#! /bin/bash

if [ "$(whoami)" != root ]
then
  echo "$0: must be root"
  exit 1
fi

run() {
  printf "\033[1;35m--> \033[1;34m$*\033[0m\n"
  "$@" || exit 1
}

collect_old_kernels() {
    re="$(echo "$@" | sed -re 's,linux-,,g' -e 's, ,|,')"
    find /usr/src -mindepth 1 -maxdepth 1 -name 'linux-*' | grep -Ev "/linux-${re}\$"
    find /boot -name 'initramfs-*' | grep -Ev "\-${re}\$"
    find /boot -name 'kernel-*' | grep -Ev "\-${re}\$"
    find /boot -name 'System.map-*' | grep -Ev "\-${re}\$"
}

already_built() {
    ver="$(echo "$1" | sed -re 's,linux-,,g')"
    ls -1 /boot | grep -Eq "^initramfs-.*${ver}\$"
}

cur_kernel="linux-$(uname -r)"
new_kernel="$(eselect kernel list | tail -1 | awk '{print $2}')"

run eselect kernel set "${new_kernel}"

if ! already_built "${new_kernel}"
then
    run cp -i /usr/src/"${cur_kernel}"/.config /usr/src/"${new_kernel}"/.config
    run genkernel --oldconfig all
fi

collect_old_kernels "${cur_kernel}" "${new_kernel}" | while read path
do
    run rm -r "${path}"
done

run grub-mkconfig -o /boot/grub/grub.cfg