fix: Resolve race condition when refitting map on date change

mapper/src/App.js

@@ -111,24 +111,41 @@ function FitBounds({ coords, mapState, end, duration }) {
     const map = useMap();
     const prevEndRef = useRef();
     const prevDurationRef = useRef();
+    const refitNeeded = useRef(false);
 
+    // Effect 1: Detects changes in `end` or `duration` and sets a flag.
     useEffect(() => {
         const prevEnd = prevEndRef.current;
         const prevDuration = prevDurationRef.current;
 
-        const endChanged = prevEnd && end.unix() !== prevEnd.unix();
-        const durationChanged = prevDuration && duration.id !== prevDuration.id;
+        // Run only after initial render where refs are populated.
+        if (prevEnd && prevDuration) {
+            const endChanged = end.unix() !== prevEnd.unix();
+            const durationChanged = duration.id !== prevDuration.id;
 
-        if ((mapState.center === null || endChanged || durationChanged) && coords.length > 0) {
+            if (endChanged || durationChanged) {
+                refitNeeded.current = true;
+            }
+        }
+
+        // Update refs for the next render's comparison.
+        prevEndRef.current = end;
+        prevDurationRef.current = duration;
+    }, [end, duration]);
+
+    // Effect 2: Acts on `coords` changes, but only if the flag is set.
+    useEffect(() => {
+        // A refit is needed on initial load (mapState.center is null)
+        // or if the flag has been set by the other effect.
+        if ((mapState.center === null || refitNeeded.current) && coords.length > 0) {
             const bounds = leaflet.latLngBounds(coords);
             if (bounds.isValid()) {
                 map.fitBounds(bounds);
             }
+            // Reset the flag after the fit is performed.
+            refitNeeded.current = false;
         }
-
-        prevEndRef.current = end;
-        prevDurationRef.current = duration;
-    }, [coords, mapState.center, map, end, duration]);
+    }, [coords, mapState.center, map]);
 
     return null;
 }