ppc_amnet/AMNet.Server/CardPresenter.cs

using System;
using System.Globalization;
using System.Linq;
using System.Threading;

namespace AMNet.Server;

/// <summary>
/// Represents a storage location to load/read cards from
/// </summary>
internal class CardPresenter
{
    private readonly Lock _cardLock = new();
    private StoredCard _currentCard;

    public record StoredCard(byte[] AccessCode, byte[] IDm, long ExpiresAt)
    {
        public bool Expired => Environment.TickCount64 >= ExpiresAt;

        public override string ToString() => FormatHexCode(AccessCode);
    }

    /// <summary>
    /// Returns the currently active card without clearing it
    /// </summary>
    public StoredCard PeekActiveCard()
    {
        lock (_cardLock)
        {
            return _currentCard;
        }
    }

    public StoredCard TakeActiveCard(bool? requireIDm = null)
    {
        lock (_cardLock)
        {
            // IDm and requireIDm are mutually exclusive
            if (_currentCard == null || (requireIDm.HasValue && (_currentCard.IDm != null) ^ requireIDm.Value))
            {
                return null;
            }

            var card = _currentCard;
            _currentCard = null;

            return card;
        }
    }

    /// <summary>
    /// Sets the card
    /// </summary>
    /// <param name="accessCode">The access code of the card to use</param>
    /// <param name="idmHex">The FeliCa card IDm, if a physical card was used</param>
    /// <param name="validFor">How long the card should be presented to the game for in milliseconds</param>
    /// <returns>Whether the card was set successfully</returns>
    public StoredCard SetCard(string accessCode, string idmHex, long validFor = 5000)
    {
        // ensure the matrix code is 20-digits long, otherwise pad with zeros
        var matrixCode = accessCode.Replace(" ", "").PadLeft(20, '0');
        var bytes = new byte[10];

        for (var i = 0; i < bytes.Length; i++)
        {
            var value = matrixCode.Substring(i * 2, 2);
            if (byte.TryParse(value, NumberStyles.HexNumber, CultureInfo.InvariantCulture, out var b))
            {
                bytes[i] = b;
            }
            else
            {
                return null;
            }
        }

        var idmBytes = !string.IsNullOrWhiteSpace(idmHex) && idmHex.Length <= 16 && idmHex.All(char.IsAsciiHexDigit) ? Convert.FromHexString(idmHex.PadLeft(16, '0')) : null;
        var card = new StoredCard(bytes, idmBytes, Environment.TickCount64 + validFor);

        lock (_cardLock)
        {
            _currentCard = card;
        }

        return card;
    }
    
    /// <summary>
    /// Formats a byte array as a hex string, inserting a space every 2 characters
    /// </summary>
    public static string FormatHexCode(byte[] code) => string.Join(" ", code.Chunk(2).Select(Convert.ToHexString));
}