using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.SqlServer.Server;
using System.Data.SqlTypes;
using System.Security.Cryptography;

namespace sha_hash
{
    public class UserDefinedFunctions

    {
        [Microsoft.SqlServer.Server.SqlFunction(IsDeterministic = true, DataAccess = DataAccessKind.None)]

        public static SqlBytes GetHash(SqlString Algorithm, [SqlFacet(MaxSize = -1)] SqlBytes Plaintext)
        {
            if (Algorithm.IsNull || Plaintext.IsNull)
                return SqlBytes.Null;
            bool HashDefined = true;
            HashAlgorithm Hash = null;
            switch (Algorithm.Value.ToUpper())
            {
                case "SHA256":
                    Hash = new SHA256Managed();
                    break;
                case "SHA384":
                    Hash = new SHA384Managed();
                    break;
                case "SHA512":
                    Hash = new SHA512Managed();
                    break;
                default:
                    HashDefined = false;
                    break;
            }
            if (!HashDefined)
            {
                throw new Exception("Unsupported hash algorithm - use SHA256, SHA384 or SHA512");
            }
            byte[] HashBytes = Hash.ComputeHash(Plaintext.Value);
            // Convert result to a SqlBytes value
            return new SqlBytes(HashBytes);
        }
    }
}