using ProjectM.Simulation;
using Unity.Burst;
using Unity.Entities;
using Unity.Mathematics;
using Unity.Transforms;

namespace ProjectM.Server
{
    /// <summary>
    /// MC-2 — integrates hostile Spitter projectiles (<see cref="EnemyProjectile"/>) server-only in the plain
    /// <see cref="SimulationSystemGroup"/> (the spits are ownerless INTERPOLATED ghosts, not predicted — like the
    /// Husks that fire them). Advances each spit along its locked Direction at Speed*dt, accumulates
    /// DistanceTravelled, and STORES <see cref="EnemyProjectile.LastStep"/> = Speed*dt so
    /// <see cref="EnemyProjectileDamageSystem"/> can rebuild the exact swept segment it traversed this tick
    /// (cur - Direction*LastStep) WITHOUT re-reading a delta in that separate system (the DR-018 swept-tunnelling
    /// discipline — a fresh delta in the damage pass is the trap). Ordered <c>[UpdateAfter(EnemyAISystem)]</c> (the
    /// spawner) so a spit moves the same tick it is born. Writes LocalTransform (replicated via the stock variant);
    /// structural-free. dt is the server fixed step here, exactly as <see cref="EnemyAISystem"/> reads it.
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    [UpdateInGroup(typeof(SimulationSystemGroup))]
    [UpdateAfter(typeof(EnemyAISystem))]
    public partial struct EnemyProjectileMoveSystem : ISystem
    {
        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            state.RequireForUpdate<EnemyProjectile>();
        }

        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            float dt = SystemAPI.Time.DeltaTime; // server fixed step in the plain group, same as EnemyAISystem
            foreach (var (xform, proj) in SystemAPI.Query<RefRW<LocalTransform>, RefRW<EnemyProjectile>>())
            {
                float step = proj.ValueRO.Speed * dt;
                float3 dir = new float3(proj.ValueRO.Direction.x, 0f, proj.ValueRO.Direction.y);
                float3 from = xform.ValueRO.Position;
                float3 pos = from + dir * step;
                pos.y = from.y; // hold the movement plane
                xform.ValueRW.Position = pos;
                proj.ValueRW.LastStep = step;
                proj.ValueRW.DistanceTravelled = proj.ValueRO.DistanceTravelled + step;
            }
        }
    }
}