ask for permissions instead of exiting when the hook fails

src/main/java/wtf/beatrice/autosqueal/Main.java

@@ -19,10 +19,15 @@ public class Main {
         LOGGER.info("Hello world!");
 
         useSystemLookAndFeel();
-        registerJNativeHook();
+        boolean hookRegistered = registerJNativeHook();
 
         // all Swing components must be created and updated on the EDT
-        SwingUtilities.invokeLater(mainWindow::init);
+        SwingUtilities.invokeLater(() -> {
+            mainWindow.init();
+            if (!hookRegistered) {
+                mainWindow.showPermissionsHelp();
+            }
+        });
     }
 
     private static void useSystemLookAndFeel() {
@@ -33,18 +38,22 @@ public class Main {
         }
     }
 
-    private static void registerJNativeHook() {
+    private static boolean registerJNativeHook() {
         LOGGER.info("Registering jnativehook library...");
         try {
             GlobalScreen.registerNativeHook();
             GlobalScreen.addNativeKeyListener(new KeyPressListener());
             LOGGER.info("Successfully registered jnativehook library!");
+            return true;
         }
         catch (NativeHookException ex) {
-            LOGGER.error("There was a problem registering the native hook.");
-            LOGGER.error(ex.getMessage());
+            LOGGER.error("There was a problem registering the native hook.", ex);
 
-            System.exit(1);
+            // without the accessibility permission the hotkey cannot be
+            // registered and the mouse cannot be moved either: the app would
+            // look alive but do nothing. don't exit: keep the window and the
+            // tray icon usable, and tell the user what is missing.
+            return false;
         }
     }
 

src/main/java/wtf/beatrice/autosqueal/ui/MainWindow.java

@@ -15,6 +15,7 @@ import java.awt.*;
 import java.awt.event.WindowAdapter;
 import java.awt.event.WindowEvent;
 import java.awt.image.BufferedImage;
+import java.io.IOException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
@@ -174,6 +175,46 @@ public class MainWindow
         Main.unregisterJNativeHook();
     }
 
+    /**
+     * Explains that the app cannot work without its permissions, and offers
+     * a shortcut to the right system settings pane. Must be called on the
+     * EDT, after the window is visible.
+     */
+    public void showPermissionsHelp() {
+        Object[] options = {"Open System Settings", "Close"};
+
+        int choice = JOptionPane.showOptionDialog(frame,
+                "autosqueal needs the accessibility permission to move the mouse and to\n"
+                        + "listen for the ctrl+alt hotkey, and the screen recording one to\n"
+                        + "show the screen preview. they cannot be granted while it is running.\n\n"
+                        + "grant them in privacy & security, then restart autosqueal.",
+                "permissions needed",
+                JOptionPane.DEFAULT_OPTION,
+                JOptionPane.WARNING_MESSAGE,
+                null,
+                options,
+                options[0]);
+
+        if (choice == 0) {
+            openPrivacySettings();
+        }
+    }
+
+    /** Opens the privacy & security pane at the accessibility section. */
+    private void openPrivacySettings() {
+        if (SystemUtil.getHostSystem() != SystemUtil.OperatingSystem.MAC_OS) {
+            return;
+        }
+
+        try {
+            new ProcessBuilder("open",
+                    "x-apple.systempreferences:com.apple.preference.security?Privacy_Accessibility")
+                    .start();
+        } catch (IOException ex) {
+            LOGGER.error("Could not open the system settings", ex);
+        }
+    }
+
     /**
      * Toggles the automation on or off. Safe to call from any thread: the actual
      * work is always marshalled to the EDT, since it touches Swing components.