#!/bin/bash

# Copyright 2020 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

. /usr/share/misc/chromeos-common.sh || exit 1
. /usr/sbin/write_gpt.sh || exit 1
. /usr/share/misc/shflags || exit 1

# Constant variables related to dlcservice.
readonly BLOCK_SIZE=4096
readonly DLC_CACHE_PATH="/var/cache/dlc"
readonly DLC_HASHTREE_FILE="hashtree"
readonly DLC_IMG_FILE="dlc.img"
readonly DLC_LIB_PATH="/var/lib/dlcservice/dlc"
readonly DLC_METADATA_PATH="/opt/google/dlc"
readonly DLC_PACKAGE="package"
readonly DLC_PRELOAD_PATH="/var/cache/dlc-images"
readonly DLC_SLOT_A="dlc_a"
readonly DLC_SLOT_B="dlc_b"
readonly DLC_TABLE_FILE="table"
readonly IMAGELOADER_JSON_FILE="imageloader.json"
readonly MOUNT_PATH="/run/imageloader"

# Command line parsing variables.
readonly FLAGS_HELP="Usage:
  [Unpacking a DLC]
  $(basename $0) --unpack --id=<id> <path>
  <path> to which the DLC image will be unpacked to.

  [Packaging a DLC]
  $(basename $0) --id=<id> <path>
  <path> from which to create the DLC image and manifest.
"
DEFINE_string "id" "" "ID name of the DLC to pack"
DEFINE_boolean "unpack" false "To unpack the DLC passed to --id" "u"

# Parse command line.
FLAGS "$@" || exit "$?"
eval set -- "${FLAGS_ARGV}"

# Setup working directory and cleanup.
WORK_DIR="$(mktemp -d)"
cleanup() {
  rm -rf "${WORK_DIR}"
}
trap cleanup EXIT

# Command line parse usage helper.
usage() {
  echo "$@"
  echo
  flags_help
  exit 1
}

# Check the correctness for command line flags.
check_flags() {
  if [[ ! -n "${FLAGS_id}" ]]; then
    usage "--id is missing"
  fi
}

# Print message prior to exiting.
die() {
  echo "ERROR: $*"
  exit 1
}

path_exists() {
  local path="$1"
  [[ -f "${path}" || -d "${path}" ]]
}

# Check if the DLC is preloadable.
is_dlc_preloadable() {
  [ -f "${DLC_PRELOAD_PATH}/${FLAGS_id}/${DLC_PACKAGE}/${DLC_IMG_FILE}" ]
}

# Locate the active DLC image from cache.
locate_dlc_image() {
  load_base_vars
  local root_part=$(get_partition_number $(rootdev -s))
  local dlc_cache_path="${DLC_CACHE_PATH}/${FLAGS_id}/${DLC_PACKAGE}"
  if [[ "${root_part}" == "${PARTITION_NUM_ROOT_A}" ]]; then
    echo "${dlc_cache_path}/${DLC_SLOT_A}/${DLC_IMG_FILE}"
  elif [[ "${root_part}" == "${PARTITION_NUM_ROOT_B}" ]]; then
    echo "${dlc_cache_path}/${DLC_SLOT_B}/${DLC_IMG_FILE}"
  else
    die "Unexpected root partition ${root_part}"
  fi
}

# Unpack (unsquashfs) the DLC image.
unpack_dlc() {
  # If the path already exists, alert user.
  if path_exists "${DIR_NAME}"; then
    die "${DIR_NAME} is a path which already exists."
  fi
  # If the DLC is preloadable, install it.
  if is_dlc_preloadable; then
    echo "Preloading DLC to not override deployed DLC images."
    dlcservice_util --install --id="${FLAGS_id}" || die "Failed to preload."
  fi
  unsquashfs -d "${DIR_NAME}" $(locate_dlc_image) || die "Failed to unpack."
}

# Checks to see if the rootfs is writable.
check_writable_rootfs() {
  if [ ! -w "/" ]; then
    local doc_url="https://chromium.googlesource.com"
    local doc_path="/chromiumos/docs/+/master/developer_mode.md#disable-verity"
    die "Disable rootfs verification to use this script." \
      "Reference: ${doc_url}${doc_path}"
  fi
}

# Unmount and delete a DLC by force.
force_delete() {
  imageloader --unmount --mount_point="${MOUNT_PATH}/${FLAGS_id}/${DLC_PACKAGE}"
  rm -rf "${DLC_CACHE_PATH}/${FLAGS_id}" "${DLC_LIB_PATH}/${FLAGS_id}" \
    "${DLC_PRELOAD_PATH}/${FLAGS_id}"
}

# Check if the directory can be packed as DLC image.
check_dlc_requirements() {
  # /root must exist in a DLC image as that is where contents reside.
  if ! [ -d "${DIR_NAME}/root" ]; then
    die "root directory is missing"
  fi
}

# Creates a squashfs image conforming to DLC requirements.
create_squashfs_image() {
  mksquashfs "${DIR_NAME}" "${DLC_IMG_FILE}" -4k-align -noappend
}

# Gets the size of a file in bytes.
get_file_size() {
  local file="$1"
  stat -c%s "${file}"
}

# Gets the number of blocks ceiling to nearest integer.
get_num_blocks() {
  local file="$1"
  local bs="$2"
  local size=$(get_file_size "${file}")
  echo "(${size} + ${bs} - 1) / ${bs}" | bc
}

# Generates the verity (hashtree and table) for the DLC image.
generate_verity() {
  local blocks=$(get_num_blocks "${DLC_IMG_FILE}" "${BLOCK_SIZE}")
  verity \
    mode=create \
    alg=sha256 \
    payload="${DLC_IMG_FILE}" \
    payload_blocks="${blocks}" \
    hashtree="${DLC_HASHTREE_FILE}" \
    salt=random \
    > "${DLC_TABLE_FILE}"
}

# Appends the hashtree generated from verity to the DLC image.
append_merkle_tree() {
  cat "${DLC_HASHTREE_FILE}" >> "${DLC_IMG_FILE}"
}

# Gets the SHA256 sum of the given file.
get_sha256sum() {
  local file="$1"
  sha256sum "${file}" | cut -d " " -f1
}

# Replace the regex with replacement in the given content.
replace_txt() {
  local content="$1"
  local regex="$2"
  local replacement="$3"
  echo "${content}" | sed -e 's/'"${regex}"'/'"${replacement}"'/g'
}

# Generates the imageloader.json file read by imageloader + used by dlcservice.
generate_imageloader_json() {
  local metadata_path="${DLC_METADATA_PATH}/${FLAGS_id}/${DLC_PACKAGE}"
  local json_path="${metadata_path}/${IMAGELOADER_JSON_FILE}"
  [ -f "${json_path}" ] || die "${json_path} does not exist"
  local json=$(cat "${json_path}")

  # Replace the image-sha256-hash.
  local image_hash=$(get_sha256sum "${DLC_IMG_FILE}")
  local ih_regex="\"image-sha256-hash\":[[:space:]]*\"[[:alnum:]]\\+\""
  local ih_rplc="\"image-sha256-hash\":\"${image_hash}\""
  local json=$(replace_txt "${json}" "${ih_regex}" "${ih_rplc}")

  # Replace the table-hash.
  local table_hash=$(get_sha256sum "${DLC_TABLE_FILE}")
  local th_regex="\"table-sha256-hash\":[[:space:]]*\"[[:alnum:]]\\+\""
  local th_rplc="\"table-sha256-hash\":\"${table_hash}\""
  local json=$(replace_txt "${json}" "${th_regex}" "${th_rplc}")

  local num_blocks=$(get_num_blocks "${DLC_IMG_FILE}" "${BLOCK_SIZE}")
  local new_size=$((${num_blocks} * ${BLOCK_SIZE}))
  # Replace the size.
  local size_regex="\"size\":[[:space:]]*\"[[:digit:]]\\+\""
  local size_rplc="\"size\":\"${new_size}\""
  local json=$(replace_txt "${json}" "${size_regex}" "${size_rplc}")

  # Replace the pre-allocated-size, just use same as size.
  local prealloc_regex="\"pre-allocated-size\":[[:space:]]*\"[[:digit:]]\\+\""
  local prealloc_rplc="\"pre-allocated-size\":\"${new_size}\""
  local json=$(replace_txt "${json}" "${prealloc_regex}" "${prealloc_rplc}")

  echo "${json}" > "${IMAGELOADER_JSON_FILE}"
  cat "${IMAGELOADER_JSON_FILE}"
}

# Writes the metadata files into the rootfs.
write_metadata_to_rootfs() {
  local metadata_path="${DLC_METADATA_PATH}/${FLAGS_id}/${DLC_PACKAGE}"
  mkdir -p "${metadata_path}"
  cp "${IMAGELOADER_JSON_FILE}" "${DLC_TABLE_FILE}" "${metadata_path}/"
}

# Writes the DLC image to dlcservice cache.
write_dlc_image() {
  local cache_path="${DLC_CACHE_PATH}/${FLAGS_id}/${DLC_PACKAGE}"
  local cache_path_A="${cache_path}/dlc_a"
  local cache_path_B="${cache_path}/dlc_b"
  mkdir -p "${cache_path_A}" "${cache_path_B}"
  echo "${cache_path_A}" "${cache_path_B}" | xargs -n 1 cp "${DLC_IMG_FILE}"
}

deploy_dlc() {
  # Check if valid DLC image.
  check_dlc_requirements

  # Create the DLC image.
  create_squashfs_image

  # Generate the verity for the DLC image.
  generate_verity

  # Append the hashtree to the DLC image.
  append_merkle_tree

  # Generate the imageloader.json from DLC image.
  generate_imageloader_json

  # Copy metadata + DLC image.
  write_metadata_to_rootfs
  write_dlc_image
}

# Main function.
main() {
  # Unpacking the DLC.
  if [ "${FLAGS_unpack}" -eq "${FLAGS_TRUE}" ]; then
    echo "Unpacking DLC (${FLAGS_id}) to: ${DIR_NAME}"
    unpack_dlc
    exit "$?"
  fi

  echo "Packing DLC (${FLAGS_id}) from: ${DIR_NAME}"
  check_writable_rootfs

  echo "Stopping dlcservice"
  stop dlcservice

  echo "Force deleting ${FLAGS_id}"
  force_delete

  echo "Creating DLC from: ${DIR_NAME}"
  deploy_dlc

  echo "Starting dlcservice"
  start dlcservice && sleep 1

  # Install the new DLC image.
  dlcservice_util --install --id="${FLAGS_id}" || die "Failed to install"
}

check_flags
if [ $# -eq 0 ]; then
  usage "<path> is missing"
fi
# Run under a subshell inside $WORK_DIR
(DIR_NAME=$(realpath "$1") && cd "${WORK_DIR}" &&  main)