NEW Add factory_method configuration to Injector

use callable as well as creator

docs/en/02_Developer_Guides/05_Extending/05_Injector.md

@@ -193,9 +193,14 @@ Note: undefined variables will be replaced with null.
 
 ## Factories
 
-Some services require non-trivial construction which means they must be created by a factory class. To do this, create
-a factory class which implements the [Factory](api:SilverStripe\Framework\Injector\Factory) interface. You can then specify
-the `factory` key in the service definition, and the factory service will be used.
+Some services require non-trivial construction which means they must be created
+by a factory.
+
+### Factory interface
+
+Create a factory class which implements the [Factory](api:SilverStripe\Framework\Injector\Factory)
+interface. You can then specify the `factory` key in the service definition,
+and the factory service will be used.
 
 An example using the `MyFactory` service to create instances of the `MyService` service is shown below:
 
@@ -224,6 +229,32 @@ class MyFactory implements SilverStripe\Core\Injector\Factory
 $instance = Injector::inst()->get('MyService');
 ```
 
+### Factory method
+
+To use any class that not implements Factory interface as a service factory
+specify `factory` and `factory_method` keys.
+
+An example of HTTP Client service with extra logging middleware:
+
+**app/_config/app.yml**
+
+```yml
+SilverStripe\Core\Injector\Injector:
+  LogMiddleware:
+    factory: 'GuzzleHttp\Middleware'
+    factory_method: 'log'
+    constructor: ['%$Psr\Log\LoggerInterface', '%$GuzzleHttp\MessageFormatter', 'info']
+  GuzzleHttp\HandlerStack:
+    factory: 'GuzzleHttp\HandlerStack'
+    factory_method: 'create'
+    calls:
+      - [push, ['%$LogMiddleware']]
+  GuzzleHttp\Client:
+    constructor:
+      -
+        handler: '%$GuzzleHttp\HandlerStack'
+```
+
 ## Dependency overrides
 
 To override the `$dependency` declaration for a class, define the following configuration file.

src/Core/Injector/Injector.php

@@ -605,8 +605,36 @@ class Injector implements ContainerInterface
             $constructorParams = [null, DataObject::CREATE_SINGLETON];
         }
 
-        $factory = isset($spec['factory']) ? $this->get($spec['factory']) : $this->getObjectCreator();
-        $object = $factory->create($class, $constructorParams);
+        if (isset($spec['factory']) && isset($spec['factory_method'])) {
+            if (!method_exists($spec['factory'], $spec['factory_method'])) {
+                throw new InvalidArgumentException(sprintf(
+                    'Factory method "%s::%s" does not exist.',
+                    $spec['factory'],
+                    $spec['factory_method']
+                ));
+            }
+
+            // If factory_method is statically callable, do not instantiate
+            // factory i.e. just call factory_method statically.
+            $factory = is_callable([$spec['factory'], $spec['factory_method']])
+                ? $spec['factory']
+                : $this->get($spec['factory']);
+            $method = $spec['factory_method'];
+            $object = call_user_func_array([$factory, $method], $constructorParams);
+        } else {
+            $factory = isset($spec['factory']) ? $this->get($spec['factory']) : $this->getObjectCreator();
+            if (!$factory instanceof Factory) {
+                throw new InvalidArgumentException(sprintf(
+                    'Factory class "%s" does not implement "%s" interface.',
+                    get_class($factory),
+                    Factory::class
+                ));
+            }
+            $object = $factory->create($class, $constructorParams);
+        }
+        if (!is_object($object)) {
+            throw new InjectorNotFoundException('Factory does not return an object');
+        }
 
         // Handle empty factory responses
         if (!$object) {

tests/php/Core/Injector/InjectorTest.php

@@ -118,6 +118,22 @@ class InjectorTest extends SapphireTest
         $injector->create('SomeClass');
     }
 
+    /**
+     * Fail creating object by factory that does not implement Factory
+     * interface.
+     */
+    public function testNotFactoryInterfaceFactory()
+    {
+        $this->expectException(\InvalidArgumentException::class);
+
+        $injector = new Injector([
+            'service' => [
+                'factory' => 'stdClass',
+            ],
+        ]);
+        $injector->get('service');
+    }
+
     public function testConfiguredInjector()
     {
         $injector = new Injector();
@@ -906,6 +922,80 @@ class InjectorTest extends SapphireTest
         $this->assertInstanceOf(TestObject::class, $injector->get('service'));
     }
 
+    /**
+     * Creating object by factory method.
+     */
+    public function testByFactoryMethodObjectCreator()
+    {
+        // Dummy service giving DateTime of tommorow.
+        $injector = new Injector([
+            'service' => [
+                'factory' => 'DateTime',
+                'factory_method' => 'add',
+                'constructor' => ['%$DateInterval'],
+            ],
+            'DateInterval' => [
+                'constructor' => ['P1D'],
+            ],
+        ]);
+
+        $this->assertInstanceOf(\DateTime::class, $injector->get('service'));
+        $this->assertEquals(
+            (new \DateTime())->add(new \DateInterval('P1D'))->format('%Y%m%d'),
+            $injector->get('service')->format('%Y%m%d')
+        );
+    }
+
+    /**
+     * Creating object by static factory method.
+     */
+    public function testByStaticFactoryMethodObjectCreator()
+    {
+        // Dummy service changing any callable to injector service with
+        // `strtoupper` as default one. Constructor disallows instantiation.
+        $injector = new Injector([
+            'service' => [
+                'factory' => 'Closure',
+                'factory_method' => 'fromCallable',
+                'constructor' => ['strtoupper'],
+            ],
+        ]);
+
+        $this->assertInstanceOf(\Closure::class, $injector->get('service'));
+
+        // Default service.
+        $this->assertEquals('ABC', $injector->get('service')('abc'));
+
+        // Create service with arguments.
+        $this->assertEquals('abc', $injector->create('service', 'strtolower')('ABC'));
+    }
+
+    public function testFactoryMethodNotReturnsObject()
+    {
+        $this->expectException(InjectorNotFoundException::class);
+
+        $injector = new Injector([
+            'service' => [
+                'factory' => 'DateTime',
+                'factory_method' => 'getTimeStamp',
+            ],
+        ]);
+        $injector->get('service');
+    }
+
+    public function testFactoryMethodNotExists()
+    {
+        $this->expectException(\InvalidArgumentException::class);
+
+        $injector = new Injector([
+            'service' => [
+                'factory' => 'stdClass',
+                'factory_method' => 'method',
+            ],
+        ]);
+        $injector->get('service');
+    }
+
     public function testMethods()
     {
         // do it again but have test object configured as a constructor dependency