From 0af9260d132961b5906963395b3090af8e7dd061 Mon Sep 17 00:00:00 2001
From: TomJGooding <101601846+TomJGooding@users.noreply.github.com>
Date: Fri, 29 Dec 2023 14:45:00 +0000
Subject: [PATCH] persist hover after table updates

---
 src/textual/widgets/_month_calendar.py | 40 ++++++++++++--------------
 tests/test_month_calendar.py           | 24 ++++++++++++++++
 2 files changed, 43 insertions(+), 21 deletions(-)

diff --git a/src/textual/widgets/_month_calendar.py b/src/textual/widgets/_month_calendar.py
index ac812bfde5..d661952e7e 100644
--- a/src/textual/widgets/_month_calendar.py
+++ b/src/textual/widgets/_month_calendar.py
@@ -80,34 +80,31 @@ def next_month(self) -> None:
         self.date += relativedelta(months=1)
 
     def _on_mount(self, _: Mount) -> None:
-        self._update_week_header()
-        self._update_calendar_days()
-        self._update_cursor_coordinate()
+        self._update_calendar_table(update_week_header=True)
 
-    def _update_week_header(self) -> None:
+    def _update_calendar_table(self, update_week_header: bool) -> None:
         table = self.query_one(DataTable)
+        old_hover_coordinate = table.hover_coordinate
         table.clear()
-        old_columns = table.columns.copy()
-        for old_column in old_columns:
-            table.remove_column(old_column)
 
-        day_names = calendar.day_abbr
-        for day in self._calendar.iterweekdays():
-            table.add_column(day_names[day])
+        if update_week_header:
+            old_columns = table.columns.copy()
+            for old_column in old_columns:
+                table.remove_column(old_column)
+
+            day_names = calendar.day_abbr
+            for day in self._calendar.iterweekdays():
+                table.add_column(day_names[day])
 
-    def _update_calendar_days(self) -> None:
-        table = self.query_one(DataTable)
-        table.clear()
         with self.prevent(DataTable.CellHighlighted):
             for week in self.calendar_dates:
                 table.add_row(*[self._format_day(date) for date in week])
 
-    def _update_cursor_coordinate(self) -> None:
-        with self.prevent(DataTable.CellHighlighted):
-            table = self.query_one(DataTable)
             date_coordinate = self._get_date_coordinate(self.date)
             table.cursor_coordinate = date_coordinate
 
+        table.hover_coordinate = old_hover_coordinate
+
     @property
     def calendar_dates(self) -> list[list[datetime.date]]:
         """
@@ -143,16 +140,17 @@ def watch_date(self, old_date: datetime.date, new_date: datetime.date) -> None:
         if not self.is_mounted:
             return
         if (new_date.month != old_date.month) or (new_date.year != old_date.year):
-            self._update_calendar_days()
-        self._update_cursor_coordinate()
+            self._update_calendar_table(update_week_header=False)
+        else:
+            table = self.query_one(DataTable)
+            date_coordinate = self._get_date_coordinate(self.date)
+            table.cursor_coordinate = date_coordinate
 
     def watch_first_weekday(self) -> None:
         self._calendar = calendar.Calendar(self.first_weekday)
         if not self.is_mounted:
             return
-        self._update_week_header()
-        self._update_calendar_days()
-        self._update_cursor_coordinate()
+        self._update_calendar_table(update_week_header=True)
 
     def watch_show_cursor(self, show_cursor: bool) -> None:
         if not self.is_mounted:
diff --git a/tests/test_month_calendar.py b/tests/test_month_calendar.py
index 05d83db333..878cb1c871 100644
--- a/tests/test_month_calendar.py
+++ b/tests/test_month_calendar.py
@@ -269,3 +269,27 @@ async def test_cell_highlighted_updates_date():
         await pilot.press("left")
         expected_date = datetime.date(2021, 6, 10)
         assert month_calendar.date == expected_date
+
+
+async def test_hover_coordinate_persists_after_month_changes():
+    app = MonthCalendarApp()  # MonthCalendar date is 2021-06-03
+    async with app.run_test() as pilot:
+        month_calendar = pilot.app.query_one(MonthCalendar)
+        table = month_calendar.query_one(DataTable)
+        await pilot.hover(MonthCalendar, offset=(3, 3))
+        assert table.hover_coordinate == Coordinate(2, 0)
+
+        month_calendar.date = datetime.date(year=2022, month=10, day=2)
+        assert table.hover_coordinate == Coordinate(2, 0)
+
+
+async def test_hover_coordinate_persists_after_first_weekday_changes():
+    app = MonthCalendarApp()  # MonthCalendar date is 2021-06-03
+    async with app.run_test() as pilot:
+        month_calendar = pilot.app.query_one(MonthCalendar)
+        table = month_calendar.query_one(DataTable)
+        await pilot.hover(MonthCalendar, offset=(3, 3))
+        assert table.hover_coordinate == Coordinate(2, 0)
+
+        month_calendar.first_weekday = 6  # Sunday
+        assert table.hover_coordinate == Coordinate(2, 0)