adding progress

Author: weaverryan

quick_tour/the_architecture.rst

@@ -1,4 +1,139 @@
 The Architecture
 ================
 
-TODO
+You are my hero! Who would have thought that you would still be here after the first
+two parts? Your efforts will be well-rewarded soon. The first two parts didn't look
+too deeply at the architecture of the framework. Because it makes Symfony stand apart
+from the framework crowd, let's dive into the architecture now.
+
+Add Logging
+-----------
+
+A new Symfony app is micro: it's basically just a routing & controller system. But
+thanks to Flex, installing more features is simple.
+
+Want a logging system? No problem:
+
+.. code-block:: terminal
+
+    $ composer require logger
+
+This installs and configures (via a recipe) the powerful `Monolog`_ library. To
+use the logger in a controller, add a new argument type-hinted with ``LoggerInterface``:
+
+    use Psr\Log\LoggerInterface;
+    // ...
+
+    public function index($name, LoggerInterface $logger)
+    {
+        $logger->info("Saying hello to $name!");
+
+        // ...
+    }
+
+That's it! The new log message be written to ``var/log/dev.log``. Of course, this
+can be configured by updating one of the config files added by the recipe.
+
+Services & Autowiring
+---------------------
+
+But wait! Something *very* cool just happened. Symfony read the ``LoggerInterface``
+type-hint and automatically figured out that it should pass us the Logger object!
+This is called *autowiring*.
+
+Every bit of work that's done in a Symfony app is done by an *object*: the Logger
+object logs things and the Twig object renders templates. These objects are called
+*services* and they are the *tools* that make you dangerous.
+
+To make life awesome, you can ask Symfony to pass you a service by using a type-hint.
+What other possible classes or interfaces could you use? Find out by running:
+
+.. code-block:: terminal
+
+    $ php bin/console debug:autowiring
+
+=============================================================== =====================================
+Class/Interface Type                                            Alias Service ID
+=============================================================== =====================================
+``Psr\Cache\CacheItemPoolInterface``                            alias for "cache.app.recorder"
+``Psr\Log\LoggerInterface``                                     alias for "monolog.logger"
+``Symfony\Component\EventDispatcher\EventDispatcherInterface``  alias for "debug.event_dispatcher"
+``Symfony\Component\HttpFoundation\RequestStack``               alias for "request_stack"
+``Symfony\Component\HttpFoundation\Session\SessionInterface``   alias for "session"
+``Symfony\Component\Routing\RouterInterface``                   alias for "router.default"
+=============================================================== =====================================
+
+This is just a short summary of the full list! And as you add more packages, this
+list of tools will grow!
+
+Creating Services
+-----------------
+
+To keep your code organized, you can even create your own services! Suppose you
+want to generate a random greeting (e.g. "Hello", "Yo", etc). Instead of putting
+this code directly in your controller, create a new class:
+
+    // src/GreetingGenerator.php
+    namespace App;
+
+    class GreetingGenerator
+    {
+        public function getRandomGreeting()
+        {
+            $greetings = ['Hey', 'Yo', 'Aloha'];
+            $greeting = $greetings[array_rand($greetings)];
+
+            return $greeting;
+        }
+    }
+
+Great! You can use this immediately in your controller::
+
+    use App\GreetingGenerator;
+    // ...
+
+    public function index($name, LoggerInterface $logger, GreetingGenerator $generator)
+    {
+        $greeting = $generator->getRandomGreeting();
+
+        $logger->info("Saying $greeting to $name!");
+
+        // ...
+    }
+
+That's it! Symfony will instantiate the ``GreetingGenerator`` automatically and
+pass it as an argument. But, could we *also* move the logger logic to ``GreetingGenerator``?
+Yes! You can use autowiring inside a service to access *other* services. The only
+difference is that it's done in the constructor:
+
+.. code-block:: diff
+
+    + use Psr\Log\LoggerInterface;
+
+    class GreetingGenerator
+    {
+    +     private $logger;
+    + 
+    +     public function __construct(LoggerInterface $logger)
+    +     {
+    +         $this->logger = $logger;
+    +     }
+
+        public function getRandomGreeting()
+        {
+            // ...
+
+     +        $this->logger->info('Using the greeting: '.$greeting);
+
+             return $greeting;
+        }
+    }
+
+Yes! This works too: no configuration, no time wasted.
+
+Event Subscriber
+----------------
+
+
+
+.. _`Monolog`: https://github.com/Seldaek/monolog