using System;
namespace myMethod
{
class computeMD5andSHA1
{
	/// <summary>
	/// 计算文件的 MD5 值
	/// </summary>
	/// <param name="fileName">要计算 MD5 值的文件名和路径</param>
	/// <returns>MD5 值16进制字符串</returns>
	public string MD5File ( string fileName )
	{
		return HashFile ( fileName , "md5" );
	}

	/// <summary>
	/// 计算文件的 sha1 值
	/// </summary>
	/// <param name="fileName">要计算 sha1 值的文件名和路径</param>
	/// <returns>sha1 值16进制字符串</returns>
	public string SHA1File ( string fileName )
	{
		return HashFile ( fileName , "sha1" );
	}


	/// <summary>
	/// 计算文件的哈希值
	/// </summary>
	/// <param name="fileName">要计算哈希值的文件名和路径</param>
	/// <param name="algName">算法:sha1,md5</param>
	/// <returns>哈希值16进制字符串</returns>
	private string HashFile ( string fileName , string algName )
	{
		if ( !System.IO.File.Exists ( fileName ) )
			return string.Empty;

		System.IO.FileStream fs = new System.IO.FileStream ( fileName , System.IO.FileMode.Open , System.IO.FileAccess.Read );
		byte[] hashBytes = HashData ( fs , algName );
		fs.Close();
		return ByteArrayToHexString ( hashBytes );
	}

	/// <summary>
	/// 计算哈希值
	/// </summary>
	/// <param name="stream">要计算哈希值的 Stream</param>
	/// <param name="algName">算法:sha1,md5</param>
	/// <returns>哈希值字节数组</returns>
	private byte[] HashData ( System.IO.Stream stream , string algName )
	{
		System.Security.Cryptography.HashAlgorithm algorithm;
		if ( algName == null )
		{
			throw new ArgumentNullException ( "algName 不能为 null" );
		}
		if ( string.Compare ( algName , "sha1" , true ) == 0 )
		{
			algorithm = System.Security.Cryptography.SHA1.Create();
		}
		else
		{
			if ( string.Compare ( algName , "md5" , true ) != 0 )
			{
				throw new Exception ( "algName 只能使用 sha1 或 md5" );
			}
			algorithm = System.Security.Cryptography.MD5.Create();
		}
		return algorithm.ComputeHash ( stream );
	}

	/// <summary>
	/// 字节数组转换为16进制表示的字符串
	/// </summary>
	private string ByteArrayToHexString ( byte[] buf )
	{
		return BitConverter.ToString ( buf ).Replace ( "-" , "" );
	}
}
}