InvoiceParser/App.xaml.cs

using System.Diagnostics;
using System.IO;
using System.Threading;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using InvoiceParser.Src;

namespace InvoiceParser;

public partial class App : Application
{
    private WebHost? _host;
    private Mutex? _singleInstance;

    protected override async void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);

        // Nothing else catches these, and a silent crash on an unattended
        // machine is exactly what the log exists to explain.
        AppDomain.CurrentDomain.UnhandledException += (_, args) =>
            Log.Error("crash", "unhandled exception", args.ExceptionObject as Exception);
        DispatcherUnhandledException += (_, args) =>
            Log.Error("crash", "unhandled UI exception", args.Exception);
        TaskScheduler.UnobservedTaskException += (_, args) =>
        {
            Log.Error("crash", "unobserved task exception", args.Exception);
            args.SetObserved();
        };

        _singleInstance = new Mutex(true, "InvoiceParserApp_SingleInstance", out bool isNew);
        if (!isNew)
        {
            // Bring the running instance forward instead of just saying it exists.
            FocusRunningInstance();
            Shutdown();
            return;
        }

        try
        {
            var config = AppConfig.Load(AppContext.BaseDirectory);

            // The login dialog would otherwise become MainWindow and end the app when it closes.
            ShutdownMode = ShutdownMode.OnExplicitShutdown;
            var emp = PromptLogin(config);
            if (emp == null)
            {
                Log.Info("login", "login cancelled");
                Shutdown();
                return;
            }
            config.ReceiverEmpNo = emp.Value.EmpNo;
            config.ReceiverFirstName = emp.Value.FirstName;
            Log.Info("login", "logged in as emp_no " + emp.Value.EmpNo);
            ShutdownMode = ShutdownMode.OnMainWindowClose;

            _host = new WebHost(config);
            await _host.StartAsync();

            var win = new MainWindow(_host.BaseUrl);
            MainWindow = win;
            win.Show();
        }
        catch (Exception ex)
        {
            Log.Error("startup", "startup failed", ex);
            MessageBox.Show("Startup failed: " + ex.Message, "Invoice Parser",
                MessageBoxButton.OK, MessageBoxImage.Error);
            Shutdown();
        }
    }

    // Returns the employee whose AdminPassword was entered, or null if cancelled.
    private static (int EmpNo, string FirstName)? PromptLogin(AppConfig cfg)
    {
        (int EmpNo, string FirstName)? empNo = null;
        var pw = new PasswordBox { FontSize = 16, Margin = new Thickness(0, 6, 0, 0) };
        var error = new TextBlock { Foreground = Brushes.Firebrick, Margin = new Thickness(0, 8, 0, 0) };
        var ok = new Button { Content = "Log in", IsDefault = true, Width = 90, Margin = new Thickness(0, 12, 8, 0) };
        var cancel = new Button { Content = "Cancel", IsCancel = true, Width = 90, Margin = new Thickness(0, 12, 0, 0) };
        var buttons = new StackPanel { Orientation = Orientation.Horizontal, HorizontalAlignment = HorizontalAlignment.Right };
        buttons.Children.Add(ok);
        buttons.Children.Add(cancel);
        var panel = new StackPanel { Margin = new Thickness(20), MinWidth = 300 };
        panel.Children.Add(new TextBlock { Text = "Admin password" });
        panel.Children.Add(pw);
        panel.Children.Add(error);
        panel.Children.Add(buttons);

        var win = new Window
        {
            Title = "Invoice Parser - Log in",
            Content = panel,
            SizeToContent = SizeToContent.WidthAndHeight,
            ResizeMode = ResizeMode.NoResize,
            WindowStartupLocation = WindowStartupLocation.CenterScreen
        };
        win.Loaded += (_, _) => pw.Focus();
        ok.Click += (_, _) =>
        {
            error.Text = "";
            try
            {
                empNo = LookupEmployee(cfg, pw.Password);
                if (empNo != null) { win.DialogResult = true; return; }
                error.Text = "Invalid password";
            }
            catch (Exception ex)
            {
                Log.Error("login", "employee lookup failed", ex);
                error.Text = "Database error: " + ex.Message;
            }
            pw.Clear();
            pw.Focus();
        };
        return win.ShowDialog() == true ? empNo : null;
    }

    private static (int EmpNo, string FirstName)? LookupEmployee(AppConfig cfg, string password)
    {
        if (!int.TryParse(password.Trim(), out var pw)) return null;
        using var conn = new Db(cfg).Open();
        using var cmd = conn.CreateCommand();
        cmd.CommandText =
            "SELECT TOP 1 emp_no, FirstName FROM posbdat.dbo.Employees " +
            "WHERE AdminPassword = @pw AND ISNULL(EmpActive, 0) = 1";
        cmd.Parameters.AddWithValue("@pw", pw);
        using var r = cmd.ExecuteReader();
        if (!r.Read()) return null;
        return (Convert.ToInt32(r.GetValue(0)), (Db.GetStr(r, "FirstName") ?? "").Trim());
    }

    [System.Runtime.InteropServices.DllImport("user32.dll")]
    private static extern bool SetForegroundWindow(IntPtr hWnd);

    [System.Runtime.InteropServices.DllImport("user32.dll")]
    private static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);

    private static void FocusRunningInstance()
    {
        const int SW_RESTORE = 9;
        var me = Process.GetCurrentProcess();
        foreach (var p in Process.GetProcessesByName(me.ProcessName))
        {
            if (p.Id == me.Id || p.MainWindowHandle == IntPtr.Zero) continue;
            ShowWindow(p.MainWindowHandle, SW_RESTORE);
            SetForegroundWindow(p.MainWindowHandle);
            return;
        }
        MessageBox.Show("Invoice Parser is already running.", "Invoice Parser",
            MessageBoxButton.OK, MessageBoxImage.Information);
    }

    protected override void OnExit(ExitEventArgs e)
    {
        // Stop the host off the UI thread: awaiting it here can deadlock on the
        // WPF SynchronizationContext, leaving a windowless process holding the
        // single-instance mutex.
        try
        {
            var host = _host;
            if (host != null)
                Task.Run(() => host.StopAsync()).Wait(TimeSpan.FromSeconds(5));
        }
        catch (Exception ex) { Log.Error("shutdown", "web host stop failed", ex); }
        Log.Info("shutdown", "exiting with code " + e.ApplicationExitCode);
        _singleInstance?.Dispose();
        base.OnExit(e);
        // Hard terminate. Environment.Exit runs finalizers and COM cleanup, which
        // hangs on WebView2's browser processes and leaves a windowless process
        // that holds the single-instance mutex and locks the exe against rebuilds.
        // Safe here: every state.json write is synchronous and already flushed,
        // and a parse abandoned mid-call is reset from "processing" to "queued"
        // by ParseWorker on the next start.
        Process.GetCurrentProcess().Kill();
    }
}