#!/usr/bin/bash

# Rebase one level down

set -eu

# if less than one arguments supplied, display usage
if [  $# -ne 1 ]
then
    echo "This script takes as input the name of the VM to rebase one level down"
    echo "Usage: $0 vm_name"
    exit 1
fi

VM_NAME=$1

if [ ! -f $VM_NAME.qcow2 ]
then
    echo "File not found $VM_NAME.qcow2"
    exit 1
fi

shopt -s lastpipe
qemu-img info --backing-chain $VM_NAME.qcow2 | grep image | wc -l | read NUMBASES
qemu-img info --backing-chain $VM_NAME.qcow2 | grep image | head  -n 3 | tail -n 1 | cut -d' ' -f2 | read NEWBASE
qemu-img info --backing-chain $VM_NAME.qcow2 | grep image | head  -n 2 | tail -n 1 | cut -d' ' -f2 | read CURRENTBASE

if [ ! $NUMBASES -ge 3 ]
then
    echo "Image must have at least 2 backing-files"
    exit 1
fi

if [ ! -f $NEWBASE -a -f $CURRENTBASE ]
then
    echo "Backingfiles not found $CURRENTBASE, $NEWBASE"
    exit 1
fi

qemu-img rebase -f qcow2 -b $NEWBASE -F qcow2 $VM_NAME.qcow2
rm $CURRENTBASE
mv $VM_NAME.qcow2 $CURRENTBASE
chmod a-w $CURRENTBASE
qemu-img create -f qcow2 -F qcow2 -b $CURRENTBASE $VM_NAME.qcow2