#! /bin/sh

tstamp=`date +%Y%m%d-%H%M%S`
label_pfx="zbk-"
usrlabel=$1
maxnum=$2
zpool="zroot"

# names of the DATASETs to exclude (datasets, not mountpoints!)
excludes="/usr/ports /usr/src /backups"

usage () {
    echo Usage:
    echo "zfssnap [label [maxnum]]"
    echo "default label: 'default'"
    echo "default maxnum: infinite"
    echo "Takes a ZFS snapshot with given custom label."
    echo "If maxnum specified, keeps the so-many newest snaps only."
    echo
    echo "Optional envvars:"
    echo "EXCLUDES  list of dataset paths to exclude from snaps. Overrides default."
    echo "EXTRA_EXCLUDES  list of dataset paths to exclude from snaps. Extends default."
    echo "default excluded DATASET paths:"
    echo $excludes
}

# build list of dataset paths to exclude
if [ "x$EXCLUDES" != x ]
then
    excludes=$EXCLUDES
elif [ "x$EXTRA_EXCLUDES" != x ]
then
    excludes="$excludes $EXTRA_EXCLUDES"
fi

# label
if [ "x$usrlabel" != "x" ]
then
    if echo "$usrlabel" | grep -qiE '^([a-z0-9]{1,10})$'
    then
        label_pfx="$label_pfx$usrlabel"
    else
        echo "Invalid label '$usrlabel'! Quitting."
        usage
        exit 1
    fi
else
    label_pfx="${label_pfx}default"
fi

# maxnum
if [ "x$maxnum" != "x" ]
then
    if ! echo "$maxnum" | grep -qE '^[0-9]+$'
    then
        echo "Invalid maxnum '$maxnum'! Terminating."
        usage
        exit 1
    fi
fi


# add timestamp to label
label="${label_pfx}-$tstamp"

# take recursive snap
zfs snapshot -r $zpool@$label || exit $?
# exclude folders
for xm in $excludes
do
    # let this fail, the ds might not exist
    zfs destroy -r $zpool$xm@$label
done

# prune dbs if requested
if [ "x$maxnum" != x ]
then
    ls /.zfs/snapshot/ | sort -rt- -k 3,4 | awk -v maxnum=$maxnum -v matchlabel=$label_pfx 'BEGIN {x=0} $0 ~ "^"matchlabel { x++; if (x>maxnum) print}' | while read snapname
    do
        zfs destroy -r $zpool@$snapname || exit $?
    done
fi