ui: add a helper to open a confirmation dialog and get the response

The new ConfirmationOverlay object along with the
BaseView.ask_confirmation helper can be used to open a confirmation
dialog and get back the decision from the user.

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

subiquitycore/ui/confirmation.py

@@ -0,0 +1,65 @@
+# Copyright 2023 Canonical, Ltd.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+from typing import Callable
+
+import urwid
+
+from subiquitycore.ui.buttons import (
+    back_btn,
+    done_btn,
+    )
+from subiquitycore.ui.utils import button_pile
+from subiquitycore.ui.stretchy import Stretchy
+
+
+class ConfirmationOverlay(Stretchy):
+    """ An overlay widget that asks the user to confirm or cancel an action.
+    """
+    def __init__(self, title: str, question: str,
+                 confirm_label: str, cancel_label: str,
+                 on_confirm: Callable[[], None],
+                 on_cancel: Callable[[], None]) -> None:
+
+        self.on_cancel_cb = on_cancel
+        self.on_confirm_cb = on_confirm
+        self.choice_made = False
+
+        widgets = [
+            urwid.Text(question),
+            urwid.Text(""),
+            button_pile([
+                back_btn(
+                    label=cancel_label, on_press=lambda u: self.on_cancel()),
+                done_btn(
+                    label=confirm_label, on_press=lambda u: self.on_confirm()),
+            ]),
+        ]
+
+        super().__init__(title, widgets, 0, 2)
+
+    def on_cancel(self) -> None:
+        self.choice_made = True
+        self.on_cancel_cb()
+
+    def on_confirm(self) -> None:
+        self.choice_made = True
+        self.on_confirm_cb()
+
+    def closed(self):
+        if self.choice_made:
+            return
+        # The caller should be careful not to close the overlay again.
+        self.on_cancel_cb()

subiquitycore/view.py

@@ -18,6 +18,7 @@
 Contains some default key navigations
 """
 
+import asyncio
 import logging
 
 from urwid import (
@@ -31,6 +32,8 @@ from subiquitycore.ui.container import (
     Pile,
     WidgetWrap,
     )
+
+from subiquitycore.ui.confirmation import ConfirmationOverlay
 from subiquitycore.ui.stretchy import StretchyOverlay
 from subiquitycore.ui.utils import disabled, undisabled
 
@@ -82,6 +85,37 @@ class BaseView(WidgetWrap):
         stretchy.opened()
         self._w = StretchyOverlay(disabled(self._w), stretchy)
 
+    async def ask_confirmation(self, title: str, question: str,
+                               confirm_label: str, cancel_label: str) -> bool:
+        """ Open a confirmation dialog using a strechy overlay.
+        If the user selects the "yes" button, the function returns True.
+        If the user selects the "no" button or closes the dialog, the function
+        returns False.
+        """
+        confirm_queue = asyncio.Queue(maxsize=1)
+
+        def on_confirm():
+            confirm_queue.put_nowait(True)
+
+        def on_cancel():
+            confirm_queue.put_nowait(False)
+
+        stretchy = ConfirmationOverlay(title=title, question=question,
+                                       confirm_label=confirm_label,
+                                       cancel_label=cancel_label,
+                                       on_confirm=on_confirm,
+                                       on_cancel=on_cancel)
+
+        self.show_stretchy_overlay(stretchy)
+
+        confirmed = await confirm_queue.get()
+        # The callback might have been called as the result of the overlay
+        # getting closed (when ESC is pressed). Therefore, the overlay may or
+        # may not still be opened.
+        self.remove_overlay(stretchy, not_found_ok=True)
+
+        return confirmed
+
     def remove_overlay(self, stretchy=None,
                        *, not_found_ok=False) -> None:
         """ Remove (frontmost) overlay from the view. """