<?php
class OrderService {
    public function process(Order $order): Result {
        DB::beginTransaction();
        $items = $order->getItems();
        foreach ($items as $item) {
            Inventory::decrement($item->sku, $item->qty);
            $ledger->record($item, LedgerType::DEBIT);
        }
        DB::commit();
        return Result::ok($order->id);
    }
}

SELECT u.id, u.name, COUNT(o.id) AS total_orders,
       SUM(o.total) AS revenue
FROM users u
LEFT JOIN orders o ON o.user_id = u.id
INNER JOIN contracts c ON c.client_id = u.id
WHERE u.active = 1
  AND o.created_at >= DATE_SUB(NOW(), INTERVAL 12 MONTH)
GROUP BY u.id
HAVING total_orders > 0
ORDER BY revenue DESC;

async function syncIntegration(endpoint, payload) {
  const res = await fetch(endpoint, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'Authorization': `Bearer ${token}`,
      'X-Request-Id': crypto.randomUUID(),
    },
    body: JSON.stringify(payload),
  });
  if (!res.ok) throw new ApiError(res.status, await res.text());
  return res.json();
}

public class PaymentGateway {
    private readonly ILogger<PaymentGateway> _logger;
    private readonly HttpClient _httpClient;

    public async Task<ChargeResponse> ChargeAsync(ChargeRequest req,
        CancellationToken ct = default) {
        _logger.LogInformation("Charging {Amount} for {Client}",
            req.Amount, req.ClientId);
        var result = await _httpClient
            .PostAsJsonAsync("/v2/charge", req, ct);
        result.EnsureSuccessStatusCode();
        return await result.Content
            .ReadFromJsonAsync<ChargeResponse>(ct);
    }
}

CREATE INDEX idx_orders_user_date
    ON orders (user_id, created_at DESC)
    INCLUDE (total, status);

function debounce(fn, wait) {
  let timer;
  return (...args) => {
    clearTimeout(timer);
    timer = setTimeout(() => fn(...args), wait);
  };
}