Tips and tricks learned over the years on maintaining legacy applications.

1. MAINTAINING LEGACY
APPLICATIONS
by Bernhard Breytenbach

2. ABOUT ME
Started with PHP in 2005
Developer at MDS Technologies
@BBreyten on Twitter
lanyrd.com/cfmmrb | joind.in/14838

3. WHAT IS LEGACY SOFTWARE?
“The secondary value of software is its
behavior... It’s achieved when the current
software meets the current needs of the
current user... But the needs of the users
change, and they do so frequently... Thus the
primary value of software is its ability to
change.”
— Robert C. Martin (Uncle Bob)

4. WHAT IS LEGACY SOFTWARE?
Legacy software is software that is unable to change easily
Software that is difficult to read and reuse

5. “DON’T MAINTAIN, REWRITE!”

6. NETSCAPE NAVIGATOR

7. THE DANGERS OF REWRITE

8. REFACTORING
Refactoring is the process of restructuring
existing code without changing its external
behavior, in order to improve readability and
reduce code complexity, as to improve source
code maintainability and create a more
expressive internal architecture or object
model to improve extensibility.
https://en.wikipedia.org/wiki/Code_refactoring

9. RULES OF REFACTORING
Small iterative changes
Make sure everything still works
Send to QA, Push to Production
Do the next small change

10. TYPES OF LEGACY SYSTEMS
Standalone App
Framework (MVC)
Plugins/Modules

11. VERSION CONTROL

12. DEPLOYMENT

13. PICK A CODING STANDARD
PSR1 & PSR2
Only one standard

14. SETUP AUTOLOADING
spl_autoload_register(function ($class)
{
$prefix = 'FooBar';
$base_dir = __DIR__ . '/src/';
$len = strlen($prefix);
if (strncmp($prefix, $class, $len) !== 0) {
return;
}
$relative_class = substr($class, $len);
$file = $base_dir . str_replace('', '/', $relative_class) . '.php';
// if the file exists, require it
if (file_exists($file)) {
require $file;
}
});

15. COMPOSER AUTOLOADING
{
"autoload": {
"psr­0": {
"FooBar":"src/",
},
"psr­4": {
"FooBar":"src/",
}
}
}
bootstrap.php
require "vendor/autoload.php"

16. DIRECTORY STRUCTURE
public/
src/
vendor/
bootstrap.php

17. MOVE FUNCTIONALITY INTO CLASSES
Get rid of includes
One class per file
Files should declare new symbols, or cause side effects, but
not do both.

18. REPLACE MAGIC NUMBERS WITH CONSTANTS
if ($status­>id === 15)
if ($user­>type === 3)
if ($code === 418)
if ($status­>id === Status::CANCELLED)
if ($user­>type === User::TYPE_ADMIN)
if ($code === Response::HTTP_I_AM_A_TEAPOT)

19. DEPENDENCY INJECTION
<?php
class UserRepository
{
public function getUsers()
{
global $db;
$sql = 'select * from users;';
return $db­>select($sql);
}
}

20. DEPENDENCY INJECTION
<?php
class UserRepository
{
public function getUsers()
{
$db = Db::getInstance();
$sql = 'select * from users;';
return $db­>select($sql);
}
}

21. DEPENDENCY INJECTION
<?php
class UserRepository
{
protected $db;
public function __construct()
{
global $db;
$this­>db = $db;
}
public function getUsers()
{
$sql = 'select * from users;';
return $this­>db­>select($sql);
}
}

22. DEPENDENCY INJECTION
<?php
class UserRepository
{
protected $db;
public function __construct($db)
{
$this­>db = $db;
}
public function getUsers()
{
$sql = 'select * from users;';
return $this­>db­>select($sql);
}
}

23. BREAK UP LARGE CLASSES/FUNCTIONS
Large functions is where classes go to hide.

24. PROTECTION LAYER
<?php
class User
{
protected $attributes = [];
public function __construct($attributes)
{
$this­>attributes = $attributes;
}
public function getId()
{
return $this­>attributes['UserName'];
}
public function getUserName()
{
return $this­>attributes['UserName'];
}
}

25. PLAN OF ACTION
Take Charge!
Baby steps
Fail fast, fail cheap

26. PLUGINS/MODULES
Globals only allowed in the master file
If global is a class, initialize in construct
All globals should be passed on as is

27. PLUGINS/MODULES
<?php
include('autoload.php');
class some_required_class_name extends some_base_class
{
private $db;
public function __construct()
{
global $db;
$this­>db = $db;
}
public function get_info($data)
{
global $token;
$infoGetter = new InfoGetter($this­>db);
return $infoGetter­>get($data­>id, $token);
}
}

28. PRESTASHOP
<?php
// Avoid direct access to the file
if (!defined('_PS_VERSION_')) {
exit;
}
require_once('bootstrap.php');
class MdsCollivery extends CarrierModule
{
protected $collivery;
protected $db;
protected $hooks = array(
'displayFooter',
'displayShoppingCart',
'displayAdminOrder',
);
public function __construct()
{
$this­>name = 'mds';
$this­>tab = 'shipping_logistics';
$this­>version = '1.0';

29. PRESTASHOP
<?php
define('_MDS_DIR_', __DIR__);
class MdsColliveryAutoloader
{
protected static $classMap = array(
'Mds_View' => 'MdsPrestashopHelpersView',
'Mds_ColliveryApi' => 'MdsPrestashopColliveryColliveryApi'
'Mds_Install' => 'MdsPrestashopInstallerInstall',
);
public static function autoload($class)
{
if (array_key_exists($class, self::$classMap)) {
class_alias(self::$classMap[$class], $class);
} else {
$classParts = explode('', $class);
$vendor = array_shift($classParts);
if ($vendor === 'Mds') {
require _MDS_DIR_ . '/' . implode('/', $classParts
}
}
}
}

30. IS IT NEVER GOOD TO REWRITE?

31. WHEN CAN I REWRITE?
The new system is vastly out of scope, or the current system
simply can’t meet the new requirements.
You have to change Programming Language/Framework
You have lots of time, money and resources

32. RULES OF A REWRITE
Both systems need to run in parallel
Spend as little time as possible between deploys
Fail fast, fail cheap
Don’t try and change everything
Use @deprecated
Work closely with the current devs
Always be ready to implement new features

33. The key to success is not perfection, but making peace with the
term good enough, and then moving on.