components/LiteCharms.Features.MidrandBooks/Payments/Events/Handlers/PayfastPaymentConfirmationReceivedEventHandler.cs

using LiteCharms.Features.Hasher;
using LiteCharms.Features.Mediator;
using LiteCharms.Features.MidrandBooks.Orders;
using LiteCharms.Features.MidrandBooks.Payments.Models;

namespace LiteCharms.Features.MidrandBooks.Payments.Events.Handlers;

public sealed class PayfastPaymentConfirmationReceivedEventHandler(IServiceProvider services, ILogger<PayfastPaymentConfirmationReceivedEvent> logger) :
    INotificationHandler<PayfastPaymentConfirmationReceivedEvent>
{
    public async ValueTask Handle(PayfastPaymentConfirmationReceivedEvent notification, CancellationToken cancellationToken)
    {
        using var activity = MediatorTelemetry.Source.StartActivity($"Quartz: {typeof(PayfastPaymentConfirmationReceivedEvent).Name}");
        activity?.SetTag("event.correlation_id", notification.CorrelationId);

        await using var scope = services.CreateAsyncScope();
        var hashService = scope.ServiceProvider.GetRequiredService<HashService>();
        var orderService = scope.ServiceProvider.GetRequiredService<OrderService>();
        var paymentService = scope.ServiceProvider.GetRequiredService<PaymentService>();
        var payfastService = scope.ServiceProvider.GetRequiredService<PayfastService>();

        var payload = notification.Payload ?? throw new Exception("Payload metadata context is null.");

        var hashResult = hashService.DecodeLongIdHash(payload.MerchantPaymentId!);
        if (hashResult.IsFailed) throw new Exception("Failed to decode application tracking hash key identifier.");

        var orderResult = await orderService.GetOrderAsync(hashResult.Value, cancellationToken);
        if (orderResult.IsFailed) throw new Exception("Target system order entity context cannot be traced.");

        var paymentResult = await paymentService.GetOrderPaymentAsync(orderResult.Value.Id, cancellationToken);
        if (paymentResult.IsFailed) throw new Exception("Target payment ledger entity cannot be resolved.");

        var isAlreadyProcessed = await paymentService.HasLedgerEntryAsync(orderResult.Value.Id, paymentResult.Value.Id, cancellationToken);
        if (isAlreadyProcessed.Value)
        {
            logger.LogWarning("Webhook reference token '{Ref}' already verified. Skipping processing routines.", payload.MerchantPaymentId);

            return;
        }

        var isAmountValid = payfastService.ValidatePaymentAmount(orderResult.Value.Total, payload.AmountGross);
        if (!isAmountValid.Value)
            throw new Exception("Security validation exception: Transaction cost variance bounds breached (Price Tampering Detected).");

        decimal.TryParse(payload.AmountGross, CultureInfo.InvariantCulture, out var gross);
        decimal.TryParse(payload.AmountFee, CultureInfo.InvariantCulture, out var fee);
        decimal.TryParse(payload.AmountNet, CultureInfo.InvariantCulture, out var net);
        string status = payload.PaymentStatus ?? "UNKNOWN";

        await payfastService.WriteLedgerEntryAsync(new CreateGatewayLedgerEntry
        {
            OrderId = orderResult.Value.Id,
            PaymentId = paymentResult.Value.Id,
            MerchantPaymentId = payload.MerchantPaymentId!,
            PayfastPaymentId = payload.PaymentId,
            CustomerEmail = payload.EmailAddress,
            AmountFee = fee,
            AmountGross = gross,
            AmountNet = net,
            PaymentStatus = status,
        }, cancellationToken);

        if (status.Equals("COMPLETE", StringComparison.OrdinalIgnoreCase))
        {
            var ledgerWriteResult = await paymentService.WriteLedgerEntryAsync(new CreateLedgerEntry
            {
                OrderId = orderResult.Value.Id,
                PaymentId = paymentResult.Value.Id,
                PaymentGatewayReference = payload.MerchantPaymentId!,
                Status = LedgerStatuses.Completed,
                CustomerId = orderResult.Value.CustomerId,
            }, cancellationToken);

            if (ledgerWriteResult.IsFailed) throw new Exception("Failed to write ledger entry for payment confirmation.");

            var completePaymentResult = await paymentService.CompletePaymentAsync(paymentResult.Value.Id, PaymentStatuses.Paid, cancellationToken);
            if (completePaymentResult.IsFailed) throw new Exception("Failed to update payment status to 'Paid'.");

            var updateOrderResult = await orderService.UpdateOrderStatusAsync(orderResult.Value.Id, OrderStatus.Completed, cancellationToken);
            if (updateOrderResult.IsFailed) throw new Exception("Failed to update order status to 'Completed'.");

            logger.LogInformation("Order payment verified secure and cleared successfully.");
        }
        else
        {
            LedgerStatuses ledgerStatus = status.Equals("CANCELLED", StringComparison.OrdinalIgnoreCase)
                ? LedgerStatuses.Cancelled
                : LedgerStatuses.Failed;

            await paymentService.WriteLedgerEntryAsync(new CreateLedgerEntry
            {
                OrderId = orderResult.Value.Id,
                PaymentId = paymentResult.Value.Id,
                PaymentGatewayReference = payload.MerchantPaymentId!,
                Status = ledgerStatus,
                CustomerId = orderResult.Value.CustomerId,
            }, cancellationToken);

            logger.LogInformation("Webhook pipeline logged non-success entry to ledger with status: {Status}", status);
        }

        activity?.SetStatus(ActivityStatusCode.Ok);
    }
}