From 581ec195b73ce6dc4fb68f8c50bd8b9e3563276e Mon Sep 17 00:00:00 2001
From: Paul Buetow <paul@buetow.org>
Date: Fri, 27 Mar 2026 15:58:28 +0200
Subject: Fix CLI replay startup on EDT

---
 src/main/java/simulator/VSMain.java     | 67 +++++++++++++++++++++++++++++++--
 src/test/java/simulator/VSMainTest.java | 54 ++++++++++++++++++++++++++
 2 files changed, 118 insertions(+), 3 deletions(-)

diff --git a/src/main/java/simulator/VSMain.java b/src/main/java/simulator/VSMain.java
index 5718b72..3332e85 100644
--- a/src/main/java/simulator/VSMain.java
+++ b/src/main/java/simulator/VSMain.java
@@ -1,9 +1,13 @@
 package simulator;
 
 import java.awt.Component;
+import java.lang.reflect.InvocationTargetException;
 import java.util.Locale;
+import java.util.Objects;
+import java.util.concurrent.atomic.AtomicReference;
 
 import javax.swing.UIManager;
+import javax.swing.SwingUtilities;
 
 import events.VSRegisteredEvents;
 import prefs.VSDefaultPrefs;
@@ -16,6 +20,10 @@ import prefs.VSPrefs;
  * @author Paul C. Buetow
  */
 public class VSMain {
+    interface SimulatorFrameFactory {
+        VSSimulatorFrame create(VSPrefs prefs, Component relativeTo);
+    }
+
     /** The global preferences */
     public static VSPrefs prefs;
 
@@ -65,6 +73,61 @@ public class VSMain {
         return filename.isEmpty() ? null : filename;
     }
 
+    static VSSimulatorFrame launchSimulatorFrame(VSPrefs prefs,
+                                                 Component relativeTo,
+                                                 String startupSimulationFile) {
+        return launchSimulatorFrame(prefs, relativeTo, startupSimulationFile,
+                                    new SimulatorFrameFactory() {
+            public VSSimulatorFrame create(VSPrefs framePrefs,
+                                           Component frameRelativeTo) {
+                return new VSSimulatorFrame(framePrefs, frameRelativeTo);
+            }
+        });
+    }
+
+    static VSSimulatorFrame launchSimulatorFrame(VSPrefs prefs,
+                                                 Component relativeTo,
+                                                 String startupSimulationFile,
+                                                 SimulatorFrameFactory factory) {
+        Objects.requireNonNull(prefs, "prefs");
+        Objects.requireNonNull(factory, "factory");
+
+        AtomicReference<VSSimulatorFrame> frameRef =
+            new AtomicReference<VSSimulatorFrame>();
+        Runnable openWindow = new Runnable() {
+            public void run() {
+                VSSimulatorFrame simulatorFrame =
+                    factory.create(prefs, relativeTo);
+                frameRef.set(simulatorFrame);
+                if (startupSimulationFile != null)
+                    simulatorFrame.openAndStartSimulator(startupSimulationFile);
+            }
+        };
+
+        runOnEventDispatchThread(openWindow);
+        return frameRef.get();
+    }
+
+    static void runOnEventDispatchThread(Runnable action) {
+        Objects.requireNonNull(action, "action");
+
+        if (SwingUtilities.isEventDispatchThread()) {
+            action.run();
+            return;
+        }
+
+        try {
+            SwingUtilities.invokeAndWait(action);
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            throw new IllegalStateException("Interrupted while launching UI",
+                                            e);
+        } catch (InvocationTargetException e) {
+            throw new IllegalStateException("Failed to launch UI",
+                                            e.getCause());
+        }
+    }
+
     /**
      * The main method.
      *
@@ -93,9 +156,7 @@ public class VSMain {
             Thread.currentThread().interrupt();
         }
 
-        VSSimulatorFrame simulatorFrame = new VSSimulatorFrame(prefs, null);
         String startupSimulationFile = resolveStartupSimulationFile(args);
-        if (startupSimulationFile != null)
-            simulatorFrame.openAndStartSimulator(startupSimulationFile);
+        launchSimulatorFrame(prefs, null, startupSimulationFile);
     }
 }
diff --git a/src/test/java/simulator/VSMainTest.java b/src/test/java/simulator/VSMainTest.java
index 5d4fb8b..8f4bffc 100644
--- a/src/test/java/simulator/VSMainTest.java
+++ b/src/test/java/simulator/VSMainTest.java
@@ -1,10 +1,22 @@
 package simulator;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.Mockito.doAnswer;
+import static org.mockito.Mockito.mock;
+
+import java.awt.Component;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
 
 import org.junit.jupiter.api.Test;
 
+import prefs.VSDefaultPrefs;
+import prefs.VSPrefs;
+
 public class VSMainTest {
     @Test
     void resolveStartupSimulationFileReturnsNullForMissingArgs() {
@@ -24,4 +36,46 @@ public class VSMainTest {
                          new String[] {"  saved-simulations/raft.dat  ",
                                        "ignored"}));
     }
+
+    @Test
+    void runOnEventDispatchThreadExecutesOnSwingEdt() {
+        AtomicBoolean ranOnEdt = new AtomicBoolean(false);
+
+        VSMain.runOnEventDispatchThread(new Runnable() {
+            public void run() {
+                ranOnEdt.set(javax.swing.SwingUtilities
+                             .isEventDispatchThread());
+            }
+        });
+
+        assertTrue(ranOnEdt.get());
+    }
+
+    @Test
+    void launchSimulatorFrameCreatesAndStartsOnSwingEdt() {
+        VSPrefs prefs = VSDefaultPrefs.init();
+        AtomicBoolean createdOnEdt = new AtomicBoolean(false);
+        AtomicReference<String> openedFilename = new AtomicReference<String>();
+        VSSimulatorFrame frame = mock(VSSimulatorFrame.class);
+        doAnswer(invocation -> {
+            openedFilename.set(invocation.getArgument(0, String.class));
+            return null;
+        }).when(frame).openAndStartSimulator("saved-simulations/raft.dat");
+
+        VSSimulatorFrame launchedFrame = VSMain.launchSimulatorFrame(
+            prefs, null, "saved-simulations/raft.dat",
+            new VSMain.SimulatorFrameFactory() {
+                public VSSimulatorFrame create(VSPrefs framePrefs,
+                                               Component relativeTo) {
+                    createdOnEdt.set(javax.swing.SwingUtilities
+                                     .isEventDispatchThread());
+                    return frame;
+                }
+            });
+
+        assertTrue(createdOnEdt.get());
+        assertNotNull(launchedFrame);
+        assertSame(frame, launchedFrame);
+        assertEquals("saved-simulations/raft.dat", openedFilename.get());
+    }
 }
-- 
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