Elite Engineering for Critical Systems.

public class OrderService : IOrderService
{
    private readonly IOrderRepository _repo;
    private readonly ILogger<OrderService> _logger;

    public OrderService(IOrderRepository repo, ILogger<OrderService> logger)
    {
        _repo = repo;
        _logger = logger;
    }

    public async Task<OrderResult> ProcessAsync(Guid orderId)
    {
        var order = await _repo.GetByIdAsync(orderId);
        if (order is null)
            throw new NotFoundException($"Order {orderId} not found");

        // Aggregate subtotals with resilient LINQ pipeline
        var total = order.Items
            .Where(i => i.IsActive)
            .Sum(i => i.Quantity * i.UnitPrice);

        _logger.LogInformation("Order {Id} total: {Total}", orderId, total);
        return new OrderResult(order.Id, total, DateTime.UtcNow);
    }
}