using Unity.Collections;
using Unity.Entities;
using Unity.Jobs;
using Unity.Mathematics;
using Unity.Transforms;
using UnityEngine;
using Random = Unity.Mathematics.Random;

[UpdateInGroup(typeof(SimulationSystemGroup))]
public class ShipSpawnerSys : JobComponentSystem
{
    private const int MaxShips = 20000;
    private const float SpawnRatePerSecond = 1000;

    private Random rand;
    private int shipCount;
    private BeginInitializationEntityCommandBufferSystem cmdBufferSystem;

    protected override void OnCreate()
    {
        rand = new Random(1);
        shipCount = 0;
        cmdBufferSystem = World.GetOrCreateSystem<BeginInitializationEntityCommandBufferSystem>();
    }

    private struct SpawnJob : IJobForEachWithEntity<ShipSpawner, LocalToWorld, Rotation>
    {
        public EntityCommandBuffer CommandBuffer;
        //public uint RandSeedOffset;
        public Random Rand;
        public float Time;
        public float Dt;
        public int SpawnCount;

        public void Execute(Entity entity, int index, [ReadOnly] ref ShipSpawner spawner, [ReadOnly] ref LocalToWorld location, [ReadOnly] ref Rotation rotation)
        {
            //Random rand = new Random((uint)((index + RandSeedOffset) % uint.MaxValue));
            for (int i = 0; i < SpawnCount; i++)
            {
                Entity ship = CommandBuffer.Instantiate(spawner.Prefab);
                float3 pos = math.transform(location.Value, new float3(Rand.NextFloat(-500f, 500f), 0, Rand.NextFloat(-20f, 20f)));
                CommandBuffer.SetComponent(ship, new Rotation { Value = rotation.Value });
                CommandBuffer.AddComponent(ship, new Velocity());
                CommandBuffer.SetComponent(ship, new Translation { Value = pos });
                CommandBuffer.AddComponent(ship, new SpawnTime { Value = Time });
            }
        }
    }

    protected override JobHandle OnUpdate(JobHandle inputDeps)
    {
        int maxToSpawn = MaxShips - shipCount;
        int spawnCount = math.min((int)(SpawnRatePerSecond * Time.deltaTime), maxToSpawn);
        shipCount += spawnCount;

        // Schedule the job that will add Instantiate commands to the EntityCommandBuffer.
        var job = new SpawnJob
        {
            CommandBuffer = cmdBufferSystem.CreateCommandBuffer(),
            //RandSeedOffset = rand.NextUInt(),
            Rand = rand,
            Time = Time.time,
            Dt = Time.deltaTime,
            SpawnCount = spawnCount,
        }.ScheduleSingle(this, inputDeps);

        // SpawnJob runs in parallel with no sync point until the barrier system executes.
        // When the barrier system executes we want to complete the SpawnJob and then play back the commands (Creating the entities and placing them).
        // We need to tell the barrier system which job it needs to complete before it can play back the commands.
        cmdBufferSystem.AddJobHandleForProducer(job);
        return job;
    }
}