#! /bin/sh
# Monitor battery via ACPI.  On change in battery status (eg, charging,
# discharging, battery below threshold) indicate this change in status
# by signaling init that the power has changed.
# 
# We signal init by creating /etc/powerstatus with a single character in
# it, viz O(kay), F(ail -- no mains, on battery), L(ow battery), and
# then sending SIGPWR to init.  This runs /etc/init.d/powerfail (on a 
# Debian system -- configured in /etc/inittab) to handle the power
# status changes appropriately.
#
# Written by Ewen McNeill <ewen@naos.co.nz>, 2003/03/02
#---------------------------------------------------------------------------
#
PATH=/sbin:/usr/sbin:/bin:/usr/bin
export PATH
CHECKINTERVAL="15";    # seconds

# Return: O(kay), F(ail), L(ow) battery status
get_powerstatus()
{
  BATTERY_CHARGE=`acpi -b|head -1`
  STATUS="O";        # Assume on mains power
  if echo "${BATTERY_CHARGE}" | grep -q discharging; then
    STATUS="F";      # On battery power

    if echo "${BATTERY_CHARGE}" | grep -q "00:0[0-9]:[0-9][0-9] remaining"; then
      STATUS="L";    # Low on battery power
    fi
  fi
  echo "${STATUS}"
}

# Signal init of new power status.
# Usage: signal_init {O|F|L}
signal_init()
{
  if [ -n "$1" ]; then
    echo "Telling init power status: $1"
    echo "$1" >/etc/powerstatus
    kill -PWR 1
  fi
}

#---------------------------------------------------------------------------
# Mainline

CURSTATUS=""

while true; do
  echo `date` `acpi -b|sed 's/  */ /g; s/^ //g'`
  NEWSTATUS=`get_powerstatus`
  if [ "${NEWSTATUS}" != "${CURSTATUS}" ]; then
    signal_init "${NEWSTATUS}"
  fi
  CURSTATUS="$NEWSTATUS"
  sleep ${CHECKINTERVAL}
done