#!/bin/sh

cd /var/log/ntpstats || exit 1

update=0
if [[ "$1" == "-u" ]]
then
    shift
    if [[ -w /var/lib/ntp ]]
    then
	update=1
    else
	echo "Error:  Can not update /var/lib/ntp" 1>&2
    fi
fi

old_good=`cat /var/lib/ntp/ntp.drift.good`
old_good2=`echo "$old_good" | sed 's/\.//'`

data_raw=$( cat loopstats.200[0-9][0-1][0-9][0-9][0-9] | head -100; \
	    (cat loopstats.200[0-9][0-1][0-9][0-9][0-9]; \
	     zcat loopstats.200[0-9][0-9][0-9][0-9][0-9].gz) | head -1000 )
#echo "$data_raw"

data=$( echo "$data_raw" | grep " 0\.00[0-9]* \(1[0-2]\|[0-9]\)\.[0-9][0-9]* 1[0-9]$" \
      | cut -d' ' -f 4 \
      | sort -n \
      | sed "s/^\(-*[0-9][0-9]*\.[0-9][0-9][0-9]\)[0-9]*$/\1/" )


tot_lines=$(( $( echo "$data_raw" | wc -l) + 0))

lines=$((`echo "$data" | wc -l` + 0))

if [[ $lines -lt 1 ]]
then
    echo "lines: $lines/$tot_lines   old good: $old_good"
    exit 0
fi

mid=$(( (lines + 1) / 2 ))

min=`echo "$data" | sed -n "1p"`
min2=`echo "$min" | sed 's/\.//'`
median=`echo "$data" | sed -n "${mid}p"`
median2=`echo "$median" | sed 's/\.//'`
max=`echo "$data" | sed -n "${lines}p"`
max2=`echo "$max" | sed 's/\.//'`

diff=$(( old_good2 - median2 ))
if [[ $diff -lt 0 ]]
then
    diff=$(( -diff ))
fi

spread=$(( (max2 - min2) / lines ))
if [[ $update -eq 1 ]]
then
    # see if we have enough valid data to consider updating ntp.drift.good
    if [[ $lines -ge 50  \
	  &&  $spread -lt 50 \
	  &&  $diff -gt 100 \
	  &&  $diff -lt 10000 ]]
    then
        echo "[`date '+%D %T'`] Updating /var/lib/ntp/ntp.drift.good to $median"
	echo "[`date '+%D %T'`] lines: $lines/$tot_lines   new good: $min/$median/$max ($spread)   old good: $old_good"
	mv /var/lib/ntp/ntp.drift.good.2 /var/lib/ntp/ntp.drift.good.3
	mv /var/lib/ntp/ntp.drift.good.1 /var/lib/ntp/ntp.drift.good.2
	mv /var/lib/ntp/ntp.drift.good.0 /var/lib/ntp/ntp.drift.good.1
	mv /var/lib/ntp/ntp.drift.good /var/lib/ntp/ntp.drift.good.0
	echo $median >/var/lib/ntp/ntp.drift.good
	chmod +r /var/lib/ntp/ntp.drift.good
    fi
else
    echo "lines: $lines/$tot_lines   new good: $min/$median/$max ($spread)   old good: $old_good"
fi