feat(cli,gui): sync with another computer's device

Two or more computers can now sync the same folders through one device in
Proton Drive. `pdfs devices join UID` and "Sync With This Computer…" on
another computer's row adopt that device as this machine's and then offer its
folders for syncing here, like a restore. Unlike "Continue This Backup Here",
the other computer goes on syncing, and the confirmation says that changes
and deletions on one reach the other.

Translated into every shipped language.

crates/pdfs-gui/src/app/pages/devices.rs

@@ -444,6 +444,10 @@ fn other_computer_row(ui: &Rc<Ui>, dev: &DeviceInfo) -> adw::ActionRow {
         prompt_restore_folders(&ui_c, Some((uid_c.clone(), name_c.clone())))
     });
     let (ui_c, uid_c, name_c) = (ui.clone(), uid.clone(), name.clone());
+    menu.item(&gettext("Sync With This Computer…"), move || {
+        prompt_join_device(&ui_c, &uid_c, &name_c)
+    });
+    let (ui_c, uid_c, name_c) = (ui.clone(), uid.clone(), name.clone());
     menu.item(&gettext("Move to This Computer…"), move || {
         prompt_migrate_device(&ui_c, &uid_c, &name_c)
     });
@@ -1100,6 +1104,69 @@ pub(crate) fn prompt_adopt_device(ui: &Rc<Ui>, uid: &str, name: &str) {
     dialog.present(win.as_ref());
 }
 
+/// Ask before syncing into another computer's device alongside it, then offer
+/// its folders for syncing here.
+///
+/// The same adoption as "Continue This Backup Here", but the other computer
+/// goes on syncing, so the dialog says what that means: the two keep the same
+/// folders in step, deletions included.
+pub(crate) fn prompt_join_device(ui: &Rc<Ui>, uid: &str, name: &str) {
+    let win = ui_window(ui);
+    let dialog = adw::AlertDialog::builder()
+        .heading(gettext("Sync With This Computer?"))
+        // Translators: {name} is the name of the other computer this one syncs with.
+        .body(gettext_f(
+            "This computer and “{name}” keep the same folders in step. A change or a deletion on one reaches the other.\n\nNew synced folders on this computer go under “{name}” in Proton Drive. Folders already synced here stay where they are. Next you choose which of its folders to sync here.",
+            &[("name", name)],
+        ))
+        .build();
+    dialog.add_response("cancel", &gettext("Cancel"));
+    dialog.add_response("join", &gettext("Sync Here"));
+    dialog.set_response_appearance("join", adw::ResponseAppearance::Suggested);
+    dialog.set_default_response(Some("cancel"));
+    dialog.set_close_response("cancel");
+    let ui = ui.clone();
+    let uid = uid.to_string();
+    // Translators: {name} is the name of the other computer this one now syncs with.
+    let done = gettext_f("Now syncing with “{name}”", &[("name", name)]);
+    dialog.connect_response(None, move |_, resp| {
+        if resp != "join" {
+            return;
+        }
+        ui.busy_begin();
+        let rx = spawn_request(
+            ui.dirs.control_socket(),
+            Request::AdoptDevice {
+                uid: Some(uid.clone()),
+            },
+        );
+        let (ui, done) = (ui.clone(), done.clone());
+        glib::spawn_future_local(async move {
+            let result = rx.recv().await;
+            ui.busy_end();
+            let failed = gettext("Couldn't sync with that computer");
+            match result {
+                Ok(Ok(Response::Ok { .. })) => {
+                    reload_sync_pages(&ui);
+                    toast(&ui, &done);
+                    // The device is this computer's now, so its own restore
+                    // picker offers the folders.
+                    prompt_restore_folders(&ui, None);
+                }
+                Ok(Ok(Response::Error { message, kind })) => {
+                    toast_failure(&ui, &failed, &message, kind)
+                }
+                _ => toast_error(
+                    &ui,
+                    &failed,
+                    &gettext("The Proton Drive service didn't respond."),
+                ),
+            }
+        });
+    });
+    dialog.present(win.as_ref());
+}
+
 /// Ask before moving another computer's folders into this computer's backup,
 /// then offer them for syncing here.
 ///