#region Disclaimer / License
// Copyright (C) 2015, The Duplicati Team
// http://www.duplicati.com, info@duplicati.com
// 
// 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, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
// 
#endregion
using System;
using System.Collections.Generic;
using System.Text;
using Duplicati.Library.Interface;
using System.IO;
using System.Security.Cryptography;

namespace Duplicati.Library.Encryption
{
    /// <summary>
    /// Implements AES encryption
    /// </summary>
    public class AESEncryption : EncryptionBase
    {

        /// <summary>
        /// The commandline option supplied if an explicit thread level should be set (--aes-set-threadlevel)
        /// </summary>
        private const string COMMANDLINE_SET_THREADLEVEL = "aes-set-threadlevel";

        /// <summary>
        /// The key used to encrypt the data
        /// </summary>
        private string m_key;

        /// <summary>
        /// The cached value for size overhead
        /// </summary>
        private static long m_cachedsizeoverhead = -1;

        /// <summary>
        /// The thread level to pass to SharpAESCrypt. 0 for default.
        /// </summary>
        private static int m_usethreadlevel = 0;

        /// <summary>
        /// Default constructor, used to read file extension and supported commands
        /// </summary>
        public AESEncryption()
        {
        }

        /// <summary>
        /// Constructs a new AES encryption/decyption instance
        /// </summary>
        /// <param name="key">The key used for encryption. The key gets stretched through SHA hashing to fit the key size requirements</param>
        public AESEncryption(string passphrase, Dictionary<string, string> options)
        {
            if(string.IsNullOrEmpty(passphrase))
                throw new ArgumentException(Strings.AESEncryption.EmptyKeyError, "passphrase");

            m_key = passphrase;

            string strTL;
            if (options != null && options.TryGetValue(COMMANDLINE_SET_THREADLEVEL, out strTL))
            {
                int useTL;
                if (int.TryParse(strTL, out useTL))
                {
                    // finally set thread level in a range of 0 (default) to 4
                    m_usethreadlevel = Math.Max(0, (Math.Min(4, useTL)));
                }
            }



        }

        #region IEncryption Members

        /// <summary>
        /// The extension that the encryption implementation adds to the filename
        /// </summary>
        /// <value>The filename extension.</value>
        public override string FilenameExtension { get { return "aes"; } }
        /// <summary>
        /// A localized description of the encryption module
        /// </summary>
        /// <value>The description.</value>
        public override string Description { get { return string.Format(Strings.AESEncryption.Description_v2); } }
        /// <summary>
        /// A localized string describing the encryption module with a friendly name
        /// </summary>
        /// <value>The display name.</value>
        public override string DisplayName { get { return Strings.AESEncryption.DisplayName; } }
        /// <summary>
        /// Dispose the specified disposing.
        /// </summary>
        /// <param name="disposing">If set to <c>true</c> disposing.</param>
        protected override void Dispose(bool disposing) { m_key = null; }

        /// <summary>
        /// Returns the size in bytes of the overhead that will be added to a file of the given size when encrypted
        /// </summary>
        /// <param name="filesize">The size of the file to encrypt</param>
        /// <returns>The size of the overhead in bytes</returns>
        public override long SizeOverhead(long filesize)
        {
            if (m_cachedsizeoverhead != -1)
                return m_cachedsizeoverhead;
            
            //If we use 1, we trigger the blocksize.
            //As the AES algorithm does not alter the size,
            // the results are the same as for the real size,
            // but a single byte encryption is much faster.
            return m_cachedsizeoverhead = base.SizeOverhead(1);
        }

        /// <summary>
        /// Encrypts the stream
        /// </summary>
        /// <param name="input">The target stream</param>
        /// <returns>An encrypted stream that can be written to</returns>
        public override Stream Encrypt(Stream input)
        {
            var cryptoStream = new SharpAESCrypt.SharpAESCrypt(m_key, input, SharpAESCrypt.OperationMode.Encrypt);
            if (m_usethreadlevel != 0) cryptoStream.MaxCryptoThreads = m_usethreadlevel;
            return cryptoStream;
        }

        /// <summary>
        /// Decrypts the stream to the output stream
        /// </summary>
        /// <param name="input">The encrypted stream</param>
        /// <returns>The unencrypted stream</returns>
        public override Stream Decrypt(Stream input)
        {
            var cryptoStream = new SharpAESCrypt.SharpAESCrypt(m_key, input, SharpAESCrypt.OperationMode.Decrypt);
            if (m_usethreadlevel != 0) cryptoStream.MaxCryptoThreads = m_usethreadlevel;
            return cryptoStream;
        }

        /// <summary>
        /// Gets a list of supported commandline arguments
        /// </summary>
        /// <value>The supported commands.</value>
        public override IList<ICommandLineArgument> SupportedCommands
        {
            get
            {
                return new List<ICommandLineArgument>(new ICommandLineArgument[] {
                    new CommandLineArgument(
                        COMMANDLINE_SET_THREADLEVEL, 
                        CommandLineArgument.ArgumentType.Enumeration, 
                        Strings.AESEncryption.AessetthreadlevelShort, 
                        Strings.AESEncryption.AessetthreadlevelLong,
                        "0", 
                        null, 
                        new string[] {"0", "1", "2", "3", "4"}
                        ),
                });
            }
        }

        #endregion
    }
}