step3/api/QuestionsApi/Services/StripeDonationGateway.cs

using Stripe;
using Stripe.Checkout;

namespace QuestionsApi.Services;

public sealed record StripeCheckoutResult(string SessionId, string CheckoutUrl);

public interface IStripeDonationGateway
{
    Task<StripeCheckoutResult> CreateCheckoutAsync(string donationId, long amountCents, CancellationToken cancellationToken);
}

public sealed class StripeDonationGateway(IConfiguration configuration) : IStripeDonationGateway
{
    public async Task<StripeCheckoutResult> CreateCheckoutAsync(string donationId, long amountCents, CancellationToken cancellationToken)
    {
        var secretKey = configuration["Stripe:SecretKey"];
        if (string.IsNullOrWhiteSpace(secretKey)) throw new InvalidOperationException("Stripe secret key is not configured.");
        var successUrl = configuration["Stripe:SuccessUrl"]
            ?? "https://doctor.ranaze.com/donation-complete.html?session_id={CHECKOUT_SESSION_ID}";
        var cancelUrl = configuration["Stripe:CancelUrl"] ?? "https://doctor.ranaze.com/donation-canceled.html";
        var client = new StripeClient(secretKey);
        var service = new SessionService(client);
        var metadata = new Dictionary<string, string> { ["donation_id"] = donationId };
        var session = await service.CreateAsync(new SessionCreateOptions
        {
            Mode = "payment",
            SuccessUrl = successUrl,
            CancelUrl = cancelUrl,
            ClientReferenceId = donationId,
            CustomerCreation = "always",
            BillingAddressCollection = "auto",
            Metadata = metadata,
            PaymentIntentData = new SessionPaymentIntentDataOptions { Metadata = metadata },
            LineItems =
            [
                new SessionLineItemOptions
                {
                    Quantity = 1,
                    PriceData = new SessionLineItemPriceDataOptions
                    {
                        Currency = "usd",
                        UnitAmount = amountCents,
                        ProductData = new SessionLineItemPriceDataProductDataOptions
                        {
                            Name = "Support MedMind",
                            Description = "One-time contribution supporting MedMind development and medical education content."
                        }
                    }
                }
            ]
        }, null, cancellationToken);
        if (string.IsNullOrWhiteSpace(session.Id) || string.IsNullOrWhiteSpace(session.Url))
            throw new InvalidOperationException("Stripe did not return a checkout URL.");
        return new StripeCheckoutResult(session.Id, session.Url);
    }
}