#!/bin/sh

POLLING_FREQUENCY=1

# ISO 8601
alias date="date '+%Y-%m-%dT%T'"

emit() {
	printf "[%s] " "$(date)"
	echo "$@"
}
get_current_level() {
	# adapted from other script i wrote, also in the public domain
	if [ "$(uname)" = "Linux" ]; then
		# this is a dirty hack.
		# acpi | awk '{print $4}' will print the battery percentage,
		# and s/,$// strips the trailing comma.
		# acpi -a will just print the power adapter status.
		printf "%b" "$(acpi | awk '{print $4}' | sed 's/,$//')"
		return 0
	elif [ "$(uname)" = "NetBSD" ]; then
		printf "%b" "$(envstat -s acpibat0:charge \
			| sed 1,2d \
			| cut -d ':' -f 2 \
			| awk '{print $1}' \
			| cut -d '.' -f 1)"
		return 0
	else
		printf "get_battery_status: unsupported OS" >>/dev/stderr
		return 1
	fi
}

! get_current_level >/dev/null \
	&& printf "Unable to get battery status on this system.\n" >>/dev/stderr \
	&& exit 1 \
	|| true

current_level=$(get_current_level)
previous_level=$current_level

emit "$(printf "Current level: %d%%" "$current_level")"

while true; do
	current_level=$(get_current_level)
	if ! [ $current_level -eq $previous_level ]; then
		[ $current_level -lt $previous_level ] \
			&& emit "$(printf "Discharged: %d%% -> %d%%\n" $previous_level $current_level )" \
			|| emit "$(printf "   Charged: %d%% -> %d%%\n" $previous_level $current_level )"
		previous_level=$current_level
	fi

	sleep $POLLING_FREQUENCY
done