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 Husk AI: each tick every Husk seeks the nearest LIVING player and strikes on
    /// contact. Husks are OWNERLESS INTERPOLATED ghosts (not predicted), so this runs SERVER-ONLY in the plain
    /// <see cref="SimulationSystemGroup"/> — writing <see cref="LocalTransform"/> directly (replicated to clients
    /// by the stock LocalTransform default variant; no hand-written <c>[GhostField]</c>). Ordered
    /// <c>[UpdateAfter(PredictedSimulationSystemGroup)]</c> (the predicted group is OrderFirst, so UpdateBefore is ignored) so a contact <see cref="DamageEvent"/> appended this
    /// tick is drained the following tick by <see cref="HealthApplyDamageSystem"/> (which runs inside the predicted
    /// group on the server). No <c>Simulate</c> filter: interpolated ghosts are not predicted and the server has
    /// no rollback, so every Husk advances exactly once per tick. Movement/attack math is the pure, deterministic
    /// <see cref="EnemyAIMath"/>; server fixed-step <c>SystemAPI.Time.DeltaTime</c> is correct here (not the
    /// rollback loop). Structural-free: the only deferred op is appending to the player's DamageEvent buffer.
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    [UpdateInGroup(typeof(SimulationSystemGroup))]
    [UpdateAfter(typeof(PredictedSimulationSystemGroup))]
    public partial struct EnemyAISystem : ISystem
    {

        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            state.RequireForUpdate<NetworkTime>();
            state.RequireForUpdate(state.GetEntityQuery(ComponentType.ReadOnly<EnemyTag>()));

        }

        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            // Snapshot living player targets once this tick (stable query order).
            var playerEntities = new NativeList<Entity>(Allocator.Temp);
            var playerPositions = new NativeList<float3>(Allocator.Temp);
            var playerRegions = new NativeList<byte>(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)
                    continue; // don't chase or strike a corpse
                playerEntities.Add(entity);
                playerPositions.Add(xform.ValueRO.Position);
                playerRegions.Add(region.ValueRO.Region);
            }

            // EB-1 fortress aggro: also snapshot live structures (Turret/Wall/Pylon AND the Fabricator all carry
            // Health since the DR-032 parity fix; the query keys on it). Snapshot ABOVE the early-return so Husks keep razing
            // the base even with every player dead/away (the locked 'push for structures' fork).
            var structureEntities = new NativeList<Entity>(Allocator.Temp);
            var structurePositions = new NativeList<float3>(Allocator.Temp);
            var structureRegions = new NativeList<byte>(Allocator.Temp);
            // Structures were deleted with the shell (2026-08-07 audit purge), so the raze-target snapshot is
            // empty. The lists stay so the aggro selection below keeps one code path; drop them when the
            // LANTERN buildables land and give enemies something to attack again.
            foreach (var (sx, sh, sr, se) in
                     SystemAPI.Query<RefRO<LocalTransform>, RefRO<Health>, RefRO<RegionTag>>()
                         .WithAll<Destructible>()
                         .WithEntityAccess())
            {
                if (sh.ValueRO.Current <= 0f)
                    continue; // skip a structure already at 0 (pending destroy this tick)
                structureEntities.Add(se);
                structurePositions.Add(sx.ValueRO.Position);
                structureRegions.Add(sr.ValueRO.Region);
            }
            // LANTERN decoy-wisp aggro: a decoy draws Husks like a fake target. Region-agnostic gather (gym).
            var decoyEntities = new NativeList<Entity>(Allocator.Temp);
            var decoyPositions = new NativeList<float3>(Allocator.Temp);
            foreach (var (dx, dh, de) in
                     SystemAPI.Query<RefRO<LocalTransform>, RefRO<Health>>()
                         .WithAll<DecoyTag>().WithEntityAccess())
            {
                if (dh.ValueRO.Current <= 0f) continue; // a spent decoy is being despawned; don't aggro a corpse
                decoyEntities.Add(de);
                decoyPositions.Add(dx.ValueRO.Position);
            }

            if (playerEntities.Length == 0 && structureEntities.Length == 0 && decoyEntities.Length == 0)
            {
                playerEntities.Dispose();
                playerPositions.Dispose();
                playerRegions.Dispose();
                structureEntities.Dispose();
                structurePositions.Dispose();
                structureRegions.Dispose();
                decoyEntities.Dispose();
                decoyPositions.Dispose();
                return;
            }

            float dt = SystemAPI.Time.DeltaTime;
            var serverTick = SystemAPI.GetSingleton<NetworkTime>().ServerTick;
            uint now = serverTick.TickIndexForValidTick;
            float decoyAggroSq = 30f * 30f; // LANTERN decoy-wisp aggro radius (world units, squared)
            // Live feel knobs (MC-0): one read, guarded at use. Server-only — clients never simulate enemies.
            var tune = SystemAPI.TryGetSingleton<TuningConfig>(out var tcfg) ? tcfg : TuningConfig.Defaults();
            float structAggro = math.max(0f, tune.StructureAggroWeight);
            var ecb = new EntityCommandBuffer(Allocator.Temp);
            bool havePhysics = SystemAPI.TryGetSingleton<PhysicsWorldSingleton>(out var physics);
            uint envMask = SystemAPI.TryGetSingleton<WorldCollisionConfig>(out var worldCol) ? worldCol.EnvironmentMask : 0u;
            uint sweepMask = envMask | worldCol.StructureMask; // DR-042 C5: also collide enemies against player-built walls
            var envFilter = new CollisionFilter { BelongsTo = ~0u, CollidesWith = sweepMask, GroupIndex = 0 };
            bool sweep = havePhysics && sweepMask != 0u;
            const float SweepRadius = 0.5f; // collide-and-slide sphere radius for Husk movement

            // Anti-stuck (1/2): DEPENETRATE every living enemy out of any env/cover it overlaps BEFORE seeking, so a
            // Husk spawned inside or shoved into a cover rock isn't frozen by a zero-fraction sweep (the sweep cannot
            // move a mover that STARTS already penetrating). One point-distance query per living enemy (<=~15/room).
            // Boss excluded (BossAISystem owns it at a larger radius).
            if (sweep)
            {
                foreach (var depenXform in SystemAPI.Query<RefRW<LocalTransform>>()
                             .WithAll<EnemyTag>().WithNone<Dying>().WithNone<TargetDummyTag>())
                    depenXform.ValueRW.Position = EnemyMoveUtil.Depenetrate(in physics, depenXform.ValueRO.Position, SweepRadius, envFilter);
            }

            foreach (var (xform, stats, cooldown, knockback, windup, region) in
                     SystemAPI.Query<RefRW<LocalTransform>, RefRO<EnemyStats>, RefRW<EnemyAttackCooldown>,
                             RefRW<KnockbackState>, RefRW<AttackWindup>, RefRO<RegionTag>>()
                         .WithAll<EnemyTag>().WithNone<Dying>().WithNone<TargetDummyTag>())
            {
                float3 pos = xform.ValueRO.Position;
                byte huskRegion = region.ValueRO.Region;

                // Knockback overrides seek/strike for its window — EnemyAISystem stays the SOLE writer of Position.
                var kb = knockback.ValueRO;
                if (kb.UntilTick != 0)
                {
                    var kbTick = new NetworkTick(kb.UntilTick);
                    if (kbTick.IsValid && kbTick.IsNewerThan(serverTick))
                    {
                        float3 kpos = pos + new float3(kb.Dir.x, 0f, kb.Dir.y) * (kb.Speed * dt);
                        kpos.y = pos.y;
                        if (sweep)
                            kpos = SweptMove(in physics, pos, kpos, SweepRadius, envFilter);
                        xform.ValueRW.Position = kpos;
                        if (kb.Speed >= tune.StaggerKnockbackSpeed)
                            windup.ValueRW.WindUpUntilTick = 0; // B2 poise: only a HEAVY hit interrupts; a light hit nudges while the wind-up keeps counting
                        continue; // recoiling: skip seek + strike this tick
                    }
                    knockback.ValueRW.UntilTick = 0; // window elapsed
                }

                // EB-1 fortress aggro: nearest of players (weight 1) + structures (StructureAggroWeight) — a wall/
                // turret is the preferred target unless a player is in the way (closer after weighting).
                EnemyAIMath.PickWeightedNearest(pos, playerPositions, playerRegions, structurePositions, structureRegions, huskRegion, structAggro, out bool tgtIsStruct, out int tgtIdx);
                // Decoy aggro (LANTERN): a decoy-wisp within range is the PREFERRED target -- overrides player/structure/core.
                int decoyIdx = -1;
                float decoyBestSq = decoyAggroSq;
                for (int di = 0; di < decoyPositions.Length; di++)
                {
                    float dsq = math.distancesq(pos.xz, decoyPositions[di].xz);
                    if (dsq <= decoyBestSq) { decoyBestSq = dsq; decoyIdx = di; }
                }
                Entity targetEntity;
                float3 targetPos;
                if (decoyIdx >= 0)
                {
                    targetEntity = decoyEntities[decoyIdx];
                    targetPos = decoyPositions[decoyIdx];
                }
                else
                {
                    if (tgtIdx < 0)
                        continue; // no decoy, no player/structure -> nothing to seek
                    targetEntity = tgtIsStruct ? structureEntities[tgtIdx] : playerEntities[tgtIdx];
                    targetPos = tgtIsStruct ? structurePositions[tgtIdx] : playerPositions[tgtIdx];
                }

                // Seek: stop just inside strike range so the Husk holds position to attack.
                float stopDistance = stats.ValueRO.AttackRange * 0.9f;
                float3 vel = EnemyAIMath.SeekVelocity(pos, targetPos, stats.ValueRO.MoveSpeed, stopDistance);
                float3 newPos = pos + vel * dt;
                newPos.y = pos.y; // hold the movement plane
                if (sweep)
                    newPos = SweptMove(in physics, pos, newPos, SweepRadius, envFilter);
                xform.ValueRW.Position = newPos;

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

                // Two-phase strike with a telegraph wind-up: commit a wind-up when first in-range + cooldown-ready,
                // then strike when it elapses. WindUpUntilTick is a [GhostField] so the client can cue the ~0.3s
                // tell; leaving range mid-windup cancels it. Tuning.AttackWindupTicks = 0/1 -> near-instant (legacy).
                bool inRange = EnemyAIMath.InAttackRange(pos, targetPos, stats.ValueRO.AttackRange);
                uint windRaw = windup.ValueRO.WindUpUntilTick;

                if (windRaw != 0)
                {
                    // B1 commitment: once inside the final ~30% of the wind-up the strike is COMMITTED — leaving
                    // range no longer cancels it (a last-instant step-back won't save you; dash i-frames or an early
                    // exit will). A committed swing the player dodged out of WHIFFS at elapse (still burns cooldown)
                    // -> the punish window, mirroring the Charger. Grunts (speed < player) can now actually land on a
                    // lingering player instead of being trivially kited (readable-but-fair).
                    var windTick = new NetworkTick(windRaw);
                    bool elapsed = !(windTick.IsValid && windTick.IsNewerThan(serverTick));
                    int remain = windTick.IsValid ? windTick.TicksSince(serverTick) : 0;
                    uint gTotal = (uint)math.max(1f, tune.GruntWindupTicks);
                    bool committed = remain > 0 && remain <= (int)(gTotal * 0.3f);
                    if (!elapsed)
                    {
                        if (!inRange && !committed)
                            windup.ValueRW.WindUpUntilTick = 0; // left range early -> cancel the wind-up
                    }
                    else
                    {
                        if (inRange && targetEntity != Entity.Null) ecb.AppendToBuffer(targetEntity, new DamageEvent
                        {
                            Amount = stats.ValueRO.AttackDamage,
                            SourceNetworkId = -1, // environment / Husk, not a player
                            SourceTick = TickUtil.NonZero(now),
                        });
                        uint cooldownTicks = (uint)math.max(1, stats.ValueRO.AttackCooldownTicks);
                        cooldown.ValueRW.NextAttackTick = TickUtil.NonZero(now + cooldownTicks);
                        windup.ValueRW.WindUpUntilTick = 0;
                    }
                }
                else if (inRange)
                {
                    uint nextRaw = cooldown.ValueRO.NextAttackTick;
                    bool ready = true;
                    if (nextRaw != 0)
                    {
                        var nextTick = new NetworkTick(nextRaw);
                        if (nextTick.IsValid && nextTick.IsNewerThan(serverTick))
                            ready = false;
                    }
                    if (ready)
                    {
                        uint windupTicks = (uint)math.max(1f, tune.GruntWindupTicks);
                        windup.ValueRW.WindUpUntilTick = TickUtil.NonZero(now + windupTicks);
                    }
                }
            }

            // --- Charger / Spitter / IsLunging passes DELETED 2026-08-07 (audit purge).
            // ChargerAuthoring, SpitterAuthoring and SwarmerAuthoring were attached to ZERO prefabs, so
            // LungeState / SpitterState / SwarmerTag were never baked and these three passes could not match a
            // single chunk at runtime — ~272 lines of Bursted code plus 734 lines of green tests certifying an
            // escalation curve that always resolved to Grunt. Recover from git if the lunge/spit behaviours are
            // wanted; the LANTERN bestiary reintroduces variety through the CreatureKit path instead.


            // --- Phase 1 B1: SEPARATION (soft-collision) so hordes stop interpenetrating. Lives INSIDE
            // EnemyAISystem (the sole enemy-Position writer; BossAISystem runs after and re-owns the boss).
            // Pairwise among LIVING enemies (MaxAlive <= ~14 + boss -> O(n^2) is trivial); an enemy mid-knockback
            // or mid-lunge keeps its committed motion (immovable this tick) but still pushes neighbours away, and
            // the BOSS is never pushed (knockback-immune identity). Enemies also yield a SMALL personal radius
            // around each player (below melee range so grunts can still strike - review B1-1). Displacement goes
            // through the same swept move so separation cannot shove anything through walls.
            {
                var sepEnt = new NativeList<Entity>(Allocator.Temp);
                var sepPos = new NativeList<float3>(Allocator.Temp);
                var sepRad = new NativeList<float>(Allocator.Temp);
                var sepMov = new NativeList<bool>(Allocator.Temp);
                foreach (var (sxf, shr, se) in SystemAPI.Query<RefRO<LocalTransform>, RefRO<HitRadius>>()
                             .WithAll<EnemyTag>().WithNone<Dying>().WithEntityAccess())
                {
                    bool movable = true;
                    if (movable && SystemAPI.HasComponent<KnockbackState>(se))
                    {
                        var k = SystemAPI.GetComponent<KnockbackState>(se);
                        if (k.UntilTick != 0 && new NetworkTick(k.UntilTick).IsNewerThan(serverTick)) movable = false;
                    }
                    sepEnt.Add(se); sepPos.Add(sxf.ValueRO.Position); sepRad.Add(shr.ValueRO.Value); sepMov.Add(movable);
                }
                float sepMaxStep = math.max(0f, tune.SeparationMaxSpeed) * dt;
                for (int i = 0; i < sepEnt.Length && sepMaxStep > 0f; i++)
                {
                    if (!sepMov[i]) continue;
                    float3 pi = sepPos[i];
                    float2 push = float2.zero;
                    for (int j = 0; j < sepEnt.Length; j++)
                    {
                        if (j == i) continue;
                        float2 d = pi.xz - sepPos[j].xz;
                        float want = (sepRad[i] + sepRad[j]) * 0.9f;
                        float distSq = math.lengthsq(d);
                        if (want <= 0f || distSq >= want * want) continue;
                        float dist = math.sqrt(distSq);
                        // Exact stacks de-overlap deterministically by index (golden angle), never randomly.
                        float2 dir = dist > 1e-4f ? d / dist : new float2(math.sin(i * 2.399963f), math.cos(i * 2.399963f));
                        push += dir * (want - dist) * 0.5f;
                    }
                    for (int pj = 0; pj < playerPositions.Length; pj++)
                    {
                        float2 d = pi.xz - playerPositions[pj].xz;
                        float want = sepRad[i] + 0.35f; // small: never blocks strike range or the Spitter cornered-hold
                        float distSq = math.lengthsq(d);
                        if (distSq >= want * want) continue;
                        float dist = math.sqrt(distSq);
                        float2 dir = dist > 1e-4f ? d / dist : new float2(1f, 0f);
                        push += dir * (want - dist);
                    }
                    if (math.lengthsq(push) < 1e-8f) continue;
                    float pushLen = math.length(push);
                    if (pushLen > sepMaxStep) push *= sepMaxStep / pushLen;
                    float3 sepTarget = pi + new float3(push.x, 0f, push.y);
                    sepTarget.y = pi.y;
                    if (sweep) sepTarget = SweptMove(in physics, pi, sepTarget, SweepRadius, envFilter);
                    var sepXf = SystemAPI.GetComponentRW<LocalTransform>(sepEnt[i]);
                    sepXf.ValueRW.Position = sepTarget;
                }
                sepEnt.Dispose(); sepPos.Dispose(); sepRad.Dispose(); sepMov.Dispose();
            }

            // Anti-stuck (2/2): the GUARANTEED backstop. An enemy that WANTS to close on its target (outside attack
            // range, not knocked/lunging/staggered) but hasn't gained ground on it for StuckUnstickTicks is phase-
            // nudged toward the nearest target (collide-and-slide bypassed) until it escapes -> a room can never
            // soft-lock on one Husk wedged in geometry the reactive slide can't solve. Progress is measured as
            // distance CLOSED toward the target (not raw displacement) so the separation jiggle can't mask a stuck
            // Husk. Server-only; EnemyNavState is not replicated. Spitters hold at range by design (excluded); the
            // boss is driven by BossAISystem (excluded).
            {
                const float StuckMinProgressPerTick = 0.02f;
                const uint  StuckUnstickTicks = 90u;   // ~1.5s of no ground gained before the nudge triggers
                const uint  NudgeBurstTicks = 45u;     // ~0.75s of phasing toward the target per trigger
                const float UnstickNudgeSpeed = 4.5f;  // units/s while phase-nudging out of geometry
                float nudgeStep = UnstickNudgeSpeed * dt;
                foreach (var (nxform, nstats, nav, nregion, nent) in
                         SystemAPI.Query<RefRW<LocalTransform>, RefRO<EnemyStats>, RefRW<EnemyNavState>, RefRO<RegionTag>>()
                             .WithAll<EnemyTag>().WithNone<Dying>().WithNone<TargetDummyTag>().WithEntityAccess())
                {
                    float3 npos = nxform.ValueRO.Position;
                    byte nRegion = nregion.ValueRO.Region;

                    bool committed = false;
                    if (SystemAPI.HasComponent<KnockbackState>(nent))
                    {
                        var k = SystemAPI.GetComponent<KnockbackState>(nent);
                        committed |= k.UntilTick != 0 && new NetworkTick(k.UntilTick).IsNewerThan(serverTick);
                    }

                    EnemyAIMath.PickWeightedNearest(npos, playerPositions, playerRegions, structurePositions, structureRegions, nRegion, structAggro, out bool nIsStruct, out int nIdx);
                    bool hasTarget = nIdx >= 0;
                    float3 nTarget = nIdx < 0 ? npos : (nIsStruct ? structurePositions[nIdx] : playerPositions[nIdx]);
                    bool wantsToClose = hasTarget && !committed
                        && math.distance(npos.xz, nTarget.xz) > nstats.ValueRO.AttackRange * 1.15f;

                    bool nudging = nav.ValueRO.NudgeUntilTick != 0 && new NetworkTick(nav.ValueRO.NudgeUntilTick).IsNewerThan(serverTick);
                    if (nudging)
                    {
                        if (wantsToClose)
                        {
                            float3 toT = nTarget - npos; toT.y = 0f;
                            float l2 = math.lengthsq(toT);
                            if (l2 > 1e-6f)
                            {
                                float3 step = math.normalize(toT) * math.min(nudgeStep, math.sqrt(l2));
                                float3 np = npos + step; np.y = npos.y;
                                nxform.ValueRW.Position = np;
                                nav.ValueRW.LastPos = np;
                                continue;
                            }
                        }
                        nav.ValueRW.NudgeUntilTick = 0; // reached range / lost target -> stop nudging
                    }

                    if (!wantsToClose)
                    {
                        nav.ValueRW.StuckTicks = 0u;
                        nav.ValueRW.LastPos = npos;
                        continue;
                    }

                    float progressToward = math.distance(nav.ValueRO.LastPos.xz, nTarget.xz) - math.distance(npos.xz, nTarget.xz);
                    uint st = progressToward < StuckMinProgressPerTick ? nav.ValueRO.StuckTicks + 1u : 0u;
                    nav.ValueRW.LastPos = npos;
                    if (st >= StuckUnstickTicks)
                    {
                        // COVER-AWARE (destructible-cover review wf_e14dd739-069 HIGH): if what blocks this enemy
                        // is a LIVE cover GHOST (BlightClutter carrier), do NOT phase-nudge — cover must genuinely
                        // hold until the player breaks it. No soft-lock is possible: the blocker is destructible,
                        // and the counter stays primed so any OTHER wedge (static geometry) still nudges next check.
                        bool blockedByCover = false;
                        if (havePhysics)
                        {
                            float3 toTgt = nTarget - npos; toTgt.y = 0f;
                            float tl = math.length(toTgt);
                            if (tl > 1e-4f && physics.CollisionWorld.SphereCast(
                                    npos, 0.35f, toTgt / tl, math.min(1.8f, tl), out var coverHit, envFilter))
                                blockedByCover = SystemAPI.HasComponent<BlightClutter>(coverHit.Entity);
                        }
                        if (!blockedByCover)
                        {
                            nav.ValueRW.NudgeUntilTick = TickUtil.NonZero(now + NudgeBurstTicks);
                            st = 0u;
                        }
                    }
                    nav.ValueRW.StuckTicks = st;
                }
            }


            ecb.Playback(state.EntityManager);

            ecb.Dispose();
            playerEntities.Dispose();
            playerPositions.Dispose();
            playerRegions.Dispose();
            structureEntities.Dispose();
            structurePositions.Dispose();
            structureRegions.Dispose();
            decoyEntities.Dispose();
            decoyPositions.Dispose();
        }

        // Swept collide-and-slide for server-authoritative enemy movement — delegates to the shared
        // EnemyMoveUtil.SweptMove (extracted so BossAISystem reuses ONE collide-and-slide impl; a fix reaches both).
        // Kept as a private wrapper so this file's many call sites read unchanged.
        static float3 SweptMove(in PhysicsWorldSingleton physics, float3 from, float3 to, float radius, CollisionFilter filter)
            => EnemyMoveUtil.SweptMove(in physics, from, to, radius, filter);
    }
}