using ProjectM.Simulation;
using Unity.Burst;
using Unity.Entities;
using Unity.NetCode;

namespace ProjectM.Server
{
    /// <summary>
    /// Server-authoritative expiry of TIMED <see cref="StatModifier"/>s. Each tick it walks every entity's
    /// server-only <see cref="TimedModifier"/> buffer; for any row whose <see cref="TimedModifier.UntilTick"/> has
    /// elapsed (wrap-safe <see cref="Unity.NetCode.NetworkTick.IsNewerThan"/> compare, never raw uint&lt;) it removes
    /// the matching StatModifier(s) by SourceId and the timed row. The shortened StatModifier [GhostField] buffer
    /// auto-replicates (OwnerSendType.All), so StatRecomputeSystem reverts the effective stat on both worlds with no
    /// change. Runs in the plain server <see cref="SimulationSystemGroup"/> (NOT the predicted loop) so it is applied
    /// exactly once and never double-removed on rollback; a DynamicBuffer mutation is not a structural change, so it
    /// is safe to mutate the iterated entity's own buffers in place.
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    [UpdateInGroup(typeof(SimulationSystemGroup))]
    public partial struct TimedModifierExpirySystem : ISystem
    {
        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            state.RequireForUpdate<NetworkTime>();
            state.RequireForUpdate(state.GetEntityQuery(ComponentType.ReadOnly<TimedModifier>()));
        }

        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            var serverTick = SystemAPI.GetSingleton<NetworkTime>().ServerTick;
            if (!serverTick.IsValid)
                return;

            foreach (var (timed, mods) in
                     SystemAPI.Query<DynamicBuffer<TimedModifier>, DynamicBuffer<StatModifier>>())
            {
                for (int i = timed.Length - 1; i >= 0; i--)
                {
                    uint until = timed[i].UntilTick;
                    if (until == 0)
                        continue; // inert (no expiry scheduled)

                    var untilTick = new NetworkTick(until);
                    if (untilTick.IsValid && untilTick.IsNewerThan(serverTick))
                        continue; // not yet due

                    TimedModifierUtil.RemoveBySourceId(mods, timed[i].SourceId);
                    timed.RemoveAtSwapBack(i);
                }
            }
        }
    }
}