feat: zoom widget de imagem

lib/pages/image_viewer/image_viewer.dart

@@ -33,6 +33,57 @@ class ImageViewer extends StatefulWidget {
 class ImageViewerController extends State<ImageViewer> {
   final FocusNode focusNode = FocusNode();
 
+  /// One [TransformationController] per image, so the zoom of one page never
+  /// leaks into its neighbours.
+  final Map<String, TransformationController> _transformations = {};
+
+  int _pointerCount = 0;
+  bool _isZoomed = false;
+
+  /// True while an image is zoomed in, so panning moves the image instead of
+  /// switching to the next one.
+  bool get isZoomed => _isZoomed;
+
+  /// The [PageView] must not compete for the gesture while pinching or while
+  /// an image is zoomed, otherwise the swipe recognizer wins the gesture arena
+  /// and pinch-to-zoom never happens.
+  bool get canSwipeToNextImage => _pointerCount < 2 && !_isZoomed;
+
+  TransformationController transformationControllerFor(Event event) =>
+      _transformations.putIfAbsent(event.eventId, () {
+        final controller = TransformationController();
+        controller.addListener(_onTransformChanged);
+        return controller;
+      });
+
+  void onPointerDown() {
+    if (!mounted) return;
+    setState(() => _pointerCount++);
+  }
+
+  void onPointerUp() {
+    if (!mounted || _pointerCount == 0) return;
+    setState(() => _pointerCount--);
+  }
+
+  void _onTransformChanged() {
+    if (!mounted) return;
+    final zoomed = _transformations.values.any(
+      (controller) => controller.value.getMaxScaleOnAxis() > 1.01,
+    );
+    if (zoomed == _isZoomed) return;
+    setState(() => _isZoomed = zoomed);
+  }
+
+  /// Resets the zoom of every image, e.g. after moving to another one.
+  void resetZooms() {
+    for (final controller in _transformations.values) {
+      if (!controller.value.isIdentity()) {
+        controller.value = Matrix4.identity();
+      }
+    }
+  }
+
   @override
   void initState() {
     super.initState();
@@ -72,6 +123,8 @@ class ImageViewerController extends State<ImageViewer> {
   }
 
   Future<void> prevImage() async {
+    if (!canGoBack) return;
+    resetZooms();
     await pageController.previousPage(
       duration: FluffyThemes.animationDuration,
       curve: FluffyThemes.animationCurve,
@@ -81,6 +134,8 @@ class ImageViewerController extends State<ImageViewer> {
   }
 
   Future<void> nextImage() async {
+    if (!canGoNext) return;
+    resetZooms();
     await pageController.nextPage(
       duration: FluffyThemes.animationDuration,
       curve: FluffyThemes.animationCurve,
@@ -112,23 +167,47 @@ class ImageViewerController extends State<ImageViewer> {
 
   static const maxScaleFactor = 1.5;
 
+  /// Closes the viewer.
+  ///
+  /// Always targets the root navigator, because the viewer is opened with
+  /// `showDialog` on the root navigator while the chat room lives in a nested
+  /// navigator of the go_router shell. Using a relative navigator here would
+  /// either pop nothing or pop the wrong route.
+  void closeAction() => Navigator.of(context, rootNavigator: true).pop();
+
   /// Go back if user swiped it away
   void onInteractionEnds(ScaleEndDetails endDetails) {
     if (PlatformInfos.usesTouchscreen == false) {
+      if (isZoomed) return;
       if (endDetails.velocity.pixelsPerSecond.dy >
           MediaQuery.sizeOf(context).height * maxScaleFactor) {
-        Navigator.of(context, rootNavigator: false).pop();
+        closeAction();
       }
     }
   }
 
   @override
   void dispose() {
+    for (final controller in _transformations.values) {
+      controller.removeListener(_onTransformChanged);
+      controller.dispose();
+    }
+    _transformations.clear();
     focusNode.dispose();
     pageController.dispose();
     super.dispose();
   }
 
   @override
-  Widget build(BuildContext context) => ImageViewerView(this);
+  Widget build(BuildContext context) => PopScope<Object?>(
+    // Claim the system back button (and predictive back gesture) for the
+    // viewer. Without this, the request can reach go_router instead, which
+    // pops the chat room out of the shell and leaves the image on screen.
+    canPop: false,
+    onPopInvokedWithResult: (didPop, _) {
+      if (didPop) return;
+      closeAction();
+    },
+    child: ImageViewerView(this),
+  );
 }