#!/bin/sh
#
# Copyright (c) 2011-2012 Codethink Ltd.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License Version 2 as
# published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
# vi:set ts=8 sw=8 noet ai nocindent:

set -e

# read input parameters
device="$1"
source_subvolume="$2"
target_subvolume="$3"
patch_file="$4"

# print usage information if not all parameters are provided
if [ -z "$device" ] ||
   [ -z "$source_subvolume" ] ||
   [ -z "$target_subvolume" ] ||
   [ -z "$patch_file" ]
then
  echo "Usage: $0 <device> <source subvolume> <target subvolume> <patch file>" >&2
  exit 1
fi

if [ ! -f "$patch_file" ]; then
  echo "Patch file \"$patch_file\" does not exist" >&2
  exit 1
fi

# mount the root btrfs file system
rootfs="$(busybox mktemp -d)"
mount -t btrfs "$device" "$rootfs"
trap "cd /; umount $rootfs && busybox rm -rf $rootfs" EXIT SIGINT SIGTERM

# switch into the root file system
cd "$rootfs"

# verify that the source subvolume exists
if [ ! -e "$source_subvolume" ]; then
  echo "Source subvolume \"$source_subvolume\" does not exist in $device" >&2
  exit 1
fi

# verify that the source subvolume is a directory
if [ ! -d "$source_subvolume" ]; then
  echo "Source subvolume \"$source_subvolume\" is not a directory" >&2
  exit 1
fi

# verify that the target subvolume does not yet exist
if [ -e "$target_subvolume" ]; then
  echo "Target subvolume \"$target_subvolume\" already exists" >&2
  exit 1
fi

# verify that the target subvolume's -run snapshot does not yet exist
if [ -e "$target_subvolume-run" ]; then
  echo "Target subvolume's \"$target_subvolume-run\" snapshot already exists" >&2
  exit 1
fi

echo "Creating snapshot \"$target_subvolume\" from \"$source_subvolume\""

# create a snapshot for the target subvolume
if ! btrfs subvolume snapshot "$source_subvolume" "$target_subvolume"; then
  echo "Failed to create the target subvolume \"$target_subvolume\"" >&2
  exit 1
fi
btrfs filesystem sync .

# switch to the target subvolume
cd "$target_subvolume"

echo "Applying the patch \"$patch_file\" to \"$target_subvolume\""

# apply the patch to this subvolume
tbdiff-deploy "$patch_file"
btrfs filesystem sync .

# leave the subvolume
cd "$rootfs"

echo "Creating snapshot \"$target_subvolume-run\" from \"$target_subvolume\""

# create a -run snapshot for the target subvolume
btrfs subvolume snapshot "$target_subvolume" "$target_subvolume-run"
btrfs filesystem sync .

echo "Copying boot files to the root file system"

# copy boot files to the root file system
busybox cp "$target_subvolume/boot/vmlinuz" "boot/vmlinuz"
busybox cp "$target_subvolume/boot/System.map" "boot/System.map"
busybox cp "$target_subvolume/extlinux.conf" "extlinux.conf"
btrfs filesystem sync .

echo "Configuring extlinux to boot from \"$target_subvolume-run\""

busybox sed -i -e "s,factory-run,$target_subvolume-run,g" "extlinux.conf"
btrfs filesystem sync .

# clear the traps
trap - EXIT SIGINT SIGTERM

# leave the root file system
cd /

# unmount the root file system
umount "$rootfs"

# remove the temporary directory
busybox rm -rf "$rootfs"

# reboot the system
busybox reboot