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 expedition zone-enemy director: while a player is OUT in the expedition region and the base is in
    /// <see cref="CyclePhase.Calm"/>, it seeds and drip-spawns one epoch-seeded combat wave around the expedition
    /// origin. The wave size + grunt/charger composition is pure <see cref="ZoneEnemyMath"/> of the
    /// <see cref="CycleRuntime.ExpeditionEpoch"/> (grunt-heavy -&gt; charger-heavy as the epoch climbs), spawned one
    /// every <see cref="ZoneEnemyDirector.SpawnIntervalTicks"/> at a deterministic ring, capped at
    /// <see cref="ZoneEnemyDirector.MaxAlive"/> concurrent (the v1 ghost-relevancy budget). Each enemy is the
    /// existing Husk ghost prefab + <c>RegionTag{Expedition}</c> + <see cref="ZoneEnemyTag"/>, so it reuses the whole
    /// combat/readability/AI stack (the per-region AI filter keeps it seeking the expedition player only). When the
    /// wave is fully spawned and every zone enemy is dead, it marks <see cref="CycleRuntime.ClearedThisEpoch"/> once —
    /// the gate's once-per-epoch Ore reward reads that on the player's return.
    ///
    /// DR-042 C7b: it ALSO writes the replicated <see cref="ExpeditionObjective"/> summary every tick, ABOVE the
    /// presence early-return (snapshot-above-early-return), so the client HUD's "enemies remaining / cleared" readout
    /// never freezes stale even when nobody is out.
    ///
    /// Ordering: <c>[UpdateAfter(ExpeditionFieldSystem)]</c> ONLY. ExpeditionFieldSystem is itself
    /// <c>[UpdateAfter(CyclePhaseSystem)]</c>, so ALSO declaring <c>[UpdateBefore(CyclePhaseSystem)]</c> here (as the
    /// v1 plan first sketched) would close a CyclePhase-&gt;Field-&gt;Zone-&gt;CyclePhase sort cycle that throws at Play
    /// world creation and is invisible to EditMode. Running after the field manager also reads the freshly-bumped
    /// epoch + current phase. Zone enemies are interpolated ghosts, moved server-only — no prediction.
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    [UpdateInGroup(typeof(SimulationSystemGroup))]
    [UpdateAfter(typeof(ExpeditionFieldSystem))]
    public partial struct ZoneEnemyDirectorSystem : ISystem
    {
        EntityQuery m_ZoneEnemies;

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

            // Per-player presence: the SPAWNER only runs while someone is OUT in the expedition (mirrors
            // ExpeditionFieldSystem). The objective readout below is written FIRST, every tick, even when nobody's out.
            int expeditionPlayers = 0;
            foreach (var region in SystemAPI.Query<RefRO<RegionTag>>().WithAll<PlayerTag>())
                if (region.ValueRO.Region == RegionId.Expedition)
                    expeditionPlayers++;

            var directorEntity = SystemAPI.GetSingletonEntity<ZoneEnemyDirector>();
            var dir = SystemAPI.GetComponent<ZoneEnemyDirector>(directorEntity);
            var zs = SystemAPI.GetComponent<ZoneEnemyState>(directorEntity);

            var cycleEntity = SystemAPI.GetSingletonEntity<CycleState>();
            var cycle = SystemAPI.GetComponent<CycleState>(cycleEntity);
            var runtime = SystemAPI.GetComponent<CycleRuntime>(cycleEntity);
            int epoch = runtime.ExpeditionEpoch;

            int aliveZone = m_ZoneEnemies.CalculateEntityCount();

            // DR-042 C7b: write the REPLICATED objective summary FIRST, above the early-returns (snapshot-above-
            // early-return) so the HUD never freezes stale. Rides the untagged CycleDirector ghost (cross-region safe).
            if (SystemAPI.HasComponent<ExpeditionObjective>(cycleEntity))
            {
                byte objState;
                short objRemaining;
                if (runtime.ClearedThisEpoch != 0 && runtime.LastRewardedEpoch != runtime.ExpeditionEpoch)
                {
                    objState = ExpeditionObjectiveState.Cleared; // cleared but not yet claimed -> "return to claim"
                    objRemaining = 0;
                }
                else if (expeditionPlayers > 0 && (aliveZone > 0 || zs.RemainingToSpawn > 0))
                {
                    objState = ExpeditionObjectiveState.Active;
                    objRemaining = (short)math.min(aliveZone + zs.RemainingToSpawn, short.MaxValue);
                }
                else
                {
                    objState = ExpeditionObjectiveState.Idle;
                    objRemaining = 0;
                }
                SystemAPI.SetComponent(cycleEntity, new ExpeditionObjective { State = objState, Remaining = objRemaining });
            }

            if (expeditionPlayers == 0)
                return; // nobody out there: the field manager owns teardown, the spawner does nothing

            var prefabs = SystemAPI.GetBuffer<ZoneEnemyPrefab>(directorEntity);
            if (prefabs.Length == 0)
                return;

            // MC-2: build the 4-type weighted mix band from the director's baked weights (shared math with the base
            // siege). GruntsPerWave/ChargersPerWave are the Grunt/Charger base counts.
            var bands = new MixBands
            {
                GruntBase = dir.GruntsPerWave,
                ChargerBase = dir.ChargersPerWave,
                SpitterBase = dir.SpitterBase,
                SwarmerSlotBase = dir.SwarmerSlotBase,
                ChargerPerEpoch = dir.ChargerPerEpoch,
                SpitterPerEpoch = dir.SpitterPerEpoch,
                SwarmerSlotPerEpoch = dir.SwarmerSlotPerEpoch,
                SwarmerPackPerEpoch = dir.SwarmerPackPerEpoch,
            };

            // (Re)seed this epoch's wave once — its OWN counter (in SLOTS; a swarmer slot is one pack).
            if (zs.SeededEpoch != epoch)
            {
                zs.SeededEpoch = epoch;
                zs.SpawnCounter = 0;
                zs.RemainingToSpawn = ZoneEnemyMath.WaveSlots(epoch, bands);
                zs.NextSpawnTick = TickUtil.NonZero(now); // first slot this tick
            }

            if (zs.RemainingToSpawn > 0)
            {
                // Spawn only in Calm (a base Siege pauses the expedition wave), one SLOT per cadence, under the cap.
                bool calm = cycle.Phase == CyclePhase.Calm;
                bool dueNow = zs.NextSpawnTick == 0 || !new NetworkTick(zs.NextSpawnTick).IsNewerThan(serverTick);
                if (calm && dueNow)
                {
                    int slot = (int)zs.SpawnCounter;
                    byte kind = ZoneEnemyMath.KindForSlot(epoch, slot, bands);
                    int packSize = kind == ZoneEnemyMath.KindSwarmer
                        ? ZoneEnemyMath.PackSizeForSlot(epoch, slot, bands, dir.SwarmerPackSize) : 1;

                    // MaxAlive counts ENTITIES; spawn the whole pack only if it fits (else WAIT — don't consume the slot).
                    if (aliveZone + packSize <= math.max(1, dir.MaxAlive))
                    {
                        float3 baseCenter = new float3(0f, 1f, 0f);
                        if (SystemAPI.TryGetSingleton<BaseAnchor>(out var anchor))
                            baseCenter = BaseGridMath.PlotCenter(anchor);
                        float3 origin = RegionMath.RegionOrigin(RegionId.Expedition, baseCenter);
                        float3 center = EnemyAIMath.RingPosition(origin, slot, math.max(1, dir.RingSlots), dir.RingRadius);
                        center.y = origin.y;

                        int prefabIdx = kind;
                        if (prefabIdx >= prefabs.Length) prefabIdx = 0; // 4-entry buffer expected; clamp defensively
                        var prefab = prefabs[prefabIdx].Prefab;
                        // Preserve the prefab's baked Scale ([GhostField]) — FromPosition would reset Scale->1.
                        var baked = state.EntityManager.GetComponentData<LocalTransform>(prefab);

                        var ecb = new EntityCommandBuffer(Allocator.Temp);
                        for (int k = 0; k < packSize; k++)
                        {
                            float3 pos = packSize > 1
                                ? EnemyAIMath.ClusterOffset(center, k, packSize, dir.ClusterTightRadius) : center;
                            pos.y = origin.y;
                            var enemy = ecb.Instantiate(prefab);
                            ecb.SetComponent(enemy, baked.WithPosition(pos));
                            ecb.AddComponent(enemy, new RegionTag { Region = RegionId.Expedition });
                            ecb.AddComponent<ZoneEnemyTag>(enemy);
                        }
                        ecb.Playback(state.EntityManager);
                        ecb.Dispose();

                        zs.SpawnCounter += 1;   // ONE slot consumed even for a pack
                        zs.RemainingToSpawn -= 1;
                        zs.NextSpawnTick = TickUtil.NonZero(now + (uint)math.max(1, dir.SpawnIntervalTicks));
                    }
                }
            }
            else if (aliveZone == 0 && runtime.ClearedThisEpoch == 0)
            {
                // Wave fully spawned AND every zone enemy dead -> a REAL clear. Mark once; the gate pays the
                // once-per-epoch Ore reward on the player's return to base.
                runtime.ClearedThisEpoch = 1;
                SystemAPI.SetComponent(cycleEntity, runtime);
            }

            SystemAPI.SetComponent(directorEntity, zs);
        }
    }
}