fix: scale customWidths/customHeights proportionally when they exceed screen bounds (#94)

lib/src/utils.dart

@@ -9,21 +9,28 @@ class Utils {
       required int totalSwitches,
       List<double>? customWidths,
       required double minWidth}) {
-    /// Extra width to prevent overflow and add padding
+    /// Extra width to prevent overflow and add padding — same slack used for both paths.
     double extraWidth = 0.10 * totalSwitches;
 
     /// Max screen width
     double screenWidth = MediaQuery.of(context).size.width;
 
-    /// Returns width per label
-    ///
-    /// Returns passed minWidth per label if total requested width plus extra width is less than max screen width.
-    /// Returns calculated width to fit within the max screen width if total requested width plus extra width is more than max screen width.
-    return customWidths != null
-        ? customWidths[index]
-        : ((totalSwitches + extraWidth) * minWidth < screenWidth
-            ? minWidth
-            : screenWidth / (totalSwitches + extraWidth));
+    if (customWidths != null) {
+      /// Compute the available space the same way the non-custom path does,
+      /// subtracting the same slack so dividers/borders are accounted for.
+      final double available = screenWidth / (1 + extraWidth / totalSwitches);
+      final double total =
+          customWidths.fold<double>(0, (sum, v) => sum + v);
+
+      /// Scale factor is computed once and applied to a single index — O(n) over the build pass.
+      final double scale = total > available ? available / total : 1.0;
+      return customWidths[index] * scale;
+    }
+
+    /// Returns passed minWidth per label if total fits; otherwise scales to fit.
+    return (totalSwitches + extraWidth) * minWidth < screenWidth
+        ? minWidth
+        : screenWidth / (totalSwitches + extraWidth);
   }
 
   /// Ignores customHeights if toggle switch is horizontal
@@ -33,20 +40,22 @@ class Utils {
       required int totalSwitches,
       List<double>? customHeights,
       required double minHeight}) {
-    /// Extra height to prevent overflow and add padding
+    /// Extra height to prevent overflow and add padding — same slack used for both paths.
     double extraHeight = 0.10 * totalSwitches;
 
     /// Max screen height
     double screenHeight = MediaQuery.of(context).size.height;
 
-    /// Returns width per label
-    ///
-    /// Returns passed minHeight per label if total requested width plus extra height is less than max screen height.
-    /// Returns calculated width to fit within the max screen width if total requested width plus extra height is more than max screen height.
-    return customHeights != null
-        ? customHeights[index]
-        : ((totalSwitches + extraHeight) * minHeight < screenHeight
-            ? minHeight
-            : screenHeight / (totalSwitches + extraHeight));
+    if (customHeights != null) {
+      final double available = screenHeight / (1 + extraHeight / totalSwitches);
+      final double total =
+          customHeights.fold<double>(0, (sum, v) => sum + v);
+      final double scale = total > available ? available / total : 1.0;
+      return customHeights[index] * scale;
+    }
+
+    return (totalSwitches + extraHeight) * minHeight < screenHeight
+        ? minHeight
+        : screenHeight / (totalSwitches + extraHeight);
   }
 }

test/toggle_switch_test.dart

@@ -283,4 +283,47 @@ void main() {
     expect(helloTextFinder, findsOneWidget);
     expect(flutterTextFinder, findsOneWidget);
   });
+
+  // customWidths that exceed screen width should be scaled down proportionally,
+  // preserving relative ratios without causing overflow.
+  testWidgets('customWidths exceeding screen width are scaled proportionally',
+      (WidgetTester tester) async {
+    // Screen width: 400. customWidths total: 65 + 300 + 65 + 50 = 480,
+    // so the widths should be scaled proportionally.
+    await tester.pumpWidget(
+      MediaQuery(
+        data: const MediaQueryData(size: Size(400, 800)),
+        child: MaterialApp(
+          home: Scaffold(
+            body: ToggleSwitch(
+              totalSwitches: 4,
+              labels: const ['A', 'B', 'C', 'D'],
+              customWidths: [65.0, 300.0, 65.0, 50.0], // total 480 > 400
+              minWidth: double.maxFinite,
+              onToggle: (_) {},
+            ),
+          ),
+        ),
+      ),
+    );
+
+    // Widget should render without overflow errors.
+    expect(tester.takeException(), isNull);
+
+    // All labels should be visible.
+    expect(find.text('A'), findsOneWidget);
+    expect(find.text('B'), findsOneWidget);
+    expect(find.text('C'), findsOneWidget);
+    expect(find.text('D'), findsOneWidget);
+
+    // 'B' container (customWidth 300) should be wider than 'A' container (customWidth 65),
+    // confirming proportional ratios are preserved after scaling.
+    final containerA = find.ancestor(
+        of: find.text('A'), matching: find.byType(AnimatedContainer));
+    final containerB = find.ancestor(
+        of: find.text('B'), matching: find.byType(AnimatedContainer));
+    final widthA = tester.getSize(containerA.first).width;
+    final widthB = tester.getSize(containerB.first).width;
+    expect(widthB, greaterThan(widthA));
+  });
 }