#!/bin/sh

get_init_sys() {
  if command -v systemctl > /dev/null && systemctl | grep -q '\-\.mount'; then
    SYSTEMD=1
  elif [ -f /etc/init.d/cron ] && [ ! -h /etc/init.d/cron ]; then
    SYSTEMD=0
  else
    echo "Unrecognised init system"
    return 1
  fi
}

do_expand_rootfs() {
  if ! [ -h /dev/root ]; then
    echo "/dev/root does not exist or is not a symlink. Don't know how to expand"
    return 0
  fi

  ROOT_PART=$(readlink /dev/root)
  PART_NUM=${ROOT_PART#mmcblk0p}
  if [ "$PART_NUM" = "$ROOT_PART" ]; then
    echo "/dev/root is not an SD card. Don't know how to expand"
    return 0
  fi

  # NOTE: the NOOBS partition layout confuses parted. For now, let's only 
  # agree to work with a sufficiently simple partition layout
  if [ "$PART_NUM" -ne 2 ]; then
    echo "Your partition layout is not currently supported by this tool. You are probably using NOOBS, in which case your root filesystem is already expanded anyway."
    return 0
  fi

  LAST_PART_NUM=$(parted /dev/mmcblk0 -ms unit s p | tail -n 1 | cut -f 1 -d:)

  if [ "$LAST_PART_NUM" != "$PART_NUM" ]; then
    echo "/dev/root is not the last partition. Don't know how to expand"
    return 0
  fi

  # Get the starting offset of the root partition
  PART_START=$(parted /dev/mmcblk0 -ms unit s p | grep "^${PART_NUM}" | cut -f 2 -d:)
  [ "$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
p
w
EOF
  ASK_TO_REBOOT=1

  # now set up an init.d script
cat <<\EOF > /etc/init.d/resize2fs_once &&
#!/bin/sh
### BEGIN INIT INFO
# Provides:          resize2fs_once
# Required-Start:
# Required-Stop:
# Default-Start: 2 3 4 5 S
# Default-Stop:
# Short-Description: Resize the root filesystem to fill partition
# Description:
### END INIT INFO
. /lib/lsb/init-functions
case "$1" in
  start)
    log_daemon_msg "Starting resize2fs_once" &&
    resize2fs /dev/root &&
    rm /etc/init.d/resize2fs_once &&
    update-rc.d resize2fs_once remove &&
    log_end_msg $?
    ;;
  *)
    echo "Usage: $0 start" >&2
    exit 3
    ;;
esac
EOF
  chmod +x /etc/init.d/resize2fs_once &&
  update-rc.d resize2fs_once defaults &&
  if [ "$INTERACTIVE" = True ]; then
    echo "Root partition has been resized."
    echo "The filesystem will be enlarged upon the next reboot"
  fi
}

get_init_sys
do_expand_rootfs