namespace ProjectM.Simulation
{
    /// <summary>
    /// Pure, Burst-safe packing of the predicted-projectile classification key
    /// (<see cref="Projectile.SpawnId"/>). Layout: <c>owner(14) | socket(2) | fireCount(12) | fork(4)</c> = 32
    /// bits exact. Reserving 2 socket bits is the review's NP-1/RS-1/DB-3 fix: under the LANTERN 4-socket kit,
    /// two sockets firing the same-prefab projectile on ONE tick carry independent per-socket fire counts that
    /// are near-guaranteed equal early (both 0->1); without a socket discriminator their SpawnIds collide and
    /// <c>ProjectileClassificationSystem</c> cross-adopts one predicted entity and orphans the other. Fork keeps
    /// all 4 low bits (Phase-4 Fork mutation fans up to 8 shots). Extracted so the collision-free property is
    /// unit-tested independently of the netcode prediction context.
    /// </summary>
    public static class ProjectileSpawnId
    {
        public const int OwnerBits = 14;
        public const int SocketBits = 2;
        public const int FireCountBits = 12;
        public const int ForkBits = 4;

        /// <summary>Pack the classification key. Inputs are masked to their bit widths (wrap, not overflow).</summary>
        public static uint Pack(int netId, int socket, uint fireCount, int fork)
        {
            return ((((uint)netId) & 0x3FFFu) << (SocketBits + FireCountBits + ForkBits)) // owner -> bits 18..31
                 | (((uint)socket & 0x3u) << (FireCountBits + ForkBits))                  // socket -> bits 16..17
                 | ((fireCount & 0x0FFFu) << ForkBits)                                     // fireCount -> bits 4..15
                 | ((uint)fork & 0xFu);                                                    // fork -> bits 0..3
        }
    }
}