using System;

namespace RgbConverter
{
    public static class Rgb
    {
        /// <summary>
        /// Gets hexadecimal representation source RGB decimal values.
        /// </summary>
        /// <param name="red">The valid decimal value for RGB is in the range 0-255.</param>
        /// <param name="green">The valid decimal valu for RGB is in the range 0-255.</param>
        /// <param name="blue">The valid decimal val for RGB is in the range 0-255.</param>
        /// <returns>Returns hexadecimal representation source RGB decimal values.</returns>
        public static string GetHexRepresentation(int red, int green, int blue)
        {
            static string IntToHex(int color)
            {
                if (color >= 255)
                {
                    return "FF";
                }

                if (color < 16)
                {
                    switch (color)
                    {
                        case 0:
                            return "00";
                        case 1:
                            return "01";
                        case 2:
                            return "02";
                        case 3:
                            return "03";
                        case 4:
                            return "04";
                        case 5:
                            return "05";
                        case 6:
                            return "06";
                        case 7:
                            return "07";
                        case 8:
                            return "08";
                        case 9:
                            return "09";
                        case 10:
                            return "0A";
                        case 11:
                            return "0B";
                        case 12:
                            return "0C";
                        case 13:
                            return "0D";
                        case 14:
                            return "0E";
                        case 15:
                            return "0F";
                    }
                }

                string hex = string.Empty;

                for (int i = 0; i < 2; i++)
                {
                    switch (color % 16)
                    {
                        case 0:
                            hex += "0";
                            break;
                        case 1:
                            hex += "1";
                            break;
                        case 2:
                            hex += "2";
                            break;
                        case 3:
                            hex += "3";
                            break;
                        case 4:
                            hex += "4";
                            break;
                        case 5:
                            hex += "5";
                            break;
                        case 6:
                            hex += "6";
                            break;
                        case 7:
                            hex += "7";
                            break;
                        case 8:
                            hex += "8";
                            break;
                        case 9:
                            hex += "9";
                            break;
                        case 10:
                            hex += "A";
                            break;
                        case 11:
                            hex += "B";
                            break;
                        case 12:
                            hex += "C";
                            break;
                        case 13:
                            hex += "D";
                            break;
                        case 14:
                            hex += "E";
                            break;
                        case 15:
                            hex += "F";
                            break;
                    }

                    color /= 16;
                }

                return hex;
            }

            return IntToHex(red) + IntToHex(green) + IntToHex(blue);
        }
    }
}