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

namespace ProjectM.Server
{
    /// <summary>
    /// Server-authoritative EXPEDITION BOSS brain — the SOLE mover/attacker of <c>.WithAll&lt;EnemyTag, BossState&gt;()</c>
    /// (EnemyAISystem's Charger MOVE pass excludes it via <c>.WithNone&lt;BossState&gt;()</c>, so exactly one system
    /// writes the boss's Position/Rotation/AttackWindup — the sole-writer invariant). Runs SERVER-ONLY in the plain
    /// <see cref="SimulationSystemGroup"/> <c>[UpdateAfter(EnemyAISystem)]</c> (a linear chain, no sort cycle), once per
    /// tick (interpolated ghost, no rollback → no Simulate filter, no IsFirstTimeFullyPredictingTick).
    ///
    /// v2 boss = a real fight (operator-locked): chase the nearest living expedition player, then a telegraphed radial
    /// SLAM — the client danger cue rides the replicated <see cref="AttackWindup"/> [GhostField] (CombatFeedbackSystem
    /// draws a boss-scale ring). At/below <see cref="Tuning.BossPhase2HealthFraction"/> HP it enters phase two: faster,
    /// slams more often, and periodically summons swarmer adds. The boss does NOT lunge (it keeps its baked LungeState
    /// idle, so EnemyAISystem's IsLunging derive sees UntilTick==0 → bit off, harmless). Knockback-immune (the stamp
    /// sites skip BossState; this system also clears any residual so nothing else can shove it). Summoned adds go
    /// through <see cref="ZoneEnemySpawnUtil"/> so they carry the SAME ZoneEnemyTag/RoomTag/RegionTag stack the
    /// room-clear gate + teardown depend on (dropping one would leak adds or clear the room early). All ticks route
    /// through <c>TickUtil.NonZero</c> and compare with <see cref="NetworkTick"/> only (never raw uint).
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    [UpdateInGroup(typeof(SimulationSystemGroup))]
    [UpdateAfter(typeof(EnemyAISystem))]
    public partial struct BossAISystem : ISystem
    {
        EntityQuery m_Bosses;
        EntityQuery m_ZoneEnemies;

        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            state.RequireForUpdate<NetworkTime>();
            m_Bosses = state.GetEntityQuery(ComponentType.ReadOnly<EnemyTag>(), ComponentType.ReadOnly<BossState>());
            state.RequireForUpdate(m_Bosses);
            m_ZoneEnemies = state.GetEntityQuery(ComponentType.ReadOnly<ZoneEnemyTag>());
        }

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

            // Living EXPEDITION players — the boss's only valid targets. Snapshot once (stable query order).
            var playerEntities = new NativeList<Entity>(Allocator.Temp);
            var playerPositions = new NativeList<float3>(Allocator.Temp);
            foreach (var (xform, health, region, entity) in
                     SystemAPI.Query<RefRO<LocalTransform>, RefRO<Health>, RefRO<RegionTag>>()
                         .WithAll<PlayerTag>().WithEntityAccess())
            {
                if (health.ValueRO.Current <= 0f || region.ValueRO.Region != RegionId.Expedition)
                    continue;
                playerEntities.Add(entity);
                playerPositions.Add(xform.ValueRO.Position);
            }

            // Collide-and-slide setup (mirrors EnemyAISystem).
            bool havePhysics = SystemAPI.TryGetSingleton<PhysicsWorldSingleton>(out var physics);
            uint envMask = SystemAPI.TryGetSingleton<WorldCollisionConfig>(out var worldCol) ? worldCol.EnvironmentMask : 0u;
            uint sweepMask = envMask | worldCol.StructureMask;
            var envFilter = new CollisionFilter { BelongsTo = ~0u, CollidesWith = sweepMask, GroupIndex = 0 };
            bool sweep = havePhysics && sweepMask != 0u;
            const float SweepRadius = 0.8f; // the boss is a big body

            int liveZone = m_ZoneEnemies.CalculateEntityCount();

            // Summon resources (phase two): the swarmer prefab + baked transform + the current room byte.
            bool haveDirector = SystemAPI.TryGetSingletonEntity<ZoneEnemyDirector>(out var directorEntity);
            Entity swarmerPrefab = Entity.Null;
            LocalTransform swarmerBaked = default;
            if (haveDirector)
            {
                var prefabs = SystemAPI.GetBuffer<ZoneEnemyPrefab>(directorEntity);
                if (prefabs.Length > ZoneEnemyMath.KindSwarmer)
                {
                    swarmerPrefab = prefabs[ZoneEnemyMath.KindSwarmer].Prefab;
                    if (swarmerPrefab != Entity.Null)
                        swarmerBaked = state.EntityManager.GetComponentData<LocalTransform>(swarmerPrefab);
                }
            }
            byte roomByte = SystemAPI.TryGetSingleton<RunInfo>(out var runInfo) ? (byte)(runInfo.CurrentRoom & 0xFF) : (byte)0;

            var ecb = new EntityCommandBuffer(Allocator.Temp);

            foreach (var (xform, stats, health, boss, windup, knockback) in
                     SystemAPI.Query<RefRW<LocalTransform>, RefRO<EnemyStats>, RefRO<Health>, RefRW<BossState>,
                             RefRW<AttackWindup>, RefRW<KnockbackState>>()
                         .WithAll<EnemyTag, BossState>())
            {
                float3 pos = xform.ValueRO.Position;

                // Knockback-immune: never recoil (A4). Zero any residual so a competing stamp can't shove the boss.
                if (knockback.ValueRO.UntilTick != 0u) knockback.ValueRW.UntilTick = 0u;

                // Phase from the boss's own Current vs (server-side, real ×BossHealthMultiplier) Max.
                float maxHp = math.max(1f, health.ValueRO.Max);
                byte phase = health.ValueRO.Current <= maxHp * Tuning.BossPhase2HealthFraction ? (byte)2 : (byte)1;
                boss.ValueRW.Phase = phase;

                // Target: nearest living expedition player.
                int tgt = -1; float bestSq = float.MaxValue;
                for (int i = 0; i < playerPositions.Length; i++)
                {
                    float d = math.distancesq(pos, playerPositions[i]);
                    if (d < bestSq) { bestSq = d; tgt = i; }
                }
                if (tgt < 0)
                    continue; // no valid target -> idle (InRoom-abort handles a fully-empty expedition)
                float3 targetPos = playerPositions[tgt];

                // Face the target (planar) at all times, incl. while telegraphing.
                float3 toTarget = targetPos - pos; toTarget.y = 0f;
                if (math.lengthsq(toTarget) > 1e-6f)
                    xform.ValueRW.Rotation = quaternion.LookRotationSafe(math.normalize(toTarget), math.up());

                // --- SLAM in progress: root (the telegraph) until it lands, then AoE all players in the ring. ---
                uint windRaw = windup.ValueRO.WindUpUntilTick;
                if (windRaw != 0u)
                {
                    var wt = new NetworkTick(windRaw);
                    if (!(wt.IsValid && wt.IsNewerThan(serverTick)))
                    {
                        float slamSq = Tuning.BossSlamRadius * Tuning.BossSlamRadius;
                        for (int i = 0; i < playerEntities.Length; i++)
                        {
                            if (math.distancesq(pos, playerPositions[i]) > slamSq)
                                continue;
                            ecb.AppendToBuffer(playerEntities[i], new DamageEvent
                            {
                                Amount = Tuning.BossSlamDamage,
                                SourceNetworkId = -1, // environment / boss, not a player
                                SourceTick = TickUtil.NonZero(now),
                            });
                        }
                        windup.ValueRW.WindUpUntilTick = 0u;
                        uint baseCd = Tuning.BossSlamCooldownTicks;
                        uint cd = phase == 2
                            ? (uint)math.max(1f, baseCd * Tuning.BossPhase2SlamCooldownMult)
                            : baseCd;
                        boss.ValueRW.SlamReadyTick = TickUtil.NonZero(now + cd);
                    }
                    continue; // rooted while winding up (the tell); rotation already written above
                }

                // --- Chase (no active slam). ---
                float speed = stats.ValueRO.MoveSpeed * (phase == 2 ? Tuning.BossPhase2SpeedMult : 1f);
                float stopDist = stats.ValueRO.AttackRange * 0.9f;
                float3 vel = EnemyAIMath.SeekVelocity(pos, targetPos, speed, stopDist);
                float3 newPos = pos + vel * dt; newPos.y = pos.y;
                if (sweep) newPos = EnemyMoveUtil.SweptMove(in physics, pos, newPos, SweepRadius, envFilter);
                xform.ValueRW.Position = newPos;

                // Slam gate: ready + a player inside (ring + a small lead) -> commit a telegraphed slam.
                bool slamReady = boss.ValueRO.SlamReadyTick == 0u
                                 || !new NetworkTick(boss.ValueRO.SlamReadyTick).IsNewerThan(serverTick);
                float lead = Tuning.BossSlamRadius + 1.5f;
                if (slamReady && math.distancesq(newPos, targetPos) <= lead * lead)
                    windup.ValueRW.WindUpUntilTick = TickUtil.NonZero(now + Tuning.BossSlamWindupTicks);

                // Summon (phase two only): ready + under the live cap + a swarmer prefab wired.
                if (phase == 2 && swarmerPrefab != Entity.Null && liveZone < Tuning.BossSummonLiveCap)
                {
                    bool summonReady = boss.ValueRO.SummonReadyTick == 0u
                                       || !new NetworkTick(boss.ValueRO.SummonReadyTick).IsNewerThan(serverTick);
                    if (summonReady)
                    {
                        int toSpawn = math.min(Tuning.BossSummonCount, Tuning.BossSummonLiveCap - liveZone);
                        for (int k = 0; k < toSpawn; k++)
                        {
                            float3 spawnPos = EnemyAIMath.ClusterOffset(newPos, k, math.max(1, toSpawn), 2.5f);
                            spawnPos.y = newPos.y;
                            ZoneEnemySpawnUtil.Spawn(ecb, swarmerPrefab, in swarmerBaked, spawnPos, RegionId.Expedition, roomByte);
                            liveZone++;
                        }
                        boss.ValueRW.SummonReadyTick = TickUtil.NonZero(now + Tuning.BossSummonCooldownTicks);
                    }
                }
            }

            ecb.Playback(state.EntityManager);
            ecb.Dispose();
            playerEntities.Dispose();
            playerPositions.Dispose();
        }
    }
}