Fix JOSM-18578 -- crash when adding MapWithAI layer multiple times.

The test looks at the last errors and warnings from the Logger, since
the issue was not being raised.

Signed-off-by: Taylor Smock <taylor.smock@kaart.com>

src/main/java/org/openstreetmap/josm/plugins/mapwithai/backend/MapWithAIDataUtils.java

@@ -309,13 +309,15 @@ public final class MapWithAIDataUtils {
         }
 
         final MapWithAILayer tLayer = layer;
-        if (SwingUtilities.isEventDispatchThread() && create) {
-            MainApplication.getLayerManager().addLayer(tLayer);
-        } else if (create) {
-            try {
-                SwingUtilities.invokeAndWait(() -> MainApplication.getLayerManager().addLayer(tLayer));
-            } catch (InvocationTargetException | InterruptedException e) {
-                Logging.error(e);
+        if (!MainApplication.getLayerManager().getLayers().contains(tLayer)) {
+            if (SwingUtilities.isEventDispatchThread() && create) {
+                MainApplication.getLayerManager().addLayer(tLayer);
+            } else if (create) {
+                try {
+                    SwingUtilities.invokeAndWait(() -> MainApplication.getLayerManager().addLayer(tLayer));
+                } catch (InvocationTargetException | InterruptedException e) {
+                    Logging.error(e);
+                }
             }
         }
 

test/unit/org/openstreetmap/josm/plugins/mapwithai/backend/MapWithAIDataUtilsTest.java

@@ -3,6 +3,7 @@ package org.openstreetmap.josm.plugins.mapwithai.backend;
 
 import static com.github.tomakehurst.wiremock.core.WireMockConfiguration.options;
 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.assertTrue;
 
@@ -38,6 +39,7 @@ import org.openstreetmap.josm.gui.mappaint.MapPaintStyles;
 import org.openstreetmap.josm.gui.mappaint.StyleSource;
 import org.openstreetmap.josm.spi.preferences.Config;
 import org.openstreetmap.josm.testutils.JOSMTestRules;
+import org.openstreetmap.josm.tools.Logging;
 
 import com.github.tomakehurst.wiremock.WireMockServer;
 
@@ -220,6 +222,16 @@ public class MapWithAIDataUtilsTest {
         }
     }
 
+    @Test
+    public void testDoubleAddLayer() {
+        Logging.clearLastErrorAndWarnings();
+        assertNull(MapWithAIDataUtils.getLayer(false));
+        assertNotNull(MapWithAIDataUtils.getLayer(true));
+        assertNotNull(MapWithAIDataUtils.getLayer(true));
+        assertTrue(Logging.getLastErrorAndWarnings().stream().filter(str -> !str.contains("Failed to locate image"))
+                .collect(Collectors.toList()).isEmpty());
+    }
+
     private static int getExpectedNumberOfBBoxes(BBox bbox) {
         double width = MapWithAIDataUtils.getWidth(bbox);
         double height = MapWithAIDataUtils.getHeight(bbox);