xsecurelock: only display clock and weather on one screen

Relying on position is weak. Use an abstract Unix socket to take some
kind of lock and declare a leader.

bin/xsecurelock-saver

@@ -22,6 +22,7 @@ import types
 import datetime
 import re
 import gi
+import socket
 
 gi.require_version("Gtk", "3.0")
 from gi.repository import Gtk, Gdk, GdkX11, GLib, GdkPixbuf, Gio
@@ -68,6 +69,8 @@ def on_win_draw(widget, cctx, ctx):
 
 def on_overlay_draw(widget, cctx, ctx):
     """Draw overlay (clock and weather)."""
+    if not ctx.leader:
+        return
     wwidth, wheight = widget.get_parent().get_size()
     cctx.set_operator(cairo.OPERATOR_OVER)
 
@@ -106,7 +109,7 @@ def on_overlay_draw(widget, cctx, ctx):
     # We can have polybar markups in it. We assume %{Tx} means to use
     # Font Awesome 6 and we ignore font color change. The parsing is
     # quite basic.
-    if ctx.weather and ctx.position == (0, 0):
+    if ctx.weather:
         data = re.sub(r"%{F[#\d+-]+?}", "", ctx.weather)
         data = re.split(r"(%{T[1-9-]})", data)
         font = ctx.font_family
@@ -156,7 +159,17 @@ def on_clock_change(ctx):
     if new_clock != ctx.clock:
         ctx.clock = (new_clock, now.strftime("%A %-d %B"))
         ctx.overlay.queue_draw()
-    GLib.timeout_add(min(60 - now.second, 3) * 1000, on_clock_change, ctx)
+    if ctx.leader is None:
+        # Do leader "election"
+        s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+        try:
+            s.bind("\0xsecurelock-saver")
+        except OSError:
+            ctx.leader = False
+        else:
+            ctx.leader = s
+    if ctx.leader:
+        GLib.timeout_add(min(60 - now.second, 3) * 1000, on_clock_change, ctx)
 
 
 def on_weather_change(monitor, f1, f2, event, ctx):
@@ -185,6 +198,7 @@ if __name__ == "__main__":
     ctx.weather = None
     ctx.clock = None
     ctx.position = (0, 0)
+    ctx.leader = None
 
     ctx.window = Gtk.Window()
     ctx.window.set_app_paintable(True)