AfRApay/AfRApay.FTM/Program.cs

using System.CommandLine;
using PCSC;
using PCSC.Monitoring;
using PCSC.Iso7816;

const int defaultAmount = 150;

var rootCommand = new RootCommand("Fancy Test Machine for AfRApay");

var listReadersOption = new Option<bool>("--list-readers", "List card readers and exit");
rootCommand.Add(listReadersOption);

var webAddrOption = new Option<Uri>("--web-addr", "Base URL for AfRApay.Web");
webAddrOption.SetDefaultValue(new Uri("http://127.0.0.1:5296"));
rootCommand.Add(webAddrOption);

rootCommand.SetHandler((listReaders, webAddr) => {
    using var context = ContextFactory.Instance.Establish(SCardScope.System);
    // Ignore Yubikeys.
    var readerNames = context.GetReaders()
                             .Where((readerName) => !readerName.Contains("Yubico"))
                             .ToArray();

    // We need at least one card reader or this won't work!
    if (readerNames.Length == 0) {
        Console.Error.WriteLine("Error: no card reader detected");
        Environment.Exit(1);
    }

    // If --list-readers is passed, list readers and exit.
    if (listReaders) {
        Console.Error.WriteLine("----------- Connected Readers ----------");
        foreach (var name in readerNames) {
            Console.WriteLine(name);
        }
        Console.Error.WriteLine("----------------------------------------");
        Environment.Exit(0);
    }

    // Setup!
    using HttpClient httpClient = new();
    httpClient.BaseAddress = webAddr;

    var     state  = TerminalState.Debit;
    decimal amount = defaultAmount;

    Console.Error.WriteLine("----------------------------------------");
    Console.Error.WriteLine("--- AfRApay FTM - Fancy Test Machine ---");
    Console.Error.WriteLine("----------------------------------------");
    Console.Error.WriteLine();
    Console.Error.WriteLine("AfRApay.Web: {0}", httpClient.BaseAddress);
    Console.Error.WriteLine();
    Console.Error.WriteLine("Hotkeys (case insensitive):");
    Console.Error.WriteLine("    [-] Debit (default)");
    Console.Error.WriteLine("    [+] Credit");
    Console.Error.WriteLine("    [=] Set amount (default: €{0:C})", amount/100M);
    Console.Error.WriteLine();
    Console.Error.WriteLine("    [B] Balance query");
    Console.Error.WriteLine("    [L] Link card (initiate from web UI)");
    Console.Error.WriteLine("  [Esc] Cancel, reset state and amount");
    Console.Error.WriteLine();
    Console.Error.WriteLine("----------------------------------------");

    // Listen for events on all connected readers.
    using var monitor = MonitorFactory.Instance.Create(SCardScope.System);
    monitor.Initialized += (_, args) => Console.WriteLine("[ Reader Initialized: {0} ]", args.ReaderName);
    monitor.MonitorException += (_, args) => {
        Console.Error.WriteLine("! ERROR: {0}", args);
        Environment.Exit(1);
    };
    monitor.StatusChanged += (_, args) => Console.WriteLine("~ {0} -> {1}", args.LastState, args.NewState);
    monitor.CardInserted += (_, args) => {
        Console.WriteLine("> TAP: {0}", Convert.ToHexString(args.Atr));
        var reader = new IsoReader(context, args.ReaderName, SCardShareMode.Shared, SCardProtocol.Any);
        HandleTap(reader, httpClient, state, amount);
    };
    monitor.CardRemoved += (_, _) => {
        Console.WriteLine("< OFF");
        Console.WriteLine(); // Write a blank line between card taps for readability.
    };
    Console.WriteLine("[ Starting... ]");
    monitor.Start(readerNames);

    // Handle hotkeys.
    while (true) {
        var key       = Console.ReadKey();
        var dontPrint = false;
        switch (key.Key) {
            case ConsoleKey.Subtract:
            case ConsoleKey.OemMinus:
                state = TerminalState.Debit;
                break;
            case ConsoleKey.Add:
            case ConsoleKey.OemPlus:
                state = TerminalState.Credit;
                break;
            case 0 when key.KeyChar == '=':
                Console.Error.Write("\b => ENTER AMOUNT: ");
                amount = Math.Abs(int.Parse(Console.ReadLine() ?? "150".Trim()));
                break;
            case ConsoleKey.L:
                state = TerminalState.Link;
                break;
            case ConsoleKey.B:
                state = TerminalState.Balance;
                break;
            case ConsoleKey.Escape:
                state  = TerminalState.Debit;
                amount = defaultAmount;
                break;
            default:
                Console.Error.Write("\b");
                dontPrint = true;
                break;
        }
            
        if (dontPrint) {
            // Invalid input, just ignore it.
        } else if (state is TerminalState.Debit or TerminalState.Credit) {
            Console.Error.WriteLine("\b => {0}: €{1}", state, amount);
        } else {
            Console.Error.WriteLine("\b => {0}", state);
        }
    }

    // ReSharper disable once FunctionNeverReturns
}, listReadersOption, webAddrOption);

return await rootCommand.InvokeAsync(args);

// Queries a card for data when one is tapped.
static async void HandleTap(IIsoReader reader, HttpClient httpClient, TerminalState state, decimal amount) {
    // Send a PCSC pseudo-APDU to query the ISO 14443 UID.
    var uidRsp = reader.Transmit(new CommandApdu(IsoCase.Case2Short, SCardProtocol.Any) {
        CLA = 0xFF,
        Instruction = InstructionCode.GetData,
        P1 = 0x00,
        P2 = 0x00,
    });
    if (!IsSucc(uidRsp)) {
        Console.Error.WriteLine("--> Card Error: SW1={0} SW2={1}", (SW1Code)uidRsp.SW1, uidRsp.SW2);
        return;
    }
    var uid = uidRsp.GetData();
    Console.WriteLine("  UID: {0}", Convert.ToHexString(uid));

    // Query the backend, which endpoint depending on terminal state.
    switch (state) {
        case TerminalState.Debit:
        case TerminalState.Credit:
            var finalAmount = Math.Abs(amount) * (state == TerminalState.Debit ? -1 : 1);
            var idempotencyKey = new byte[16];
            Random.Shared.NextBytes(idempotencyKey);
            var ik = Convert.ToHexString(idempotencyKey);
            await CallPut(httpClient, $"/api/card/{Convert.ToHexString(uid)}/transaction/{ik}?amount={finalAmount}");
            break;
        case TerminalState.Link:
            await CallGet(httpClient, $"/api/card/{Convert.ToHexString(uid)}/link");
            break;
        case TerminalState.Balance:
            await CallGet(httpClient, $"/api/card/{Convert.ToHexString(uid)}/balance");
            break;
        default:
            Console.Error.WriteLine("UNKNOWN TERMINAL STATE: {0}", state);
            break;
    }
}

// Was the command successful?
static bool IsSucc(Response rsp) {
    return rsp is { SW1: (byte)SW1Code.Normal, SW2: 0x00 };
}

static async Task<string> CallGet(HttpClient client, string path) {
    Console.WriteLine("  -> GET {0}", path);
    var rsp = await client.GetStringAsync(path);
    Console.WriteLine("  <- {0}", rsp);
    return rsp;
}

static async Task<string> CallPut(HttpClient client, string path) {
    Console.WriteLine("  -> PUT {0}", path);
    var rsp = await client.PutAsync(path, new StringContent("")).Result.Content.ReadAsStringAsync();
    Console.WriteLine("  <- {0}", rsp);
    return rsp;
}

// Terminal State.
internal enum TerminalState {
    Debit,
    Credit,
    Link,
    Balance,
};