#!/bin/bash
#Args
img=$1

#Usage checks
if [[ -z $img ]]; then
  echo "Usage: $0 imagefile.img"
  exit -1
fi
if [[ ! -e $img ]]; then
  echo "ERROR: $img is not a file..."
  exit -2
fi
if (( EUID != 0 )); then
   echo "ERROR: You need to be running as root."
   exit -3
fi

#Check that what we need is installed
A=`which parted 2>&1`
if (( $? != 0 )); then
   echo "ERROR: parted is not installed."
   exit -4
fi

#Gather info
beforesize=`ls -lah $img | cut -d ' ' -f 5`
partstart=`parted -m $img unit B print | tail -n 1 | cut -d ':' -f 2 | tr -d 'B\n'`
loopback=`losetup -f --show -o $partstart $img`

#Make pi expand rootfs on next boot
mountdir=`mktemp -d`
mount $loopback $mountdir

if [ `md5sum $mountdir/etc/rc.local | cut -d ' ' -f 1` != "a27a4d8192ea6ba713d2ddd15a55b1df" ]; then
echo Creating new /etc/rc.local
mv $mountdir/etc/rc.local $mountdir/etc/rc.local.bak
cat <<\EOF > $mountdir/etc/rc.local
#!/bin/bash
/usr/bin/raspi-config --expand-rootfs
rm -f /etc/rc.local; cp -f /etc/rc.local.bak /etc/rc.local; reboot
exit 0
EOF
chmod +x $mountdir/etc/rc.local
fi
umount $mountdir

#Shrink filesystem
e2fsck -f $loopback
minsize=`resize2fs -P $loopback | cut -d ':' -f 2 | tr -d ' '`
minsize=`expr $minsize + 20000 | tr -d '\n'`
resize2fs -p $loopback $minsize
if [[ $? != 0 ]]; then
  echo ERROR: resize2fs failed...
  mount $loopback $mountdir
  mv $mountdir/etc/rc.local.bak $mountdir/etc/rc.local
  umount $mountdir
  losetup -d $loopback
  exit $rc
fi
sleep 1

#Shrink partition
losetup -d $loopback
partnewsize=`expr $minsize \* 4096 | tr -d '\n'`
newpartend=`expr $partstart + $partnewsize | tr -d '\n'`
part1=`parted $img rm 2`
part2=`parted $img unit B mkpart primary $partstart $newpartend`

#Truncate the file
endresult=`parted -m $img unit B print free | tail -1 | cut -d ':' -f 2 | tr -d 'B\n'`
truncate -s $endresult $img
aftersize=`ls -lah $img | cut -d ' ' -f 5`

echo "Shrunk $img from $beforesize to $aftersize"