shoc-backend/SeaHaven.Services/Interfaces/ISessionStampCache.cs

namespace SeaHaven.Services.Interfaces
{
    /// <summary>
    /// The process-wide cache of expected session stamp values, keyed by user id.
    /// Registered as a singleton.
    /// </summary>
    public interface ISessionStampCache
    {
        /// <summary>Changes on every removal; a read that spans one is not cached.</summary>
        long Generation { get; }

        /// <summary>True with the cached value (null: the account matches nothing) while it is fresh.</summary>
        bool TryGet(string userId, out string? expected);

        /// <summary>Caches a value read at <paramref name="generation"/>, unless a removal has happened since.</summary>
        void Set(string userId, string? expected, long generation);

        void Remove(string userId);
    }
}