#!/bin/sh
#
# Returns 0 (true) if on AC power
# 1 (false) if not on AC power
# 255 (false) if can't tell
#
# Example shell script:
# if on_ac_power; then
# echo We're on AC power
# else
# echo Can't say we're on AC power
# fi

set -e

# sysfs
#
# This algorithm is complicated by the possibility of multiple AC
# adapters. We scan the ac_adapter/power_supply directory looking for adapters
# that have known states. If any adapter is on-line, we return 0. If
# no adapters are on-line but one or more are off-line, we return 1.
#
OFF_LINE_P=no

if [ -d /sys/class/power_supply/ ]; then
for FN in /sys/class/power_supply/*; do
if test -d "${FN}" && test -r "${FN}/type"; then
type="$(cat ${FN}/type)"
if test "x${type}" = "xMains"; then
if [ -r "${FN}/online" ]; then
online="$(cat ${FN}/online)"
[ "$online" = 1 ] && exit 0
[ "$online" = 0 ] && OFF_LINE_P=yes
fi
fi
fi
done
[ "${OFF_LINE_P}" = "yes" ] && exit 1
fi

# ACPI
# same algorithm as above, a fallback only when the generic sysfs interface
# is not available (old kernels only)
if /sbin/acpi_available && [ -d /proc/acpi/ac_adapter ]; then
for FN in /proc/acpi/ac_adapter/*; do
if [ -d "${FN}" ]; then
if [ -r "${FN}/state" ]; then
grep --quiet on-line "${FN}/state" && exit 0
grep --quiet off-line "${FN}/state" && OFF_LINE_P=yes
elif [ -r "${FN}/status" ]; then
grep --quiet on-line "${FN}/status" && exit 0
grep --quiet off-line "${FN}/status" && OFF_LINE_P=yes
fi
fi
done
[ "${OFF_LINE_P}" = "yes" ] && exit 1
fi

# PMU
if [ -r /proc/pmu/info ]; then
exec awk </proc/pmu/info '
BEGIN { FS=":"; ret = 255 }
/^AC Power.*1$/ { ret = 0; exit }
/^AC Power.*0$/ { ac = 1 }
/^Battery.*/ {
if ($2 ~/0/ && ac == 1)
ret = 0
else
ret = 1
exit }
END { exit ret }
'
fi

# APM
if [ -r /proc/apm ] && /sbin/apm_available; then
exec awk </proc/apm '
BEGIN { ret = 255 }
/^[0-9.a-zA-Z]* [0-9.]* 0x.. 0x../ {
if ($4 == "0x01") { ret = 0; exit }
else if ($4 == "0x00") { ret = 1; exit }
}
END { exit ret }
'
fi

# nothing is available
exit 255