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

public class EmptyCheckEnumerable<T> : IEnumerable<T>
{
    public EmptyCheckEnumerable(IEnumerable<T> src){
        this.src = src;
    }
    readonly IEnumerable<T> src;

    Enumerator current;
    public IEnumerator<T> GetEnumerator() {
        if (current != null && current.cacheOne) return current;
        else return current = new Enumerator(src.GetEnumerator());
    }

    public bool IsEmpty {
        get {
            GetEnumerator();
            return current.IsEmpty;
        }
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
        return GetEnumerator();
    }

    class Enumerator : IEnumerator<T>
    {
        public Enumerator(IEnumerator<T> src){
            this.src = src;
        }
        readonly IEnumerator<T> src;
        internal bool cacheOne;
        bool? isEmpty = null;

        public bool IsEmpty {
            get {
                if (isEmpty.HasValue) return isEmpty.Value;
                // We need to "peek"
                var res = src.MoveNext();
                isEmpty = !res;
                cacheOne = true;
                if (isEmpty) Dispose();
                return isEmpty.Value;
            }
        }

        public T Current {
            get { return src.Current; }
        }

        public void Dispose() {
            src.Dispose();
        }

        object System.Collections.IEnumerator.Current {
            get { return src.Current; }
        }

        public bool MoveNext() {
            if (cacheOne) {
                cacheOne = false;
                return !isEmpty.Value;
            } else {
                var res = src.MoveNext();
                if (!isEmpty.HasValue) isEmpty = !res;
                return res;
            }
        }

        public void Reset() {
            throw new NotImplementedException();
        }
    }
}