source: branches/eraser6/Eraser/UpdateForm.cs @ 516

/* 
 * $Id$
 * 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.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Net;
using System.Reflection;
using System.IO;
using System.Xml;
using Eraser.Util;
using System.Net.Cache;

namespace Eraser
{
    public partial class UpdateForm : Form
    {
        /// <summary>
        /// Constructor.
        /// </summary>
        public UpdateForm()
        {
            InitializeComponent();

            updates = new UpdateManager();
            updateListDownloader.RunWorkerAsync();
        }

        #region Update List retrieval
        /// <summary>
        /// Downloads and parses the list of updates available for this client.
        /// </summary>
        /// <param name="sender">The object triggering this event/</param>
        /// <param name="e">Event argument.</param>
        private void updateListDownloader_DoWork(object sender, DoWorkEventArgs e)
        {
            try
            {
                updates.OnProgressEvent += updateListDownloader_ProgressChanged;
                updates.GetUpdates();
            }
            finally
            {
                updates.OnProgressEvent -= updateListDownloader_ProgressChanged;
            }
        }

        /// <summary>
        /// Called when progress has been made in the update list download.
        /// </summary>
        /// <param name="sender">The object triggering this event/</param>
        /// <param name="e">Event argument.</param>
        private void updateListDownloader_ProgressChanged(object sender, UpdateManager.ProgressEventArgs e)
        {
            if (InvokeRequired)
            {
                Invoke(new UpdateManager.ProgressEventFunction(updateListDownloader_ProgressChanged),
                    sender, e);
                return;
            }

            progressPb.Style = ProgressBarStyle.Continuous;
            progressPb.Value = (int)(e.OverallProgressPercentage * 100);
            progressLbl.Text = e.Message;

            if (progressPb.Value == 100)
                progressProgressLbl.Text = S._("Processing update list...");
        }

        /// <summary>
        /// Displays the parsed updates on the updates list view, filtering and displaying
        /// only those relevant to the current system's architecture.
        /// </summary>
        /// <param name="sender">The object triggering this event/</param>
        /// <param name="e">Event argument.</param>
        private void updateListDownloader_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            //The Error property will normally be null unless there are errors during the download.
            if (e.Error != null)
            {
                MessageBox.Show(this, e.Error.Message, S._("Eraser"),
                    MessageBoxButtons.OK, MessageBoxIcon.Error);
                Close();
                return;
            }

            progressPanel.Visible = false;

            updatesPanel.Show();
            updatesPanel.Visible = true;
            updatesPanel.ResumeLayout();

            //Get a list of translatable categories (this will change as more categories
            //are added)
            Dictionary<string, string> updateCategories = new Dictionary<string, string>();
            updateCategories.Add("updates", S._("Updates"));
            updateCategories.Add("plugins", S._("Plugins"));

            //Only include those whose architecture is compatible with ours.
            List<string> compatibleArchs = new List<string>();
            {
                //any is always compatible.
                compatibleArchs.Add("any");

                KernelAPI.SYSTEM_INFO info = new KernelAPI.SYSTEM_INFO();
                KernelAPI.GetSystemInfo(out info);
                switch (info.processorArchitecture)
                {
                    case KernelAPI.SYSTEM_INFO.ProcessorArchitecture.PROCESSOR_ARCHITECTURE_AMD64:
                        compatibleArchs.Add("x64");
                        break;

                    case KernelAPI.SYSTEM_INFO.ProcessorArchitecture.PROCESSOR_ARCHITECTURE_IA64:
                        compatibleArchs.Add("ia64");
                        break;

                    case KernelAPI.SYSTEM_INFO.ProcessorArchitecture.PROCESSOR_ARCHITECTURE_INTEL:
                        compatibleArchs.Add("x86");
                        break;
                }
            }

            foreach (string key in updates.Categories)
            {
                ListViewGroup group = new ListViewGroup(updateCategories.ContainsKey(key) ?
                    updateCategories[key] : key);
                updatesLv.Groups.Add(group);

                foreach (UpdateManager.Update update in updates[key])
                {
                    //Skip if this update won't work on our current architecture.
                    if (compatibleArchs.IndexOf(update.Architecture) == -1)
                        continue;

                    ListViewItem item = new ListViewItem(update.Name);
                    item.SubItems.Add(update.Version.ToString());
                    item.SubItems.Add(update.Publisher);
                    item.SubItems.Add(update.FileSize.ToString());

                    item.Tag = update;
                    item.Group = group;
                    item.Checked = true;

                    updatesLv.Items.Add(item);
                    uiUpdates.Add(update, new UpdateData(update, item));
                }
            }
        }
        #endregion

        #region Update downloader
        /// <summary>
        /// Handles the Install button click; fetches and installs the updates selected.
        /// </summary>
        /// <param name="sender">The object triggering this event/</param>
        /// <param name="e">Event argument.</param>
        private void updatesBtn_Click(object sender, EventArgs e)
        {
            updatesPanel.Visible = false;
            downloadingPnl.Show();
            List<UpdateManager.Update> updatesToInstall =
                new List<UpdateManager.Update>();

            //Collect the items that need to be installed
            foreach (ListViewItem item in updatesLv.Items)
                if (item.Checked)
                {
                    item.Remove();
                    item.SubItems.RemoveAt(1);
                    item.SubItems.RemoveAt(1);
                    downloadingLv.Items.Add(item);

                    updatesToInstall.Add((UpdateManager.Update)item.Tag);
                }
                else
                    uiUpdates.Remove((UpdateManager.Update)item.Tag);

            //Then run the thread.
            downloader.RunWorkerAsync(updatesToInstall);
        }

        /// <summary>
        /// Background thread to do the downloading and installing of updates.
        /// </summary>
        /// <param name="sender">The object triggering this event/</param>
        /// <param name="e">Event argument.</param>
        private void downloader_DoWork(object sender, DoWorkEventArgs e)
        {
            try
            {
                updates.OnProgressEvent += downloader_ProgressChanged;
                object downloadedUpdates = updates.DownloadUpdates((List<UpdateManager.Update>)e.Argument);
                e.Result = downloadedUpdates;
            }
            finally
            {
                updates.OnProgressEvent -= downloader_ProgressChanged;
            }
        }

        /// <summary>
        /// Handles the download progress changed event.
        /// </summary>
        /// <param name="sender">The object triggering this event/</param>
        /// <param name="e">Event argument.</param>
        private void downloader_ProgressChanged(object sender, UpdateManager.ProgressEventArgs e)
        {
            if (InvokeRequired)
            {
                Invoke(new UpdateManager.ProgressEventFunction(downloader_ProgressChanged),
                    sender, e);
                return;
            }

            UpdateData update = uiUpdates[(UpdateManager.Update)e.UserState];
            int amountLeft = (int)((1 - e.ProgressPercentage) * update.Update.FileSize);

            if (e is UpdateManager.ProgressErrorEventArgs)
            {
                update.Error = ((UpdateManager.ProgressErrorEventArgs)e).Exception;
                update.LVItem.ImageIndex = 3;
                update.LVItem.SubItems[1].Text = S._("Error");
                update.LVItem.ToolTipText = update.Error.Message;
            }
            else
            {
                if (amountLeft == 0)
                {
                    update.LVItem.ImageIndex = -1;
                    update.LVItem.SubItems[1].Text = S._("Downloaded");
                }
                else
                {
                    update.LVItem.ImageIndex = 0;
                    update.LVItem.SubItems[1].Text = amountLeft.ToString();
                }
            }

            downloadingItemLbl.Text = e.Message;
            downloadingItemPb.Value = (int)(e.ProgressPercentage * 100);
            downloadingOverallPb.Value = (int)(e.OverallProgressPercentage * 100);

            long amountToDownload = 0;
            foreach (ListViewItem lvItem in downloadingLv.Items)
                try
                {
                    amountToDownload +=
                        Convert.ToInt32(lvItem.SubItems[1].Text);
                }
                catch (FormatException)
                {
                }

            downloadingOverallLbl.Text = string.Format(S._("Overall progress: {0} bytes left"),
                amountToDownload);
        }

        /// <summary>
        /// Handles the completion of updating event
        /// </summary>
        /// <param name="sender">The object triggering this event/</param>
        /// <param name="e">Event argument.</param>
        private void downloader_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            if (e.Error != null)
            {
                MessageBox.Show(this, e.Error.Message, S._("Eraser"), MessageBoxButtons.OK,
                    MessageBoxIcon.Error);
                Close();
                return;
            }

            downloadingPnl.Visible = false;
            installingPnl.Show();

            foreach (ListViewItem item in downloadingLv.Items)
            {
                item.Remove();
                installingLv.Items.Add(item);

                UpdateData update = uiUpdates[(UpdateManager.Update)item.Tag];
                if (update.Error == null)
                    item.SubItems[1].Text = string.Empty;
                else
                    item.SubItems[1].Text = string.Format(S._("Error: {0}"),
                        update.Error.Message);
            }

            installer.RunWorkerAsync(e.Result);
        }
        #endregion

        #region Update installer
        /// <summary>
        /// Background thread to install downloaded updates
        /// </summary>
        /// <param name="sender">The object triggering this event/</param>
        /// <param name="e">Event argument.</param>
        private void installer_DoWork(object sender, DoWorkEventArgs e)
        {
            try
            {
                updates.OnProgressEvent += installer_ProgressChanged;
                updates.InstallUpdates(e.Argument);
            }
            finally
            {
                updates.OnProgressEvent -= installer_ProgressChanged;
            }
        }

        /// <summary>
        /// Handles the progress events generated during update installation.
        /// </summary>
        /// <param name="sender">The object triggering this event/</param>
        /// <param name="e">Event argument.</param>
        private void installer_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            if (InvokeRequired)
            {
                Invoke(new UpdateManager.ProgressEventFunction(installer_ProgressChanged),
                    sender, e);
                return;
            }

            UpdateData update = uiUpdates[(UpdateManager.Update)e.UserState];
            if (e is UpdateManager.ProgressErrorEventArgs)
            {
                update.Error = ((UpdateManager.ProgressErrorEventArgs)e).Exception;
                update.LVItem.ImageIndex = 3;
                update.LVItem.SubItems[1].Text = string.Format(S._("Error: {0}"),
                    update.Error.Message);
            }
            else
                switch (update.LVItem.ImageIndex)
                {
                    case -1:
                        update.LVItem.ImageIndex = 1;
                        break;
                    case 1:
                        update.LVItem.ImageIndex = 2;
                        break;
                }
        }
        #endregion

        /// <summary>
        /// The Update manager instance used by this form.
        /// </summary>
        UpdateManager updates;

        /// <summary>
        /// Maps listview items to the UpdateManager.Update object.
        /// </summary>
        Dictionary<UpdateManager.Update, UpdateData> uiUpdates =
            new Dictionary<UpdateManager.Update, UpdateData>();

        /// <summary>
        /// Manages information associated with the update.
        /// </summary>
        private class UpdateData
        {
            /// <summary>
            /// Constructor.
            /// </summary>
            /// <param name="update">The UpdateManager.Update object containing the
            /// internal representation of the update.</param>
            /// <param name="item">The ListViewItem used for the display of the
            /// update.</param>
            public UpdateData(UpdateManager.Update update, ListViewItem item)
            {
                Update = update;
                LVItem = item;
                Error = null;
            }

            /// <summary>
            /// The UpdateManager.Update object containing the internal representation
            /// of the update.
            /// </summary>
            public UpdateManager.Update Update;

            /// <summary>
            /// The ListViewItem used for the display of the update.
            /// </summary>
            public ListViewItem LVItem;

            /// <summary>
            /// The error raised when downloading/installing the update, if any. Null
            /// otherwise.
            /// </summary>
            public Exception Error;
        }
    }

    public class UpdateManager
    {
        /// <summary>
        /// Represents an update available on the server.
        /// </summary>
        public struct Update
        {
            public string Name;
            public Version Version;
            public string Publisher;
            public string Architecture;
            public long FileSize;
            public string Link;
        }

        /// <summary>
        /// Specialised progress event argument, containing message describing
        /// current action, and overall progress percentage.
        /// </summary>
        public class ProgressEventArgs : ProgressChangedEventArgs
        {
            public ProgressEventArgs(float progressPercentage, float overallPercentage,
                object userState, string message)
                : base((int)(progressPercentage * 100), userState)
            {
                this.progressPercentage = progressPercentage;
                this.overallProgressPercentage = overallPercentage;
                this.message = message;
            }

            /// <summary>
            /// Gets the asynchronous task progress percentage.
            /// </summary>
            public new float ProgressPercentage
            {
                get
                {
                    return progressPercentage;
                }
            }

            /// <summary>
            /// Gets the asynchronous task overall progress percentage.
            /// </summary>
            public float OverallProgressPercentage
            {
                get
                {
                    return overallProgressPercentage;
                }
            }

            /// <summary>
            /// Gets the message associated with the current task.
            /// </summary>
            public string Message
            {
                get
                {
                    return message;
                }
            }

            float progressPercentage;
            float overallProgressPercentage;
            string message;
        }

        /// <summary>
        /// Extends the ProgressEventArgs further by allowing for the inclusion of
        /// an exception.
        /// </summary>
        public class ProgressErrorEventArgs : ProgressEventArgs
        {
            /// <summary>
            /// Constructor.
            /// </summary>
            /// <param name="e">The base ProgressEventArgs object.</param>
            /// <param name="ex">The exception</param>
            public ProgressErrorEventArgs(ProgressEventArgs e, Exception ex)
                : base(e.ProgressPercentage, e.OverallProgressPercentage, e.UserState, e.Message)
            {
                this.exception = ex;
            }

            /// <summary>
            /// The exception associated with the progress event.
            /// </summary>
            public Exception Exception
            {
                get
                {
                    return exception;
                }
            }

            private Exception exception;
        }

        /// <summary>
        /// Retrieves the update list from the server.
        /// </summary>
        public void GetUpdates()
        {
            WebRequest.DefaultCachePolicy = new HttpRequestCachePolicy(
                HttpRequestCacheLevel.Refresh);
            HttpWebRequest req = (HttpWebRequest)
                WebRequest.Create("http://eraser.sourceforge.net/updates?action=listupdates&" +
                    "version=" + Assembly.GetExecutingAssembly().GetName().Version.ToString());
            
            using (WebResponse resp = req.GetResponse())
            using (Stream strm = resp.GetResponseStream())
            {
                //Download the response
                int bytesRead = 0;
                byte[] buffer = new byte[16384];
                List<byte> responseBuffer = new List<byte>();
                while ((bytesRead = strm.Read(buffer, 0, buffer.Length)) != 0)
                {
                    byte[] tmpDest = new byte[bytesRead];
                    Buffer.BlockCopy(buffer, 0, tmpDest, 0, bytesRead);
                    responseBuffer.AddRange(tmpDest);

                    float progress = responseBuffer.Count / (float)resp.ContentLength;
                    OnProgress(new ProgressEventArgs(progress, progress, null,
                        string.Format(S._("{0} of {1} bytes downloaded"),
                            responseBuffer.Count, resp.ContentLength)));
                }

                //Parse it.
                using (MemoryStream mStrm = new MemoryStream(responseBuffer.ToArray()))
                    ParseUpdateList(mStrm);
            }
        }

        /// <summary>
        /// Parses the list of updates provided by the server
        /// </summary>
        /// <param name="strm">The stream containing the XML data.</param>
        private void ParseUpdateList(Stream strm)
        {
            //Move the XmlReader to the root node
            updates.Clear();
            mirrors.Clear();
            XmlReader rdr = XmlReader.Create(strm);
            rdr.ReadToFollowing("updateList");

            //Read the descendants of the updateList node (which are categories,
            //except for the <mirrors> element)
            XmlReader categories = rdr.ReadSubtree();
            bool cont = categories.ReadToDescendant("updates");
            while (cont)
            {
                if (categories.NodeType == XmlNodeType.Element)
                {
                    if (categories.Name == "mirrors")
                    {
                        Dictionary<string, string> mirrorsList =
                            ParseMirror(categories.ReadSubtree());
                        Dictionary<string, string>.Enumerator e = mirrorsList.GetEnumerator();
                        while (e.MoveNext())
                            this.mirrors.Add(e.Current.Key, e.Current.Value);
                    }
                    else
                        updates.Add(categories.Name, ParseUpdateCategory(categories.ReadSubtree()));
                }

                cont = categories.Read();
            }
        }

        /// <summary>
        /// Parses a list of mirrors.
        /// </summary>
        /// <param name="rdr">The XML reader object representing the &lt;mirrors&gt; node</param>
        /// <returns>The list of mirrors defined by the element.</returns>
        private static Dictionary<string, string> ParseMirror(XmlReader rdr)
        {
            Dictionary<string, string> result = new Dictionary<string,string>();
            if (!rdr.ReadToDescendant("mirror"))
                return result;

            //Load every element.
            do
            {
                if (rdr.Name != "mirror")
                    continue;

                result.Add(rdr.ReadElementContentAsString(), rdr.GetAttribute("location"));
            }
            while (rdr.ReadToNextSibling("mirror"));

            return result;
        }

        /// <summary>
        /// Parses a specific category and its assocaited updates.
        /// </summary>
        /// <param name="rdr">The XML reader object representing the element and its children.</param>
        /// <returns>A list of updates in the category.</returns>
        private static List<Update> ParseUpdateCategory(XmlReader rdr)
        {
            List<Update> result = new List<Update>();
            if (!rdr.ReadToDescendant("item"))
                return result;

            //Load every element.
            do
            {
                if (rdr.Name != "item")
                    continue;

                Update update = new Update();
                update.Name = rdr.GetAttribute("name");
                update.Version = new Version(rdr.GetAttribute("version"));
                update.Publisher = rdr.GetAttribute("publisher");
                update.Architecture = rdr.GetAttribute("architecture");
                update.FileSize = Convert.ToInt64(rdr.GetAttribute("filesize"));
                update.Link = rdr.ReadElementContentAsString();

                result.Add(update);
            }
            while (rdr.ReadToNextSibling("item"));

            return result;
        }

        /// <summary>
        /// Downloads the list of updates.
        /// </summary>
        /// <param name="updates">The updates to retrieve and install.</param>
        /// <returns>An opaque object for use with InstallUpdates.</returns>
        public object DownloadUpdates(List<Update> updates)
        {
            string mirror = "http://eraser.sourceforge.net";
            //Create a folder to hold all our updates.
            DirectoryInfo tempDir = new DirectoryInfo(Path.GetTempPath());
            tempDir = tempDir.CreateSubdirectory("eraser" + Environment.TickCount.ToString());

            int currUpdate = 0;
            Dictionary<string, Update> tempFilesMap = new Dictionary<string, Update>();
            foreach (Update update in updates)
            {
                try
                {
                    //Decide on the URL to connect to. The Link of the update may
                    //be a relative path (relative to the selected mirror) or an
                    //absolute path (which we have no choice)
                    Uri reqUri = new Uri(update.Link);
                    if (!reqUri.IsAbsoluteUri)
                        reqUri = new Uri(new Uri(mirror), update.Link);

                    //Then grab the download.
                    HttpWebRequest req = (HttpWebRequest)WebRequest.Create(reqUri);
                    using (WebResponse resp = req.GetResponse())
                    {
                        byte[] tempBuffer = new byte[16384];
                        string tempFilePath = Path.Combine(
                            tempDir.FullName, string.Format("{0}-{1}", ++currUpdate,
                            Path.GetFileName(reqUri.GetComponents(UriComponents.Path, UriFormat.Unescaped))));

                        using (Stream strm = resp.GetResponseStream())
                        using (FileStream tempStrm = new FileStream(tempFilePath, FileMode.CreateNew))
                        using (BufferedStream bufStrm = new BufferedStream(tempStrm))
                        {
                            //Copy the information into the file stream
                            int readBytes = 0;
                            while ((readBytes = strm.Read(tempBuffer, 0, tempBuffer.Length)) != 0)
                            {
                                bufStrm.Write(tempBuffer, 0, readBytes);

                                //Compute progress
                                float itemProgress = tempStrm.Position / (float)resp.ContentLength;
                                float overallProgress = (currUpdate - 1 + itemProgress) / updates.Count;
                                OnProgress(new ProgressEventArgs(itemProgress, overallProgress,
                                    update, string.Format(S._("Downloading: {0}"), update.Name)));
                            }
                        }

                        //Store the filename-to-update mapping
                        tempFilesMap.Add(tempFilePath, update);

                        //Let the event handler know the download is complete.
                        OnProgress(new ProgressEventArgs(1.0f, currUpdate - 1,
                            update, string.Format(S._("Downloaded: {0}"), update.Name)));
                    }
                }
                catch (Exception e)
                {
                    OnProgress(new ProgressErrorEventArgs(new ProgressEventArgs(1.0f,
                        (float)currUpdate / updates.Count, update,
                            string.Format(S._("Error downloading {0}: {1}"), update.Name, e.Message)),
                        e));
                }
            }

            return tempFilesMap;
        }

        public void InstallUpdates(object downloadObject)
        {
            Dictionary<string, Update> tempFiles = (Dictionary<string, Update>)downloadObject;
            Dictionary<string, Update>.KeyCollection files = tempFiles.Keys;
            int currItem = 0;

            try
            {
                foreach (string path in files)
                {
                    Update item = tempFiles[path];
                    float progress = (float)currItem++ / files.Count;
                    OnProgress(new ProgressEventArgs(0.0f, progress,
                        item, string.Format(S._("Installing {0}"), item.Name)));

                    System.Diagnostics.ProcessStartInfo info = new System.Diagnostics.ProcessStartInfo();
                    info.FileName = path;
                    info.UseShellExecute = true;

                    System.Diagnostics.Process process = System.Diagnostics.Process.Start(info);
                    process.WaitForExit(Int32.MaxValue);
                    if (process.ExitCode == 0)
                        OnProgress(new ProgressEventArgs(1.0f, progress,
                            item, string.Format(S._("Installed {0}"), item.Name)));
                    else
                        OnProgress(new ProgressErrorEventArgs(new ProgressEventArgs(1.0f,
                            progress, item, string.Format(S._("Error installing {0}"), item.Name)),
                            new Exception(string.Format(S._("The installer exited with an error code {0}"),
                                process.ExitCode))));
                }
            }
            finally
            {
                //Clean up after ourselves
                foreach (string file in files)
                {
                    DirectoryInfo tempDir = null;
                    {
                        FileInfo info = new FileInfo(file);
                        tempDir = info.Directory;
                    }

                    tempDir.Delete(true);
                }
            }
        }

        /// <summary>
        /// Prototype of the callback functions from this object.
        /// </summary>
        /// <param name="sender">The source of the event.</param>
        /// <param name="arg">The ProgressEventArgs object holding information
        /// about the progress of the current operation.</param>
        public delegate void ProgressEventFunction(object sender, ProgressEventArgs arg);

        /// <summary>
        /// Called when the progress of the operation changes.
        /// </summary>
        public ProgressEventFunction OnProgressEvent;

        /// <summary>
        /// Helper function: invokes the OnProgressEvent delegate.
        /// </summary>
        /// <param name="arg">The ProgressEventArgs object holding information
        /// about the progress of the current operation.</param>
        private void OnProgress(ProgressEventArgs arg)
        {
            if (OnProgressEvent != null)
                OnProgressEvent(this, arg);
        }

        /// <summary>
        /// Retrieves the categories available.
        /// </summary>
        public Dictionary<string, List<Update>>.KeyCollection Categories
        {
            get
            {
                return updates.Keys;
            }
        }

        /// <summary>
        /// Retrieves all updates available.
        /// </summary>
        public Dictionary<string, List<Update>> Updates
        {
            get
            {
                return updates;
            }
        }

        /// <summary>
        /// Retrieves the updates in the given category.
        /// </summary>
        /// <param name="key">The category to retrieve.</param>
        /// <returns>All updates in the given category.</returns>
        public List<Update> this[string key]
        {
            get
            {
                return updates[key];
            }
        }

        /// <summary>
        /// The list of mirrors to download updates from.
        /// </summary>
        private Dictionary<string, string> mirrors = new Dictionary<string, string>();

        /// <summary>
        /// The list of updates downloaded.
        /// </summary>
        private Dictionary<string, List<Update>> updates =
            new Dictionary<string, List<Update>>();
    }
}