/// <summary>
        /// Installs the given pending update.
        /// </summary>
        /// <param name="pendingUpdate">The update to install.</param>
        /// <param name="downloadProgress">The action to callback with download progress updates.</param>
        /// <param name="installerStarted">The action called when the installer has started.</param>
        public void InstallPendingUpdate(PendingUpdate pendingUpdate, Action<double> downloadProgress, Action installerStarted)
        {
            log.Info("Installing update: " + pendingUpdate);
            if (pendingUpdate == null)
            {
                throw new ArgumentNullException("pendingUpdate", "No update pending");
            }

            var currentProcess = Process.GetCurrentProcess();
            var tempDirectory = string.Format(CultureInfo.InvariantCulture, "{0}-{1}-update", currentProcess.ProcessName, currentProcess.Id);
            var workingDirectory = Path.GetTempPath().PathCombine(tempDirectory);
            var installFile = pendingUpdate.InstallFileName == null
                ? "AutoUpdate.exe"
                : pendingUpdate.InstallFileName;

            var installPath = workingDirectory.PathCombine(installFile);
            var signatureUri = new Uri(pendingUpdate.UpdateFileUri.ToString() + ".signature");

            log.Debug(string.Format(CultureInfo.InvariantCulture, "Working directory:{0} install path:{1}", workingDirectory, installPath));
            Directory.CreateDirectory(workingDirectory);

            // Allow other processes to read the temp file but not write it
            using (var fileStream = new FileStream(installPath, FileMode.Create, FileAccess.Write, FileShare.Read))
            {
                var buffer = new byte[0x10000];
                var webClient = new WebClient();

                // TODO: progress updates
                // Download the install to the file
                log.Info("Downloading install file: " + pendingUpdate.UpdateFileUri);
                using (var inputStream = webClient.OpenRead(pendingUpdate.UpdateFileUri))
                {
                    long length;
                    bool hasLength = webClient.TryGetContentLength(out length);
                    long totalRead = 0;
                    var bytesRead = inputStream.Read(buffer, 0, buffer.Length);

                    while (bytesRead > 0)
                    {
                        totalRead += bytesRead;
                        UpdateProgress(downloadProgress, hasLength, totalRead, length);

                        fileStream.Write(buffer, 0, bytesRead);
                        bytesRead = inputStream.Read(buffer, 0, buffer.Length);
                    }
                }

                fileStream.Flush();

                // Verify the download
                log.Info("Verifying install file: " + installPath);
                var signature = webClient.DownloadData(signatureUri);
                if (!UpdateSettings.UpdateKeys.IsValidSignature(installPath, signature))
                {
                    log.Warn("Invalid signature detected on install file.");
                    InvalidSignatureDetected(this, new InvalidSignatureEventArgs());
                    return;
                }
            }

            var psi = new ProcessStartInfo()
            {
                CreateNoWindow = false,
                FileName = installPath,
                UseShellExecute = false
            };

            // Run the installer
            // NOTE: There is a possible race condition here if another user somehow manages to write to the update 
            // file before the new process starts. It would make sense to adjust the install file ACLs before releasing
            // the lock on the file.
            log.Info("Running install file: " + installPath);
            var process = Process.Start(psi);
            installerStarted();

            process.WaitForExit();
        }