Preparing for Senior PHP Programmer role at Altero

I would implement a token bucket algorithm using Redis for distributed rate limiting:

class RateLimiter
{
    private Redis $redis;
    private string $key;
    
    public function checkLimit(string $clientId, int $limit, int $window): bool
    {
        $key = "rate:{$clientId}";
        $current = $this->redis->get($key);
        
        if (!$current) {
            $this->redis->setex($key, $window, 1);
            return true;
        }
        
        if ($current >= $limit) {
            return false;
        }
        
        $this->redis->incr($key);
        return true;
    }
}

This implementation would be crucial for Altero's platform to prevent API abuse while serving 500,000+ clients across Baltic markets.

OAuth 2.0 is an authorization framework, while JWT is a token format. In Altero's context:

OAuth 2.0:

• Use for third-party lender authentication
• Managing client credentials for different financial institutions
• Handling authorization flows

JWT:

• Storing user session information
• Passing authenticated user claims between services
• Stateless authentication for internal microservices

Example JWT implementation:

class JwtAuthenticator
{
    public function generateToken(array $claims): string
    {
        return JWT::encode([
            'sub' => $claims['user_id'],
            'role' => $claims['role'],
            'exp' => time() + 3600,
            'iat' => time(),
        ], getenv('JWT_SECRET'));
    }
}

For Altero's platform connecting multiple lenders, I would implement URI versioning:

# routes/api.php
Route::prefix('api/v1')->group(function () {
    Route::get('/lenders/{lender}/offers', [OfferController::class, 'index']);
});

Route::prefix('api/v2')->group(function () {
    Route::get('/lenders/{lender}/offers', [OfferControllerV2::class, 'index']);
});

Key considerations:

• Maintain backward compatibility
• Document changes between versions
• Use semantic versioning
• Implement version sunset policies
• Support at least two versions simultaneously

For Altero's loan comparison platform, I would implement:

1. Circuit Breaker Pattern:

class CircuitBreaker
{
    private Redis $redis;
    private int $threshold = 5;
    private int $timeout = 60;

    public function execute(callable $operation)
    {
        if ($this->isOpen()) {
            throw new CircuitBreakerOpenException();
        }

        try {
            return $operation();
        } catch (TimeoutException $e) {
            $this->recordFailure();
            throw $e;
        }
    }
}

2. Implement retry mechanisms with exponential backoff
3. Use RabbitMQ for async processing of long-running operations
4. Set appropriate timeout values for different types of operations
5. Implement fallback mechanisms for critical operations

For Altero's loan comparison functionality:

class LoanOffersController
{
    public function getOffers(Request $request): JsonResponse
    {
        return Cache::remember("offers:{$request->criteria}", 300, function () {
            return $this->lenderService->aggregateOffers(
                parallel([
                    fn() => $this->fetchLenderAOffers(),
                    fn() => $this->fetchLenderBOffers(),
                ])
            );
        });
    }
}

Key implementations:

• Parallel processing using Swoole/RoadRunner
• Redis caching for frequently accessed data
• Queue background updates for non-real-time data
• Implement circuit breakers for each lender
• Use event-driven architecture for real-time updates

For Altero's financial transactions:

class IdempotentTransaction
{
    public function execute(string $idempotencyKey, callable $operation)
    {
        return DB::transaction(function () use ($idempotencyKey, $operation) {
            $lock = Lock::get("transaction:{$idempotencyKey}");
            
            if ($existing = $this->findExistingTransaction($idempotencyKey)) {
                return $existing;
            }
            
            $result = $operation();
            $this->storeTransaction($idempotencyKey, $result);
            
            return $result;
        });
    }
}

Implementation includes:

• Unique idempotency keys
• Distributed locking
• Transaction logging
• Response caching
• Explicit expiration policies

For Altero's financial platform:

1. Implementation of security headers:

class SecurityMiddleware
{
    public function handle($request, Closure $next)
    {
        $response = $next($request);
        return $response->withHeaders([
            'Strict-Transport-Security' => 'max-age=31536000; includeSubDomains',
            'Content-Security-Policy' => "default-src 'self'",
            'X-Content-Type-Options' => 'nosniff',
            'X-Frame-Options' => 'DENY'
        ]);
    }
}

2. Additional measures:

• SSL/TLS encryption (minimum TLS 1.2)
• OAuth 2.0 with refresh tokens
• Rate limiting
• Request signing
• Input validation and sanitization
• Audit logging
• IP whitelisting for partner institutions
• Regular security audits

I would implement a retry mechanism using the following approach:

1. Set up a main queue for loan applications and a retry queue
2. Implement x-dead-letter-exchange and x-dead-letter-routing-key arguments
3. Use message headers to track retry count:

$properties = [
    'delivery_mode' => AMQPMessage::DELIVERY_MODE_PERSISTENT,
    'application_headers' => new AMQPTable([
        'x-retry-count' => 0
    ])
];

$channel->basic_publish($message, 'loan_exchange', 'loan_applications', true, false, $properties);

4. When processing fails, check retry count:

if ($retryCount < $maxRetries) {
    $headers['x-retry-count'] = $retryCount + 1;
    // Republish with exponential backoff
    $delay = pow(2, $retryCount) * 1000; // milliseconds
    // Publish to delay queue
} else {
    // Move to dead letter queue for manual review
}

This ensures failed loan applications are retried with exponential backoff, crucial for handling temporary issues with lender integrations.

The three exchange types serve different routing purposes:

1. Direct Exchange:

• Messages are routed based on exact matching routing key
• Ideal for direct lender-specific queues

$channel->exchange_declare('lender_exchange', 'direct');
$channel->queue_bind($queueName, 'lender_exchange', 'lender.latvian_bank');

2. Fanout Exchange:

• Broadcasts messages to all bound queues
• Perfect for notifications to all lenders

$channel->exchange_declare('broadcast_exchange', 'fanout');
// All bound queues receive the message

3. Topic Exchange:

• Routes messages based on wildcard patterns
• Useful for regional or product-based routing

$channel->exchange_declare('regional_exchange', 'topic');
// Routes like 'latvia.personal_loans.*' or 'estonia.#'

For Altero's platform, I'd use direct exchange for specific lender integrations, fanout for system-wide updates, and topic for region-specific processing (Latvia, Lithuania, Estonia markets).

For a loan processing system, I would implement DLQ handling as follows:

1. Configure Dead Letter Exchange:

$channel->exchange_declare('dlx_exchange', 'direct');
$channel->queue_declare('dead_letter_queue', false, true, false, false, false, new AMQPTable([
    'x-dead-letter-exchange' => 'dlx_exchange',
    'x-dead-letter-routing-key' => 'failed_loans'
]));

2. Implement message tracking:

class DeadLetterHandler {
    public function processFailedMessage(AMQPMessage $message) {
        $headers = $message->get('application_headers');
        $failureReason = $headers->get('x-death')[0]['reason'];
        
        // Log failure for monitoring
        $this->logger->error('Loan application failed', [
            'reason' => $failureReason,
            'loan_id' => $message->get('loan_id'),
            'lender' => $message->get('lender')
        ]);
        
        // Store in database for manual review
        $this->failedLoansRepository->store($message->getBody());
    }
}

3. Implement monitoring and alerting for DLQ size and patterns
4. Create an admin interface for manual review and reprocessing

This ensures no loan applications are lost and provides visibility into integration issues with different lenders.

For Altero's platform handling 500,000+ clients, I would implement these scaling strategies:

1. Clustering:

// Configure multiple nodes
$connection = new AMQPStreamConnection([
    ['host' => 'rabbit1', 'port' => 5672],
    ['host' => 'rabbit2', 'port' => 5672]
], $credentials);

2. Queue Sharding:

// Implement consistent hashing for queue distribution
$shardKey = crc32($loanApplication->getLenderId()) % $totalShards;
$queueName = "loans.shard_{$shardKey}";

3. Message Batching:

$channel->batch_basic_publish($message1, 'exchange', 'routing_key');
$channel->batch_basic_publish($message2, 'exchange', 'routing_key');
$channel->publish_batch();

4. Consumer Scaling:

// Implement worker pools
$channel->basic_qos(null, 100, false); // Prefetch count

5. Performance Monitoring:

$channel->set_qos(0, 1000, true); // Global QoS settings

This ensures the system can handle peak loads across multiple markets (Latvia, Lithuania, Estonia) efficiently.

For Altero's loan comparison platform, I would implement priority queuing as follows:

1. Define Priority Queues:

$channel->queue_declare('high_priority_loans', false, true, false, false, false, new AMQPTable([
    'x-max-priority' => 10
]));

2. Message Priority Assignment:

class LoanPriorityService {
    public function assignPriority(LoanApplication $application): int {
        return match($application->getType()) {
            'premium_client' => 10,
            'returning_client' => 8,
            'high_value_loan' => 7,
            'standard' => 5
        };
    }
}

// Publishing with priority
$properties = [
    'priority' => $priorityService->assignPriority($application)
];
$channel->basic_publish($message, 'loan_exchange', 'loans', true, false, $properties);

3. Consumer Implementation:

$callback = function($msg) {
    $priority = $msg->get('priority');
    // Process based on priority
};
$channel->basic_consume('high_priority_loans', '', false, false, false, false, $callback);

This ensures important loan applications (like high-value loans or premium clients) are processed first.

For a financial system like Altero's platform, message persistence is crucial. Here's how I would implement it:

1. Exchange Declaration:

$channel->exchange_declare('loan_exchange', 'direct', false, true, false);
// durable = true ensures exchange survives broker restart

2. Queue Declaration:

$channel->queue_declare('loan_applications', false, true, false, false);
// durable = true for queue persistence

3. Message Publishing:

$msg = new AMQPMessage(
    json_encode([
        'loan_id' => $id,
        'amount' => $amount,
        'lender' => $lender
    ]),
    [
        'delivery_mode' => AMQPMessage::DELIVERY_MODE_PERSISTENT,
        'content_type' => 'application/json',
        'timestamp' => time()
    ]
);

4. Consumer Acknowledgments:

$callback = function($msg) {
    try {
        $this->processLoanApplication($msg->body);
        $msg->ack(); // Explicit acknowledgment
    } catch (Exception $e) {
        $msg->nack(false, true); // Requeue on failure
    }
};

$channel->basic_consume('loan_applications', '', false, false, false, false, $callback);

This ensures no loan applications are lost during system failures or broker restarts, which is critical for maintaining the integrity of financial transactions.

For loan application reporting in a system like Altero that handles 500,000+ clients, I would implement the following optimizations:

1. Use EXPLAIN to analyze query execution plan
2. Implement proper indexing on join conditions and WHERE clauses
3. Consider these specific optimizations:
   • Use JOIN instead of subqueries where possible
   • Implement covering indexes for frequently used columns
   • Use FORCE INDEX when needed to override MySQL's choice
4. Example of an optimized query:

SELECT 
    la.id, 
    la.status,
    c.name,
    l.offer_amount
FROM loan_applications la
FORCE INDEX (idx_status_date)
JOIN clients c ON la.client_id = c.id
JOIN lender_offers l ON la.id = l.application_id
WHERE la.status = 'pending'
    AND la.created_at > DATE_SUB(NOW(), INTERVAL 30 DAY)

5. Consider partitioning tables by date range for historical data

For a financial platform handling €500M+ in loans, efficient indexing is crucial:

1. Implement compound indexes based on query patterns:

CREATE INDEX idx_loan_status_date ON loans(status, created_at);
CREATE INDEX idx_client_region ON clients(country_code, city);

2. Use covering indexes for frequently accessed data:

• Include all columns needed by common queries
• Avoid over-indexing to maintain write performance

3. Specific strategies:

• Hash indexes for exact matches (e.g., loan IDs)
• B-tree indexes for range queries (e.g., date ranges)
• Partial indexes for specific conditions

4. Regular maintenance:

• Monitor index usage with performance_schema
• Remove unused indexes
• Regularly update statistics

For Altero's multi-country operation (Latvia, Lithuania, Estonia), I would implement:

1. Geographic-based sharding:

class DatabaseShardManager {
    private function determineShardKey(string $country): string {
        return match($country) {
            'LV' => 'shard_latvia',
            'LT' => 'shard_lithuania',
            'EE' => 'shard_estonia',
            default => throw new InvalidCountryException()
        };
    }
}

2. Implement consistent hashing for load distribution
3. Use a master database for cross-shard queries
4. Maintain shared lookup tables for common data
5. Consider using ProxySQL for routing queries
6. Implement cross-shard transaction handling using:
   • Two-phase commit protocol
   • Eventual consistency where appropriate

For managing multiple lender integrations:

1. Implement Event Sourcing:

class LoanApplicationEvent {
    private DateTime $timestamp;
    private string $lenderId;
    private string $eventType;
    private array $payload;
    
    public function recordEvent(string $type, array $data): void {
        // Record event to event store
    }
}

2. Use RabbitMQ (mentioned in requirements) for:

   • Async processing of lender responses
   • Message queuing for retry mechanisms
   • Dead letter queues for failed integrations

3. Implement:

   • Idempotency keys for all operations
   • Distributed transactions where necessary
   • Status reconciliation jobs

For a high-traffic financial platform:

1. Implement Redis for:

class CacheService {
    public function getCachedLenderOffers(string $region): array {
        $key = "lender_offers:{$region}";
        return $this->redis->get($key) ?? $this->fetchAndCacheLenderOffers($region);
    }
}

2. Multi-level caching strategy:

   • L1: Application cache (APCu)
   • L2: Redis for distributed caching
   • L3: Database

3. Cache invalidation strategies:

   • Time-based for rate information
   • Event-based for lender updates
   • Region-based cache segments

For a system processing multiple loan applications simultaneously:

1. Implement retry mechanism:

class TransactionManager {
    public function executeWithRetry(callable $transaction, int $maxRetries = 3): mixed {
        for ($i = 0; $i < $maxRetries; $i++) {
            try {
                return $transaction();
            } catch (DeadlockException $e) {
                if ($i === $maxRetries - 1) throw $e;
                usleep(random_int(100000, 300000)); // Random backoff
            }
        }
    }
}

2. Deadlock prevention:

   • Consistent order of table access
   • Shorter transaction times
   • Row-level locking where possible
   • Using NOWAIT or SKIP LOCKED options

3. Monitoring:

   • Log deadlock incidents
   • Alert on frequent occurrences
   • Regular analysis of deadlock patterns

I would implement the Repository pattern to abstract the data layer for loan comparisons like this:

interface LoanRepositoryInterface {
    public function findByCustomerCriteria(CustomerCriteria $criteria): Collection;
    public function findBestOffers(array $parameters): Collection;
    public function getLendersByMarket(string $market): Collection;
}

class MysqlLoanRepository implements LoanRepositoryInterface {
    private PDO $connection;
    
    public function findByCustomerCriteria(CustomerCriteria $criteria): Collection {
        // Implementation for MySQL
    }
    
    public function findBestOffers(array $parameters): Collection {
        // Complex queries to find best matching offers across lenders
    }
    
    public function getLendersByMarket(string $market): Collection {
        // Get lenders for specific Baltic market (LV, LT, EE)
    }
}

This pattern would help maintain clean separation between business logic and data access, especially important when working with multiple lenders across Baltic markets.

The Strategy pattern would be perfect for handling different loan calculation methods across various lenders:

interface LoanCalculationStrategy {
    public function calculateMonthlyPayment(float $amount, float $interest, int $term): float;
}

class AnnuityLoanCalculator implements LoanCalculationStrategy {
    public function calculateMonthlyPayment(float $amount, float $interest, int $term): float {
        // Annuity calculation logic
    }
}

class LinearLoanCalculator implements LoanCalculationStrategy {
    public function calculateMonthlyPayment(float $amount, float $interest, int $term): float {
        // Linear calculation logic
    }
}

class LoanCalculationService {
    private LoanCalculationStrategy $strategy;
    
    public function setStrategy(LoanCalculationStrategy $strategy): void {
        $this->strategy = $strategy;
    }
    
    public function calculatePayment(float $amount, float $interest, int $term): float {
        return $this->strategy->calculateMonthlyPayment($amount, $interest, $term);
    }
}

This would allow flexible switching between different calculation methods based on lender requirements or market specifics.

For Altero's reporting system, I would implement CQRS like this:

// Command side
class CreateLoanApplication {
    public function execute(LoanApplicationData $data): void {
        // Write to main database
    }
}

// Query side
class LoanReportQuery {
    private ReadOnlyConnection $readConnection;
    
    public function getMarketStatistics(string $market): array {
        // Read from optimized read replica
        return $this->readConnection->query(
            "SELECT COUNT(*), SUM(amount) FROM loan_applications 
             WHERE market = :market 
             GROUP BY status",
            ['market' => $market]
        );
    }
}

// Event handler to sync data
class LoanApplicationCreatedHandler {
    public function handle(LoanApplicationCreatedEvent $event): void {
        // Update read model using RabbitMQ for async processing
    }
}

This separation would be particularly useful for generating the required business unit reports while maintaining system performance.

For loan status updates across the platform, I would implement the Observer pattern like this:

interface LoanStatusObserver {
    public function onStatusUpdate(LoanApplication $application, string $newStatus): void;
}

class LoanApplication implements SplSubject {
    private array $observers = [];
    private string $status;
    
    public function attach(LoanStatusObserver $observer): void {
        $this->observers[] = $observer;
    }
    
    public function updateStatus(string $newStatus): void {
        $this->status = $newStatus;
        foreach ($this->observers as $observer) {
            $observer->onStatusUpdate($this, $newStatus);
        }
    }
}

class NotificationService implements LoanStatusObserver {
    public function onStatusUpdate(LoanApplication $application, string $newStatus): void {
        // Send notifications to customer
    }
}

class LenderUpdateService implements LoanStatusObserver {
    public function onStatusUpdate(LoanApplication $application, string $newStatus): void {
        // Update lender through API
    }
}

This would ensure all necessary parties (customer, lender, internal systems) are notified of status changes automatically.

I would implement the Factory pattern for loan products considering the multi-market nature of Altero:

interface LoanProduct {
    public function calculateTerms(): array;
    public function getRequirements(): array;
}

class PersonalLoan implements LoanProduct {
    private string $market; // LV, LT, or EE
    
    public function __construct(string $market) {
        $this->market = $market;
    }
    // Implementation
}

class BusinessLoan implements LoanProduct {
    // Implementation
}

class LoanProductFactory {
    public function createLoan(string $type, string $market): LoanProduct {
        return match($type) {
            'personal' => new PersonalLoan($market),
            'business' => new BusinessLoan($market),
            default => throw new InvalidArgumentException('Unknown loan type')
        };
    }
}

This would allow for easy expansion when adding new loan types or entering new markets.

For Altero's lending platform, I would organize the codebase using DDD principles like this:

// Domain Layer
namespace Domain\LoanApplication {
    class LoanApplication {
        private ApplicationStatus $status;
        private Money $requestedAmount;
        private Collection $offers;
        
        public function submitToLenders(): void {
            // Domain logic
        }
    }
}

// Application Layer
namespace Application\Service {
    class LoanApplicationService {
        private LoanApplicationRepository $repository;
        private LenderIntegrationService $lenderService;
        
        public function processApplication(ApplicationDTO $dto): void {
            // Application orchestration
        }
    }
}

// Infrastructure Layer
namespace Infrastructure\Persistence {
    class DoctrineApplicationRepository implements LoanApplicationRepository {
        // Implementation
    }
}

// API Layer
namespace Api\Controller {
    class LoanApplicationController {
        public function submit(Request $request): Response {
            // API endpoint logic
        }
    }
}

This structure would support the complex business rules of loan comparison while maintaining clean separation of concerns and making the system easier to maintain and scale across different Baltic markets.

For a FinTech platform handling sensitive loan data across Baltic states, I would implement:

1. At-rest encryption:

• Use AES-256-GCM encryption for stored data
• Utilize PHP's sodium_crypto_* functions for modern encryption
• Store encryption keys in a separate secure location (AWS KMS or HashiCorp Vault)

2. In-transit encryption:

• Enforce TLS 1.3 for all API communications with lenders
• Implement perfect forward secrecy
• Use strong cipher suites

Example implementation:

class DataEncryption {
    public function encrypt(string $sensitiveData): string {
        $key = $this->getEncryptionKey();
        $nonce = random_bytes(SODIUM_CRYPTO_SECRETBOX_NONCEBYTES);
        $cipher = sodium_crypto_secretbox(
            $sensitiveData,
            $nonce,
            $key
        );
        return base64_encode($nonce . $cipher);
    }
}

Working with MySQL in a loan comparison platform, I would implement:

1. Prepared Statements:

public function getLoanApplications(int $userId): array {
    $stmt = $this->pdo->prepare(
        "SELECT * FROM loan_applications WHERE user_id = :userId"
    );
    $stmt->bindParam(':userId', $userId, PDO::PARAM_INT);
    $stmt->execute();
    return $stmt->fetchAll(PDO::FETCH_ASSOC);
}

2. Input Validation:

• Use Symfony/Laravel validation components
• Implement type hinting
• Use strict_types declaration

3. ORM Usage:

• Utilize Doctrine/Eloquent for safe database operations
• Implement Repository pattern for data access abstraction

For a platform handling 500+ million EUR in loans, I would implement:

1. Event-based logging system using RabbitMQ:

class AuditLogger {
    public function logFinancialOperation(
        string $operation,
        array $data,
        string $userId
    ): void {
        $this->rabbitMQ->publish([
            'operation' => $operation,
            'data' => $data,
            'user_id' => $userId,
            'timestamp' => new DateTime(),
            'ip_address' => $_SERVER['REMOTE_ADDR'],
            'market' => $this->getCurrentMarket() // LV/LT/EE
        ]);
    }
}

2. Structured logging with:

• Operation type
• Timestamp
• User ID
• IP address
• Market identifier (Latvia/Lithuania/Estonia)
• Before/After states
• Status/Result

For a Baltic FinTech platform, I would implement:

1. Data Management:

class PersonalDataManager {
    public function handleRightToBeForgotten(int $userId): void {
        $this->anonymizeUserData($userId);
        $this->deleteNonEssentialData($userId);
        $this->logDeletionRequest($userId);
        $this->notifyThirdParties($userId);
    }
}

2. Key Features:

• Right to access/export data
• Right to be forgotten
• Data minimization
• Explicit consent tracking
• Data processing agreements with lenders
• Cross-border data transfer compliance (EU/Baltic states)

3. Technical Implementation:

• Data encryption
• Audit trails
• Automated data retention policies
• Geographic data storage constraints

For an API handling multiple lender integrations:

1. Authentication & Authorization:

class ApiSecurityMiddleware {
    public function handle(Request $request): Response {
        if (!$this->validateApiKey($request)) {
            return new Response('Unauthorized', 401);
        }
        if (!$this->rateLimitCheck($request)) {
            return new Response('Too Many Requests', 429);
        }
        return $next($request);
    }
}

2. Security Measures:

• OAuth 2.0 / JWT authentication
• Rate limiting
• IP whitelisting for lender APIs
• Request signing
• HTTPS enforcement
• API versioning
• Request/Response validation

For the loan comparison platform's frontend:

1. Output Encoding:

class OutputSanitizer {
    public function sanitize(string $input): string {
        return htmlspecialchars($input, ENT_QUOTES, 'UTF-8');
    }
}

2. Security Headers:

header("Content-Security-Policy: default-src 'self'");
header("X-XSS-Protection: 1; mode=block");
header("X-Frame-Options: DENY");

3. Additional Measures:

• Input validation
• CSRF tokens
• Modern framework security features (Symfony/Laravel)
• Regular security audits
• Cookie security (HttpOnly, Secure flags)