Rewriting 12-Year-Old Code

Did you ever have to maintain a 12-year-old application? Dead code and tables everywhere, static methods, database queries in between HTML tags and some pages still in PHP3. This presentation will lead you through a progressive rewrite from very old legacy to the latest shiny version of PHP. Learn how to automate legacy testing, how to seamlessly jump between the old and new parts, and how to overcome other challenges that arise from dealing with legacy.

Transcript

1. foolab.ca | @foolabca
   Rewriting

   12-Year-Old Code
   ConFoo, Montreal - February 25, 2016
   

   View Slide

2. Anna Filina
   • Developer
   • Problem solver
   • Trainer
   • Advisor
   • FooLab + ConFoo
   2
   

   View Slide

3. You Inherited a

   10-Year-Old Codebase
   

   View Slide

4. You Inherited a

   12-Year-Old Codebase
   

   View Slide

5. You Inherited a

   15-Year-Old Codebase
   

   View Slide

6. You Inherited a

   15-Year-Old Codebase
   Code Doesn't Age Like Wine
   

   View Slide

7. The web was 600 pixels wide
   7
   

   View Slide

8. Feeling old yet?
   • Y2K bug
   • Google launched AdWords
   • There was no Twitter, no Facebook, no iTunes
   • Internet Explorer 5
   • ICQ was starting to be cool
   • Rounded corners = status symbol
   8
   

   View Slide

9. Objectives
   • Reduce mistakes
   • Increase dev. speed
   • Reduce tech. debt
   • Avoid getting stuck
   • Increase confidence
   9
   

   View Slide

10. Code Smells
    

    View Slide

11. Global functions
    include("functions.php");
    MyClass::myMethod(); // namespaced function?
    11
    

    View Slide

12. False security
    $clean = htmlentities($_POST['input_field']);
    // use filter functions or a framework
    // use prepared statements
    12
    

    View Slide

13. What happened at order 20117?
    if ($order_id > 20117) {
    // use this sql
    } else {
    // use that sql
    }
    // weakness = time to refactor
    13
    

    View Slide

14. Average legacy code file
    • 3000-6000 lines of code.
    • Half of it is commented "in case we need it later".
    • Method length of 800 lines.
    • Abuse of helper classes.
    • Sometimes no classes at all.
    14
    

    View Slide

15. Complex call graph
    $instance = Model::getInstanceByCode($code);
    class Model
    {
    public static function getInstanceByCode($code)
    {
    //...
    $instances = Cache::getCache($cacheIndex);
    }
    }
    class Cache
    {
    public static function getCache($cacheIndex)
    {
    //...
    $cache = File::getFileContent($filePath);
    }
    }
    15
    

    View Slide

16. Codebase
    • 5,000 classes.
    • 20,000 methods.
    • 1,500,000 lines of code.
    16
    

    View Slide

17. Strategy
    • Make a strategy based on
    contraints
    • Full rewrite vs progressive
    ◦ By class
    ◦ By module
    ◦ By HTTP call
    • How to run code side-by-side
    ◦ Session sharing
    17
    

    View Slide

18. Before You Code
    

    View Slide

19. Data can be lost, stuff can break
    • Backup: test restore
    • Staging environment: app versions, configs
    • Simulate deployments/upgrades
    • Automate tests before code changes
    • Make a risk assessment
    ◦ Don't be too optimistic
    ◦ Account for side-effects
    19
    

    View Slide

20. Refactoring Example
    

    View Slide

21. PHP 3 to PHP 5.6
    • HTML + PHP + SQL in same file
    • Includes all over the place
    • IFs that concatenate SQL
    • Previous rewrite attempt
    ◦ Failed, made things worse
    ◦ Folders of dead code
    ◦ Classes with static functions (no instances)
    21
    

    View Slide

22. Solution
    • Rewrite complex forms in Symfony
    ◦ mod_rewrite for concerned pages
    • Rewrite biggest module as OOP
    ◦ Design extraction
    ◦ Automated tests
    ◦ Flexible architecture
    22
    

    View Slide

23. Design Extraction
    

    View Slide

24. Avoid code bias
    • Old code → design docs
    • Validate design docs
    ◦ Clarify business rules
    • Improve design
    ◦ Reduce tech. debt
    ◦ More flexible
    • Design docs → new code
    24
    

    View Slide

25. Code-Level Advice
    

    View Slide

26. Infrastructure
    • Set up logging
    ◦ Monolog if PHP version allows
    ◦ file_put_contents if really old version
    • Set up testing
    ◦ Mocking static methods: Patchwork or equivalent
    ◦ Cache API call output
    26
    

    View Slide

27. Code duplication
    • Sometimes, the bug is repeated 80+ times
    • Remove duplications ASAP
    27
    

    View Slide

28. Fix long methods
    • Extract broken part into its own method
    • Write unit tests for it
    • Fix it
    • Call it from the mega-method
    28
    

    View Slide

29. More Stories
    

    View Slide

30. ASP Classic to PHP 5.6
    • 15+ spaghetti and hacks
    • Language no longer supported
    • Huge ERP with lots of code
    30
    

    View Slide

31. Solution
    • Symfony to rewrite page by page
    • mod_rewrite for concerned pages
    • DB session adapter in both apps
    • Page in any language = HTTP request
    ◦ Guzzle tests FTW!
    31
    

    View Slide

32. Guzzle tests
    32
    

    View Slide

33. PHP 5.3 to PHP 5.6
    • 12+ spaghetti and hacks
    • Uses deprecated functions
    • Can't run on PHP 5.6
    33
    

    View Slide

34. Solution
    • Split servers into 5.3 and 5.6 for fresh start
    • REST and modern design patterns
    • AngularJS frontend
    34
    

    View Slide

35. Splitting the app
    35
    

    View Slide

36. Alias is your friend (5.3 server)
    Alias "/module-name" "/var/www/project/angular"
    
    RewriteBase /module-name/
    
    36
    

    View Slide

37. Stuck?
    

    View Slide

38. Try something new
    • Bounce ideas
    ◦ New people to avoid tunnel vision
    • Has this been done before?
    • Can I try another approach?
    38
    

    View Slide

39. Ask refactoring experts
    • Pick their brain
    • Read their blog
    • Hire one for a day
    ◦ Refactoring strategy
    ◦ Remove roadblocks
    ◦ Guidance (one day per week to steer in right direction)
    39
    

    View Slide

40. Takeaways
    • Plan before you act
    • Use known tools & methodologies
    • Get inspiration from others
    • Refactoring gets easier
    • Every problem has a solution
    40
    

    View Slide

41. Anna Filina
    • Development.
    • Fix bugs & performance issues.
    • Workshops on testing, Symfony & API.
    • Advisor on testing strategy, legacy code.
    41
    

    View Slide

42. @afilina afilina.com
    

    View Slide