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 player-cast zone driver (Vortex / LightZone — the LANTERN Aoe/zone Sparks). Borrows the
    /// <see cref="GeyserEruptSystem"/> skeleton — the INVERTED invalid-tick guard (a born-0 <see cref="ZoneEffect.NextTick"/>
    /// is lazy-stamped born-correct, never storm-fires) and the <c>= now + period</c> reschedule — but is
    /// ENEMY-ONLY (NO friendly fire), stamps <see cref="DamageEvent.SourceNetworkId"/> = the caster's NetworkId
    /// (kills credit the caster — NOT the -1 environment convention), and has NO region gate (a no-world gym).
    /// A <see cref="ZoneEffectFlag.Vortex"/> zone ALSO writes a gentle inward <see cref="KnockbackState"/> every
    /// tick (EnemyAISystem drives it, sole Position writer), so runs BEFORE EnemyAISystem. DestroyEntity when
    /// <see cref="ZoneEffect.ExpireTick"/> elapses (server-authoritative ghost despawn). Ticks via
    /// <see cref="TickUtil.NonZero"/>; compared with <see cref="NetworkTick"/> only.
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    [UpdateInGroup(typeof(SimulationSystemGroup))]
    [UpdateAfter(typeof(PredictedSimulationSystemGroup))]
    [UpdateBefore(typeof(EnemyAISystem))]
    public partial struct ZonePulseSystem : ISystem
    {
        const uint k_PulsePeriodTicks = 30u;   // damage cadence (~0.5s at 60 ticks/sec)
        const float k_VortexPullSpeed = 4f;     // gentle inward drift for a Vortex (world units/sec)
        const float k_VortexDeadzoneSq = 0.25f; // don't re-aim (or NaN) an enemy already at the zone centre

        ComponentLookup<KnockbackState> m_KnockbackLookup;
        ComponentLookup<BossState> m_BossLookup;

        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            state.RequireForUpdate<NetworkTime>();
            state.RequireForUpdate<ZoneEffect>();
            m_KnockbackLookup = state.GetComponentLookup<KnockbackState>(isReadOnly: false);
            m_BossLookup = state.GetComponentLookup<BossState>(isReadOnly: true);
        }

        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            var serverTick = SystemAPI.GetSingleton<NetworkTime>().ServerTick;
            if (!serverTick.IsValid) return;
            uint now = serverTick.TickIndexForValidTick;
            uint stamp = TickUtil.NonZero(now);
            uint reschedule = TickUtil.NonZero(now + k_PulsePeriodTicks);
            m_KnockbackLookup.Update(ref state);
            m_BossLookup.Update(ref state);

            // Living enemies once this tick (entities + positions; stable query order).
            var enemyEntities = new NativeList<Entity>(Allocator.Temp);
            var enemyPositions = new NativeList<float3>(Allocator.Temp);
            foreach (var (lt, hp, e) in
                     SystemAPI.Query<RefRO<LocalTransform>, RefRO<Health>>()
                         .WithAll<EnemyTag>().WithNone<Dying>().WithEntityAccess())
            {
                if (hp.ValueRO.Current <= 0f) continue;
                enemyEntities.Add(e);
                enemyPositions.Add(lt.ValueRO.Position);
            }

            var ecb = new EntityCommandBuffer(Allocator.Temp);

            foreach (var (zone, lt, zoneEntity) in
                     SystemAPI.Query<RefRW<ZoneEffect>, RefRO<LocalTransform>>().WithEntityAccess())
            {
                var ze = zone.ValueRO;

                // Lifetime: despawn the zone ghost when the leash elapses (server-authoritative).
                if (ze.ExpireTick != 0u && !new NetworkTick(ze.ExpireTick).IsNewerThan(serverTick))
                {
                    ecb.DestroyEntity(zoneEntity);
                    continue;
                }

                float3 center = lt.ValueRO.Position;
                float radiusSq = ze.Radius * ze.Radius;
                bool vortex = (ze.Flags & ZoneEffectFlag.Vortex) != 0;

                // Vortex pull: gentle inward drift EVERY tick (re-stamped, one tick; EnemyAISystem applies it).
                if (vortex)
                {
                    for (int i = 0; i < enemyEntities.Length; i++)
                    {
                        float2 to = center.xz - enemyPositions[i].xz;
                        float d2 = math.lengthsq(to);
                        if (d2 > radiusSq || d2 <= k_VortexDeadzoneSq) continue;
                        var e = enemyEntities[i];
                        if (!m_KnockbackLookup.HasComponent(e) || m_BossLookup.HasComponent(e)) continue;
                        m_KnockbackLookup[e] = new KnockbackState
                        {
                            Dir = math.normalize(to),
                            Speed = k_VortexPullSpeed,
                            UntilTick = TickUtil.NonZero(now + 1u),
                        };
                    }
                }

                // Damage pulse: INVERTED invalid-tick guard (a born-0 NextTick lazy-stamps born-correct, never storms).
                uint next = ze.NextTick;
                if (next == 0u || !new NetworkTick(next).IsValid)
                {
                    zone.ValueRW.NextTick = reschedule;
                    continue;
                }
                if (new NetworkTick(next).IsNewerThan(serverTick)) continue; // still counting down

                for (int i = 0; i < enemyEntities.Length; i++)
                {
                    if (math.distancesq(enemyPositions[i].xz, center.xz) > radiusSq) continue;
                    ecb.AppendToBuffer(enemyEntities[i], new DamageEvent
                    {
                        Amount = ze.DamagePerPulse,
                        SourceNetworkId = ze.CasterNetworkId,
                        SourceTick = stamp,
                    });
                }
                zone.ValueRW.NextTick = reschedule;
            }

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