#!/bin/bash

usage() { echo "Usage: $0 [-s] imagefile.img [newimagefile.img]"; exit -1; }

should_skip_autoexpand=false

while getopts ":s" opt; do
  case "${opt}" in
    s) should_skip_autoexpand=true ;;
    *) usage ;;
  esac
done
shift $((OPTIND-1))

#Args
img=$1

#Usage checks
if [[ -z $img ]]; then
  usage
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

#Copy to new file if requested
if [ -n "$2" ]; then
  echo "Copying $1 to $2..."
  cp --reflink=auto --sparse=always "$1" "$2"
  if (( $? != 0 )); then
    echo "ERROR: Could not copy file..."
    exit -5
  fi
  img=$2
fi

#Gather info
beforesize=`ls -lah $img | cut -d ' ' -f 5`
partnum=`parted -m $img unit B print | tail -n 1 | cut -d ':' -f 1 | tr -d '\n'`
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`
currentsize=`tune2fs -l $loopback | grep 'Block count' | tr -d ' ' | cut -d ':' -f 2 | tr -d '\n'`
blocksize=`tune2fs -l $loopback | grep 'Block size' | tr -d ' ' | cut -d ':' -f 2 | tr -d '\n'`

#Check if we should make pi expand rootfs on next boot
if [ "$should_skip_autoexpand" = false ]; then
  #Make pi expand rootfs on next boot
  mountdir=`mktemp -d`
  mount $loopback $mountdir

  if [ `md5sum $mountdir/etc/rc.local | cut -d ' ' -f 1` != "c4eb22d9aa99915af319287d194d4529" ]; then
    echo Creating new /etc/rc.local
    mv $mountdir/etc/rc.local $mountdir/etc/rc.local.bak
    ###Do not touch the following 6 lines including EOF###
cat <<\EOFE > $mountdir/etc/rc.local
#!/bin/bash
do_expand_rootfs() {
  ROOT_PART=$(cat /proc/cmdline | tr -s ' ' '\n' | grep root= | cut -d '=' -f 2)
  if [[ "$ROOT_PART" != /dev/mmcblk0* ]] ; then
    echo $ROOT_PART is not an SD card...
    return 0
  fi
  PART_NUM=$(echo $ROOT_PART | cut -d 'p' -f 2)

  # Get the starting offset of the root partition
  PART_START=$(fdisk -l /dev/mmcblk0 | grep $ROOT_PART | tr -s ' ' | cut -d ' ' -f 2)
  [ "$PART_START" ] || return 1
  # Return value will likely be error for fdisk as it fails to reload the
  # partition table because the root fs is mounted
  fdisk /dev/mmcblk0 <<EOF
p
d
$PART_NUM
n
p
$PART_NUM
$PART_START

w

EOF

cat <<EOF > /etc/rc.local &&
#!/bin/sh
resize2fs $ROOT_PART
rm -f /etc/rc.local; cp -f /etc/rc.local.bak /etc/rc.local; /etc/rc.local

EOF
reboot
exit
}
do_expand_rootfs
rm -f /etc/rc.local; cp -f /etc/rc.local.bak /etc/rc.local; /etc/rc.local
exit 0
EOFE
    ###End no touch zone###
    chmod +x $mountdir/etc/rc.local
  fi
  umount $mountdir
else
  echo Skipping autoexpanding process...
fi

#Make sure filesystem is ok
e2fsck -f $loopback
minsize=`resize2fs -P $loopback | cut -d ':' -f 2 | tr -d ' ' | tr -d '\n'`
if [[ $currentsize -eq $minsize ]]; then
  echo ERROR: Image already shrunk to smallest size
  exit -6
fi

#Add some free space to the end of the filesystem
if [[ `expr $currentsize - $minsize - 5000` -gt 0 ]]; then
  minsize=`expr $minsize + 5000 | tr -d '\n'`
elif [[ `expr $currentsize - $minsize - 1000` -gt 0 ]]; then
  minsize=`expr $minsize + 1000 | tr -d '\n'`
elif [[ `expr $currentsize - $minsize - 100` -gt 0 ]]; then
  minsize=`expr $minsize + 100 | tr -d '\n'`
fi

#Shrink filesystem
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 \* $blocksize | tr -d '\n'`
newpartend=`expr $partstart + $partnewsize | tr -d '\n'`
part1=`parted $img rm $partnum`
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"