Validators.cs

using System.Text.RegularExpressions;
using NanoXLSX.Exceptions;
 
 
namespace NanoXLSX.Utils
{
    public static class Validators
    {

        public static void ValidateGenericColor(string hexCode, bool allowEmpty = false)
        {
            string argbMessage = ValidateColorInternal(hexCode, true, allowEmpty);
            string rgbMessage = null;
            if ( argbMessage != null)
            {
                rgbMessage = ValidateColorInternal(hexCode, false, allowEmpty);
                if (rgbMessage != null)
                {
                    throw new StyleException(argbMessage);
                }
            }
        }

        public static void ValidateColor(string hexCode, bool useAlpha, bool allowEmpty = false)
        {
            string message = ValidateColorInternal(hexCode, useAlpha, allowEmpty);
            if (message != null)
            {
                throw new StyleException(message);
            }
        }

        private static string ValidateColorInternal(string hexCode, bool useAlpha, bool allowEmpty)
        {
            if (string.IsNullOrEmpty(hexCode))
            {
                if (allowEmpty)
                {
                    return null;
                }
                return "The color expression cannot be null or empty";
            }
 
            int length = useAlpha ? 8 : 6;
            if (hexCode.Length != length)
            {
                return "The value '" + hexCode + "' is invalid. A valid value must contain " + length + " hex characters";
            }
            if (!Regex.IsMatch(hexCode, "[a-fA-F0-9]{6,8}"))
            {
               return "The expression '" + hexCode + "' is not a valid hex value";
            }
            return null;
        }
    }
}