#!/bin/bash

set -e

usage () {
  >&2 echo 'makekernel version #VERSION#'
  >&2 echo 'usage:'
  >&2 echo '  makekernel [ -a | --allowDownload ] [ -c $version | --compileVersion=$version ]:'
  >&2 echo '    download and compile kernel'
  >&2 echo '      -a | --allowDownload:'
  >&2 echo '        allow to download complete source instead of patch if necessary'
  >&2 echo '      -c | --compileVersion $version:'
  >&2 echo '        download and compile version $version instead of most current stable'
  >&2 echo '  makekernel ( -s | --showVersion ):'
  >&2 echo '    show version of most current stable kernel'
  exit 1
}

dlExVer () {
  wget -nd "$1.xz"
  wget -nd "$1.sign"
  xz -d "$2.xz"
  if ! gpg --verify $2{.sign,}
  then
    >&2 echo 'ERROR: Wrong signature! Closing.'
    exit 1
  fi
  rm "$2.sign"
}

. #ETCDIR#/makekernel.conf

if [ "$(whoami)" == "root" ]
then
  >&2 echo 'ERROR: Do not call as root! Closing.'
  exit 1
fi

eval set -- "$(
  getopt -o ac:s \
    --long allowDownload \
    --long compileVersion: \
    --long showVersion \
    -n "$(basename "$0")" \
  -- "$@" || echo usage
)"

allowDownload=false
forceVersion=false
showVersion=false

while true
do
  case "$1" in
    -a|--allowDownload)
      ${allowDownload} && usage
      ${showVersion} && usage
      allowDownload=true
    ;;
    -c|--compileVersion)
      ${forceVersion} && usage
      ${showVersion} && usage
      curVer="$2"
      forceVersion=true
      shift
    ;;
    -s|--showVersion)
      ${allowDownload} && usage
      ${forceVersion} && usage
      ${showVersion} && usage
      showVersion=true
    ;;
    --)
      shift
      break
    ;;
    *)
      >&2 echo "ERROR: Option \"$1\" unknown in the end! Closing."
      usage
  esac
  shift
done

[ $# -ne 0 ] && usage

if ${showVersion}
then
  mainVersion="$(
    curl 'https://cdn.kernel.org/pub/linux/kernel/' 2> /dev/null | \
      tr '>/' '\n' | \
      grep '^v.*$' | \
      sort -V | \
      tail -n1
  )"
  curl "https://cdn.kernel.org/pub/linux/kernel/${mainVersion}/" 2> /dev/null | \
    tr '<>' '\n\n' | \
    grep '^linux-.*\.tar\.xz$' | \
    sed 's/^linux-\(.*\)\.tar\.xz$/\1/' | \
    sort -V | \
    tail -n1
  exit 0
fi

[ -z "${curVer}" ] && curVer="$("$0" -s)"
mainVer="$(
  echo "${curVer}" | \
    sed 's|^\([0-9]\+\.[0-9]\+\)\(\..*\)\?$|\1|'
)"
if [ "${curVer}" == "${mainVer}" ]
then
  minPreVer='#invalid#'
  mainPreVer="${curVer%.*}.$[${curVer##*.}-1]"
else
  minPreVer="${mainVer}.$[${curVer##*.}-1]"
  mainPreVer='#invalid#'
fi

# possible updates with patches from old sources are:
#  - "recompile" old source
#  - "minor" incremental (e.g. 4.7.2 -> 4.7.3)
#  - make a "stablePatch" (e.g. 4.7 -> 4.7.3)
#  - "major" incremental (e.g. 4.6 -> 4.7)
# alternative (if allowed):
#  - download complete source

if [ -d "${kernelDir}/linux-${curVer}" ]
then
  updateType='recompile'
  patchSrc=''
  dlSrc=''
elif [ -d "${kernelDir}/linux-${minPreVer}" ]
then
  updateType='minor'
  srcDir="linux-${minPreVer}"
  patch="patch-${minPreVer}-${curVer##*.}"
  patchSrc="https://cdn.kernel.org/pub/linux/kernel/v${curVer%%.*}.x/incr/${patch}"
  dlSrc=''
elif [ -d "${kernelDir}/linux-${mainVer}" ]
then
  updateType='stablePatch'
  srcDir="linux-${mainVer}"
  patch="patch-${curVer}"
  patchSrc="https://cdn.kernel.org/pub/linux/kernel/v${curVer%%.*}.x/${patch}"
  dlSrc=''
elif [ -d "${kernelDir}/linux-${mainPreVer}" ]
then
  updateType='major'
  srcDir="linux-${mainPreVer}"
  patch="patch-${curVer}"
  patchSrc="https://cdn.kernel.org/pub/linux/kernel/v${curVer%%.*}.x/${patch}"
  dlSrc=''
elif ${allowDownload}
then
  updateType='download'
  patchSrc=''
  dlSrc="https://cdn.kernel.org/pub/linux/kernel/v${curVer%%.*}.x/linux-${curVer}.tar"
else
  >&2 echo 'No patch method available and download of complete source not allowed! Closing.'
  usage
fi

cd "${kernelDir}"
echo "update type: ${updateType}"

if [ -n "${patchSrc}" ]
then
  dlExVer "${patchSrc}" "${patch}"
  cp -r "${srcDir}" "linux-${curVer}"
  cd "linux-${curVer}"
  patch -p1 -i "../${patch}"
  rm "../${patch}"
elif [ -n "${dlSrc}" ]
then
  dlExVer "${dlSrc}" "linux-${curVer}.tar"
  tar -xf "linux-${curVer}.tar"
  rm "linux-${curVer}.tar"
fi

cd "${kernelDir}/linux-${curVer}"
[ ! -r .config ] && zcat /proc/config.gz > .config

make clean
make oldconfig
make
grep -q '^# CONFIG_MODULES is not set$' .config || make modules_install

kernelImg="$(find ${kernelDir}/linux-${curVer}/arch/ -type f -iname '*image')"
if [ $(echo "${kernelImg}" | wc -l) -ne 1 ]
then
  >&2 echo 'ERROR: Did not find exactly one compiled kernel image:'
  >&2 echo "${kernelImg}"
  >&2 echo 'Closing.'
  exit 1
fi

echo 'becoming root ...'

su -c ' \
  . #ETCDIR#/makekernel.conf && \
  before_install_hook && \
  install -m644 --owner=root "'"${kernelImg}"'" "/boot/vmlinuz-'"${curVer}"'" && \
  grub-mkconfig -o /boot/grub/grub.cfg && \
  after_install_hook \
'

echo 'Success.'