#!/bin/bash

# Confirm root. If not error and exit.
if [ "$EUID" -ne 0 ]
  then echo "You are not root. Come back when you are."
  exit
fi

# Show kernel installed and newest for download:
echo -e "The current running kernel is $(uname -r).\nVersion $(sudo -u nobody curl -sL https://www.kernel.org/ | awk -F'/' '/latest_link/{getline; sub(/.*linux-/, ""); sub(/\.tar\.xz.*/, ""); print}') is the latest stable kernel."

# Ask to confirm new kernel build:
while true; do
   read -p "Would you like to proceed? [Y\\n]" yn
   case $yn in
     [Yy]* ) echo "Go make some coffee."; break;;
     [Nn]* ) exit;;
        * ) echo "Please answer yes or no.";;
   esac
done

# Get current stable:
VERSION=$(sudo -u nobody curl -sL https://www.kernel.org/ | awk -F'/' '/latest_link/{getline; sub(/.*kernel.org\//, ""); sub(/".*/, ""); print}')

# Get current dir and cd to /usr/src
CWD=$PWD
cd /usr/src

# Rsync kernel source
if [ ! -z $VERSION ]; then
  sudo -u nobody rsync -avPz rsync://rsync.kernel.org/$VERSION /tmp/
else
  echo "Unable to reach kernel.org via rsync. Check Interent connection or any firewall rules that may prevent this."
  exit
fi

# Remove URL from version
VERSION=$(echo "./$VERSION" | cut -d'/' -f6)

# Copy file, change its permissions and delete the old.
rsync -avP /tmp/$VERSION /usr/src/ && chown root: /usr/src/$VERSION && rm -vf /tmp/$VERSION

# Extract downloaded kernel
if tar -xvf "/usr/src/$VERSION"; then
  echo "Extraction Complete."
else
  echo "Tar file failed to extract. Check connection to kernel.org"
  exit
fi

# Remove tar file
rm -v "/usr/src/$VERSION"
# Remove .tar.xz from $VERSION
VERSION=$(echo $VERSION | sed -e 's/\.tar\.xz//g')

# Move into directory
cd "/usr/src/$VERSION"

# Copy old config
cp /boot/config-`uname -r` /usr/src/$VERSION/.config

## Uncomment if on an non-EFI system.
# If using EFI, break
if [ -d /sys/firmware/efi ]; then
  break 2>/dev/null
else
  # Else comment out EFI settings in config. More may be needed in the future.
  sed -i 's/CONFIG_SYSTEM_TRUSTED_KEYS/#CONFIG_SYSTEM_TRUSTED_KEYS/g;s/CONFIG_MODULE_SIG_KEY/#CONFIG_MODULE_SIG_KEY/g;' .config
fi

# Build with config with defaults
yes "" | make oldconfig

# Finish building
nice make -j $(nproc) bindeb-pkg

# Make for BTF
export BTF_VERSION=$(echo $VERSION | awk -F- '{ print $2 }')
cd tools/bpf/resolve_btfids/
make
cp -a resolve_btfids /usr/src/linux-headers-$BTF_VERSION/tools/bpf/resolve_btfids/
cd -

# Make modules
make modules

# Install modules
su -c "make modules_install install"

# Get version again. Seems to get lost without this.
VERSION=$(sudo -u nobody curl -sL https://www.kernel.org/ | awk -F'/' '/latest_link/{getline; sub(/.*linux-/, ""); sub(/\.tar\.xz.*/, ""); print}');

# Install debs
for i in $(ls /usr/src | awk '$0 !~ /dbg/ && $0 ~ /'"$VERSION"'/ && $0 ~ /deb/'); do dpkg -i /usr/src/$i; done

# Remove debs
for i in $(ls /usr/src | awk "/$VERSION/ && /changes$|buildinfo$|.deb$/"); do rm -vf /usr/src/$i; done

# Clean unneeded files
make clean
make distclean

# Change back to original dir.
cd $CWD

DPKG=$(dpkg -l | grep "linux-image-$VERSION")

# Link some modules
rsync -avP /sys/kernel/btf/vmlinux /usr/lib/modules/$VERSION*/build/
ln -sf /usr/lib/modules/linux-$VERSION/vmlinux.xz /boot/
rsync -avP /usr/src/linux-$VERSION/tools/ /usr/src/linux-headers-$VERSION*/tools/

# If package for new kernel installed, print to user or a message to trouble-shoot errors:
if [ ! -z "$DPKG" ]; then echo -e "Kernel $VERSION is now installed.\nReboot to load this kernel into memory.\n"; else "It appears this kernel did not install successfully. You will want to re-run this program with 'kernup 2> log_name' to diagnose any problems."; fi