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

namespace TechbloxModdingAPI
{
    public ref struct OptionalRef<T> where T : unmanaged, IEntityComponent
    {
        private bool exists;
        private NB<T> array;
        private uint index;
        private EntityInitializer initializer;

        public OptionalRef(NB<T> array, uint index)
        {
            exists = true;
            this.array = array;
            this.index = index;
            initializer = default;
        }
        
        /// <summary>
        /// Wraps the initializer data, if present.
        /// </summary>
        /// <param name="obj">The object with the initializer</param>
        public OptionalRef(EcsObjectBase obj)
        {
            if (obj.InitData.Valid)
            {
                initializer = obj.InitData.Initializer(obj.Id);
                exists = true;
            }
            else
            {
                initializer = default;
                exists = false;
            }
            array = default;
            index = default;
        }

        /// <summary>
        /// Returns the value or a default value if empty. Supports objects that are being initialized.
        /// </summary>
        /// <returns>The value or the default value</returns>
        public ref T Get()
        {
            if (!exists) return ref CompRefCache<T>.Default;
            if (initializer.EGID == EGID.Empty)
                return ref array[index];
            return ref initializer.GetOrCreate<T>();
        }

        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="TR">The struct type to cache</typeparam>
        private struct CompRefCache<TR> where TR : unmanaged
        {
            public static TR Default;
        }
    }
}