namespace Supercell.Laser.Server.SCID
{
    using System.Collections.Concurrent;
    using System.Security.Cryptography;
    using System.Text;

    internal sealed class SCIDSession
    {
        public byte[] PinHash;
        public DateTime ExpiresAt;
        public int AttemptsLeft;
        public bool Registration;
        public bool Validated;
    }

    internal static class SCIDSessions
    {
        private static readonly ConcurrentDictionary<string, SCIDSession> Sessions = new(StringComparer.OrdinalIgnoreCase);

        public static string Create(string identity, bool registration)
        {
            Cleanup();
            string pin = RandomNumberGenerator.GetInt32(100000, 1000000).ToString();
            Sessions[identity] = new SCIDSession
            {
                PinHash = Hash(pin),
                ExpiresAt = DateTime.UtcNow.AddMinutes(5),
                AttemptsLeft = 5,
                Registration = registration
            };
            return pin;
        }

        public static bool Validate(string identity, string pin, bool registration)
        {
            if (!Sessions.TryGetValue(identity, out SCIDSession session) ||
                session.ExpiresAt <= DateTime.UtcNow || session.Registration != registration)
            {
                Sessions.TryRemove(identity, out _);
                return false;
            }

            lock (session)
            {
                byte[] pinHash = Hash(pin ?? string.Empty);
                if (session.AttemptsLeft <= 0 || !CryptographicOperations.FixedTimeEquals(session.PinHash, pinHash))
                {
                    session.AttemptsLeft--;
                    if (session.AttemptsLeft <= 0)
                        Sessions.TryRemove(identity, out _);
                    return false;
                }

                session.Validated = true;
                return true;
            }
        }

        public static bool IsValidated(string identity, bool registration)
        {
            return Sessions.TryGetValue(identity, out SCIDSession session) &&
                   session.ExpiresAt > DateTime.UtcNow &&
                   session.Registration == registration && session.Validated;
        }

        public static void Remove(string identity)
        {
            Sessions.TryRemove(identity, out _);
        }

        private static void Cleanup()
        {
            DateTime now = DateTime.UtcNow;
            foreach (var session in Sessions)
            {
                if (session.Value.ExpiresAt <= now)
                    Sessions.TryRemove(session.Key, out _);
            }
        }

        private static byte[] Hash(string value)
        {
            return SHA256.HashData(Encoding.UTF8.GetBytes(value));
        }
    }
}