[openrocket#1100] Implement multi-document behavior for macOS

Note: this is not yet "final" there are still a number of fixes that need to happen, such as fixing the application menu (which is not responsive after closing everyhing) and a high memory usage even in closed down mode

swing/src/net/sf/openrocket/gui/main/BasicFrame.java

@@ -34,6 +34,7 @@
 import net.miginfocom.swing.MigLayout;
 import net.sf.openrocket.aerodynamics.WarningSet;
 import net.sf.openrocket.appearance.DecalImage;
+import net.sf.openrocket.arch.SystemInfo;
 import net.sf.openrocket.document.OpenRocketDocument;
 import net.sf.openrocket.document.OpenRocketDocumentFactory;
 import net.sf.openrocket.document.StorageOptions;
@@ -1687,7 +1688,8 @@ private boolean closeAction() {
 		ComponentAnalysisDialog.hideDialog();
 
 		frames.remove(this);
-		if (frames.isEmpty()) {
+		// Don't quit the application on macOS
+		if (frames.isEmpty() && (SystemInfo.getPlatform() != SystemInfo.Platform.MAC_OS)) {
 			log.info("Last frame closed, exiting");
 			System.exit(0);
 		}
@@ -1704,6 +1706,31 @@ public void printAction() {
 		new PrintDialog(this, document, rotation).setVisible(true);
 	}
 
+	/**
+	 * Opens a new design file or the last design file, if set in the preferences.
+	 * Can be used for reopening the application or opening it the first time.
+	 */
+	public static void reopen() {
+		if (!Application.getPreferences().isAutoOpenLastDesignOnStartupEnabled()) {
+			BasicFrame.newAction();
+		} else {
+			String lastFile = MRUDesignFile.getInstance().getLastEditedDesignFile();
+			if (lastFile != null) {
+				log.info("Opening last design file: " + lastFile);
+				if (!BasicFrame.open(new File(lastFile), null)) {
+					MRUDesignFile.getInstance().removeFile(lastFile);
+					BasicFrame.newAction();
+				}
+				else {
+					MRUDesignFile.getInstance().addFile(lastFile);
+				}
+			}
+			else {
+				BasicFrame.newAction();
+			}
+		}
+	}
+
 
 	/**
 	 * Open a new design window with a basic rocket+stage.

swing/src/net/sf/openrocket/startup/OSXSetup.java

@@ -5,6 +5,7 @@
 import java.awt.desktop.OpenFilesHandler;
 import java.awt.desktop.PreferencesHandler;
 import java.awt.desktop.QuitHandler;
+import java.awt.desktop.AppReopenedListener;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -50,6 +51,11 @@ final class OSXSetup {
 		r.cancelQuit();
 	};
 
+	private static final AppReopenedListener APP_REOPENED_HANDLER = (e) -> {
+		log.info("App re-opened");
+		BasicFrame.reopen();
+	};
+
 	/**
 	 * The handler for the About item in the OSX app menu
 	 */
@@ -92,6 +98,7 @@ static void setupOSX() {
 			osxDesktop.setAboutHandler(ABOUT_HANDLER);
 			osxDesktop.setPreferencesHandler(PREFERENCES_HANDLER);
 			osxDesktop.setQuitHandler(QUIT_HANDLER);
+			osxDesktop.addAppEventListener(APP_REOPENED_HANDLER);
 
 			// Set the dock icon to the largest icon
 			final Image dockIcon = Toolkit.getDefaultToolkit().getImage(

swing/src/net/sf/openrocket/startup/SwingStartup.java

@@ -220,23 +220,7 @@ private void runInEDT(String[] args) {
 		// Starting action (load files or open new document)
 		log.info("Opening main application window");
 		if (!handleCommandLine(args)) {
-			if (!Application.getPreferences().isAutoOpenLastDesignOnStartupEnabled()) {
-				BasicFrame.newAction();
-			} else {
-				String lastFile = MRUDesignFile.getInstance().getLastEditedDesignFile();
-				if (lastFile != null) {
-					if (!BasicFrame.open(new File(lastFile), null)) {
-						MRUDesignFile.getInstance().removeFile(lastFile);
-						BasicFrame.newAction();
-					}
-					else {
-						MRUDesignFile.getInstance().addFile(lastFile);
-					}
-				}
-				else {
-					BasicFrame.newAction();
-				}
-			}
+			BasicFrame.reopen();
 		}
 
 		// Check whether update info has been fetched or whether it needs more time