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 dummy spawner. On its first update it reads the baked
    /// <see cref="TrainingDummySpawner"/> singleton and instantiates <c>Count</c> training-dummy
    /// ghosts in a row, spaced <c>Spacing</c> world-units apart along +X starting at <c>Origin</c>.
    /// It then destroys the spawner singleton entity so <c>RequireForUpdate<TrainingDummySpawner></c>
    /// is no longer satisfied and the system stops running (idempotent: dummies are spawned exactly once).
    /// Runs in the default <see cref="SimulationSystemGroup"/> (NOT the prediction loop) since spawning is
    /// a non-predicted, server-authoritative event; the dummies replicate to clients as interpolated ghosts.
    /// All structural changes are batched through an <see cref="EntityCommandBuffer"/>.
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    public partial struct TrainingDummySpawnSystem : ISystem
    {
        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            state.RequireForUpdate<TrainingDummySpawner>();
        }

        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            // Grab both the singleton entity (to destroy when done) and its baked config.
            var spawnerEntity = SystemAPI.GetSingletonEntity<TrainingDummySpawner>();
            var spawner = SystemAPI.GetComponent<TrainingDummySpawner>(spawnerEntity);

            var ecb = new EntityCommandBuffer(Allocator.Temp);

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

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

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