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

namespace ProjectM.Server
{
    /// <summary>
    /// Server-only procedural expedition-field manager. Re-keyed off PER-PLAYER PRESENCE (no global phase): it
    /// counts players whose server-only <see cref="RegionTag"/> is the Expedition region, and on the
    /// empty-&gt;occupied edge (a new sortie) bumps <see cref="CycleRuntime.ExpeditionEpoch"/> and scatters
    /// <see cref="ResourceFieldSpawner.Count"/> resource-node ghosts (seeded by the epoch) around the expedition
    /// origin, each RegionTag{Expedition}; on the occupied-&gt;empty edge (the LAST player left) it destroys every
    /// node. So the field lives as long as anyone is out there, not on a global timer. Plain server
    /// SimulationSystemGroup. Server-authoritative; clients despawn nodes via GhostDespawnSystem. Per-epoch
    /// reproducible (the seed is the monotonic int epoch, compared by equality — never tick math, never 0).
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    [UpdateInGroup(typeof(SimulationSystemGroup))]
    [UpdateAfter(typeof(CyclePhaseSystem))]
    public partial struct ExpeditionFieldSystem : ISystem
    {
        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            state.RequireForUpdate<ResourceFieldSpawner>();
            state.RequireForUpdate<CycleState>();
        }

        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            var cycleEntity = SystemAPI.GetSingletonEntity<CycleState>();
            var runtime = SystemAPI.GetComponent<CycleRuntime>(cycleEntity);
            var spawner = SystemAPI.GetSingleton<ResourceFieldSpawner>();

            // Per-player presence: is anyone currently out in the expedition region?
            int expeditionPlayers = 0;
            foreach (var region in SystemAPI.Query<RefRO<RegionTag>>().WithAll<PlayerTag>())
                if (region.ValueRO.Region == RegionId.Expedition)
                    expeditionPlayers++;
            bool occupied = expeditionPlayers > 0;
            bool wasOccupied = runtime.PrevExpeditionOccupied != 0;

            // empty -> occupied: a new sortie begins; bump the epoch so the field reseeds fresh.
            if (occupied && !wasOccupied)
                runtime.ExpeditionEpoch += 1;

            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);

            var ecb = new EntityCommandBuffer(Allocator.Temp);

            // SPAWN: a player is out and this epoch has not been seeded yet.
            if (occupied
                && runtime.LastSpawnedEpoch != runtime.ExpeditionEpoch
                && spawner.Prefab != Entity.Null)
            {
                var baseXform = SystemAPI.GetComponent<LocalTransform>(spawner.Prefab);
                var prefabNode = SystemAPI.GetComponent<ResourceNode>(spawner.Prefab);
                var rng = new Random((uint)math.max(1, runtime.ExpeditionEpoch));
                int count = math.max(1, spawner.Count);
                for (int i = 0; i < count; i++)
                {
                    var node = ecb.Instantiate(spawner.Prefab);

                    float ang = rng.NextFloat(0f, math.PI * 2f);
                    float rad = spawner.Radius * math.sqrt(rng.NextFloat(0f, 1f));
                    var xform = baseXform;
                    xform.Position = origin + new float3(math.cos(ang) * rad, 0f, math.sin(ang) * rad);
                    ecb.SetComponent(node, xform);

                    // Round-robin the resource type (Aether / Ore / Biomass) over the prefab's baked node.
                    var rn = prefabNode;
                    rn.ResourceId = (byte)(ResourceId.Aether + (byte)(i % 3));
                    ecb.SetComponent(node, rn);
                }
                runtime.LastSpawnedEpoch = runtime.ExpeditionEpoch;
            }

            // DESTROY: the last player left the expedition — clear the whole field.
            if (wasOccupied && !occupied)
            {
                foreach (var (rn, e) in SystemAPI.Query<RefRO<ResourceNode>>().WithEntityAccess())
                    ecb.DestroyEntity(e);
            }

            runtime.PrevExpeditionOccupied = (byte)(occupied ? 1 : 0);
            SystemAPI.SetComponent(cycleEntity, runtime);

            ecb.Playback(state.EntityManager);
        }
    }
}