Bogus Roman Number

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

namespace Work.Darkstar.Framework.Fun
{
    [DefaultValue(ROMANSYMBOL.I)]
    internal enum ROMANSYMBOL
    {
        I = 1,
        V = 5,
        X = 10,
        L = 50,
        C = 100,
        D = 500,
        M = 1000
    }

    /// <summary>
    /// Bogus RomanNumber implementation from zen@darkstar.work is under GPL 3
    /// RomanNumber is under GPL 3
    /// See the GNU Library General Public License for more details.
    /// </summary>
    internal class RomanNumber
    {

        private static readonly string RomanSymbols = "IVXLCDM";
        private List<ROMANSYMBOL> romanString;

        internal List<ROMANSYMBOL> RomanString
        {
            get
            {
                return romanString;
            }
            set
            {
                // TODO: implement correct parsing here and throw exception
                romanString = value;
            }
        }

        internal RomanNumber()
        {
            RomanString = new List<ROMANSYMBOL>();
        }

        internal List<ROMANSYMBOL> Parse(string rString)
        {
            List<ROMANSYMBOL> rList = new List<ROMANSYMBOL>();

            foreach (char ch in rString)
            {
                if (!RomanSymbols.Contains(ch))
                {
                    throw new InvalidOperationException(
                        String.Format("Invalid Symbol {0} in string {1}", ch, rString));
                }
            }

            // TODO: Parse correct concatenations of Roman Symbols

            return rList;
        }

        public override String ToString()
        {
            string s = string.Empty;
            foreach (ROMANSYMBOL r in RomanString)
            {
                s += Enum.GetName(typeof(ROMANSYMBOL), r);
            }
            return s;
        }

        public int ToInt()
        {
            int ir = 0;

            string s = this.ToString();
            while (s.Contains("IV"))
            {
                ir += 4;
                s.Replace("IV", "");
            }
            while (s.Contains("IX"))
            {
                ir += 9;
                s.Replace("IX", "");
            }
            while (s.Contains("XL"))
            {
                ir += 40;
                s.Replace("XL", "");
            }
            while (s.Contains("XC"))
            {
                ir += 90;
                s.Replace("XC", "");
            }
            while (s.Contains("CD"))
            {
                ir += 400;
                s.Replace("CD", "");
            }
            while (s.Contains("CM"))
            {
                ir += 900;
                s.Replace("CM", "");
            }

            while (s.Contains("I"))
            {
                ir += 1;
                s.Replace("I", "");
            }
            while (s.Contains("V"))
            {
                ir += 5;
                s.Replace("V", "");
            }
            while (s.Contains("X"))
            {
                ir += 10;
                s.Replace("X", "");
            }
            while (s.Contains("L"))
            {
                ir += 50;
                s.Replace("L", "");
            }
            while (s.Contains("C"))
            {
                ir += 100;
                s.Replace("C", "");
            }
            while (s.Contains("D"))
            {
                ir += 500;
                s.Replace("D", "");
            }
            while (s.Contains("M"))
            {
                ir += 1000;
                s.Replace("M", "");
            }

            if (ir <= 0)
            {
                throw new InvalidOperationException("Roman Numbers must be greater than 0");
            }

            return ir;
        }
    }
}