InvoiceParser/App.xaml.cs

using System.Diagnostics;
using System.IO;
using System.Threading;
using System.Windows;
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);
            _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();
        }
    }

    [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();
    }
}