using System;
using Unity.Collections;
using Unity.Entities;
using Unity.Jobs;
using Unity.Physics;

namespace HexagonSurvive.HexPhysics
{
    [UpdateInGroup(typeof(InitializationSystemGroup))]
    public partial class BatchRaycastSystem : SystemBase
    {
        private NativeArray<RaycastTaskData> _data;

        protected override void OnCreate()
        {
            RequireForUpdate<PhysicsWorldSingleton>();
            _data = new NativeArray<RaycastTaskData>(16, Allocator.Persistent);

            for (int i = 0; i < _data.Length; i++)
                _data[i] = new RaycastTaskData { isDisposed = true };
        }

        protected override void OnUpdate()
        {
            Dependency.Complete();

            Dependency = new RaycastJob
            {
                collisionWorld = SystemAPI.GetSingleton<PhysicsWorldSingleton>().CollisionWorld,
                inputs = _data
            }.Schedule(_data.Length, Dependency);
        }

        protected override void OnDestroy()
        {
            _data.Dispose();
        }

        /// <summary>
        /// Schedule a raycast task and you can get that result next frame.
        /// </summary>
        /// <param name="input">Input data</param>
        /// <returns>Id of the task.</returns>
        /// <exception cref="Exception">Thrown if the buffer is full.</exception>
        public int ScheduleRaycastTask(RaycastInput input)
        {
            Dependency.Complete();

            for (int i = 0; i < _data.Length; i++)
            {
                if (_data[i].isDisposed)
                {
                    _data[i] = new RaycastTaskData { input = input };
                    return i;
                }
            }

            throw new Exception("Raycast task buffer is too small! Expand it!");
        }

        /// <summary>
        /// Get the hit result of the task by id.
        /// </summary>
        /// <param name="id">Task id</param>
        /// <param name="hit">The hit result</param>
        /// <returns>If the task is done and the return value is valid.</returns>
        public bool GetRaycastTaskResult(int id, out RaycastHit hit)
        {
            Dependency.Complete();

            if (_data[id].isDisposed)
            {
                hit = default;
                return false;
            }

            hit = _data[id].hit;
            _data[id] = new RaycastTaskData { isDisposed = true };
            return true;
        }
    }
}