i3-batwarn

#!/bin/bash

#############################################
# This is a simple battery warning script.  #
# It uses i3's nagbar to display warnings.  #
#                                           #
# @author agribu                            #
#############################################

BATTERY="$(echo '/sys/class/power_supply/BAT'?)"	# Battery file
WARNING_THRESHOLD='30'					# Set energy limit in percent, where warning should be displayed
EMERGENCY_THRESHOLD='15'				# Set energy limit in percent, where emergency should be displayed
LOCK_FILE='/var/lock/battery_state.lock'		# Lock file location
PID_FILE="/run/user/${UID}/nagbar.pid"			# Save pid for killing later

# get battery status
get_status() {
	cat "${BATTERY}/status"
}

# get current capacity
get_percentage() {
	cat "${BATTERY}/capacity"
}

is_nagbar_active() {
	[ -s "${PID_FILE}" ] && ps -e | grep "$(cat "${PID_FILE}")" | grep -q "i3-nagbar"
}

display_nagbar() {
	if is_nagbar_active ; then
		echo "pidfile in order, nothing to do"
	else
		rm -f "${PID_FILE}"
		/usr/bin/i3-nagbar -t "${1}" -m "${2}" &
		echo "$!" > "${PID_FILE}"
	fi
}

display_emergency() {
	display_nagbar 'error' "Battery almost depleted ($(get_percentage)%)! Find charger quickly!"
}

display_warning() {
	display_nagbar 'warning' "Low battery ($(get_percentage)%)! Find charger!"
}

kill_nagbar() {
	if is_nagbar_active ; then
		kill "$(cat "${PID_FILE}")"
	fi
	if is_nagbar_active ; then
		kill -9 "$(cat "${PID_FILE}")"
	fi
	rm -f "${PID_FILE}"
}

await_status() {
	# We'll just assume the charge won't get higher unless you plug in
	while [ "$(get_status)" != "Charging" ] ; do
		if [ -n "${1}" ] && [ "$(get_percentage)" -lt "${1}" ] ; then
			# Let's not do that again! Empty up ${1}
			shift
			kill_nagbar
			display_emergency
		fi
		sleep 2
	done
	kill_nagbar
}

main() {
	if [ "$(get_status)" = "Discharging" ] ; then
		if [ "$(get_percentage)" -lt "${EMERGENCY_THRESHOLD}" ] ; then
			display_emergency
			await_status &
		elif [ "$(get_percentage)" -lt "${WARNING_THRESHOLD}" ] ; then
			display_warning
			await_status "${EMERGENCY_THRESHOLD}" &
		fi
	fi
}

(
	flock -x -w 10 200 && main || exit 1
) 200> "${LOCK_FILE}"
rm -f "${LOCK_FILE}"