source: trunk/eraser6/Eraser.DefaultPlugins/ErasureMethods/FirstLast16KB.cs @ 1756

/* 
 * $Id$
 * Copyright 2008-2010 The Eraser Project
 * Original Author: Joel Low <lowjoel@users.sourceforge.net>
 * Modified By:
 * 
 * This file is part of Eraser.
 * 
 * Eraser is free software: you can redistribute it and/or modify it under the
 * terms of the GNU General Public License as published by the Free Software
 * Foundation, either version 3 of the License, or (at your option) any later
 * version.
 * 
 * Eraser 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 General Public License for more details.
 * 
 * A copy of the GNU General Public License can be found at
 * <http://www.gnu.org/licenses/>.
 */

using System;
using System.Collections.Generic;
using System.Text;

using Eraser.Manager;
using Eraser.Util;
using System.IO;
using System.Threading;
using System.Windows.Forms;

namespace Eraser.DefaultPlugins
{
    sealed class FirstLast16KB : ErasureMethod
    {
        public FirstLast16KB()
        {
            try
            {
                //Try to retrieve the set erasure method
                if (DefaultPlugin.Settings.FL16Method != Guid.Empty)
                    method = ErasureMethodManager.GetInstance(
                        DefaultPlugin.Settings.FL16Method);
                else if (ManagerLibrary.Settings.DefaultFileErasureMethod != Guid)
                    method = ErasureMethodManager.GetInstance(
                        ManagerLibrary.Settings.DefaultFileErasureMethod);
                else
                    method = ErasureMethodManager.GetInstance(new Gutmann().Guid);
            }
            catch (ErasureMethodNotFoundException)
            {
                MessageBox.Show(S._("The First/last 16KB erasure method " +
                    "requires another erasure method to erase the file.\n\nThis must " +
                    "be set in the Plugin Settings dialog."), Name, MessageBoxButtons.OK,
                    MessageBoxIcon.Error, MessageBoxDefaultButton.Button1,
                    S.IsRightToLeft(null) ? MessageBoxOptions.RtlReading : 0);
            }
        }

        public override string Name
        {
            get { return S._("First/last 16KB Erasure"); }
        }

        public override int Passes
        {
            get { return 0; } //Variable number, depending on defaults.
        }

        public override Guid Guid
        {
            get { return new Guid("{0C2E07BF-0207-49a3-ADE8-46F9E1499C01}"); }
        }

        public override long CalculateEraseDataSize(ICollection<string> paths, long targetSize)
        {
            //If we have no default or we are the default then throw an exception
            if (method == null || method.Guid == Guid)
                throw new InvalidOperationException(S._("The First/last 16KB erasure method " +
                    "requires another erasure method to erase the file.\n\nThis must " +
                    "be set in the Plugin Settings dialog."));

            //Amount of data required to be written.
            long amountToWrite = 0;
            if (paths == null)
            {
                if (targetSize <= DataSize)
                    amountToWrite = targetSize;
                else
                    amountToWrite = DataSize * 2;
            }
            else
                amountToWrite = paths.Count * DataSize * 2;

            //The final amount has to be multiplied by the number of passes.
            return amountToWrite * method.Passes;
        }

        public override void Erase(Stream strm, long erasureLength, Prng prng,
            ErasureMethodProgressFunction callback)
        {
            //If we have no default or we are the default then throw an exception
            if (method == null || method.Guid == Guid)
                throw new InvalidOperationException(S._("The First/last 16KB erasure method " +
                    "requires another erasure method to erase the file.\n\nThis must " +
                    "be set in the Plugin Settings dialog."));

            //Make sure that the erasureLength passed in here is the maximum value
            //for the size of long, since we don't want to write extra or write
            //less.
            if (erasureLength != long.MaxValue)
                throw new ArgumentException(S._("The amount of data erased should not be " +
                    "limited, since this is a self-limiting erasure method."));

            //If the target stream is shorter than or equal to 32kb, just forward it to
            //the default function.
            if (strm.Length < DataSize * 2)
            {
                method.Erase(strm, erasureLength, prng, callback);
                return;
            }

            //We need to intercept the callback function as we run the erasure method
            //twice on two parts of the file.
            long dataSize = method.CalculateEraseDataSize(null, DataSize * 2);
            ErasureMethodProgressFunction customCallback =
                delegate(long lastWritten, long totalData, int currentPass)
                {
                    callback(lastWritten, dataSize, currentPass);
                };

            //Seek to the beginning and write 16kb.
            strm.Seek(0, SeekOrigin.Begin);
            method.Erase(strm, dataSize, prng, callback == null ? null: customCallback);

            //Seek to the end - 16kb, and write.
            strm.Seek(-dataSize, SeekOrigin.End);
            method.Erase(strm, long.MaxValue, prng, callback == null ? null : customCallback);
        }

        /// <summary>
        /// The amount of data to be erased from the header and the end of the file.
        /// </summary>
        private const long DataSize = 16 * 1024;

        private ErasureMethod method;
    }
}