Рефакторинг и аварии старого PHP-проекта

final class LegacyTotalTest extends TestCase
{
    public function testLegacyTotalForKnownOrder(): void
    {
        $result = legacyTotal(['price' => 100, 'discount' => 10]);
        self::assertSame(90, $result);
    }
}

interface Clock { public function now(): DateTimeImmutable; }

final class LegacyClock implements Clock
{
    public function now(): DateTimeImmutable { return new DateTimeImmutable('now'); }
}

$taxRate = 0.20;
function total(float $price): float
{
    global $taxRate;
    return $price * (1 + $taxRate);
}

if ($newCheckout->supports($request)) {
    return $newCheckout->handle($request);
}
return $legacyApplication->handle($request);

if ($flags->enabled('new_pricing', $user->id)) {
    return $newPricing->calculate($cart);
}
return $legacyPricing->calculate($cart);

interface Mailer { public function send(Message $message): void; }

final class NativeMailAdapter implements Mailer
{
    public function send(Message $message): void
    {
        mail($message->to, $message->subject, $message->body);
    }
}

$requestId = $_SERVER['HTTP_X_REQUEST_ID'] ?? bin2hex(random_bytes(8));
$logger->error('HTTP 500', [
    'request_id' => $requestId,
    'route' => $routeName,
    'release' => getenv('APP_RELEASE'),
]);

$logger->info('checkout.started', ['request_id' => $requestId]);
$logger->warning('payment.slow', ['request_id' => $requestId, 'elapsed_ms' => 2400]);
$logger->error('checkout.failed', ['request_id' => $requestId]);

$logger->info('order.completed', [
    'event' => 'order.completed',
    'request_id' => $requestId,
    'release' => $release,
    'duration_ms' => $durationMs,
    'result' => 'success',
]);

$bucket = crc32($userId) % 100;
$handler = $bucket < 5 ? $newHandler : $stableHandler;
$response = $handler->handle($request);
$metrics->observe('checkout_errors', $response->status >= 500, ['variant' => $bucket < 5 ? 'canary' : 'stable']);

$pdo->exec('ALTER TABLE orders DROP COLUMN legacy_status');

function loadLegacyOrder(PDO $pdo, int $id): array
{
    $stmt = $pdo->prepare('SELECT id, legacy_status FROM orders WHERE id = ?');
    $stmt->execute([$id]);
    return $stmt->fetch(PDO::FETCH_ASSOC);
}

$ready = $database->ping()
    && $cache->ping()
    && $migrations->isCurrent();
http_response_code($ready ? 200 : 503);

$input = ['quantity' => 0, 'coupon' => 'X'];
$result = legacyCheckout($input, new FrozenClock('2026-07-14T10:00:00Z'));
var_dump($result);

$oldResult = $legacyCalculator->calculate($input);
$newResult = $newCalculator->calculate($input);
if ($oldResult !== $newResult) {
    $logger->warning('shadow_mismatch', compact('oldResult', 'newResult'));
}
return $oldResult;

$database = new FaultInjectingDatabase(
    inner: $realDatabase,
    failAfterWrites: 1,
);
$service->execute($command);

$flags->disable('new_checkout');
$traffic->routeTo($stableRelease);
$incident->record('mitigation_applied', ['release' => $stableRelease]);

$newSecret = $secrets->createVersion('payment-api');
$deploy->useSecretVersion($newSecret->version);
$secrets->revokeVersion($oldVersion);

$postmortem = [
    'impact' => $impact,
    'timeline' => $timeline,
    'contributing_factors' => $factors,
    'actions' => $preventiveActions,
];