checkupdates: Fix for shared module

Cache result of checkupdates in temporary file, that gets updated after
15 seconds. It's a workaround for shared custom/pacman module that can
   only run for one bar at once. Usually it causes the module to work
   only in one bar. This way all bars should show the same output.

.config/waybar/scripts/checkupdates

@@ -1,5 +1,26 @@
 #!/bin/sh
+count_file=/tmp/waybar/module/pacman/count
+threshold_date="$(date -d 'now - 15 seconds' +%s)"
+
+while pgrep checkupdates | grep -v $$; do
+    sleep 1
+done
+
+if [ -f "$count_file" ]; then
+    last_update="$(stat --format='%Y' "$count_file")"
+    if [ "$last_update" -ge "$threshold_date" ]; then
+        count="$(cat "$count_file")"
+    else
         count="$(checkupdates-with-aur | wc -l)"
+        mkdir -p /tmp/waybar/module/pacman
+        echo "$count" > /tmp/waybar/module/pacman/count
+    fi
+else
+    count="$(checkupdates-with-aur | wc -l)"
+    mkdir -p /tmp/waybar/module/pacman
+    echo "$count" > /tmp/waybar/module/pacman/count
+fi
+
 
 class="ok"
 if [ "$count" -gt 0 ]; then