#!/bin/sh

# Create sparse file of 20MB which can be used by QEMU.

if [ "$1" = "-e" -o "$1" = "--empty" ] ; then
  # Create new hard disk image file.
  rm -f hdd.img
  truncate -s 20M hdd.img
  echo "Created new hard disk image file 'hdd.img' with 20MB size."
elif [ "$1" = "-f" -o "$1" = "--folder" ] ; then
  if [ ! "$(id -u)" = "0" ] ; then
    echo "Using option '-f' (or '--folder') requires root permissions."
    exit 1
  fi
  
  rm -f hdd.img
  truncate -s 20M hdd.img
  echo "Created new hard disk image file 'hdd.img' with 20MB size."
  
  LOOP_DEVICE=$(losetup -f)
  losetup $LOOP_DEVICE hdd.img
  echo "Attached hard disk image file to loop device."
  
  mkfs.ext2 $LOOP_DEVICE
  echo "Hard disk image file has been formatted with Ext2 filesystem."
  
  mkdir folder
  mount hdd.img folder
  echo "Mounted hard disk image file to temporary folder."
  
  mkdir -p folder/minimal/rootfs
  mkdir -p folder/minimal/work
  echo "Overlay structure has been created."
  
  echo "This file is on external hard disk." > folder/minimal/rootfs/overlay.txt 
  echo "Created sample text file."

  umount folder
  rm -rf folder
  echo "Unmounted hard disk image file."
  
  losetup -d $LOOP_DEVICE
  echo "Detached hard disk image file from loop device."
  
  chown $(logname) hdd.img
  echo "Applied original ownership to hard disk image file."
elif [ "$1" = "-s" -o "$1" = "--sparse" ] ; then
  if [ ! "$(id -u)" = "0" ] ; then
    echo "Using option '-s' (or '--sparse') requires root permissions."
    exit 1
  fi
  
  rm -f hdd.img
  truncate -s 20M hdd.img
  echo "Created new hard disk image file 'hdd.img' with 20MB size."
  
  LOOP_DEVICE_HDD=$(losetup -f)
  losetup $LOOP_DEVICE_HDD hdd.img
  echo "Attached hard disk image file to loop device."
  
  mkfs.vfat $LOOP_DEVICE_HDD
  echo "Hard disk image file has been formatted with FAT filesystem."
  
  mkdir sparse
  mount hdd.img sparse
  echo "Mounted hard disk image file to temporary folder."
  
  rm -f sparse/minimal.img
  truncate -s 1M sparse/minimal.img
  echo "Created new overlay image file with 1MB size."

  LOOP_DEVICE_OVL=$(losetup -f)
  losetup $LOOP_DEVICE_OVL sparse/minimal.img
  echo "Attached overlay image file to loop device."

  mkfs.ext2 $LOOP_DEVICE_OVL
  echo "Overlay image file has been formatted with Ext2 filesystem."

  mkdir ovl
  mount sparse/minimal.img ovl
  echo "Mounted overlay image file to temporary folder."
  
  mkdir -p ovl/rootfs
  mkdir -p ovl/work
  echo "Overlay structure has been created."
  
  echo "Create sample text file."
  echo "This file is on external hard disk." > ovl/rootfs/overlay.txt

  chown -R root:root ovl
  echo "Applied root ownership to overlay content."

  umount ovl
  sleep 1
  rm -rf ovl
  echo "Unmounted overlay image file."

  losetup -d $LOOP_DEVICE_OVL
  sleep 1
  echo "Overlay image file has been detached from loop device."

  umount sparse  
  sleep 1
  rm -rf sparse
  echo "Unmounted hard disk image file."
  
  losetup -d $LOOP_DEVICE_HDD
  sleep 1
  echo "Hard disk image file has been detached from loop device."
  
  chown $(logname) hdd.img
  echo "Applied original ownership to hard disk image file."
elif [ "$1" = "-h" -o "$1" = "--help" ] ; then
  cat << CEOF
  Usage: $0 [OPTION]
  This utility generates 20MB sparse file 'hdd.img' which can be used as QEMU
  disk image where all filesystem changes from the live session are persisted.
  
  -e, --empty     Create empty sparse image file which is not formatted.
  -f, --folder    Create sparse image file formatted with Ext2 filesystem which
                  contains compatible overlay folder structure.
  -h, --help      Prints this help information.
  -s, --sparse    Create sparse image file formatted with FAT filesystem which
                  contains sparse image file 'minimal.img' (1MB) formatted with
                  Ext2 filesystem which contains the actual overlay structure.
CEOF

elif [ "$1" = "" ] ; then
  echo "No option specified. Use '-h' or '--help' for more info."
else
  echo "Option '$1' is not recognized. Use '-h' or '--help' for more info."
fi