namespace Common
{
    /// <summary>
    /// 利用GzipStream進(jìn)行壓縮和解壓
    /// </summary>
    public class GZipUtil
    {
        private static GZipStream gZipStream = null;
        /// <summary>
        /// 壓縮
        /// </summary>
        /// <param name="srcBytes"></param>
        /// <returns></returns>
        public static byte[] Compress(byte[] srcBytes)
        {
            MemoryStream ms = new MemoryStream(srcBytes);
            gZipStream = new GZipStream(ms, CompressionMode.Compress);
            gZipStream.Write(srcBytes, 0, srcBytes.Length);
            gZipStream.Close();
            return ms.ToArray();
        }
        /// <summary>
        /// 解壓
        /// </summary>
        /// <param name="srcBytes"></param>
        /// <returns></returns>
        public static byte[] Decompress(byte[] srcBytes)
        {
            MemoryStream srcMs = new MemoryStream(srcBytes);
            gZipStream = new GZipStream(srcMs, CompressionMode.Decompress);
            MemoryStream ms = new MemoryStream();
            byte[] buffer = new byte[40960];
            int n;
            while ((n = gZipStream.Read(buffer, 0, buffer.Length)) > 0)
            {
                ms.Write(buffer, 0, n);
            }
            gZipStream.Close();
            return ms.ToArray();
        }

        /// <summary>
        /// 將指定的字節(jié)數(shù)組壓縮,并寫入到目標(biāo)文件
        /// </summary>
        /// <param name="srcBuffer">指定的源字節(jié)數(shù)組</param>
        /// <param name="destFile">指定的目標(biāo)文件</param>
        public static void CompressData(byte[] srcBuffer, string destFile)
        {
            FileStream destStream = null;
            GZipStream compressedStream = null;
            try
            {
                //打開文件流
                destStream = new FileStream(destFile, FileMode.OpenOrCreate, FileAccess.Write);
                //指定壓縮的目的流（這里是文件流）
                compressedStream = new GZipStream(destStream, CompressionMode.Compress, true);
                //往目的流中寫數(shù)據(jù)，而流將數(shù)據(jù)寫到指定的文件
                compressedStream.Write(srcBuffer, 0, srcBuffer.Length);
            }
            catch (Exception ex)
            {
                throw new Exception(String.Format("壓縮數(shù)據(jù)寫入文件{0}時(shí)發(fā)生錯誤", destFile), ex);
            }
            finally
            {
                // Make sure we allways close all streams              
                if (null != compressedStream)
                {
                    compressedStream.Close();
                    compressedStream.Dispose();
                }

                if (null != destStream)
                    destStream.Close();
            }
        }
        /// <summary>
        /// 將指定的文件解壓,返回解壓后的數(shù)據(jù)
        /// </summary>
        /// <param name="srcFile">指定的源文件</param>
        /// <returns>解壓后得到的數(shù)據(jù)</returns>
        public static byte[] DecompressData(string srcFile)
        {
            if (false == File.Exists(srcFile))
                throw new FileNotFoundException(String.Format("找不到指定的文件{0}", srcFile));
            FileStream sourceStream = null;
            GZipStream decompressedStream = null;
            byte[] quartetBuffer = null;
            try
            {
                sourceStream = new FileStream(srcFile, FileMode.Open, FileAccess.Read, FileShare.Read);

                decompressedStream = new GZipStream(sourceStream, CompressionMode.Decompress, true);

                // Read the footer to determine the length of the destiantion file
                //GZIP文件格式說明:
                //10字節(jié)的頭，包含幻數(shù)、版本號以及時(shí)間戳
                //可選的擴(kuò)展頭，如原文件名
                //文件體，包括DEFLATE壓縮的數(shù)據(jù)
                //8字節(jié)的尾注，包括CRC-32校驗(yàn)和以及未壓縮的原始數(shù)據(jù)長度(4字節(jié)) 文件大小不超過4G

                //為Data指定byte的長度，故意開大byte數(shù)據(jù)的范圍
                //讀取未壓縮的原始數(shù)據(jù)長度
                quartetBuffer = new byte[4];
                long position = sourceStream.Length - 4;
                sourceStream.Position = position;
                sourceStream.Read(quartetBuffer, 0, 4);

                int checkLength = BitConverter.ToInt32(quartetBuffer, 0);
                byte[] data;
                if (checkLength <= sourceStream.Length)
                {
                    data = new byte[Int16.MaxValue];
                }
                else
                {
                    data = new byte[checkLength + 100];
                }
                //每100byte從解壓流中讀出數(shù)據(jù)，并將讀出的數(shù)據(jù)Copy到Data byte[]中，這樣就完成了對數(shù)據(jù)的解壓
                byte[] buffer = new byte[100];

                sourceStream.Position = 0;

                int offset = 0;
                int total = 0;

                while (true)
                {
                    int bytesRead = decompressedStream.Read(buffer, 0, 100);

                    if (bytesRead == 0)
                        break;

                    buffer.CopyTo(data, offset);

                    offset += bytesRead;
                    total += bytesRead;
                }
                //剔除多余的byte
                byte[] actualdata = new byte[total];

                for (int i = 0; i < total; i++)
                    actualdata[i] = data[i];

                return actualdata;
            }
            catch (Exception ex)
            {
                throw new Exception(String.Format("從文件{0}解壓數(shù)據(jù)時(shí)發(fā)生錯誤", srcFile), ex);
            }
            finally
            {
                if (sourceStream != null)
                    sourceStream.Close();

                if (decompressedStream != null)
                    decompressedStream.Close();
            }
        }

    }
}