window: Adjust to image size when opening

Give LpImage a native with that should feel nice.
When opening a new window with a new image the window size
is determined by LpImage's natural width.
The image size and EXIF data is loaded before the image such
that the window can be shown in the right dimension while
loading the actual image.

src/window.rs

@@ -30,6 +30,8 @@ use ashpd::WindowIdentifier;
 
 use gtk_macros::spawn;
 
+use std::cell::RefCell;
+
 use crate::config;
 use crate::util;
 use crate::widgets::{LpImage, LpImagePage, LpImageView, LpPropertiesView};
@@ -77,6 +79,9 @@ mod imp {
         pub properties_view: TemplateChild<LpPropertiesView>,
         #[template_child]
         pub drop_target: TemplateChild<gtk::DropTarget>,
+
+        pub watch_image_size: RefCell<Option<gtk::ExpressionWatch>>,
+        pub watch_image_error: RefCell<Option<gtk::ExpressionWatch>>,
     }
 
     #[glib::object_subclass]
@@ -449,6 +454,56 @@ impl LpWindow {
         self.action_set_enabled("win.toggle-properties", enabled);
     }
 
+    pub fn image_size_ready(&self) {
+        // if visible for whatever reason, don't do any resize
+        if self.is_visible() {
+            self.disconnect_present_watches();
+            return;
+        }
+
+        let image = self
+            .imp()
+            .image_view
+            .current_page_strict()
+            .map(|page| page.image());
+
+        if let Some(image) = image {
+            if image.image_size() > (0, 0) {
+                log::debug!("Showing window because image size is ready");
+                // this let's the window determine the default size from LpImage's natural size
+                self.set_default_size(-1, -1);
+                self.disconnect_present_watches();
+                self.present();
+            }
+        }
+    }
+
+    pub fn image_error(&self) {
+        if self.is_visible() {
+            self.disconnect_present_watches();
+            return;
+        }
+
+        let current_page = self.imp().image_view.current_page_strict();
+
+        if let Some(page) = current_page {
+            if page.error().is_some() {
+                log::debug!("Showin window because loading image failed");
+                self.disconnect_present_watches();
+                self.present();
+            }
+        }
+    }
+
+    fn disconnect_present_watches(&self) {
+        if let Some(watch) = self.imp().watch_image_size.take() {
+            watch.unwatch();
+        }
+        if let Some(watch) = self.imp().watch_image_error.take() {
+            watch.unwatch();
+        }
+    }
+
     // Adapted from https://gitlab.gnome.org/GNOME/eog/-/blob/master/src/eog-window.c:eog_window_obtain_desired_size
     pub fn resize_from_dimensions(&self, img_width: i32, img_height: i32) {
         let imp = self.imp();