warn-battery

#!/usr/bin/env bash
# warns me when battery is at 10 percent
# there are other battery modules but I sort
# of wanted to emulate mac's behaviour:
#
# Warn me once, when battery goes under 10%
# and then wait till battery goes above 15%
# before warning again

readonly BATTERY_NAME="${1:?Must provide battery name (e.g. BAT0) as first argument}"
declare BATTERY_PERC
declare WARNED=0 # state machine

set_battery_perc() {
	BATTERY_PERC=$(cat /sys/class/power_supply/"$BATTERY_NAME"/capacity) || return 1
}

is_charging() {
	local status
	status=$(cat /sys/class/power_supply/"$BATTERY_NAME"/status) || return 1
	[[ "$status" == 'Charging' ]]
}

# make sure that we can get the battery percentage
set_battery_perc "${BATTERY_NAME}" || exit $?

while true; do
	# if already charging, skip check
	is_charging && {
		WARNED=0
		sleep 60 && continue
	}
	set_battery_perc "${BATTERY_NAME}"
	if ((WARNED == 0)); then
		# hasn't been warned, check if battery is under 10%
		((BATTERY_PERC <= 10)) && notify -u critical 'Battery low!' && WARNED=1
	elif ((WARNED == 1)); then
		((BATTERY_PERC <= 5)) && notify -u critical 'Battery critical!' && WARNED=2
	else # WARNED = 2
		((BATTERY_PERC > 15)) && WARNED=0
	fi
	sleep 60
done