Add navigation support for small screens

data/resources/ui/content.ui

@@ -9,6 +9,13 @@
         <child>
           <object class="AdwHeaderBar" id="headerbar">
             <property name="show-start-title-buttons" bind-source="Content" bind-property="compact" bind-flags="sync-create"/>
+            <child type="start">
+              <object class="GtkButton" id="back">
+                <property name="visible" bind-source="Content" bind-property="compact" bind-flags="sync-create"/>
+                <property name="icon-name">go-previous-symbolic</property>
+                <property name="action-name">content.go-back</property>
+              </object>
+            </child>
             <child type="end">
               <object class="GtkMenuButton" id="room_menu">
                 <property name="icon-name">view-more-symbolic</property>

data/resources/ui/session.ui

@@ -2,18 +2,18 @@
 <interface>
   <template class="Session" parent="AdwBin">
     <child>
-      <object class="AdwLeaflet" id="session">
+      <object class="AdwLeaflet" id="leaflet">
         <child>
           <object class="Sidebar" id="sidebar">
-            <property name="compact" bind-source="session" bind-property="folded" bind-flags="sync-create" />
+            <property name="compact" bind-source="leaflet" bind-property="folded" bind-flags="sync-create" />
             <property name="categories" bind-source="Session" bind-property="categories" bind-flags="sync-create" />
             <property name="selected-room" bind-source="Session" bind-property="selected-room" bind-flags="sync-create | bidirectional" />
           </object>
         </child>
         <child>
           <object class="Content" id="content">
-            <property name="compact" bind-source="session" bind-property="folded" bind-flags="sync-create" />
-            <property name="room" bind-source="Session" bind-property="selected-room" bind-flags="sync-create" />
+            <property name="compact" bind-source="leaflet" bind-property="folded" bind-flags="sync-create" />
+            <property name="room" bind-source="Session" bind-property="selected-room" bind-flags="sync-create | bidirectional" />
           </object>
         </child>
       </object>

src/session/content/content.rs

@@ -38,6 +38,9 @@ mod imp {
             Self::bind_template(klass);
             klass.set_accessible_role(gtk::AccessibleRole::Group);
 
+            klass.install_action("content.go-back", None, move |widget, _, _| {
+                widget.set_room(None);
+            });
             klass.install_action("content.send-text-message", None, move |widget, _, _| {
                 widget.send_text_message();
             });

src/session/mod.rs

@@ -44,6 +44,8 @@ mod imp {
     #[derive(Debug, Default, CompositeTemplate)]
     #[template(resource = "/org/gnome/FractalNext/session.ui")]
     pub struct Session {
+        #[template_child]
+        pub leaflet: TemplateChild<adw::Leaflet>,
         #[template_child]
         pub sidebar: TemplateChild<Sidebar>,
         #[template_child]
@@ -170,6 +172,13 @@ impl Session {
             return;
         }
 
+        let leaflet = priv_.leaflet.get();
+        if selected_room.is_some() {
+            leaflet.navigate(adw::NavigationDirection::Forward);
+        } else {
+            leaflet.navigate(adw::NavigationDirection::Back);
+        }
+
         priv_.selected_room.replace(selected_room);
 
         self.notify("selected-room");

src/session/sidebar/selection.rs

@@ -267,21 +267,23 @@ impl Selection {
 
         let mut selected = GTK_INVALID_LIST_POSITION;
 
-        if let Some(model) = self.model() {
-            for i in 0..=model.n_items() {
-                let room = model
-                    .item(i)
-                    .and_then(|o| o.downcast::<gtk::TreeListRow>().ok())
-                    .and_then(|r| r.item())
-                    .and_then(|o| o.downcast::<Room>().ok());
-                if room == selected_room {
-                    selected = i;
-                    break;
+        if room.is_some() {
+            if let Some(model) = self.model() {
+                for i in 0..model.n_items() {
+                    let r = model
+                        .item(i)
+                        .and_then(|o| o.downcast::<gtk::TreeListRow>().ok())
+                        .and_then(|r| r.item())
+                        .and_then(|o| o.downcast::<Room>().ok());
+                    if r == room {
+                        selected = i;
+                        break;
+                    }
                 }
             }
         }
 
-        priv_.selected_room.replace(selected_room);
+        priv_.selected_room.replace(room);
 
         if old_selected != selected {
             priv_.selected.replace(selected);