fix: history only saves on drag end + throttle drag updates

Fixed two critical issues with draggable bars:

1. History now only saves on drag end (not during dragging):
   - Added isDragging state to MainConverter
   - onValueChange callback now accepts dragging boolean parameter
   - History useEffect skips saving when isDragging is true
   - On mouseup/touchend, call onValueChange with dragging=false to trigger save
   - Prevents hundreds of history entries from a single drag

2. Throttled drag updates for better performance:
   - Added lastUpdateTime ref to track update frequency
   - Limited updates to 60fps (every 16ms)
   - Prevents React from being overwhelmed with rapid state updates
   - Smoother, more responsive dragging experience

How it works:
- During drag: onValueChange(value, unit, true) → isDragging=true → history skips
- On drag end: onValueChange(value, unit, false) → isDragging=false → history saves
- Drag move: throttled to max 60 updates per second

This should make bars update smoothly during drag and history
clean with only one entry per drag operation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

components/converter/MainConverter.tsx

@@ -32,6 +32,7 @@ export default function MainConverter() {
   const [favorites, setFavorites] = useState<string[]>([]);
   const [copiedUnit, setCopiedUnit] = useState<string | null>(null);
   const [showVisualComparison, setShowVisualComparison] = useState(false);
+  const [isDragging, setIsDragging] = useState(false);
 
   const measures = getAllMeasures();
   const units = getUnitsForMeasure(selectedMeasure);
@@ -92,8 +93,10 @@ export default function MainConverter() {
     setFavorites(getFavorites());
   }, []);
 
-  // Save to history when conversion happens
+  // Save to history when conversion happens (but not during dragging)
   useEffect(() => {
+    if (isDragging) return; // Don't save to history while dragging
+
     const numValue = parseNumberInput(inputValue);
     if (numValue !== null && selectedUnit && conversions.length > 0) {
       // Save first conversion to history
@@ -108,7 +111,7 @@ export default function MainConverter() {
         window.dispatchEvent(new Event('historyUpdated'));
       }
     }
-  }, [inputValue, selectedUnit, conversions, selectedMeasure]);
+  }, [inputValue, selectedUnit, conversions, selectedMeasure, isDragging]);
 
   // Handle search selection
   const handleSearchSelect = useCallback((unit: string, measure: Measure) => {
@@ -124,8 +127,9 @@ export default function MainConverter() {
   }, []);
 
   // Handle value change from draggable bars
-  const handleValueChange = useCallback((value: number, unit: string) => {
+  const handleValueChange = useCallback((value: number, unit: string, dragging: boolean) => {
     // When dragging a bar, switch to that unit as the source
+    setIsDragging(dragging);
     setInputValue(value.toString());
     setSelectedUnit(unit);
   }, []);

components/converter/VisualComparison.tsx

@@ -7,7 +7,7 @@ import { formatNumber, cn } from '@/lib/utils';
 interface VisualComparisonProps {
   conversions: ConversionResult[];
   color: string;
-  onValueChange?: (value: number, unit: string) => void;
+  onValueChange?: (value: number, unit: string, dragging: boolean) => void;
 }
 
 export default function VisualComparison({
@@ -19,6 +19,7 @@ export default function VisualComparison({
   const dragStartX = useRef<number>(0);
   const dragStartWidth = useRef<number>(0);
   const activeBarRef = useRef<HTMLDivElement | null>(null);
+  const lastUpdateTime = useRef<number>(0);
   // Calculate percentages for visual bars using logarithmic scale
   const withPercentages = useMemo(() => {
     if (conversions.length === 0) return [];
@@ -93,6 +94,11 @@ export default function VisualComparison({
   const handleMouseMove = useCallback((e: MouseEvent) => {
     if (!draggingUnit || !activeBarRef.current || !onValueChange) return;
 
+    // Throttle updates to every 16ms (~60fps)
+    const now = Date.now();
+    if (now - lastUpdateTime.current < 16) return;
+    lastUpdateTime.current = now;
+
     const barWidth = activeBarRef.current.offsetWidth;
     const deltaX = e.clientX - dragStartX.current;
     const deltaPercentage = (deltaX / barWidth) * 100;
@@ -112,13 +118,20 @@ export default function VisualComparison({
     // Calculate new value from percentage
     const newValue = calculateValueFromPercentage(newPercentage, minValue, maxValue);
 
-    onValueChange(newValue, draggingUnit);
+    onValueChange(newValue, draggingUnit, true); // true = currently dragging
   }, [draggingUnit, conversions, onValueChange, calculateValueFromPercentage]);
 
   const handleMouseUp = useCallback(() => {
+    if (draggingUnit && onValueChange) {
+      // Find the current value for the dragged unit
+      const conversion = conversions.find(c => c.unit === draggingUnit);
+      if (conversion) {
+        onValueChange(conversion.value, draggingUnit, false); // false = drag ended
+      }
+    }
     setDraggingUnit(null);
     activeBarRef.current = null;
-  }, []);
+  }, [draggingUnit, conversions, onValueChange]);
 
   // Touch drag handlers
   const handleTouchStart = useCallback((e: React.TouchEvent, unit: string, currentPercentage: number, barElement: HTMLDivElement) => {
@@ -134,6 +147,11 @@ export default function VisualComparison({
   const handleTouchMove = useCallback((e: TouchEvent) => {
     if (!draggingUnit || !activeBarRef.current || !onValueChange) return;
 
+    // Throttle updates to every 16ms (~60fps)
+    const now = Date.now();
+    if (now - lastUpdateTime.current < 16) return;
+    lastUpdateTime.current = now;
+
     e.preventDefault(); // Prevent scrolling while dragging
     const touch = e.touches[0];
     const barWidth = activeBarRef.current.offsetWidth;
@@ -152,13 +170,20 @@ export default function VisualComparison({
 
     const newValue = calculateValueFromPercentage(newPercentage, minValue, maxValue);
 
-    onValueChange(newValue, draggingUnit);
+    onValueChange(newValue, draggingUnit, true); // true = currently dragging
   }, [draggingUnit, conversions, onValueChange, calculateValueFromPercentage]);
 
   const handleTouchEnd = useCallback(() => {
+    if (draggingUnit && onValueChange) {
+      // Find the current value for the dragged unit
+      const conversion = conversions.find(c => c.unit === draggingUnit);
+      if (conversion) {
+        onValueChange(conversion.value, draggingUnit, false); // false = drag ended
+      }
+    }
     setDraggingUnit(null);
     activeBarRef.current = null;
-  }, []);
+  }, [draggingUnit, conversions, onValueChange]);
 
   // Add/remove global event listeners for drag
   useEffect(() => {