littleshop/LittleShop/Services/BTCPayServerService.cs

using BTCPayServer.Client;
using BTCPayServer.Client.Models;
using LittleShop.Enums;
using Newtonsoft.Json.Linq;

namespace LittleShop.Services;

public interface IBTCPayServerService
{
    Task<string> CreateInvoiceAsync(decimal amount, CryptoCurrency currency, string orderId, string? description = null);
    Task<InvoiceData?> GetInvoiceAsync(string invoiceId);
    Task<bool> ValidateWebhookAsync(string payload, string signature);
}

public class BTCPayServerService : IBTCPayServerService
{
    private readonly BTCPayServerClient _client;
    private readonly IConfiguration _configuration;
    private readonly ILogger<BTCPayServerService> _logger;
    private readonly string _storeId;
    private readonly string _webhookSecret;
    private readonly string _baseUrl;

    public BTCPayServerService(IConfiguration configuration, ILogger<BTCPayServerService> logger)
    {
        _configuration = configuration;
        _logger = logger;

        _baseUrl = _configuration["BTCPayServer:BaseUrl"] ?? throw new ArgumentException("BTCPayServer:BaseUrl not configured");
        var apiKey = _configuration["BTCPayServer:ApiKey"] ?? throw new ArgumentException("BTCPayServer:ApiKey not configured");
        _storeId = _configuration["BTCPayServer:StoreId"] ?? throw new ArgumentException("BTCPayServer:StoreId not configured");
        _webhookSecret = _configuration["BTCPayServer:WebhookSecret"] ?? "";

        _logger.LogInformation("Initializing BTCPay Server connection to {BaseUrl} with Store ID: {StoreId}", _baseUrl, _storeId);

        // Create HttpClient with certificate bypass for internal networks
        var httpClient = new HttpClient(new HttpClientHandler()
        {
            ServerCertificateCustomValidationCallback = (message, cert, chain, errors) => true
        });

        _client = new BTCPayServerClient(new Uri(_baseUrl), apiKey, httpClient);
    }

    public async Task<string> CreateInvoiceAsync(decimal amount, CryptoCurrency currency, string orderId, string? description = null)
    {
        var paymentMethod = GetPaymentMethod(currency);

        var metadata = new JObject
        {
            ["orderId"] = orderId,
            ["requestedCurrency"] = currency.ToString(),
            ["paymentMethod"] = paymentMethod
        };

        if (!string.IsNullOrEmpty(description))
        {
            metadata["itemDesc"] = description;
        }

        // Create invoice in GBP (fiat) - BTCPay will handle crypto conversion
        var request = new CreateInvoiceRequest
        {
            Amount = amount,
            Currency = "GBP", // Always use fiat currency for the amount
            Metadata = metadata,
            Checkout = new CreateInvoiceRequest.CheckoutOptions
            {
                Expiration = TimeSpan.FromHours(24),
                PaymentMethods = new[] { paymentMethod }, // Specify which crypto to accept
                DefaultPaymentMethod = paymentMethod
            }
        };

        try
        {
            _logger.LogDebug("Creating BTCPay invoice - Amount: {Amount} GBP, Payment Method: {PaymentMethod}, Order: {OrderId}",
                amount, paymentMethod, orderId);

            var invoice = await _client.CreateInvoice(_storeId, request);

            _logger.LogInformation("✅ Created BTCPay invoice {InvoiceId} for Order {OrderId} - Amount: {Amount} GBP, Method: {PaymentMethod}, Checkout: {CheckoutLink}",
                invoice.Id, orderId, amount, paymentMethod, invoice.CheckoutLink);

            return invoice.Id;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "❌ Failed to create BTCPay invoice - Amount: {Amount} GBP, Method: {PaymentMethod}, Store: {StoreId}, BaseUrl: {BaseUrl}",
                amount, paymentMethod, _storeId, _baseUrl);

            // Always throw - never generate fake invoices
            throw;
        }
    }

    public async Task<InvoiceData?> GetInvoiceAsync(string invoiceId)
    {
        try
        {
            return await _client.GetInvoice(_storeId, invoiceId);
        }
        catch
        {
            return null;
        }
    }

    public Task<bool> ValidateWebhookAsync(string payload, string signature)
    {
        try
        {
            // BTCPay Server uses HMAC-SHA256 with format "sha256=<hex>"
            if (!signature.StartsWith("sha256="))
            {
                return Task.FromResult(false);
            }

            var expectedHash = signature.Substring(7); // Remove "sha256=" prefix
            var secretBytes = System.Text.Encoding.UTF8.GetBytes(_webhookSecret);
            var payloadBytes = System.Text.Encoding.UTF8.GetBytes(payload);

            using var hmac = new System.Security.Cryptography.HMACSHA256(secretBytes);
            var computedHash = hmac.ComputeHash(payloadBytes);
            var computedHashHex = Convert.ToHexString(computedHash).ToLowerInvariant();

            return Task.FromResult(expectedHash.Equals(computedHashHex, StringComparison.OrdinalIgnoreCase));
        }
        catch
        {
            return Task.FromResult(false);
        }
    }

    private static string GetCurrencyCode(CryptoCurrency currency)
    {
        return currency switch
        {
            CryptoCurrency.BTC => "BTC",
            CryptoCurrency.XMR => "XMR", 
            CryptoCurrency.USDT => "USDT",
            CryptoCurrency.LTC => "LTC",
            CryptoCurrency.ETH => "ETH",
            CryptoCurrency.ZEC => "ZEC",
            CryptoCurrency.DASH => "DASH",
            CryptoCurrency.DOGE => "DOGE",
            _ => "BTC"
        };
    }

    private static string GetPaymentMethod(CryptoCurrency currency)
    {
        return currency switch
        {
            CryptoCurrency.BTC => "BTC",
            CryptoCurrency.XMR => "XMR",
            CryptoCurrency.USDT => "USDT_ETH", // USDT on Ethereum
            CryptoCurrency.LTC => "LTC",
            CryptoCurrency.ETH => "ETH",
            CryptoCurrency.ZEC => "ZEC",
            CryptoCurrency.DASH => "DASH", 
            CryptoCurrency.DOGE => "DOGE",
            _ => "BTC"
        };
    }
}