using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using GamecraftModdingAPI.Blocks;
using Svelto.DataStructures;
using Svelto.ECS;

namespace GamecraftModdingAPI
{
    public struct OptionalRef<T> where T : unmanaged
    {
        private bool exists;
        private NB<T> array;
        private uint index;

        public OptionalRef(NB<T> array, uint index)
        {
            exists = true;
            this.array = array;
            this.index = index;
        }

        public OptionalRef(ref T value)
        {
            exists = true;
            array = default;
            index = default;
        }

        public ref T Get(T def = default)
        {
            if (exists)
                return ref array[index];
            return ref CompRefCache<T>._default;
        }

        public bool Exists => exists;

        public static implicit operator T(OptionalRef<T> opt) => opt.Get();

        public static implicit operator bool(OptionalRef<T> opt) => opt.exists;

        /*public delegate ref TR Mapper<TR>(ref T component) where TR : unmanaged;
        public unsafe delegate TR* PMapper<TR>(T* component) where TR : unmanaged;
        
        public unsafe OptionalRef<TR> Map<TR>(PMapper<TR> mapper) where TR : unmanaged =>
            exists ? new OptionalRef<TR>(ref *mapper(pointer)) : new OptionalRef<TR>();*/

        /// <summary>
        /// Creates an instance of a struct T that can be referenced.
        /// </summary>
        /// <typeparam name="T">The struct type to cache</typeparam>
        private struct CompRefCache<T> where T : unmanaged
        {
            public static T _default;
        }
    }
}