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.

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1. foolab.ca | @foolabca Rewriting
 12-Year-Old Code ConFoo, Montreal - February 25, 2016
2. Anna Filina • Developer • Problem solver • Trainer • Advisor • FooLab + ConFoo 2
3. You Inherited a
 10-Year-Old Codebase
4. You Inherited a
 12-Year-Old Codebase
5. You Inherited a
 15-Year-Old Codebase
6. You Inherited a
 15-Year-Old Codebase Code Doesn't Age Like Wine
7. The web was 600 pixels wide 7
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
9. Objectives • Reduce mistakes • Increase dev. speed • Reduce tech. debt • Avoid getting stuck • Increase confidence 9
10. Code Smells
11. Global functions include("functions.php"); MyClass::myMethod(); // namespaced function? 11
12. False security $clean = htmlentities($_POST['input_field']); // use filter functions or a framework // use prepared statements 12
13. What happened at order 20117? if ($order_id > 20117) { // use this sql } else { // use that sql } // weakness = time to refactor 13
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
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
16. Codebase • 5,000 classes. • 20,000 methods. • 1,500,000 lines of code. 16
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
18. Before You Code
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
20. Refactoring Example
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
22. Solution • Rewrite complex forms in Symfony ◦ mod_rewrite for concerned pages • Rewrite biggest module as OOP ◦ Design extraction ◦ Automated tests ◦ Flexible architecture 22
23. Design Extraction
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
25. Code-Level Advice
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
27. Code duplication • Sometimes, the bug is repeated 80+ times • Remove duplications ASAP 27
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
29. More Stories
30. ASP Classic to PHP 5.6 • 15+ spaghetti and hacks • Language no longer supported • Huge ERP with lots of code 30
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
32. Guzzle tests 32
33. PHP 5.3 to PHP 5.6 • 12+ spaghetti and hacks • Uses deprecated functions • Can't run on PHP 5.6 33
34. Solution • Split servers into 5.3 and 5.6 for fresh start • REST and modern design patterns • AngularJS frontend 34
35. Splitting the app 35
36. Alias is your friend (5.3 server) Alias "/module-name" "/var/www/project/angular" <Directory "/var/www/project/angular"> RewriteBase /module-name/ </Directory> 36
37. Stuck?
38. Try something new • Bounce ideas ◦ New people to avoid tunnel vision • Has this been done before? • Can I try another approach? 38
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
40. Takeaways • Plan before you act • Use known tools & methodologies • Get inspiration from others • Refactoring gets easier • Every problem has a solution 40
41. Anna Filina • Development. • Fix bugs & performance issues. • Workshops on testing, Symfony & API. • Advisor on testing strategy, legacy code. 41
42. @afilina afilina.com