Взорвать шаблон в C#

The code here is unfinished because I had second thoughts about my logic. The idea is to walk through each character and decide if it was a number, or open or close parenthesis and save that information into a string, using the number to repeat what is in the parenthesis. and alowing for iteration in the event that another statement is inside the parenthesis.

For example :
2(ab)16(cd)3(a4(bc)d)

would equate to :
ABABCDCDCDCDCDCDCDCDCDCDCDCDCDCDCDCDABCBCBCBCDABCBCBCBCDABCBCBCBCD

static string ExplodeString(string holder)
        {

            bool firstRun = true;
            int c = 0;
            string holderStr = "";
            int numOpen = 0;
            int numClose = 0;
            string numBuilder = "";
            int rptNum = 0;
            string holderTmp = "";
            int numOpenBraces = 0;
            string finalStr = "";
            int numCloseBraces = 0;

            if (holder.Contains("("))
            {

                int num = 4; //buffer number of chars to process for first parenthese
                while (num >0 || numOpen > numClose)
                {
                    
                    if (char.IsNumber(holder[c]) && numOpen == 0)
                    {
                        numBuilder += holder[c];
                        int.TryParse(numBuilder, out rptNum);
                        Console.WriteLine(numBuilder);
                    }
                    else if (holder[c].Equals('('))
                    {
                        Console.WriteLine("Open found!");
                        numOpen++;
                        if (numOpen > 1)
                        {
                            holderStr += holder[c];
                        }
                    }
                    else if (holder[c].Equals(')'))
                    {
                        Console.WriteLine("Close found!");
                        numClose++;
                        if (numOpen > 1)
                        {
                            holderStr += holder[c];
                        }
                    }
                    else
                    {
                        Console.WriteLine("Building string...");
                        holderStr += holder[c];
                    }
                    c++;
                    num--;
                }
                
                finalStr = String.Concat(Enumerable.Repeat(holderStr,rptNum));
                Console.WriteLine(finalStr);
                while (finalStr.Contains('('))
                {
                    finalStr = ExplodeString(finalStr);
                }
            }
            Console.WriteLine(finalStr);
            return finalStr;
        }