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

namespace ProjectM.Server
{
    /// <summary>
    /// Server-only turret fire (hitscan) — EnemyAISystem reversed. Snapshots living Husks once (entity, planar
    /// pos, region); each turret picks the nearest Husk in ITS region within Range and, on a NetworkTick
    /// cooldown stored in <see cref="PlacedStructure.NextTick"/>, appends a direct <c>DamageEvent</c>
    /// (SourceNetworkId=-1) to it. Reuses HealthApplyDamageSystem (already destroys EnemyTag at HP&lt;=0) — no
    /// projectile, no tunnelling, no friendly-fire. Plain server SimulationSystemGroup
    /// <c>[UpdateAfter(PredictedSimulationSystemGroup)]</c> (the predicted group is OrderFirst → UpdateBefore is
    /// ignored); the appended DamageEvent drains next tick (~16ms), consistent with EnemyAISystem. Self-gates:
    /// Husks only exist during the Defend wave.
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    [UpdateInGroup(typeof(SimulationSystemGroup))]
    [UpdateAfter(typeof(PredictedSimulationSystemGroup))]
    public partial struct TurretFireSystem : ISystem
    {
        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            state.RequireForUpdate<NetworkTime>();
            state.RequireForUpdate(state.GetEntityQuery(ComponentType.ReadOnly<Turret>()));
        }

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

            var huskEntities = new NativeList<Entity>(Allocator.Temp);
            var huskPos = new NativeList<float2>(Allocator.Temp);
            var huskRegion = new NativeList<byte>(Allocator.Temp);
            foreach (var (xform, health, region, e) in
                     SystemAPI.Query<RefRO<LocalTransform>, RefRO<Health>, RefRO<RegionTag>>()
                         .WithAll<EnemyTag>().WithEntityAccess())
            {
                if (health.ValueRO.Current <= 0f)
                    continue;
                huskEntities.Add(e);
                huskPos.Add(xform.ValueRO.Position.xz);
                huskRegion.Add(region.ValueRO.Region);
            }

            if (huskEntities.Length == 0)
            {
                huskEntities.Dispose(); huskPos.Dispose(); huskRegion.Dispose();
                return;
            }

            var ecb = new EntityCommandBuffer(Allocator.Temp);

            foreach (var (ps, turret, xform, region) in
                     SystemAPI.Query<RefRW<PlacedStructure>, RefRO<Turret>, RefRO<LocalTransform>, RefRO<RegionTag>>())
            {
                uint nextRaw = ps.ValueRO.NextTick;
                if (nextRaw != 0)
                {
                    var nextTick = new NetworkTick(nextRaw);
                    if (nextTick.IsValid && nextTick.IsNewerThan(serverTick))
                        continue; // still cooling down
                }

                float2 tp = xform.ValueRO.Position.xz;
                byte treg = region.ValueRO.Region;
                float rangeSq = turret.ValueRO.Range * turret.ValueRO.Range;

                int best = -1;
                float bestSq = float.MaxValue;
                for (int i = 0; i < huskEntities.Length; i++)
                {
                    if (huskRegion[i] != treg)
                        continue;
                    float sq = math.distancesq(huskPos[i], tp);
                    if (sq <= rangeSq && sq < bestSq)
                    {
                        bestSq = sq;
                        best = i;
                    }
                }

                if (best >= 0)
                {
                    ecb.AppendToBuffer(huskEntities[best], new DamageEvent
                    {
                        Amount = turret.ValueRO.Damage,
                        SourceNetworkId = -1,
                    });
                    uint cd = (uint)math.max(1, turret.ValueRO.CooldownTicks);
                    ps.ValueRW.NextTick = TickUtil.NonZero(now + cd);
                }
            }

            ecb.Playback(state.EntityManager);
            ecb.Dispose();
            huskEntities.Dispose(); huskPos.Dispose(); huskRegion.Dispose();
        }
    }
}