add print-job-arrived hook system

EpsonPrintService/PrintServerBootstrapper.cs

@@ -1,6 +1,7 @@
 using Inspectron.Epson;
 using Inspectron.Epson.PrintServer;
 using Inspectron.Epson.PrintServer.ConfigurationSources;
+using Inspectron.Epson.PrintServer.Hooks;
 using Inspectron.Epson.PrintServer.JobSources;
 using Inspectron.Epson.PrintServer.JobStatusReporters;
 using Inspectron.Epson.PrintServer.PrinterAssinment;
@@ -17,6 +18,7 @@ public class PrintServerBootstrapper
 {
     private readonly EpsonPrintServiceConfiguration _config;
     private readonly CancellationTokenSource _cts;
+    private readonly List<PrintJobArrivedHandler> _arrivedHandlers = new();
     private StandardKernel? _kernel;
 
     public bool IsRunning { get; private set; }
@@ -27,6 +29,17 @@ public class PrintServerBootstrapper
         _cts = cts;
     }
 
+    /// <summary>
+    /// Register a handler that fires once per print job as it arrives from the job source,
+    /// before it's enqueued on the printer queue. Register all handlers before calling <see cref="StartAsync"/>.
+    /// Handler exceptions are logged and swallowed; they never block a print.
+    /// </summary>
+    public void OnPrintJobArrived(PrintJobArrivedHandler handler)
+    {
+        if (IsRunning) throw new InvalidOperationException("Register hooks before StartAsync().");
+        _arrivedHandlers.Add(handler);
+    }
+
     public async Task StartAsync()
     {
         _kernel = new StandardKernel();
@@ -80,6 +93,10 @@ public class PrintServerBootstrapper
         _kernel.Bind<IReceiptConverterFactory>().To<ReceiptConverterFactory>().InSingletonScope();
         _kernel.Bind<IJobStatusReporter>().To<JamesStatusReporter>();
         _kernel.Bind<PrintServer>().ToSelf().InSingletonScope();
+        foreach (var handler in _arrivedHandlers)
+        {
+            _kernel.Bind<PrintJobArrivedHandler>().ToConstant(handler);
+        }
         _kernel.Bind<IDiscoveredPrintersReceiver>().To<JamesDiscoveredPrintersReceiver>().InSingletonScope();
         _kernel.Bind<PrinterDiscoveryBackgroundTask>().ToSelf().InSingletonScope();
         _kernel.Bind<HeartbeatBackgroundTask>().ToSelf().InSingletonScope();