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. Edge-triggered off the cycle phase (via the server-only
    /// <see cref="CycleRuntime.PrevPhase"/>): on ENTERING Expedition for a not-yet-seeded cycle it scatters
    /// <see cref="ResourceFieldSpawner.Count"/> resource-node ghosts (seeded by CycleNumber via
    /// <see cref="Unity.Mathematics.Random"/>) around the expedition region origin, each
    /// <see cref="RegionTag"/>{Expedition}; on LEAVING Expedition it destroys every node. Runs in the plain
    /// server SimulationSystemGroup <c>[UpdateAfter(CyclePhaseSystem)]</c> so the phase edge is observed the
    /// same tick. Server-authoritative; clients despawn nodes via GhostDespawnSystem. Per-cycle reproducible
    /// (the seed is the monotonic int CycleNumber, compared by equality — never tick math; never seed 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 cycle = SystemAPI.GetComponent<CycleState>(cycleEntity);
            var runtime = SystemAPI.GetComponent<CycleRuntime>(cycleEntity);
            var spawner = SystemAPI.GetSingleton<ResourceFieldSpawner>();

            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 edge: entered Expedition for a cycle we have not seeded yet.
            if (cycle.Phase == CyclePhase.Expedition
                && runtime.LastSpawnedCycle != cycle.CycleNumber
                && 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, cycle.CycleNumber));
                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.LastSpawnedCycle = cycle.CycleNumber;
            }

            // DESTROY edge: left Expedition — clear the whole field.
            if (runtime.PrevPhase == CyclePhase.Expedition && cycle.Phase != CyclePhase.Expedition)
            {
                foreach (var (rn, e) in SystemAPI.Query<RefRO<ResourceNode>>().WithEntityAccess())
                    ecb.DestroyEntity(e);
            }

            runtime.PrevPhase = cycle.Phase;
            SystemAPI.SetComponent(cycleEntity, runtime);

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