first).
+ *
+ * @package Drupal\social_graphql\GraphQL
+ */
+interface DecoratableTypeResolverInterface {
+
+  /**
+   * Create a new decoratable type resolver.
+   *
+   * @param \Drupal\graphql\GraphQL\DecoratableTypeResolverInterface|null $resolver
+   *   The previous type resolver if any.
+   */
+  public function __construct(?DecoratableTypeResolverInterface $resolver);
+
+  /**
+   * Allows this type resolver to be called by the GraphQL library.
+   *
+   * Takes care of chaining the various type resolvers together and invokes the
+   * `resolve` method for each concrete implementation in the chain.
+   *
+   * @param mixed $object
+   *   The object to resolve to a concrete type.
+   *
+   * @return string
+   *   The resolved GraphQL type name.
+   *
+   * @throws \RuntimeException
+   *   When a type was passed for which no type resolver exists in the chain.
+   */
+  public function __invoke($object) : string;
+
+}

tests/src/Kernel/TypeResolver/DecoratableTypeResolverTest.php

@@ -0,0 +1,70 @@
+<?php
+
+namespace Drupal\Tests\graphql\Kernel\TypeResolver;
+
+use Drupal\graphql\GraphQL\DecoratableTypeResolver;
+use Drupal\node\NodeInterface;
+use Drupal\Tests\graphql\Kernel\GraphQLTestBase;
+
+/**
+ * Test the pages type resolver.
+ */
+class DecoratableTypeResolverTest extends GraphQLTestBase {
+
+  /**
+   * The type resolver.
+   *
+   * @var \Drupal\graphql\GraphQL\DecoratableTypeResolverInterface
+   */
+  protected $resolver;
+
+  /**
+   * The decorated type resolver.
+   *
+   * @var \Drupal\graphql\GraphQL\DecoratableTypeResolverInterface
+   */
+  protected $decoratedResolver;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp(): void {
+    parent::setUp();
+    $this->resolver = $this->getMockForAbstractClass(DecoratableTypeResolver::class, [NULL]);
+    $this->resolver->method('resolve')
+      ->willReturnCallback(function ($object) {
+        return ucfirst($object->bundle());
+      });
+
+    $this->decoratedResolver = $this->getMockForAbstractClass(DecoratableTypeResolver::class, [$this->resolver]);
+    $this->decoratedResolver->method('resolve')
+      ->willReturnCallback(function ($object) {
+        if ($object->bundle(
+          ) === 'article') {
+            return 'DecoratedArticle';
+        }
+        return NULL;
+      });
+
+  }
+
+  /**
+   * Test the decoration.
+   */
+  public function testDecoration(): void {
+    $newsNode = $this->createMock(NodeInterface::class);
+    $newsNode->method('bundle')
+      ->willReturn('news');
+
+    $articleNode = $this->createMock(NodeInterface::class);
+    $articleNode->method('bundle')
+      ->willReturn('article');
+
+    $this->assertEquals('News', $this->resolver->__invoke($newsNode));
+    $this->assertEquals('Article', $this->resolver->__invoke($articleNode));
+
+    $this->assertEquals('News', $this->decoratedResolver->__invoke($newsNode));
+    $this->assertEquals('DecoratedArticle', $this->decoratedResolver->__invoke($articleNode));
+  }
+
+}