Allow zooming in image viewer (#227)

* Allow zooming in image viewer

* Use thumbnailProvider as initial provider

* Set maximum zoom level to 100%

* Implement custom swipe listener in remote_photo_view

* Dart format

* Disable swipe gestures when zoomed in (prevents panning)

mobile/lib/modules/asset_viewer/ui/remote_photo_view.dart

@@ -0,0 +1,114 @@
+import 'package:cached_network_image/cached_network_image.dart';
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter/src/widgets/framework.dart';
+import 'package:photo_view/photo_view.dart';
+
+enum _RemoteImageStatus { empty, thumbnail, full }
+
+class _RemotePhotoViewState extends State<RemotePhotoView> {
+  late CachedNetworkImageProvider _imageProvider;
+  _RemoteImageStatus _status = _RemoteImageStatus.empty;
+  bool _zoomedIn = false;
+
+  static const int swipeThreshold = 100;
+
+  @override
+  Widget build(BuildContext context) {
+    bool allowMoving = _status == _RemoteImageStatus.full;
+
+    return PhotoView(
+        imageProvider: _imageProvider,
+        minScale: PhotoViewComputedScale.contained,
+        maxScale: allowMoving ? 1.0 : PhotoViewComputedScale.contained,
+        enablePanAlways: true,
+        scaleStateChangedCallback: _scaleStateChanged,
+        onScaleEnd: _onScaleListener);
+  }
+
+  void _onScaleListener(BuildContext context, ScaleEndDetails details,
+      PhotoViewControllerValue controllerValue) {
+    // Disable swipe events when zoomed in
+    if (_zoomedIn) return;
+
+    if (controllerValue.position.dy > swipeThreshold) {
+      widget.onSwipeDown();
+    } else if (controllerValue.position.dy < -swipeThreshold) {
+      widget.onSwipeUp();
+    }
+  }
+
+  void _scaleStateChanged(PhotoViewScaleState state) {
+    _zoomedIn = state == PhotoViewScaleState.zoomedIn;
+  }
+
+  CachedNetworkImageProvider _authorizedImageProvider(String url) {
+    return CachedNetworkImageProvider(url,
+        headers: {"Authorization": widget.authToken}, cacheKey: url);
+  }
+
+  void _performStateTransition(
+      _RemoteImageStatus newStatus, CachedNetworkImageProvider provider) {
+    // Transition to same status is forbidden
+    if (_status == newStatus) return;
+    // Transition full -> thumbnail is forbidden
+    if (_status == _RemoteImageStatus.full &&
+        newStatus == _RemoteImageStatus.thumbnail) return;
+
+    if (!mounted) return;
+
+    setState(() {
+      _status = newStatus;
+      _imageProvider = provider;
+    });
+  }
+
+  void _loadImages() {
+    CachedNetworkImageProvider thumbnailProvider =
+        _authorizedImageProvider(widget.thumbnailUrl);
+    _imageProvider = thumbnailProvider;
+
+    thumbnailProvider
+        .resolve(const ImageConfiguration())
+        .addListener(ImageStreamListener((ImageInfo imageInfo, _) {
+      _performStateTransition(_RemoteImageStatus.thumbnail, thumbnailProvider);
+    }));
+
+    CachedNetworkImageProvider fullProvider =
+        _authorizedImageProvider(widget.imageUrl);
+    fullProvider
+        .resolve(const ImageConfiguration())
+        .addListener(ImageStreamListener((ImageInfo imageInfo, _) {
+      _performStateTransition(_RemoteImageStatus.full, fullProvider);
+    }));
+  }
+
+  @override
+  void initState() {
+    _loadImages();
+    super.initState();
+  }
+}
+
+class RemotePhotoView extends StatefulWidget {
+  const RemotePhotoView(
+      {Key? key,
+      required this.thumbnailUrl,
+      required this.imageUrl,
+      required this.authToken,
+      required this.onSwipeDown,
+      required this.onSwipeUp})
+      : super(key: key);
+
+  final String thumbnailUrl;
+  final String imageUrl;
+  final String authToken;
+
+  final void Function() onSwipeDown;
+  final void Function() onSwipeUp;
+
+  @override
+  State<StatefulWidget> createState() {
+    return _RemotePhotoViewState();
+  }
+}