#!/usr/bin/env bash
set -euo pipefail

builder_image=""
linux_version=""
source_url=""
config_url=""
workdir=""
output=""

while [[ $# -gt 0 ]]; do
  case "$1" in
    --builder-image) builder_image="$2"; shift 2 ;;
    --linux-version) linux_version="$2"; shift 2 ;;
    --source-url) source_url="$2"; shift 2 ;;
    --config-url) config_url="$2"; shift 2 ;;
    --workdir) workdir="$2"; shift 2 ;;
    --output) output="$2"; shift 2 ;;
    *) echo "unknown arg: $1" >&2; exit 1 ;;
  esac
done

: "${builder_image:?missing --builder-image}"
: "${linux_version:?missing --linux-version}"
: "${source_url:?missing --source-url}"
: "${config_url:?missing --config-url}"
: "${workdir:?missing --workdir}"
: "${output:?missing --output}"

mkdir -p "$workdir" "$(dirname "$output")"
workdir="$(cd "$workdir" && pwd)"
output_dir="$(cd "$(dirname "$output")" && pwd)"
output="$output_dir/$(basename "$output")"
container_script="$workdir/build-kernel-container.sh"
cat > "$container_script" <<'SCRIPT'
#!/usr/bin/env bash
set -euo pipefail
export DEBIAN_FRONTEND=noninteractive
apt-get update
apt-get install -y --no-install-recommends \
  bc bison build-essential ca-certificates curl flex libelf-dev libssl-dev pahole python3 rsync xz-utils
cd /work
curl -fsSL "$KERNEL_SOURCE_URL" -o linux.tar.xz
curl -fsSL "$KERNEL_CONFIG_URL" -o kernel.config
rm -rf linux-src out
mkdir -p linux-src out
tar -xf linux.tar.xz -C linux-src --strip-components=1
cd linux-src
cp /work/kernel.config .config
make olddefconfig
make -j"$(nproc)" vmlinux
cp vmlinux /work/out/vmlinux
SCRIPT
chmod +x "$container_script"
mkdir -p "$workdir/out"

docker run --rm \
  -e KERNEL_SOURCE_URL="$source_url" \
  -e KERNEL_CONFIG_URL="$config_url" \
  -v "$workdir:/work" \
  "$builder_image" \
  /work/build-kernel-container.sh

cp "$workdir/out/vmlinux" "$output"