source: branches/eraser6/Manager/Task.cs @ 935

/* 
 * $Id$
 * Copyright 2008 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 System.IO;
using System.Text.RegularExpressions;
using System.Runtime.Serialization;
using System.ComponentModel;
using Eraser.Util;
using System.Security.Permissions;

namespace Eraser.Manager
{
    /// <summary>
    /// Deals with an erase task.
    /// </summary>
    [Serializable]
    public class Task : ISerializable
    {
        #region Serialization code
        protected Task(SerializationInfo info, StreamingContext context)
        {
            Name = (string)info.GetValue("Name", typeof(string));
            Targets = (ErasureTargetsCollection)info.GetValue("Targets", typeof(ErasureTargetsCollection));
            Targets.Owner = this;
            Log = (Logger)info.GetValue("Log", typeof(Logger));

            Schedule schedule = (Schedule)info.GetValue("Schedule", typeof(Schedule));
            if (schedule.GetType() == Schedule.RunNow.GetType())
                Schedule = Schedule.RunNow;
            else if (schedule.GetType() == Schedule.RunOnRestart.GetType())
                Schedule = Schedule.RunOnRestart;
            else if (schedule is RecurringSchedule)
                Schedule = schedule;
            else
                throw new InvalidDataException(S._("An invalid type was found when loading " +
                    "the task schedule"));
        }

        [SecurityPermission(SecurityAction.Demand, SerializationFormatter = true)]
        public virtual void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            info.AddValue("Name", Name);
            info.AddValue("Schedule", Schedule);
            info.AddValue("Targets", Targets);

            lock (Log)
                info.AddValue("Log", Log);
        }
        #endregion

        /// <summary>
        /// Constructor.
        /// </summary>
        public Task()
        {
            Name = string.Empty;
            Targets = new ErasureTargetsCollection(this);
            Schedule = Schedule.RunNow;
            Log = new Logger();
        }

        /// <summary>
        /// Cancels the task from running, or, if the task is queued for running,
        /// removes the task from the queue.
        /// </summary>
        public void Cancel()
        {
            Executor.UnqueueTask(this);
            Canceled = true;
        }

        /// <summary>
        /// The Executor object which is managing this task.
        /// </summary>
        public Executor Executor { get; internal set; }

        /// <summary>
        /// The name for this task. This is just an opaque value for the user to
        /// recognize the task.
        /// </summary>
        public string Name { get; set; }

        /// <summary>
        /// The name of the task, used for display in UI elements.
        /// </summary>
        public string UIText
        {
            get
            {
                //Simple case, the task name was given by the user.
                if (Name.Length != 0)
                    return Name;

                string result = string.Empty;
                if (Targets.Count < 3)
                    //Simpler case, small set of data.
                    foreach (ErasureTarget tgt in Targets)
                        result += tgt.UIText + ", ";
                else
                    //Ok, we've quite a few entries, get the first, the mid and the end.
                    for (int i = 0; i < Targets.Count; i += Targets.Count / 3)
                        result += Targets[i].UIText + ", ";
                return result.Substring(0, result.Length - 2);
            }
        }

        /// <summary>
        /// Gets the status of the task - whether it is being executed.
        /// </summary>
        public bool Executing { get; private set; }

        /// <summary>
        /// Gets whether this task is currently queued to run. This is true only
        /// if the queue it is in is an explicit request, i.e will run when the
        /// executor is idle.
        /// </summary>
        public bool Queued { get; internal set; }

        /// <summary>
        /// Gets whether the task has been cancelled from execution.
        /// </summary>
        public bool Canceled { get; internal set; }

        /// <summary>
        /// The set of data to erase when this task is executed.
        /// </summary>
        public ErasureTargetsCollection Targets { get; private set; }

        /// <summary>
        /// The schedule for running the task.
        /// </summary>
        public Schedule Schedule { get; set; }

        /// <summary>
        /// The log entries which this task has accumulated.
        /// </summary>
        public Logger Log { get; private set; }

        #region Events
        /// <summary>
        /// The prototype for events handling just a task object as the event argument.
        /// </summary>
        /// <param name="e">The task object.</param>
        public delegate void TaskEventFunction(TaskEventArgs e);

        /// <summary>
        /// The prototype for events handling the progress changed event.
        /// </summary>
        /// <param name="e">The new progress value.</param>
        public delegate void ProgressEventFunction(TaskProgressEventArgs e);

        /// <summary>
        /// The start of the execution of a task.
        /// </summary>
        public event TaskEventFunction TaskStarted;

        /// <summary>
        /// The event object holding all event handlers.
        /// </summary>
        public event ProgressEventFunction ProgressChanged;

        /// <summary>
        /// The completion of the execution of a task.
        /// </summary>
        public event TaskEventFunction TaskFinished;

        /// <summary>
        /// Broadcasts the task execution start event.
        /// </summary>
        /// <param name="e"></param>
        internal void OnTaskStarted(TaskEventArgs e)
        {
            if (TaskStarted != null)
                TaskStarted(e);
            Executing = true;
        }

        /// <summary>
        /// Broadcasts a ProgressChanged event.
        /// </summary>
        /// <param name="e">The new progress value.</param>
        internal void OnProgressChanged(TaskProgressEventArgs e)
        {
            if (ProgressChanged != null)
                ProgressChanged(e);
        }

        /// <summary>
        /// Broadcasts the task execution completion event.
        /// </summary>
        /// <param name="e"></param>
        internal void OnTaskFinished(TaskEventArgs e)
        {
            if (TaskFinished != null)
                TaskFinished(e);
            Executing = false;
        }
        #endregion
    }

    /// <summary>
    /// Represents a generic target of erasure
    /// </summary>
    [Serializable]
    public abstract class ErasureTarget : ISerializable
    {
        #region Serialization code
        protected ErasureTarget(SerializationInfo info, StreamingContext context)
        {
            Guid methodGuid = (Guid)info.GetValue("Method", typeof(Guid));
            if (methodGuid == Guid.Empty)
                method = ErasureMethodManager.Default;
            else
                method = ErasureMethodManager.GetInstance(methodGuid);
        }

        [SecurityPermission(SecurityAction.Demand, SerializationFormatter = true)]
        public virtual void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            info.AddValue("Method", method.Guid);
        }
        #endregion

        /// <summary>
        /// Constructor.
        /// </summary>
        protected ErasureTarget()
        {
        }

        /// <summary>
        /// The method used for erasing the file. If the variable is equal to
        /// ErasureMethodManager.Default then the default is queried for the
        /// task type.
        /// </summary>
        public abstract ErasureMethod Method
        {
            get;
            set;
        }

        /// <summary>
        /// Checks whether a method has been selected for this target. This is
        /// because the Method property will return non-default erasure methods
        /// only.
        /// </summary>
        public bool MethodDefined
        {
            get
            {
                return method != ErasureMethodManager.Default;
            }
        }

        /// <summary>
        /// The task which owns this target.
        /// </summary>
        public Task Task { get; internal set; }

        /// <summary>
        /// Retrieves the text to display representing this task.
        /// </summary>
        public abstract string UIText
        {
            get;
        }

        /// <summary>
        /// Retrieves the amount of data that needs to be written in order to
        /// complete the erasure.
        /// </summary>
        public abstract long TotalData
        {
            get;
        }

        /// <summary>
        /// Erasure method to use for the target.
        /// </summary>
        protected ErasureMethod method { get; set; }
    }

    /// <summary>
    /// Class representing a tangible object (file/folder) to be erased.
    /// </summary>
    [Serializable]
    public abstract class FileSystemObjectTarget : ErasureTarget
    {
        #region Serialization code
        protected FileSystemObjectTarget(SerializationInfo info, StreamingContext context)
            : base(info, context)
        {
            path = (string)info.GetValue("Path", typeof(string));
        }

        [SecurityPermission(SecurityAction.Demand, SerializationFormatter = true)]
        public override void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            base.GetObjectData(info, context);
            info.AddValue("Path", path);
        }
        #endregion

        /// <summary>
        /// Constructor.
        /// </summary>
        protected FileSystemObjectTarget()
        {
        }

        /// <summary>
        /// Retrieves the list of files/folders to erase as a list.
        /// </summary>
        /// <param name="totalSize">Returns the total size in bytes of the
        /// items.</param>
        /// <returns>A list containing the paths to all the files to be erased.</returns>
        internal abstract List<string> GetPaths(out long totalSize);

        /// <summary>
        /// Adds ADSes of the given file to the list.
        /// </summary>
        /// <param name="list">The list to add the ADS paths to.</param>
        /// <param name="file">The file to look for ADSes</param>
        protected void GetPathADSes(List<string> list, out long totalSize, string file)
        {
            totalSize = 0;

            try
            {
                //Get the ADS names
                List<string> adses = Util.File.GetADSes(new FileInfo(file));

                //Then prepend the path.
                foreach (string adsName in adses)
                {
                    string adsPath = file + ':' + adsName;
                    list.Add(adsPath);
                    Util.StreamInfo info = new Util.StreamInfo(adsPath);
                    totalSize += info.Length;
                }
            }
            catch (UnauthorizedAccessException e)
            {
                //The system cannot read the file, assume no ADSes for lack of
                //more information.
                Task.Log.LastSessionEntries.Add(new LogEntry(e.Message, LogLevel.Error));
            }
        }

        /// <summary>
        /// The path to the file or folder referred to by this object.
        /// </summary>
        public string Path
        {
            get { return path; }
            set { path = value; }
        }

        public override ErasureMethod Method
        {
            get
            {
                if (method != ErasureMethodManager.Default)
                    return method;
                return ErasureMethodManager.GetInstance(
                    ManagerLibrary.Instance.Settings.DefaultFileErasureMethod);
            }
            set
            {
                method = value;
            }
        }

        public override string UIText
        {
            get { return Path; }
        }

        public override long TotalData
        {
            get
            {
                long totalSize = 0;
                List<string> paths = GetPaths(out totalSize);
                return Method.CalculateEraseDataSize(paths, totalSize);
            }
        }

        private string path;
    }

    /// <summary>
    /// Class representing a unused space erase.
    /// </summary>
    [Serializable]
    public class UnusedSpaceTarget : ErasureTarget
    {
        #region Serialization code
        protected UnusedSpaceTarget(SerializationInfo info, StreamingContext context)
            : base(info, context)
        {
            Drive = (string)info.GetValue("Drive", typeof(string));
            EraseClusterTips = (bool)info.GetValue("EraseClusterTips", typeof(bool));
        }

        [SecurityPermission(SecurityAction.Demand, SerializationFormatter = true)]
        public override void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            base.GetObjectData(info, context);
            info.AddValue("Drive", Drive);
            info.AddValue("EraseClusterTips", EraseClusterTips);
        }
        #endregion

        /// <summary>
        /// Constructor.
        /// </summary>
        public UnusedSpaceTarget()
        {
        }

        public override ErasureMethod Method
        {
            get
            {
                if (method != ErasureMethodManager.Default)
                    return method;
                return ErasureMethodManager.GetInstance(
                    ManagerLibrary.Instance.Settings.DefaultUnusedSpaceErasureMethod);
            }
            set
            {
                method = value;
            }
        }

        public override string UIText
        {
            get { return S._("Unused disk space ({0})", Drive); }
        }

        public override long TotalData
        {
            get
            {
                VolumeInfo info = VolumeInfo.FromMountpoint(Drive);
                return Method.CalculateEraseDataSize(null, info.AvailableFreeSpace);
            }
        }

        /// <summary>
        /// The drive to erase
        /// </summary>
        public string Drive { get; set; }

        /// <summary>
        /// Whether cluster tips should be erased.
        /// </summary>
        public bool EraseClusterTips { get; set; }
    }

    /// <summary>
    /// Class representing a file to be erased.
    /// </summary>
    [Serializable]
    public class FileTarget : FileSystemObjectTarget
    {
        #region Serialization code
        protected FileTarget(SerializationInfo info, StreamingContext context)
            : base(info, context)
        {
        }
        #endregion

        /// <summary>
        /// Constructor.
        /// </summary>
        public FileTarget()
        {
        }

        internal override List<string> GetPaths(out long totalSize)
        {
            List<string> result = new List<string>();
            totalSize = 0;
            GetPathADSes(result, out totalSize, Path);

            totalSize += new FileInfo(Path).Length;
            result.Add(Path);
            return result;
        }
    }

    /// <summary>
    /// Represents a folder and its files which are to be erased.
    /// </summary>
    [Serializable]
    public class FolderTarget : FileSystemObjectTarget
    {
        #region Serialization code
        protected FolderTarget(SerializationInfo info, StreamingContext context)
            : base(info, context)
        {
            includeMask = (string)info.GetValue("IncludeMask", typeof(string));
            excludeMask = (string)info.GetValue("ExcludeMask", typeof(string));
            deleteIfEmpty = (bool)info.GetValue("DeleteIfEmpty", typeof(bool));
        }

        [SecurityPermission(SecurityAction.Demand, SerializationFormatter = true)]
        public override void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            base.GetObjectData(info, context);
            info.AddValue("IncludeMask", includeMask);
            info.AddValue("ExcludeMask", excludeMask);
            info.AddValue("DeleteIfEmpty", deleteIfEmpty);
        }
        #endregion

        /// <summary>
        /// Constructor.
        /// </summary>
        public FolderTarget()
        {
        }

        internal override List<string> GetPaths(out long totalSize)
        {
            //Get a list to hold all the resulting paths.
            List<string> result = new List<string>();

            //Open the root of the search, including every file matching the pattern
            DirectoryInfo dir = new DirectoryInfo(Path);

            //List recursively all the files which match the include pattern.
            FileInfo[] files = GetFiles(dir);

            //Then exclude each file and finalize the list and total file size
            totalSize = 0;
            if (ExcludeMask.Length != 0)
            {
                string regex = Regex.Escape(ExcludeMask).Replace("\\*", ".*").
                    Replace("\\?", ".");
                Regex excludePattern = new Regex(regex, RegexOptions.IgnoreCase);
                foreach (FileInfo file in files)
                    if ((file.Attributes & FileAttributes.ReparsePoint) == 0 &&
                        excludePattern.Matches(file.FullName).Count == 0)
                    {
                        totalSize += file.Length;
                        GetPathADSes(result, out totalSize, file.FullName);
                        result.Add(file.FullName);
                    }
            }
            else
                foreach (FileInfo file in files)
                {
                    if ((file.Attributes & FileAttributes.ReparsePoint) != 0)
                        continue;

                    totalSize += file.Length;
                    GetPathADSes(result, out totalSize, file.FullName);
                    result.Add(file.FullName);
                }

            //Return the filtered list.
            return result;
        }

        /// <summary>
        /// Gets all files in the provided directory.
        /// </summary>
        /// <param name="info">The directory to look files in.</param>
        /// <returns>A list of files found in the directory matching the IncludeMask
        /// property.</returns>
        private FileInfo[] GetFiles(DirectoryInfo info)
        {
            List<FileInfo> result = new List<FileInfo>();
            foreach (DirectoryInfo dir in info.GetDirectories())
                try
                {
                    result.AddRange(GetFiles(dir));
                }
                catch (Exception e)
                {
                    //Ignore, but log.
                    Task.Log.LastSessionEntries.Add(new LogEntry(S._("Could not erase {0} because {1}",
                        dir.FullName, e.Message), LogLevel.Error));
                }

            if (includeMask.Length == 0)
                result.AddRange(info.GetFiles());
            else
                result.AddRange(info.GetFiles(includeMask, SearchOption.TopDirectoryOnly));
            return result.ToArray();
        }

        /// <summary>
        /// A wildcard expression stating the condition for the set of files to include.
        /// The include mask is applied before the exclude mask is applied. If this value
        /// is empty, all files and folders within the folder specified is included.
        /// </summary>
        public string IncludeMask
        {
            get { return includeMask; }
            set { includeMask = value; }
        }

        /// <summary>
        /// A wildcard expression stating the condition for removing files from the set
        /// of included files. If this value is omitted, all files and folders extracted
        /// by the inclusion mask is erased.
        /// </summary>
        public string ExcludeMask
        {
            get { return excludeMask; }
            set { excludeMask = value; }
        }

        /// <summary>
        /// Determines if Eraser should delete the folder after the erase process.
        /// </summary>
        public bool DeleteIfEmpty
        {
            get { return deleteIfEmpty; }
            set { deleteIfEmpty = value; }
        }

        private string includeMask = string.Empty;
        private string excludeMask = string.Empty;
        private bool deleteIfEmpty = true;
    }

    [Serializable]
    public class RecycleBinTarget : FileSystemObjectTarget
    {
        #region Serialization code
        protected RecycleBinTarget(SerializationInfo info, StreamingContext context)
            : base(info, context)
        {
        }
        #endregion

        public RecycleBinTarget()
        {
        }

        internal override List<string> GetPaths(out long totalSize)
        {
            totalSize = 0;
            List<string> result = new List<string>();
            string[] rootDirectory = new string[] {
                    "$RECYCLE.BIN",
                    "RECYCLER"
                };

            foreach (DriveInfo drive in DriveInfo.GetDrives())
            {
                foreach (string rootDir in rootDirectory)
                {
                    DirectoryInfo dir = new DirectoryInfo(
                        System.IO.Path.Combine(
                            System.IO.Path.Combine(drive.Name, rootDir),
                            System.Security.Principal.WindowsIdentity.GetCurrent().
                                User.ToString()));
                    if (!dir.Exists)
                        continue;

                    GetRecyclerFiles(dir, ref result, ref totalSize);
                }
            }

            return result;
        }

        /// <summary>
        /// Retrieves all files within this folder, without exclusions.
        /// </summary>
        /// <param name="info">The DirectoryInfo object representing the folder to traverse.</param>
        /// <param name="paths">The list of files to store path information in.</param>
        /// <param name="totalSize">Receives the total size of the files.</param>
        private void GetRecyclerFiles(DirectoryInfo info, ref List<string> paths,
            ref long totalSize)
        {
            try
            {
                foreach (FileSystemInfo fsInfo in info.GetFileSystemInfos())
                {
                    if (fsInfo is FileInfo)
                    {
                        paths.Add(fsInfo.FullName);
                        totalSize += ((FileInfo)fsInfo).Length;
                        GetPathADSes(paths, out totalSize, fsInfo.FullName);
                    }
                    else
                        GetRecyclerFiles((DirectoryInfo)fsInfo, ref paths, ref totalSize);
                }
            }
            catch (UnauthorizedAccessException e)
            {
                Task.Log.LastSessionEntries.Add(new LogEntry(e.Message, LogLevel.Error));
            }
        }

        /// <summary>
        /// Retrieves the text to display representing this task.
        /// </summary>
        public override string UIText
        {
            get
            {
                return S._("Recycle Bin");
            }
        }
    }

    /// <summary>
    /// Maintains a collection of erasure targets.
    /// </summary>
    [Serializable]
    public class ErasureTargetsCollection : IList<ErasureTarget>, ICollection<ErasureTarget>,
        IEnumerable<ErasureTarget>, ISerializable
    {
        #region Constructors
        internal ErasureTargetsCollection(Task owner)
        {
            this.list = new List<ErasureTarget>();
            this.owner = owner;
        }

        internal ErasureTargetsCollection(Task owner, int capacity)
            : this(owner)
        {
            list.Capacity = capacity;
        }

        internal ErasureTargetsCollection(Task owner, IEnumerable<ErasureTarget> targets)
            : this(owner)
        {
            list.AddRange(targets);
        }
        #endregion

        #region Serialization Code
        protected ErasureTargetsCollection(SerializationInfo info, StreamingContext context)
        {
            list = (List<ErasureTarget>)info.GetValue("list", typeof(List<ErasureTarget>));
        }

        [SecurityPermission(SecurityAction.Demand, SerializationFormatter = true)]
        public virtual void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            info.AddValue("list", list);
        }
        #endregion

        #region IEnumerable<ErasureTarget> Members
        public IEnumerator<ErasureTarget> GetEnumerator()
        {
            return list.GetEnumerator();
        }
        #endregion

        #region IEnumerable Members
        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }
        #endregion

        #region ICollection<ErasureTarget> Members
        public void Add(ErasureTarget item)
        {
            item.Task = owner;
            list.Add(item);
        }

        public void Clear()
        {
            foreach (ErasureTarget item in list)
                Remove(item);
        }

        public bool Contains(ErasureTarget item)
        {
            return list.Contains(item);
        }

        public void CopyTo(ErasureTarget[] array, int arrayIndex)
        {
            list.CopyTo(array, arrayIndex);
        }

        public int Count
        {
            get
            {
                return list.Count;
            }
        }

        public bool IsReadOnly
        {
            get
            {
                return false;
            }
        }

        public bool Remove(ErasureTarget item)
        {
            int index = list.IndexOf(item);
            if (index < 0)
                return false;

            RemoveAt(index);
            return true;
        }
        #endregion

        #region IList<ErasureTarget> Members
        public int IndexOf(ErasureTarget item)
        {
            return list.IndexOf(item);
        }

        public void Insert(int index, ErasureTarget item)
        {
            item.Task = owner;
            list.Insert(index, item);
        }

        public void RemoveAt(int index)
        {
            list.RemoveAt(index);
        }

        public ErasureTarget this[int index]
        {
            get
            {
                return list[index];
            }
            set
            {
                list[index] = value;
            }
        }
        #endregion

        /// <summary>
        /// The owner of this list of targets.
        /// </summary>
        public Task Owner
        {
            get
            {
                return owner;
            }
            internal set
            {
                owner = value;
                foreach (ErasureTarget target in list)
                    target.Task = owner;
            }
        }

        /// <summary>
        /// The owner of this list of targets. All targets added to this list
        /// will have the owner set to this object.
        /// </summary>
        private Task owner;

        /// <summary>
        /// The list bring the data store behind this object.
        /// </summary>
        private List<ErasureTarget> list;
    }

    /// <summary>
    /// A base event class for all event arguments involving a task.
    /// </summary>
    public class TaskEventArgs : EventArgs
    {
        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="task">The task being run.</param>
        public TaskEventArgs(Task task)
        {
            this.task = task;
        }

        /// <summary>
        /// The executing task.
        /// </summary>
        public Task Task
        {
            get { return task; }
        }

        private Task task;
    }

    /// <summary>
    /// A Event argument object containing the progress of the task.
    /// </summary>
    public class TaskProgressEventArgs : TaskEventArgs
    {
        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="task">The task being run.</param>
        public TaskProgressEventArgs(Task task)
            : base(task)
        {
        }

        /// <summary>
        /// A number from 0 to 1 detailing the overall progress of the task.
        /// </summary>
        public float OverallProgress
        {
            get { return overallProgress; }
        }

        /// <summary>
        /// The amount of time left for the operation to complete, in seconds.
        /// </summary>
        public TimeSpan TimeLeft
        {
            get { return timeLeft; }
            internal set { timeLeft = value; }
        }

        /// <summary>
        /// The current erasure target - the current item being erased.
        /// </summary>
        public ErasureTarget CurrentTarget
        {
            get { return currentTarget; }
            internal set { currentTarget = value; }
        }

        /// <summary>
        /// The current index of the target.
        /// </summary>
        public int CurrentTargetIndex
        {
            get { return currentTargetIndex; }
            internal set { currentTargetIndex = value; }
        }

        /// <summary>
        /// The total number of passes to complete before this erasure method is
        /// completed.
        /// </summary>
        public int CurrentTargetTotalPasses
        {
            get { return currentTargetTotalPasses; }
            internal set { currentTargetTotalPasses = value; }
        }

        /// <summary>
        /// A number from 0 to 1 detailing the overall progress of the item.
        /// </summary>
        public float CurrentItemProgress
        {
            get { return currentItemProgress; }
            internal set { currentItemProgress = value; }
        }

        /// <summary>
        /// The file name of the item being erased.
        /// </summary>
        public string CurrentItemName
        {
            get { return currentItemName; }
            internal set { currentItemName = value; }
        }

        /// <summary>
        /// The pass number of a multi-pass erasure method.
        /// </summary>
        public int CurrentItemPass
        {
            get { return currentItemPass; }
            internal set { currentItemPass = value; }
        }

        /// <summary>
        /// The progress made by the current target.
        /// </summary>
        internal float CurrentTargetProgress
        {
            set
            {
                overallProgress = Math.Min(
                    (value + (float)(CurrentTargetIndex - 1)) / Task.Targets.Count,
                    1.0f);
            }
        }

        private float overallProgress;
        private TimeSpan timeLeft = new TimeSpan(0, 0, -1);

        private ErasureTarget currentTarget;
        private int currentTargetIndex;
        private int currentTargetTotalPasses;

        private float currentItemProgress;
        private string currentItemName;
        private int currentItemPass = 1;
    }
}