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Rewriting 15-Year-Old Code

Rewriting 15-Year-Old Code

Anna Filina

November 15, 2017
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  1. @afilina
    Rewriting 15-Year-Old Code
    BuildStuff, Vilnius - November 15, 2017

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  2. Anna Filina
    • Project rescue
    • Legacy code
    • Development
    • Conferences
    • Private workshops
    • Canada

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  3. You inherited a

    17-year-old codebase
    Code doesn't age like wine.

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  4. The Web Was 600px Wide

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  5. Feeling Old Yet?
    • Y2K bug.
    • Internet Explorer 5.
    • ICQ was starting to be cool.
    • Rounded corners = status symbol.

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  6. Mixed Concerns
    mysql_query('...');
    $total = 0;
    foreach ($products as $p) {
    $total += $p['qty'] * $p['price'];
    }
    ?>
    Total: = $total ?>

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  7. Poorly Named Variables
    $a = //...
    $array = //...
    $item3 = //...
    $tempItem = //...

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  8. Global Functions & Constants
    include("functions.php");
    MyClass::myMethod(); // namespaced function?
    myMethod(DEV_MODE);

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  9. Inexplicable Conditions
    if ($order_id > 20117) {
    // use this sql
    } else {
    // use that sql
    }
    // weakness = time to refactor

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  10. Long Methods
    public function importCsv($path, $googleApiKey, $databaseDsn, $databaseUser, $databasePassword)
    {
    // Convert CSV to array of conferences
    $lines = file($path);
    $csv = array_map('str_getcsv', $lines);
    $conferences = [];
    foreach ($csv as $line) {
    $conference = new Conference();
    $conference->name = $line[0];
    $conference->location = $line[1];
    $conferences[] = $conference;
    // Get coordinates for location
    $location = urlencode($conference->location);
    $url = 'https://maps.googleapis.com/maps/api/geocode/json?address='.$location.'&key='.$googleApiKey;
    $curl = curl_init();
    curl_setopt($curl, CURLOPT_URL, $url);
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
    $response = curl_exec($curl);
    curl_close($curl);
    $json = json_decode($response);
    if (count($json->results) == 0) {
    continue;
    }
    $latitude = $json->results[0]->geometry->location->lat;
    $longitude = $json->results[0]->geometry->location->lng;
    $coordinates = $latitude.','.$longitude;
    $conference->coordinates = $coordinates;
    // Save conference to database
    $pdo = new PDO($databaseDsn, $databaseUser, $databasePassword);
    $statement = $pdo->prepare('REPLACE INTO conference (name, location, coordinates) VALUES (?, ?, ?)');
    $statement->execute([
    $conference->name,
    $conference->location,
    $conference->coordinates,
    ]);

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  11. 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.

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

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  13. Before you code

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  14. Strategy
    • Make a strategy based on
    constraints.
    • Full rewrite vs progressive:
    ◦By class.
    ◦By feature/module.
    ◦By HTTP call.
    • How to run code side-by-side:
    ◦DB/Session sharing.
    ◦mod_rewrite.

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  15. Data Can Be Lost, Stuff Can Break
    • Backup: test restore.
    • Nullify sensitive data.
    • Staging: simulate deployments/
    upgrades/batch processes.
    • Automate tests before code
    changes.
    • Make a risk assessment:
    ◦ Don't be too optimistic.
    ◦ Account for side-effects.

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  16. Build With Real Legacy Data

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  17. (Failed) rewrite example

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  18. 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).

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

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  20. New feature should not
    take longer than a sprint.

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  21. Design extraction

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  22. Avoid Code Bias
    • Old code → design docs.
    • Validate design docs:
    ◦Clarify business rules.
    • Improve design:
    ◦Reduce technical debt.
    ◦More flexible.
    • Design docs → new code.

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  23. Code Duplication
    • Sometimes, the bug is
    repeated 80+ times.
    • Remove duplications
    ASAP.

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  24. Fix Long Methods
    • Extract broken part into its own method.
    • Write unit tests for it.
    • Fix it.
    • Call it from the mega-method.

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  25. Spot Logical Groups
    Code block
    Comment
    Code block
    Comment
    Convert CSV to array of conferences.
    Get coordinates for conference location.
    Save conference to database.
    Code block
    Comment

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  26. Extract & Test
    Code block
    Comment
    Code block
    Method
    Code block
    Comment
    Call method

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  27. Name
    Code block
    Method
    Code block
    Method
    Call method
    Call method
    Code block
    Method
    Call method
    getConferencesFromCsv
    getLocationCoordinates
    saveConference

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  28. Rewrite example #2

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

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

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  31. Guzzle Tests

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  32. On Testing
    Before you code
    You better test
    So that on weekends
    You may rest.
    -- Anna Filina

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  33. Testing Static Methods
    $mock = Mockery::mock('alias:SomeClass');
    $mock->shouldReceive('staticMethod')->andReturn(42);

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

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  35. Takeaways
    • Make a strategy.
    • You touch it, you refactor it.
    • Use known tools & methodologies.
    • Get inspiration from others.
    • Refactoring gets easier.
    • Every problem has a solution.

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  36. Refactoring: Improving the
    Design of Existing Code
    Martin Fowler

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  37. @afilina afilina.com

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