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

namespace ProjectM.Server
{
    /// <summary>
    /// Server-only, one-shot upgrade-pickup spawner (mirrors TrainingDummySpawnSystem). On its first
    /// update it reads the baked <see cref="UpgradePickupSpawner"/> singleton and instantiates
    /// <c>Count</c> pickup ghosts in a row, spaced <c>Spacing</c> world-units apart along +X starting at
    /// <c>Origin</c>, then destroys the singleton so the system idles (spawned exactly once). Runs in the
    /// default <see cref="SimulationSystemGroup"/> (NOT the prediction loop); pickups replicate to clients
    /// as interpolated ghosts. Structural changes are batched through an <see cref="EntityCommandBuffer"/>.
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    public partial struct UpgradePickupSpawnSystem : ISystem
    {
        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            state.RequireForUpdate<UpgradePickupSpawner>();
        }

        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            var spawnerEntity = SystemAPI.GetSingletonEntity<UpgradePickupSpawner>();
            var spawner = SystemAPI.GetComponent<UpgradePickupSpawner>(spawnerEntity);

            var ecb = new EntityCommandBuffer(Allocator.Temp);

            if (spawner.Prefab != Entity.Null)
            {
                for (int i = 0; i < spawner.Count; i++)
                {
                    var pickup = ecb.Instantiate(spawner.Prefab);
                    var position = spawner.Origin + new float3(i * spawner.Spacing, 0f, 0f);
                    ecb.SetComponent(pickup, LocalTransform.FromPosition(position));
                }
            }

            // One-shot: remove the spawner so RequireForUpdate fails and the system idles.
            ecb.DestroyEntity(spawnerEntity);

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