using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
namespace BITKit
{
    public interface IEntryGroup { }
    public interface IEntryElement
    {
        void Entry();
        void Exit();
    }

    [System.Serializable]
    public class EntryGroup<T> : IEntryGroup where T : IEntryElement
    {
        public int index = -1;
        public List<T> list = new();
        int m_index;
        public void Entry(T t)
        {
            if (t is not null)
            {
                list.TryAdd(t);

            }
            index = list.IndexOf(t);
            EnsureConfiguration();
        }
        public void Entry(int index)
        {
            if (index < list.Count)
            {
                this.index = index;
            }
        }
        public void Entry(Func<IEntryElement,bool> entryFactory)
        {
            var index = list.FindIndex(x => entryFactory.Invoke(x));
            Entry(index);
        }
        public void Entry()
        {
            index = 0;
            EnsureConfiguration();
        }

        public void Exit()
        {
            index = -1;
            EnsureConfiguration();
        }
        public bool TryGetEntried(out T value)
        {
            EnsureConfiguration();
            if (index is not -1)
            {
                value = list[index];
                return true;
            }
            value = default;
            return false;
        }
        void EnsureConfiguration()
        {
            if (MathE.Equals(this.index, m_index))
            {

            }
            else
            {
                if (m_index is not -1)
                {
                    list[m_index].Exit();
                }
                if (index is not -1)
                {
                    list[index].Entry();
                }
            }
            m_index = index;
        }
    }
}