ui/curses: implement game view widget focusing

pqcli/ui/curses/views/game_view/focusable.py

@@ -0,0 +1,28 @@
+import contextlib
+import typing as T
+
+from pqcli.ui.curses.event_handler import EventHandler
+
+
+class Focusable:
+    def __init__(self, *args: T.Any, **kwargs: T.Any) -> None:
+        self._focused = False
+        self._on_focus_change = EventHandler()
+        super().__init__(*args, **kwargs)
+
+    @property
+    def focused(self) -> bool:
+        return self._focused
+
+    @focused.setter
+    def focused(self, focused: bool) -> None:
+        self._focused = focused
+        self._on_focus_change()
+
+    @contextlib.contextmanager
+    def _focus_standout(self, win: T.Any) -> T.Generator:
+        if self._focused:
+            self._win.standout()
+        yield
+        if self._focused:
+            self._win.standend()