#!/bin/bash

MAIN_LVMS="backups"

VGS=LVM
SNAPSHOTS_SIZE=10G
SNAPSHOTS_CYCLE=10
SUFFIX=_snapshot_

function error() {
	echo -e "Subject: [$(cat /etc/hostname)] Error rotating LVM snapshots\n\nOn $(date)\nError: $1\n" | sendmail root 
        echo "ERROR: $1"
        exit 1
}

# some functions
function removeSnapshot()
{
	local name=$1${SUFFIX}$2
	echo "Removing snapshot $name"
	lvremove -f $VGS/$name || error "Removing Snapshot $name"
}

function updateSnapshot()
{
	local from=${1}${SUFFIX}$2
	local to=${1}${SUFFIX}$(($2+1))
	echo "Rename snapshot $from -> $to"
	lvrename $VGS $from $to || error "Updating Snapshot $from -> $to"
}

function createSnapshot()
{
	local name=${1}${SUFFIX}1
	echo "Create snapshot $name"
	lvcreate --snapshot --size $SNAPSHOTS_SIZE --name $name /dev/$VGS/$1 || error "Creating the new snapshot $name"
}

function rotateSnapshot()
{
	# calc the number of current snapshots
	local current=$(lvs --noheadings | grep ${1}${SUFFIX} | wc -l )
	echo "Number of snapshots: $current"

	# discard the latests snapshot
	if [ $current -ge $SNAPSHOTS_CYCLE ]; then 
		echo "Discarding Snapshots..."
		for i in $(seq $current -1 $SNAPSHOTS_CYCLE) ; do
			removeSnapshot $1 $i
			current=$(( $current - 1 )) 
		done
	fi

	# rotate snapshots
	if [ $current -gt 0 ]; then 
		echo "Rotating Snapshots..."
		for i in $(seq $current -1 1); do
			updateSnapshot $1 $i
		done
	fi

	# create new snapshot
	createSnapshot $1
}

for l in $MAIN_LVMS; do
	rotateSnapshot $l
done