// /***************************************************************************
// The Disc Image Chef
// ----------------------------------------------------------------------------
//
// Filename       : Adler32Context.cs
// Author(s)      : Natalia Portillo <claunia@claunia.com>
//
// Component      : Checksums.
//
// --[ Description ] ----------------------------------------------------------
//
//     Implements an Adler-32 algorithm.
//
// --[ License ] --------------------------------------------------------------
//
//     This library is free software; you can redistribute it and/or modify
//     it under the terms of the GNU Lesser General Public License as
//     published by the Free Software Foundation; either version 2.1 of the
//     License, or (at your option) any later version.
//
//     This library is distributed in the hope that it will be useful, but
//     WITHOUT ANY WARRANTY; without even the implied warranty of
//     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
//     Lesser General Public License for more details.
//
//     You should have received a copy of the GNU Lesser General Public
//     License along with this library; if not, see <http://www.gnu.org/licenses/>.
//
// ----------------------------------------------------------------------------
// Copyright © 2011-2016 Natalia Portillo
// ****************************************************************************/

using System;
using System.Text;
using System.IO;

namespace DiscImageChef.Checksums
{
    public class Adler32Context
    {
        UInt16 sum1, sum2;
        const UInt16 AdlerModule = 65521;

        /// <summary>
        /// Initializes the Adler-32 sums
        /// </summary>
        public void Init()
        {
            sum1 = 1;
            sum2 = 0;
        }

        /// <summary>
        /// Updates the hash with data.
        /// </summary>
        /// <param name="data">Data buffer.</param>
        /// <param name="len">Length of buffer to hash.</param>
        public void Update(byte[] data, uint len)
        {
            for(int i = 0; i < len; i++)
            {
                sum1 = (ushort)((sum1 + data[i]) % AdlerModule);
                sum2 = (ushort)((sum2 + sum1) % AdlerModule);
            }
        }

        /// <summary>
        /// Updates the hash with data.
        /// </summary>
        /// <param name="data">Data buffer.</param>
        public void Update(byte[] data)
        {
            Update(data, (uint)data.Length);
        }

        /// <summary>
        /// Returns a byte array of the hash value.
        /// </summary>
        public byte[] Final()
        {
            UInt32 finalSum = (uint)((sum2 << 16) | sum1);
            return BigEndianBitConverter.GetBytes(finalSum);
        }

        /// <summary>
        /// Returns a hexadecimal representation of the hash value.
        /// </summary>
        public string End()
        {
            UInt32 finalSum = (uint)((sum2 << 16) | sum1);
            StringBuilder adlerOutput = new StringBuilder();

            for(int i = 0; i < BigEndianBitConverter.GetBytes(finalSum).Length; i++)
            {
                adlerOutput.Append(BigEndianBitConverter.GetBytes(finalSum)[i].ToString("x2"));
            }

            return adlerOutput.ToString();
        }

        /// <summary>
        /// Gets the hash of a file
        /// </summary>
        /// <param name="filename">File path.</param>
        public static byte[] File(string filename)
        {
            byte[] hash;
            File(filename, out hash);
            return hash;
        }

        /// <summary>
        /// Gets the hash of a file in hexadecimal and as a byte array.
        /// </summary>
        /// <param name="filename">File path.</param>
        /// <param name="hash">Byte array of the hash value.</param>
        public static string File(string filename, out byte[] hash)
        {
            FileStream fileStream = new FileStream(filename, FileMode.Open);
            UInt16 localSum1, localSum2;
            UInt32 finalSum;

            localSum1 = 1;
            localSum2 = 0;

            localSum1 = (ushort)((localSum1 + fileStream.ReadByte()) % AdlerModule);
            localSum2 = (ushort)((localSum2 + localSum1) % AdlerModule);

            finalSum = (uint)((localSum2 << 16) | localSum1);

            hash = BitConverter.GetBytes(finalSum);

            StringBuilder adlerOutput = new StringBuilder();

            for(int i = 0; i < hash.Length; i++)
            {
                adlerOutput.Append(hash[i].ToString("x2"));
            }

            return adlerOutput.ToString();
        }

        /// <summary>
        /// Gets the hash of the specified data buffer.
        /// </summary>
        /// <param name="data">Data buffer.</param>
        /// <param name="len">Length of the data buffer to hash.</param>
        /// <param name="hash">Byte array of the hash value.</param>
        public static string Data(byte[] data, uint len, out byte[] hash)
        {
            UInt16 localSum1, localSum2;
            UInt32 finalSum;

            localSum1 = 1;
            localSum2 = 0;

            for(int i = 0; i < len; i++)
            {
                localSum1 = (ushort)((localSum1 + data[i]) % AdlerModule);
                localSum2 = (ushort)((localSum2 + localSum1) % AdlerModule);
            }

            finalSum = (uint)((localSum2 << 16) | localSum1);

            hash = BitConverter.GetBytes(finalSum);

            StringBuilder adlerOutput = new StringBuilder();

            for(int i = 0; i < hash.Length; i++)
            {
                adlerOutput.Append(hash[i].ToString("x2"));
            }

            return adlerOutput.ToString();
        }

        /// <summary>
        /// Gets the hash of the specified data buffer.
        /// </summary>
        /// <param name="data">Data buffer.</param>
        /// <param name="hash">Byte array of the hash value.</param>
        public static string Data(byte[] data, out byte[] hash)
        {
            return Data(data, (uint)data.Length, out hash);
        }
    }
}