#!/bin/sh
#
# Shutdown system if it has been idle for 1 hour and no active users are logged
# in.
#
# Usage: This script is mainly used on a home server used for building FreeBSD
# World and kernels. As soon it is done it can shutdown if not being used
# anymore. The system has Wake-On-Lan support and can thus be activated again
# from remote.
#
# Please run from cron every CRON_INTERVAL minutes:
# */5 * * * * * /usr/local/bin/power-saver
#
# Rick van der Zwet <info@rickvanderzwet.nl> 
#

CRON_INTERVAL=5
MAX_LOAD=0.10
MAX_IDLE=45

# Abuse this trick to force a quicker shutdown by ignoring some users
IDLE_USER=${1:-1}
# Shutdown delay is NOT considered idle time, but just a save guard.
SHUTDOWN_DELAY=${2:-15}


# Stored as <epoch> <load>
DAT_FILE='/tmp/power-saver.dat'

# Current values
EPOCH=`date "+%s"`
LOAD_15=`sysctl vm.loadavg | awk '{print $5}'`

# Empty file needs to be created and filled
echo "$EPOCH $LOAD_15" >> $DAT_FILE || exit 1

# Check if countdown has already been started
ps -x | grep -q '[0-9] shutdown' && exit 0

# Check if all users are no longer active
SHORTEST_IDLE=`w -ih | awk -vIDLE_USER=$IDLE_USER '{if (NR == IDLE_USER) print $5}'`
# Hack to make sure time is always in minutes
SHORTEST_IDLE_IN_MIN=`echo $SHORTEST_IDLE | awk -F: '{if (NF > 1){print $1 * 60 + $2}else{print $1}}'`
if [ -z "$SHORTEST_IDLE_IN_MIN" ]; then
  # No users are currently logged in
  continue
elif [ "$SHORTEST_IDLE_IN_MIN" = "-" ]; then
  # User is still active an minute ago
  exit 0
elif [ $SHORTEST_IDLE_IN_MIN -le $MAX_IDLE ]; then
  # User is still active less than MAX_IDLE ago
  exit 0
fi

# Count the amount entries we are current on our way
IDLE_COUNTS=`awk -vMAX_LOAD=$MAX_LOAD -vMAX_IDLE=$MAX_IDLE -vEPOCH=$EPOCH \
  'BEGIN{MIN_TIME=EPOCH-MAX_IDLE * 60;s=0}{if ($1 > MIN_TIME && $2 < MAX_LOAD){s += 1}}END{print s}' $DAT_FILE`

# We are idle for over $MAX_IDLE time, starting shutdown
if [ $IDLE_COUNTS -ge `expr $MAX_IDLE / $CRON_INTERVAL` ]; then
  shutdown -p "+$SHUTDOWN_DELAY" "Cancel: sudo killall -SIGTERM shutdown"
fi