using System;

using System.Collections.Generic;

public class Program

{

    public  void Main()

        {

            var color = "123";

            List<string> myColors = new List<string>();

            myColors.Add("123");

            myColors.Add("1230");

            myColors.Add("1231");

            myColors.Add("1234");

            myColors.Add("123C");

            myColors.Add("123C0");

​

            var expectedColor = SearchNextAvaliable(color, myColors);

            Console.WriteLine("Expected " + expectedColor);

        }

     private string SearchNextAvaliable(string color, List<string> myColors)

        {

            var returnColor = string.Empty;

​

            //get the color recursively

            if (RecursiveGetNextColor(myColors, color, out returnColor))

            {

                color = returnColor;

                return color;

            }

            else //error or not found

            {

                return "Exception";

            }

        }

          private bool RecursiveGetNextColor(List<string> myColors, string targetColor, out string returnColor)

        {

            var newLast = string.Empty;

            returnColor = newLast;

​

            //call function here to get the next posibility  'LastCharPosition is counting backwards where 1 is the last character

            newLast = NextColor(targetColor, 0);

​

            //if unable to get a next color return not found

            if (targetColor.Equals(newLast, StringComparison.CurrentCultureIgnoreCase))

            {

                return false;

            }

​

            if (myColors.BinarySearch(newLast) >= 0 && newLast != "ZZZZZZZZZ")

            {

                return RecursiveGetNextColor(myColors, newLast, out returnColor);

            }

​

            //done means that the newlast was not found in the current colors

            returnColor = newLast; //set the new color by ref

            return true;

        }

​

        //this algorithm generates a posible next color for CUF, this is later compared to current colors to decide if usable or not

        //LastCharPosition is counting backwards where 1 is the last character

        private string NextColor(string color, int lastCharPosition)

        {

            var stringLength = color.Length;

            int lastChar;

​

            //if there is space to add chars

            if (stringLength <= 9)

            {

                lastChar = char.Parse(color.Substring(stringLength - 1).ToUpper());

​

                //if this is the last posibility for this lenght = "Z"

                if (lastChar >= 90)

                {

                    if (stringLength == 9)

                    {

                        if (lastCharPosition < 9)

                        {

                            //Andres 7-29-08 changed 0 to 1 due to an infinite loop

                            return NextColor(color, lastCharPosition + 1);

                        }

                        else

                        {

                            return color;

                        }

                    }

                    else

                    {

                        //add a char with the first posibility =0

                        return string.Format("{0}0", color);

                    }

                }

                //the current last character can be increazed

                else

                {

                    //checks range of last char

                    if (lastChar >= 65 || lastChar >= 48 && lastChar <= 57)

                    {

                        //if the character is a 9 set it as A

                        if (lastChar == 57)

                        {

                            lastChar = 65;

                        }

                        else

                        {

                            lastChar = lastChar + 1;

                        }

​

                        //replace last char

                        return color.Substring(0, stringLength - 1 + lastCharPosition) + (char)lastChar;

                    }

                    //the char range is not recognized therfore add a 0 since we can

                    else

                    {

                        return string.Format("{0}0", color);

                    }

                }

            }

            //there is no more space to add chars, convert the color to a 9 digit color and make a recursive call

            else

            {

                color = color.Replace(" ", string.Empty);

                stringLength = color.Length;

​

                //if too big still, remove center

                if (stringLength > 9)

                {

                    color = TruncateColor(color);

                }

​

                if (color != "ZZZZZZZZZ")

                {

                    return NextColor(color, 0);

                }

                else

                {

                    return color;

                }

            }

        }

​

        private string TruncateColor(string color)

        {

            //remove blanks

            color = color.Replace(" ", "");

            var ItemMasterColorColumnMaxLength = 9;

            //if is still too big then remove center

            if (color.Length > ItemMasterColorColumnMaxLength)

            {

                //MCM 5/7/09  The prior was truncating to 9 chars, not allowing a charater to be added, changed to truncate to 8 chars

                var halfTheLength = ItemMasterColorColumnMaxLength / 2;

                color = color.Substring(0, halfTheLength) + color.Substring(color.Length - halfTheLength);

            }

​

            return color;

        }

}