/* ====================================================================
   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
==================================================================== */

/* ================================================================
 * About NPOI
 * Author: Tony Qu 
 * Author's email: tonyqus (at) gmail.com 
 * Author's Blog: tonyqus.wordpress.com.cn (wp.tonyqus.cn)
 * HomePage: http://www.codeplex.com/npoi
 * Contributors:
 * 
 * ==============================================================*/

using System.Text;

namespace Npoi.Core.Util
{
    using System;
    using System.IO;
    
    /// <summary>
    /// CRC Verification
    /// </summary>
    public class CRC32
    {

        protected ulong[] crc32Table;


        /// <summary>
        /// Initializes a new instance of the <see cref="CRC32"/> class.
        /// </summary>
        public CRC32()
        {
            const ulong ulPolynomial = 0xEDB88320;
            ulong dwCrc;
            crc32Table = new ulong[256];
            int i, j;
            for (i = 0; i < 256; i++)
            {
                dwCrc = (ulong)i;
                for (j = 8; j > 0; j--)
                {
                    if ((dwCrc & 1) == 1)
                        dwCrc = (dwCrc >> 1) ^ ulPolynomial;
                    else
                        dwCrc >>= 1;
                }
                crc32Table[i] = dwCrc;
            }
        }

        /// <summary>
        ///  CRC Bytes.
        /// </summary>
        /// <param name="buffer">The buffer.</param>
        /// <returns></returns>
        public ulong ByteCRC(ref byte[] buffer)
        {
            ulong ulCRC = 0xffffffff;
            ulong len;
            len = (ulong)buffer.Length;
            for (ulong buffptr = 0; buffptr < len; buffptr++)
            {
                ulong tabPtr = ulCRC & 0xFF;
                tabPtr = tabPtr ^ buffer[buffptr];
                ulCRC = ulCRC >> 8;
                ulCRC = ulCRC ^ crc32Table[tabPtr];
            }
            return ulCRC ^ 0xffffffff;
        }


        /// <summary>
        /// String CRC
        /// </summary>
        /// <param name="sInputString">the string</param>
        /// <returns></returns>
        public ulong StringCRC(string sInputString)
        {
            byte[] buffer = EncodingX.Default.GetBytes(sInputString);
            return ByteCRC(ref buffer);
        }

        /// <summary>
        /// File CRC
        /// </summary>
        /// <param name="sInputFilename">the input file</param>
        /// <returns></returns>
        public long FileCRC(string sInputFilename)
        {
            using (FileStream inFile = new System.IO.FileStream(sInputFilename, System.IO.FileMode.Open, System.IO.FileAccess.Read))
            {
                byte[] bInput = new byte[inFile.Length];
                inFile.Read(bInput, 0, bInput.Length);

                return (long)ByteCRC(ref bInput);
            }
        }

        /// <summary>
        /// Stream CRC
        /// </summary>
        /// <param name="inFile">the input stream</param>
        /// <returns></returns>
        public long StreamCRC(Stream inFile)
        {
            try
            {
                byte[] bInput = new byte[inFile.Length];
                inFile.Read(bInput, 0, bInput.Length);
                inFile.Dispose();

                return (long)ByteCRC(ref bInput);
            }
            catch (IOException)
            {
                throw;
            }
        }
    }

}