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>
    /// Phase 1.7 "Blade Dash" boon (<see cref="BoonFlag.DashTrail"/>): while a player is inside its dash blink window,
    /// living enemies within <see cref="k_Radius"/> of the player take damage — one hit per enemy per dash. SERVER-ONLY
    /// (enemies are interpolated ghosts the client never predicts — mirrors the melee cleave / cone / projectile-damage
    /// pattern), inside the predicted group after <see cref="DashSystem"/> (dash state committed) and before
    /// <c>HealthApplyDamageSystem</c> (the DamageEvent drains the same tick). Enemies carry no <c>DashState</c>, so the
    /// dash-i-frame negation branch in HealthApplyDamageSystem is skipped — harmless.
    ///
    /// Dedup is keyed to <see cref="DashState.StartTick"/> (which is <c>TickUtil.NonZero(now)</c> on every dash and has
    /// NO reliable clear edge on a release server): <see cref="DashTrailState.Hit"/> is cleared whenever the current
    /// StartTick differs from <see cref="DashTrailState.LastStartTick"/>. Server-only ⇒ no rollback, so persisting the
    /// accumulator across ticks is safe. A per-tick radius test (run every blink tick) approximates the swept path; the
    /// per-tick dash step (&lt;~0.6u) is well inside the radius, so a thin enemy is not tunnelled. Hit-set overflow stops
    /// adding (a possible re-hit on a very crowded dash — accepted v1 cap).
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    [UpdateInGroup(typeof(PredictedSimulationSystemGroup))]
    [UpdateAfter(typeof(DashSystem))]
    [UpdateBefore(typeof(HealthApplyDamageSystem))]
    public partial struct DashTrailDamageSystem : ISystem
    {
        const float k_Radius = 1.6f;   // planar hit radius around the dashing player (tunable)
        const float k_Damage = 12f;    // per-enemy damage for a dash pass (tunable)

        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            state.RequireForUpdate<NetworkTime>();
            state.RequireForUpdate<DashTrailState>();
        }

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

            // Snapshot living enemies once (positions + radii + entities), stable query order.
            var enemyEntities = new NativeList<Entity>(Allocator.Temp);
            var enemyPositions = new NativeList<float3>(Allocator.Temp);
            var enemyRadii = new NativeList<float>(Allocator.Temp);
            foreach (var (tx, hr, hp, te) in
                     SystemAPI.Query<RefRO<LocalTransform>, RefRO<HitRadius>, RefRO<Health>>()
                         .WithAll<EnemyTag>().WithNone<Dying>().WithEntityAccess())
            {
                if (hp.ValueRO.Current <= 0f) continue;
                enemyEntities.Add(te);
                enemyPositions.Add(tx.ValueRO.Position);
                enemyRadii.Add(hr.ValueRO.Value);
            }

            if (enemyEntities.Length == 0)
            {
                enemyEntities.Dispose(); enemyPositions.Dispose(); enemyRadii.Dispose();
                return;
            }

            uint stamp = TickUtil.NonZero(serverTick.TickIndexForValidTick);
            var ecb = new EntityCommandBuffer(Allocator.Temp);

            foreach (var (xform, dash, trail, owner, fx) in
                     SystemAPI.Query<RefRO<LocalTransform>, RefRO<DashState>, RefRW<DashTrailState>,
                             RefRO<GhostOwner>, RefRO<BoonEffects>>()
                         .WithAll<PlayerTag, Simulate>())
            {
                if ((fx.ValueRO.Flags & BoonFlag.DashTrail) == 0)
                    continue;

                uint startRaw = dash.ValueRO.StartTick;
                if (startRaw == 0u)
                    continue; // never dashed

                // Inside the blink (i-frame) window [StartTick, IFrameUntilTick)?
                var startTick = new NetworkTick(startRaw);
                var untilTick = new NetworkTick(dash.ValueRO.IFrameUntilTick);
                bool dashing = startTick.IsValid && untilTick.IsValid
                    && !startTick.IsNewerThan(serverTick) && untilTick.IsNewerThan(serverTick);
                if (!dashing)
                    continue;

                // New dash → reset the per-dash hit set (StartTick changes every dash; no reliable DashState clear).
                if (trail.ValueRO.LastStartTick != startRaw)
                {
                    trail.ValueRW.Hit.Clear();
                    trail.ValueRW.LastStartTick = startRaw;
                }

                float3 p = xform.ValueRO.Position;
                int ownerId = owner.ValueRO.NetworkId;
                for (int i = 0; i < enemyEntities.Length; i++)
                {
                    var enemy = enemyEntities[i];
                    if (HitContains(trail.ValueRO, enemy))
                        continue;
                    float2 d = new float2(enemyPositions[i].x - p.x, enemyPositions[i].z - p.z);
                    float reach = k_Radius + enemyRadii[i];
                    if (math.lengthsq(d) > reach * reach)
                        continue;

                    if (trail.ValueRO.Hit.Length >= trail.ValueRO.Hit.Capacity) break; // hit-cap: never damage an enemy we can't record (else re-hit every tick)
                    ecb.AppendToBuffer(enemy, new DamageEvent
                    {
                        Amount = k_Damage,
                        SourceNetworkId = ownerId, // a real player id (legit Charger whiff-punish credit)
                        SourceTick = stamp,
                    });
                    if (trail.ValueRO.Hit.Length < trail.ValueRO.Hit.Capacity)
                        trail.ValueRW.Hit.Add(enemy);
                }
            }

            ecb.Playback(state.EntityManager);
            ecb.Dispose();
            enemyEntities.Dispose();
            enemyPositions.Dispose();
            enemyRadii.Dispose();
        }

        static bool HitContains(in DashTrailState trail, Entity e)
        {
            for (int i = 0; i < trail.Hit.Length; i++)
                if (trail.Hit[i] == e) return true;
            return false;
        }
    }
}