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 Husk wave/threat director: a state machine that escalates the swarm. In <c>Lull</c> it waits
    /// until the lull timer expires, then starts the next wave (count = <c>BaseCount + (wave-1)*CountPerWave</c>). In
    /// <c>Spawning</c> it spawns one Husk every <c>SpawnIntervalTicks</c> at a deterministic ring slot around the
    /// <see cref="BaseAnchor"/>, round-robin over the <see cref="WaveEnemyPrefab"/> pool, until the wave is fully
    /// spawned; then it waits for the field to be cleared (no live <see cref="EnemyTag"/>) before returning to
    /// <c>Lull</c>. Plain <see cref="SimulationSystemGroup"/>, server-authoritative (Husks are interpolated ghosts).
    /// Replaces the flat <c>EnemySpawnSystem</c> sustain. Tick gating uses the wrap-safe <see cref="NetworkTick"/>
    /// compare + <see cref="TickUtil.NonZero"/>.
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    [UpdateInGroup(typeof(SimulationSystemGroup))]
    public partial struct WaveSystem : ISystem
    {
        EntityQuery m_AliveHusks;

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

        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            var serverTick = SystemAPI.GetSingleton<NetworkTime>().ServerTick;
            if (!serverTick.IsValid)
                return;
            uint now = serverTick.TickIndexForValidTick;
            // Player-driven loop: the base-defense wave only spawns during a Siege.
            if (SystemAPI.TryGetSingleton<CycleState>(out var cycle) && cycle.Phase != CyclePhase.Siege)
                return;

            var director = SystemAPI.GetSingleton<WaveDirector>();
            var directorEntity = SystemAPI.GetSingletonEntity<WaveDirector>();
            var prefabs = SystemAPI.GetBuffer<WaveEnemyPrefab>(directorEntity);
            if (prefabs.Length == 0)
                return;

            var wave = SystemAPI.GetComponent<WaveState>(directorEntity);

            // Ring centre on the base plot when present.
            float3 center = new float3(0f, 1f, 0f);
            if (SystemAPI.TryGetSingleton<BaseAnchor>(out var baseAnchor))
                center = BaseGridMath.PlotCenter(baseAnchor);

            // Due when no action is scheduled yet (NextActionTick 0) or the scheduled tick is at/behind now.
            bool dueNow = wave.NextActionTick == 0 || !new NetworkTick(wave.NextActionTick).IsNewerThan(serverTick);

            if (wave.Phase == WavePhase.Lull)
            {
                if (dueNow)
                {
                    // Start the next (bigger) wave.
                    wave.WaveNumber += 1;
                    wave.RemainingToSpawn =
                        math.max(1, director.BaseCount + (wave.WaveNumber - 1) * director.CountPerWave);
                    wave.Phase = WavePhase.Spawning;
                    wave.NextActionTick = TickUtil.NonZero(now); // spawn the first Husk this tick
                }
            }
            else // Spawning
            {
                if (wave.RemainingToSpawn > 0)
                {
                    if (dueNow)
                    {
                        int slots = math.max(1, director.RingSlots);
                        int prefabIdx = wave.SpawnCounter % prefabs.Length;
                        float3 pos = EnemyAIMath.RingPosition(center, wave.SpawnCounter, slots, director.RingRadius);
                        pos.y = center.y;

                        var ecb = new EntityCommandBuffer(Allocator.Temp);
                        var husk = ecb.Instantiate(prefabs[prefabIdx].Prefab);
                        ecb.SetComponent(husk, LocalTransform.FromPosition(pos));
                        // Husks belong to the base region (hidden from expedition players by relevancy).
                        ecb.AddComponent(husk, new RegionTag { Region = RegionId.Base });
                        ecb.Playback(state.EntityManager);
                        ecb.Dispose();

                        wave.SpawnCounter += 1;
                        wave.RemainingToSpawn -= 1;
                        wave.NextActionTick = TickUtil.NonZero(now + (uint)math.max(1, director.SpawnIntervalTicks));
                    }
                }
                else if (m_AliveHusks.CalculateEntityCount() == 0)
                {
                    // Wave cleared: calm before the next.
                    wave.Phase = WavePhase.Lull;
                    wave.NextActionTick = TickUtil.NonZero(now + (uint)math.max(1, director.LullTicks));
                }
            }

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