widgets: clock: Add a simple clock widget

This is intended to be reused by any app that shows the clock as part
of the status bar at the top of the display.

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>

wasp/widgets.py

@@ -8,9 +8,11 @@ The widget library allows common fragments of logic and drawing code to be
 shared between applications.
 """
 
+import fonts
 import icons
 import wasp
 import watch
+
 from micropython import const
 
 class BatteryMeter:
@@ -70,6 +72,47 @@ class BatteryMeter:
 
             self.level = level
 
+class Clock:
+    """Small clock widget."""
+    def __init__(self, enabled=True):
+        self.on_screen = None
+        self.enabled = enabled
+
+    def draw(self):
+        """Redraw the clock from scratch.
+
+        The container is required to clear the canvas prior to the redraw
+        and the clock is only drawn if it is enabled.
+        """
+        self.on_screen = None
+        self.update()
+
+    def update(self):
+        """Update the clock widget if needed.
+
+        This is a lazy update that only redraws if the time has changes
+        since the last call *and* the clock is enabled.
+
+        :returns: An time tuple if the time has changed since the last call,
+                  None otherwise.
+        """
+        now = wasp.watch.rtc.get_localtime()
+        on_screen = self.on_screen
+
+        if on_screen and on_screen == now:
+            return None
+
+        if self.enabled and (not on_screen or now[4] != on_screen[4]):
+            t1 = '{:02}:{:02}'.format(now[3], now[4])
+
+            draw = wasp.watch.drawable
+            draw.set_font(fonts.sans28)
+            draw.set_color(0xe73c)
+            draw.string(t1, 52, 12, 138)
+
+        self.on_screen = now
+        return now
+
 class NotificationBar:
     """Show BT status and if there are pending notifications."""
     def __init__(self, x=8, y=8):