fix(projects/khora): use calendar colors for events

Color day and week event cards with their calendar color and choose a contrasting foreground instead of showing only a colored marker.

Assisted-by: pi (gpt-5.6-sol)

projects/khora/khora/colors.py

@@ -61,6 +61,20 @@ def display_color(value: str | None) -> str:
     return _DEFAULT
 
 
+def contrasting_foreground(value: str | None) -> str:
+    """Choose black or white for readable text over a calendar color."""
+    color = display_color(value).lstrip("#")
+    if len(color) == 3:
+        color = "".join(channel * 2 for channel in color)
+    red, green, blue = (int(color[index : index + 2], 16) / 255 for index in (0, 2, 4))
+
+    def linear(channel: float) -> float:
+        return channel / 12.92 if channel <= 0.04045 else ((channel + 0.055) / 1.055) ** 2.4
+
+    luminance = 0.2126 * linear(red) + 0.7152 * linear(green) + 0.0722 * linear(blue)
+    return "#000000" if luminance > 0.179 else "#ffffff"
+
+
 def _xterm_color(index: int) -> str:
     if index < 16:
         return _ANSI[index]

projects/khora/khora/window.py

@@ -8,7 +8,7 @@ gi.require_version("Adw", "1")
 gi.require_version("Gtk", "4.0")
 from gi.repository import Adw, Gio, GLib, Gtk, Pango
 
-from .colors import display_color
+from .colors import contrasting_foreground, display_color
 from .khal_adapter import KhalRepository
 from .model import Calendar, Event, event_slot_range, period_label, shifted_date, week_dates
 
@@ -40,6 +40,7 @@ class KhoraWindow(Adw.ApplicationWindow):
 
         assert repository is not None
         self._visible_calendars = {calendar.name for calendar in repository.calendars}
+        self._event_color_providers: dict[str, Gtk.CssProvider] = {}
         self._view_content = Gtk.Box(orientation=Gtk.Orientation.VERTICAL)
         self._time_indicator: Gtk.Widget | None = None
         self._rendered_today = dt.date.today()
@@ -293,7 +294,7 @@ class KhoraWindow(Adw.ApplicationWindow):
                     xalign=0,
                     ellipsize=Pango.EllipsizeMode.END,
                     tooltip_text=event.summary,
-                    css_classes=["all-day-event"],
+                    css_classes=["all-day-event", self._event_color_class(event.color)],
                 )
                 box.append(event_label)
             headers.append(box)
@@ -331,14 +332,10 @@ class KhoraWindow(Adw.ApplicationWindow):
                 lines=2,
                 ellipsize=Pango.EllipsizeMode.END,
                 tooltip_text=f"{event.time_label} · {event.summary}",
-                css_classes=["timed-event"],
+                css_classes=["timed-event", self._event_color_class(event.color)],
             )
             summary = GLib.markup_escape_text(event.summary)
-            color = display_color(event.color)
-            label.set_markup(
-                f'<span foreground="{color}">▌</span> '
-                f"<b>{summary}</b>\n<small>{event.time_label}</small>"
-            )
+            label.set_markup(f"<b>{summary}</b>\n<small>{event.time_label}</small>")
             column.attach(label, 0, start, 1, end - start)
 
         overlay = Gtk.Overlay(child=column)
@@ -383,6 +380,29 @@ class KhoraWindow(Adw.ApplicationWindow):
         offset = round(elapsed_minutes / (24 * 60) * GRID_HEIGHT)
         self._time_indicator.set_margin_top(max(0, offset - 4))
 
+    def _event_color_class(self, value: str | None) -> str:
+        color = display_color(value)
+        class_name = f"event-color-{color.lstrip('#').lower()}"
+        if class_name not in self._event_color_providers:
+            provider = Gtk.CssProvider()
+            foreground = contrasting_foreground(value)
+            provider.load_from_string(
+                f"""
+                .timed-event.{class_name},
+                .all-day-event.{class_name} {{
+                  background-color: {color};
+                  color: {foreground};
+                }}
+                """
+            )
+            Gtk.StyleContext.add_provider_for_display(
+                self.get_display(),
+                provider,
+                Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION,
+            )
+            self._event_color_providers[class_name] = provider
+        return class_name
+
     @staticmethod
     def _event_row(event: Event) -> Adw.ActionRow:
         details = f"{event.time_label} · {event.calendar}"

projects/khora/tests/test_colors.py

@@ -1,4 +1,4 @@
-from khora.colors import display_color
+from khora.colors import contrasting_foreground, display_color
 
 
 def test_preserves_html_colors() -> None:
@@ -16,3 +16,8 @@ def test_converts_xterm_color_cube() -> None:
 def test_unknown_colors_use_accent_fallback() -> None:
     assert display_color("auto") == "#3584e4"
     assert display_color("chartreuse, probably") == "#3584e4"
+
+
+def test_chooses_contrasting_event_text() -> None:
+    assert contrasting_foreground("dark blue") == "#ffffff"
+    assert contrasting_foreground("yellow") == "#000000"