using System.Collections.Concurrent;
using Steamworks;

namespace SVSim.EmulatedEntrypoint.Services;

public class SteamSessionService : IDisposable
{
    private readonly ConcurrentDictionary<string, ulong> _validatedSessionTickets = new();
    private readonly object _initLock = new();
    private bool _steamInitialized;

    private const int ShadowVerseAppId = 453480;

    /// <summary>
    /// Validates if a given session ticket is valid, and matches up with the given steamid.
    /// </summary>
    /// <param name="ticket">the ticket, represented as a hexadecimal string</param>
    /// <param name="steamId">the steamid that should be associated with the ticket</param>
    /// <returns>whether the ticket is valid for the given steamid</returns>
    public bool IsTicketValidForUser(string ticket, ulong steamId)
    {
        if (string.IsNullOrEmpty(ticket))
        {
            // Caller already shouldn't pass null/empty here, but a misshaped request body
            // (e.g. wrong casing) used to NRE on the ConcurrentDictionary lookup below.
            // Fail cleanly so the auth pipeline returns 401 instead of crashing the request.
            return false;
        }

        if (_validatedSessionTickets.TryGetValue(ticket, out ulong storedSteamId))
        {
            return storedSteamId == steamId;
        }

        EnsureSteamInitialized();

        List<byte> ticketBytes = new List<byte>();
        for (int i = 0; i < ticket.Length; i += 2)
        {
            ticketBytes.Add(Convert.ToByte(ticket.Substring(i, 2), 16));
        }

        var steamCheckResults = SteamServer.BeginAuthSession(ticketBytes.ToArray(), new SteamId { Value = steamId });
        if (steamCheckResults)
        {
            _validatedSessionTickets.TryAdd(ticket, steamId);
        }

        return steamCheckResults;
    }

    private void EnsureSteamInitialized()
    {
        if (_steamInitialized) return;
        lock (_initLock)
        {
            if (_steamInitialized) return;
            SteamServer.Init(ShadowVerseAppId, new SteamServerInit
            {
                GamePort = default,
                QueryPort = default
            });
            _steamInitialized = true;
        }
    }

    public void Dispose()
    {
        if (_steamInitialized)
        {
            SteamServer.Shutdown();
        }
    }
}