auto-switch tuned profiles on battery

I'm not sure if a looping script like this is the best way to accomplish
this. I don't understand why TuneD doesn't provide this functionality
itself, like TLP does.

roles/laptop/files/power_monitor.service

@@ -0,0 +1,6 @@
+[Service]
+Environment=STARTUP_WAIT=30s
+ExecStart=/usr/local/bin/power_monitor.sh
+
+[Install]
+WantedBy=default.target

roles/laptop/files/power_monitor.sh

@@ -0,0 +1,43 @@
+#! /bin/bash
+# Original stolen from Kobus van Schoor:
+# https://kobusvs.co.za/blog/power-profile-switching/
+
+BAT=$(echo /sys/class/power_supply/BAT*)
+BAT_STATUS="$BAT/status"
+BAT_CAP="$BAT/capacity"
+LOW_BAT_PERCENT=50
+
+AC_PROFILE="desktop"
+BAT_PROFILE="balanced"
+LOW_BAT_PROFILE="laptop-battery-powersave"
+
+# wait a while if needed
+[[ -z $STARTUP_WAIT ]] || sleep "$STARTUP_WAIT"
+
+# start the monitor loop
+prev=0
+
+while true; do
+    # read the current state
+    if [[ $(cat "$BAT_STATUS") == "Discharging" ]]; then
+        if [[ $(cat "$BAT_CAP") -gt $LOW_BAT_PERCENT ]]; then
+            profile=$BAT_PROFILE
+        else
+            profile=$LOW_BAT_PROFILE
+        fi
+    else
+        profile=$AC_PROFILE
+    fi
+
+    # set the new profile
+    if [[ $prev != "$profile" ]]; then
+        echo setting power profile to $profile
+        # powerprofilesctl set $profile
+        tuned-adm profile $profile
+    fi
+
+    prev=$profile
+
+    # wait for the next power change event
+    inotifywait -qq "$BAT_STATUS" "$BAT_CAP"
+done

roles/laptop/handlers/main.yml

@@ -2,5 +2,7 @@
 - name: restart tlp
   service: name=tlp.service state=restarted
 
-- name: restart lowbatt
-  service: name=lowbatt.timer state=restarted
+- name: restart power monitor
+  service:
+    name: power_monitor.service
+    state: restarted

roles/laptop/tasks/tuned.yml

@@ -13,3 +13,38 @@
     state: started
   tags:
     - tuned
+
+- name: Install inotify-tools
+  pacman:
+    name: inotify-tools
+    state: present
+  tags:
+    - tuned
+
+- name: Install power monitor script
+  copy:
+    src: power_monitor.sh
+    dest: /usr/local/bin/
+    mode: 0755
+  notify:
+    - restart power monitor
+  tags:
+    - tuned
+
+- name: Copy power monitor service
+  copy:
+    src: power_monitor.service
+    dest: /etc/systemd/system/
+  notify:
+    - reload systemd config
+    - restart power monitor
+  tags:
+    - tuned
+
+- name: Enable and start power monitor service
+  service:
+    name: power_monitor.service
+    enabled: yes
+    state: started
+  tags:
+    - tuned