buttons: Add SpoilerButton class showing spoiler header.

This commit adds a button that would allow user to view the spoiler
content, i.e., onclick of button is SpoilerView popup.

Tests added.
Co-authored by: Preet Mishra (<[email protected]>).

Author: Ezio-Sarthak

tests/ui_tools/test_buttons.py

@@ -7,6 +7,7 @@
 from zulipterminal.config.keys import keys_for_command
 from zulipterminal.ui_tools.buttons import (
     MessageLinkButton,
+    SpoilerButton,
     StarredButton,
     StreamButton,
     TopButton,
@@ -414,6 +415,66 @@ def test_keypress_EXIT_TOGGLE_TOPIC(self, mocker, topic_button, key, widget_size
         topic_button.view.left_panel.show_stream_view.assert_called_once_with()
 
 
+class TestSpoilerButton:
+    @pytest.fixture(autouse=True)
+    def mock_external_classes(self, mocker):
+        self.controller = mocker.Mock()
+        self.super_init = mocker.patch(BUTTONS + ".urwid.Button.__init__")
+        self.connect_signal = mocker.patch(BUTTONS + ".urwid.connect_signal")
+
+    def spoiler_button(
+        self, header_len=0, header=[""], content=[""], display_attr=None
+    ):
+        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):
+        self.update_widget = mocker.patch(BUTTONS + ".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, header, header_len, expected_cursor_position, display_attr=None
+    ):
+        self.selectable_icon = mocker.patch(BUTTONS + ".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, mocker):
+        mocked_button = self.spoiler_button()
+
+        mocked_button.show_spoiler()
+
+        mocked_button.controller.show_spoiler.assert_called_once_with(
+            mocked_button.content
+        )
+
+
 class TestMessageLinkButton:
     @pytest.fixture(autouse=True)
     def mock_external_classes(self, mocker):

zulipterminal/ui_tools/buttons.py

@@ -1,6 +1,6 @@
 import re
 from functools import partial
-from typing import Any, Callable, Dict, Optional, Tuple, Union, cast
+from typing import Any, Callable, Dict, List, Optional, Tuple, Union, cast
 from urllib.parse import urljoin, urlparse
 
 import urwid
@@ -154,6 +154,36 @@ def __init__(self, controller: Any, width: int, count: int = 0) -> None:
         )
 
 
+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 StarredButton(TopButton):
     def __init__(self, controller: Any, width: int, count: int = 0) -> None:
         button_text = f"Starred messages [{primary_key_for_command('ALL_STARRED')}]"