using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        string first = "\uD83D\uDC4Ar\uD83D\uDC4A\uD83D\uDC4A";

        var list = new List<string>();

        var itor = new EmojiIterator(first);

        while(itor.MoveNext())

            list.Add(itor.Sequence);

​

        for (int i = 0; i < 20; i++)

        {

           Console.Write(list[i % list.Count] + "\r");

        }

    }

}

​

public class EmojiIterator

    {

        private string _text;

        private int _head, _next;

        private int _index, _length;

​

        public EmojiIterator(string text)

        {

            _text = text;

            Reset();

        }

​

        public int Char { get { return _head; } }

        public int Offset { get { return _index; } set { _index = value; _length = 0; _next = -1; } }

        public int SequenceLength { get { return _length; } }

        public string Sequence { get { return _text.Substring(_index, _length); } }

​

        public bool MoveNext()

        {

            try

            {

                _index += _length;

                _length = 0;

                if (_next >= 0)

                    _head = _next;

                else if (_index < _text.Length)

                    _head = char.ConvertToUtf32(_text, _index);

                else

                    return false;

​

                FindSequence(_head);

            }

            catch

            {

                _next = -1;

            }

​

            return true;

        }

​

        public void Reset()

        {

            _next = -1;

            _index = _length = 0;

        }

​

        private void GetNextChar()

        {

            _next = char.ConvertToUtf32(_text, _index + _length);

        }

​

        private void UseNextChar()

        {

            _length += 2;

            _next = -1;

        }

​

        private void FindSequence(int headChar)

        {

            if (headChar <= 0xffff)

                _length++;

            else

                _length += 2;

​

            GetNextChar();

​

            if (headChar > 0xffff && CheckFlagOrTagSequence(headChar))

                return;

​

            CheckEmojiSequence();

        }

​

        //emoji_zwj_sequence := emoji_zwj_element ( ZWJ emoji_zwj_element )+

        //ZWJ := \x{200d}

        //emoji_zwj_element :=

        //  emoji_character

        //| emoji_presentation_sequence

        //| emoji_modifier_sequence

        private void ZWJ()

        {

            _length++; // <<ZWJ>>

            GetNextChar();

            if (_next >= 0)

                FindSequence(_next);

        }

​

        private void CheckZWJ()

        {

            GetNextChar();

            if (_next == 0x200d) //ZWJ

                ZWJ();

        }

​

        private void CheckEmojiSequence()

        {

            if (_next > 0xffff) //supplementary planes

            {

                //emoji_modifier_sequence := emoji_modifier_base emoji_modifier

                if (_next >= 0x1f3fb && _next <= 0x1f3ff) //emoji_modifier

                {

                    _length += 2; // <<emoji_modifier>>

                    CheckZWJ();

                }

            }

            //emoji variation selector

            //emoji_presentation_sequence := emoji_character emoji_presentation_selector

            //emoji_presentation_selector := \x{FE0F}

            else if (_next == 0xfe0f)

            {

                _length++; // <<emoji_presentation_selector>>

                CheckZWJ();

            }

            else if (_next == 0x200d) //ZWJ

                ZWJ();

        }

​

        private bool CheckFlagOrTagSequence(int head)

        {

            //emoji_flag_sequence := regional_indicator regional_indicator

            if (IsRegionalIndicatorSymbol(head) && IsRegionalIndicatorSymbol(_next))

            {

                UseNextChar(); // <<regional_indicator>> #2nd

                return true;

            }

​

            //emoji_tag_sequence := tag_base tag_spec tag_end

            //tag_base           := emoji_character

            //                  | emoji_modifier_sequence

            //                  | emoji_presentation_sequence

            //tag_spec           := [\x{E0020}-\x{E007E}]+

            //tag_end            := \x{E007F} (CANCEL TAG)

            if (IsTagComponent(_next))

            {

                do

                {

                    _length += 2; // <<tag_spec>>

                    GetNextChar();

                }

                while (IsTagComponent(_next));

​

                if (_next == 0xe007f)

                    UseNextChar(); // <<tag_end>>

​

                return true;

            }

​

            return false;

        }

​

        private static bool IsRegionalIndicatorSymbol(int ch)

        {

            return ch >= 0x1f1e6 && ch <= 0x1f1ff;

        }

​

        private static bool IsTagComponent(int ch)

        {

            return ch >= 0xe0020 && ch <= 0xe007e;

        }

    }