using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;

namespace BITKit
{
    public static class MathE
    {
        public static bool Equals<T>(params T[] objs)
        {
            var a = objs.FirstOrDefault();
            foreach (var b in objs)
            {
                if (a.Equals(b))
                {
                    a = b;
                    continue;
                }
                else
                {
                    return false;
                }
            }

            return true;
        }

        public static IEnumerable<T> Subtract<T>(IEnumerable<T> a, IEnumerable<T> b) where T : IEnumerable
        {
            List<T> list = new();
            foreach (var x in a)
            {
                if (b.Contains(x))
                {

                }
                else
                {
                    list.Add(x);
                }
            }

            return list;
        }

        public static bool Contains<T>(IEnumerable<T> a, IEnumerable<T> b)
        {
            foreach (var x in b)
            {
                if (a.Contains(x))
                {

                }
                else
                {
                    return false;
                }
            }

            return true;
        }
        public static IEnumerable<T[]> Combinations<T>(IEnumerable<T> source)
        {
            if (null == source) throw new ArgumentNullException(nameof(source));
            T[] data = source.ToArray();
            return Enumerable.Range(0, 1 << (data.Length) - 1)
                .Select(index => data.Where((v, i) => (index & (1 << i)) != 0).ToArray());
        }
    }
}