buttons: Add SpoilerButton class showing spoiler header.

Author: rsashank

tests/ui_tools/test_buttons.py

@@ -14,6 +14,7 @@
     MessageLinkButton,
     ParsedNarrowLink,
     PMButton,
+    SpoilerButton,
     StarredButton,
     StreamButton,
     TopButton,
@@ -308,6 +309,75 @@ def test_keypress_USER_INFO(
         pop_up.assert_called_once_with(user_button.user_id)
 
 
+class TestSpoilerButton:
+    @pytest.fixture(autouse=True)
+    def mock_external_classes(self, mocker: MockerFixture) -> None:
+        self.controller = mocker.Mock()
+        self.super_init = mocker.patch(MODULE + ".urwid.Button.__init__")
+        self.connect_signal = mocker.patch(MODULE + ".urwid.connect_signal")
+
+    def spoiler_button(
+        self,
+        header_len: int = 0,
+        header: List[Any] = [""],
+        content: List[Any] = [""],
+        display_attr: Optional[str] = None,
+    ) -> SpoilerButton:
+        self.content = content
+        self.header_len = header_len
+        self.header = header
+        self.display_attr = display_attr
+        return SpoilerButton(self.controller, header_len, header, content, display_attr)
+
+    def test_init(self, mocker: MockerFixture) -> None:
+        self.update_widget = mocker.patch(MODULE + ".SpoilerButton.update_widget")
+
+        mocked_button = self.spoiler_button()
+
+        assert mocked_button.controller == self.controller
+        assert mocked_button.content == self.content
+        self.super_init.assert_called_once_with("")
+        self.update_widget.assert_called_once_with(
+            self.header_len, self.header, self.display_attr
+        )
+        assert self.connect_signal.called
+
+    @pytest.mark.parametrize(
+        "header, header_len, expected_cursor_position",
+        [
+            (["Test"], 4, 5),
+            (["Check"], 5, 6),
+        ],
+    )
+    def test_update_widget(
+        self,
+        mocker: MockerFixture,
+        header: List[Any],
+        header_len: int,
+        expected_cursor_position: int,
+        display_attr: Optional[str] = None,
+    ) -> None:
+        self.selectable_icon = mocker.patch(MODULE + ".urwid.SelectableIcon")
+
+        # The method update_widget() is called in SpoilerButton's init.
+        mocked_button = self.spoiler_button(
+            header=header, header_len=header_len, display_attr=display_attr
+        )
+        self.selectable_icon.assert_called_once_with(
+            header, cursor_position=expected_cursor_position
+        )
+        assert isinstance(mocked_button._w, AttrMap)
+
+    def test_show_spoiler(self) -> None:
+        mocked_button = self.spoiler_button()
+
+        mocked_button.show_spoiler()
+
+        mocked_button.controller.show_spoiler.assert_called_once_with(
+            mocked_button.content
+        )
+
+
 class TestEmojiButton:
     @pytest.mark.parametrize(
         "emoji_unit, to_vary_in_message, count",

zulipterminal/ui_tools/buttons.py

@@ -317,6 +317,36 @@ def keypress(self, size: urwid_Size, key: str) -> Optional[str]:
         return super().keypress(size, key)
 
 
+class SpoilerButton(urwid.Button):
+    def __init__(
+        self,
+        controller: Any,
+        header_len: int,
+        header: List[Any],
+        content: List[Any],
+        display_attr: Optional[str],
+    ) -> None:
+        self.controller = controller
+        self.content = content
+
+        super().__init__("")
+        self.update_widget(header_len, header, display_attr)
+        urwid.connect_signal(self, "click", callback=self.show_spoiler)
+
+    def update_widget(
+        self, header_len: int, header: List[Any], display_attr: Optional[str] = None
+    ) -> None:
+        """
+        Overrides the existing button widget for custom styling.
+        """
+        # Set cursor position next to header_len to avoid the cursor.
+        icon = urwid.SelectableIcon(header, cursor_position=header_len + 1)
+        self._w = urwid.AttrMap(icon, display_attr, focus_map="selected")
+
+    def show_spoiler(self, *_: Any) -> None:
+        self.controller.show_spoiler(self.content)
+
+
 class TopicButton(TopButton):
     def __init__(
         self,