//

// © Copyright Henrik Ravn 2004

//

// Use, modification and distribution are subject to the Boost Software License, Version 1.0. 

// (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

//

using System;

using System.Runtime.InteropServices;

using System.Text;

namespace DotZLib

{

    #region ChecksumGeneratorBase

    /// <summary>

    /// Implements the common functionality needed for all <see cref="ChecksumGenerator"/>s

    /// </summary>

    /// <example></example>

    public abstract class ChecksumGeneratorBase : ChecksumGenerator

    {

        /// <summary>

        /// The value of the current checksum

        /// </summary>

        protected uint _current;

        /// <summary>

        /// Initializes a new instance of the checksum generator base - the current checksum is 

        /// set to zero

        /// </summary>

        public ChecksumGeneratorBase()

        {

            _current = 0;

        }

        /// <summary>

        /// Initializes a new instance of the checksum generator basewith a specified value

        /// </summary>

        /// <param name="initialValue">The value to set the current checksum to</param>

        public ChecksumGeneratorBase(uint initialValue)

        {

            _current = initialValue;

        }

        /// <summary>

        /// Resets the current checksum to zero

        /// </summary>

        public void Reset() { _current = 0; }

        /// <summary>

        /// Gets the current checksum value

        /// </summary>

        public uint Value { get { return _current; } }

        /// <summary>

        /// Updates the current checksum with part of an array of bytes

        /// </summary>

        /// <param name="data">The data to update the checksum with</param>

        /// <param name="offset">Where in <c>data</c> to start updating</param>

        /// <param name="count">The number of bytes from <c>data</c> to use</param>

        /// <exception cref="ArgumentException">The sum of offset and count is larger than the length of <c>data</c></exception>

        /// <exception cref="NullReferenceException"><c>data</c> is a null reference</exception>

        /// <exception cref="ArgumentOutOfRangeException">Offset or count is negative.</exception>

        /// <remarks>All the other <c>Update</c> methods are implmeneted in terms of this one. 

        /// This is therefore the only method a derived class has to implement</remarks>

        public abstract void Update(byte[] data, int offset, int count);

        /// <summary>

        /// Updates the current checksum with an array of bytes.

        /// </summary>

        /// <param name="data">The data to update the checksum with</param>

        public void Update(byte[] data)

        {

            Update(data, 0, data.Length);

        }

        /// <summary>

        /// Updates the current checksum with the data from a string

        /// </summary>

        /// <param name="data">The string to update the checksum with</param>

        /// <remarks>The characters in the string are converted by the UTF-8 encoding</remarks>

        public void Update(string data)

        {

			Update(Encoding.UTF8.GetBytes(data));

        }

        /// <summary>

        /// Updates the current checksum with the data from a string, using a specific encoding

        /// </summary>

        /// <param name="data">The string to update the checksum with</param>

        /// <param name="encoding">The encoding to use</param>

        public void Update(string data, Encoding encoding)

        {

            Update(encoding.GetBytes(data));

        }

    }

    #endregion

    #region CRC32

    /// <summary>

    /// Implements a CRC32 checksum generator

    /// </summary>

    public sealed class CRC32Checksum : ChecksumGeneratorBase    

    {

        #region DLL imports

        [DllImport("ZLIB1.dll", CallingConvention=CallingConvention.Cdecl)]

        private static extern uint crc32(uint crc, int data, uint length);

        #endregion

        /// <summary>

        /// Initializes a new instance of the CRC32 checksum generator

        /// </summary>

        public CRC32Checksum() : base() {}

        /// <summary>

        /// Initializes a new instance of the CRC32 checksum generator with a specified value

        /// </summary>

        /// <param name="initialValue">The value to set the current checksum to</param>

        public CRC32Checksum(uint initialValue) : base(initialValue) {}

        /// <summary>

        /// Updates the current checksum with part of an array of bytes

        /// </summary>

        /// <param name="data">The data to update the checksum with</param>

        /// <param name="offset">Where in <c>data</c> to start updating</param>

        /// <param name="count">The number of bytes from <c>data</c> to use</param>

        /// <exception cref="ArgumentException">The sum of offset and count is larger than the length of <c>data</c></exception>

        /// <exception cref="NullReferenceException"><c>data</c> is a null reference</exception>

        /// <exception cref="ArgumentOutOfRangeException">Offset or count is negative.</exception>

        public override void Update(byte[] data, int offset, int count)

        {

            if (offset < 0 || count < 0) throw new ArgumentOutOfRangeException();

            if ((offset+count) > data.Length) throw new ArgumentException();

            GCHandle hData = GCHandle.Alloc(data, GCHandleType.Pinned);

            try

            {

                _current = crc32(_current, hData.AddrOfPinnedObject().ToInt32()+offset, (uint)count);

            }

            finally

            {

                hData.Free();

            }

        }

    }

    #endregion

    #region Adler

    /// <summary>

    /// Implements a checksum generator that computes the Adler checksum on data

    /// </summary>

    public sealed class AdlerChecksum : ChecksumGeneratorBase    

    {

        #region DLL imports

        [DllImport("ZLIB1.dll", CallingConvention=CallingConvention.Cdecl)]

        private static extern uint adler32(uint adler, int data, uint length);

        #endregion

        /// <summary>

        /// Initializes a new instance of the Adler checksum generator

        /// </summary>

        public AdlerChecksum() : base() {}

        /// <summary>

        /// Initializes a new instance of the Adler checksum generator with a specified value

        /// </summary>

        /// <param name="initialValue">The value to set the current checksum to</param>

        public AdlerChecksum(uint initialValue) : base(initialValue) {}

        /// <summary>

        /// Updates the current checksum with part of an array of bytes

        /// </summary>

        /// <param name="data">The data to update the checksum with</param>

        /// <param name="offset">Where in <c>data</c> to start updating</param>

        /// <param name="count">The number of bytes from <c>data</c> to use</param>

        /// <exception cref="ArgumentException">The sum of offset and count is larger than the length of <c>data</c></exception>

        /// <exception cref="NullReferenceException"><c>data</c> is a null reference</exception>

        /// <exception cref="ArgumentOutOfRangeException">Offset or count is negative.</exception>

        public override void Update(byte[] data, int offset, int count)

        {

            if (offset < 0 || count < 0) throw new ArgumentOutOfRangeException();

            if ((offset+count) > data.Length) throw new ArgumentException();

            GCHandle hData = GCHandle.Alloc(data, GCHandleType.Pinned);

            try

            {

                _current = adler32(_current, hData.AddrOfPinnedObject().ToInt32()+offset, (uint)count);

            }

            finally

            {

                hData.Free();

            }

        }

    }

    #endregion

}