Dictionary<string, string> combinations = new Dictionary<string, string>
{
  	{ "ㅗㅏ", "ㅘ" },
    { "ㅗㅐ", "ㅙ" },
    { "ㅜㅓ", "ㅝ" },
    { "ㅜㅐ", "ㅞ" },
    { "ㅡㅣ", "ㅢ" },
    { "ㅜㅣ", "ㅟ" },
    { "ㅗㅣ", "ㅚ" }
};

        string[] chosungs = { "ㄱ", "ㄲ", "ㄴ", "ㄷ", "ㄸ", "ㄹ", "ㅁ", "ㅂ", "ㅃ", "ㅅ", "ㅆ", "ㅇ", "ㅈ", "ㅉ", "ㅊ", "ㅋ", "ㅌ", "ㅍ", "ㅎ" };
        string[] jungsungs = { "ㅏ", "ㅐ", "ㅑ", "ㅒ", "ㅓ", "ㅔ", "ㅕ", "ㅖ", "ㅗ", "ㅘ", "ㅙ", "ㅚ", "ㅛ", "ㅜ", "ㅝ", "ㅞ", "ㅟ", "ㅠ", "ㅡ", "ㅢ", "ㅣ" };
        string[] jongsungs = { "", "ㄱ", "ㄲ", "ㄳ", "ㄴ", "ㄵ", "ㄶ", "ㄷ", "ㄹ", "ㄺ", "ㄻ", "ㄼ", "ㄽ", "ㄾ", "ㄿ", "ㅀ", "ㅁ", "ㅂ", "ㅄ", "ㅅ", "ㅆ", "ㅇ", "ㅈ", "ㅊ", "ㅋ", "ㅌ", "ㅍ", "ㅎ" };

        private int getChosungIndex(string chosung)
        {
            return Array.IndexOf(chosungs, chosung);
        }

        private int getJungsungIndex(string jungsung)
        {
            return Array.IndexOf(jungsungs, jungsung);
        }

        private int getJongsungIndex(string jongsung)
        {
            return Array.IndexOf(jongsungs, jongsung);
        }

        private bool isContained(string[] array, int index, string input)
        {
            if (idnex < 0 || index + 1 > input.Length)
            {
                return false;
            }
            else
            {
                return array.Contains(input[index].ToString());
            }
        }

        private string mergeSyllable(string currentChosung, string currentJungsung, string currentJongsung)
        {
            int chosungIndex = getChosungIndex(currentChosung);
            int jungsungIndex = getJungsungIndex(currentJungsung);
            int jongsungIndex = getJongsungIndex(currentJongsung);

            int syllableCode = 0xAC00 + (chosungIndex * 21 + jungsungIndex) * 28 + jongsungIndex;

            var currentSyllable = ((char)syllableCode).ToString();

            return currentSyllable;
        }

        private (string, string, string) deviceSyllable(char syllable)
        {
            ushort UnicodeHangeulBase = 0xAC00;
            ushort check = Convert.ToUInt16(syllable);
            int Code = check - UnicodeHangeulBase;

            int JongsungCode = Code % 28;
            Code = (Code - JongsungCode) / 28;

            int JungsungCode = Code % 21;
            Code = (Code - JungsungCode) / 21;

            int ChosungCode = Code;

            string chosung = chosungs[ChosungCode];
            string jungsung = jungsungs[JungsungCode];
            string jongsung = jongsungs[JongsungCode];

            return (chosung, jungsung, jongsung);
        }

        private string getCompletedText(string input)
        {
            string chosung = string.Empty;
            string jungsung = string.Empty;
            string jongsung = string.Empty;

            StringBuilder result = new StringBuilder();

            if (input.Length == 1)
            {
                return input;
            }

            for (int i = 0; i < input.Length; i++)
            {
                if (chosungs.Contains(input[i].ToString()))
                {
                    if (isContained(jungsungs, i + 1, input))
                    {
                        chosung = input[i].ToString();
                    }
                    else if (!string.IsNullOrEmpty(chosung) && !string.IsNullOrEmpty(jungsung))
                    {
                        jongsung = input[i].ToString();
                        result.Remove(result.Length - 1, 1);
                        var syllable = mergeSyllable(chosung, jungsung, jongsung);
                        result.Append(syllable);
                        chosung = string.Empty;
                        jungsung = string.Empty;
                        jongsung = string.Empty;
                    }
                    else
                    {
                        result.Append(input[i]);
                        continue;
                    }
                }
                else if (jungsungs.Contains(input[i].ToString()))
                {
                    if (isContained(chosungs, i - 1, input))
                    {
                        jungsung = input[i].ToString();
                        var syllable = mergeSyllable(chosung, jungsung, jongsung);
                        result.Append(syllable);
                    }
                    else if (isContained(jungsungs, i - 1, input) && combinations.ContainsKey(input.Substring(i - 1, 2)))
                    {
                        jungsung = combinations[input.Substring(i - 1, 2)];
											  if(string.IsNullOrEmpty(chosung))
												{
													rresult.Remove(result.Length - 1, 1);
													result.Append(jungsung);
													continue;
												}
												else
												{
													result.Remove(result.Length - 1, 1);
                        	var syllable = mergeSyllable(chosung, jungsung, jongsung);
                        	result.Append(syllable);
												}                       
                    }
                    else
                    {
                        result.Append(input[i]);
                        continue;
                    }
                }
                else
                {
                    result.Append(input[i]);
                }
            }

            return result.ToString();
        }

        private void KeyPad_Click(object sender, EventArgs e)
        {
            var key = getKeyPadValue((Panel)sender);

            textBox.Text += key;

            StringBuilder result = new StringBuilder();

            foreach (char ch in txtUserName.Text)
            {
                if (chosungs.Contains(ch.ToString()) || jungsungs.Contains(ch.ToString()))
                {
                    result.Append(ch);
                    continue;
                }

                var (initial, medial, final) = deviceSyllable(ch);

                result.Append(initial);
                result.Append(medial);
                result.Append(final);
            }

            var combinedText = getCompletedText(result.ToString());
            textBox.Text = combinedText;
            textBox.SelectionStart = textBox.Text.Length;
        }