Update resource definition API to allow extending schema

src/JsonApi.php

@@ -31,9 +31,13 @@ final class JsonApi implements RequestHandlerInterface
         $this->baseUrl = $baseUrl;
     }
 
-    public function resource(string $type, $adapter, Closure $buildSchema = null): void
+    public function resource(string $type): ResourceType
     {
-        $this->resources[$type] = new ResourceType($type, $adapter, $buildSchema);
+        if (! isset($this->resources[$type])) {
+            $this->resources[$type] = new ResourceType($type);
+        }
+
+        return $this->resources[$type];
     }
 
     public function getResources(): array

src/ResourceType.php

@@ -2,7 +2,6 @@
 
 namespace Tobyz\JsonApiServer;
 
-use Closure;
 use Tobyz\JsonApiServer\Adapter\AdapterInterface;
 use Tobyz\JsonApiServer\Schema\Type;
 
@@ -10,14 +9,12 @@ final class ResourceType
 {
     private $type;
     private $adapter;
-    private $buildSchema;
+    private $schemaCallbacks = [];
     private $schema;
 
-    public function __construct(string $type, AdapterInterface $adapter, Closure $buildSchema = null)
+    public function __construct(string $type)
     {
         $this->type = $type;
-        $this->adapter = $adapter;
-        $this->buildSchema = $buildSchema;
     }
 
     public function getType(): string
@@ -25,19 +22,31 @@ final class ResourceType
         return $this->type;
     }
 
+    public function adapter(AdapterInterface $adapter)
+    {
+        $this->adapter = $adapter;
+
+        return $this;
+    }
+
     public function getAdapter(): AdapterInterface
     {
         return $this->adapter;
     }
 
+    public function schema(callable $callback)
+    {
+        $this->schemaCallbacks[] = $callback;
+
+        return $this;
+    }
+
     public function getSchema(): Type
     {
         if (! $this->schema) {
             $this->schema = new Type;
 
-            if ($this->buildSchema) {
-                ($this->buildSchema)($this->schema);
-            }
+            run_callbacks($this->schemaCallbacks, [$this->schema]);
         }
 
         return $this->schema;