using System.Text;

namespace SWModules
{
    /// <summary>
    ///     The SafeEncoding Class is a child of the UTF8 Encoding class,
    ///     which implements input checking on the GetChars Methods, that
    ///     avoids exceptions when the input characters exceed decimal
    ///     value 127. Any values larger than 127 are converted to
    ///     carriage returns.
    /// </summary>
    public class SafeEncoding : UTF8Encoding
    {
        private const byte Nonprintreplacement = 13;
        private static SafeEncoding _utf8;

        /// <summary>
        ///     Returns a static instance of the SafeEncoding class
        /// </summary>
        public new static SafeEncoding UTF8
        {
            get { return _utf8 ?? (_utf8 = new SafeEncoding()); }
        }

        /// <summary>
        ///     Checks for values above 127 and replaces with selected character
        /// </summary>
        /// <param name="bytes">The byte array containing the sequence of bytes to decode.</param>
        /// <returns>A character array containing the results of decoding the specified sequence of bytes.</returns>
        public static char[] GetChars(byte[] bytes)
        {
            for (var i = 0; i < bytes.Length; i++)
                if (bytes[i] > 127)
                    bytes[i] = Nonprintreplacement;
            try
            {
                return UTF8Encoding.UTF8.GetChars(bytes);
            }
            catch
            {
                return null;
            }
        }

        /// <summary>
        ///     Checks for values above 127 and replaces with selected character
        /// </summary>
        /// <param name="bytes">The byte array containing the sequence of bytes to decode.</param>
        /// <param name="byteIndex">The index of the first byte to decode. </param>
        /// <param name="byteCount">The number of bytes to decode. </param>
        /// <returns>A character array containing the results of decoding the specified sequence of bytes.</returns>
        public static char[] GetChars(byte[] bytes, int byteIndex, int byteCount)
        {
            for (var i = byteIndex; i < byteIndex + byteCount; i++)
                if (bytes[i] > 127)
                    bytes[i] = Nonprintreplacement;
            try
            {
                return UTF8Encoding.UTF8.GetChars(bytes, byteIndex, byteCount);
            }
            catch
            {
                return null;
            }
        }
    }
}