#!/bin/sh

set -e

KERNFRAG=${KERNFRAG:-/etc/kernfrag}

RUNNING_CONFIG=$(mktemp --suffix=-kern-config)
zcat /proc/config.gz > "$RUNNING_CONFIG"

# We do want to expand tmpdir now rather than later,
# and mktemp should give us a path without spaces.
# shellcheck disable=SC2064
trap "{ rm $RUNNING_CONFIG; }" EXIT

err() {
	printf "kern: %s\n" "$@" >&2
}

errx() {
	err "$@"
	exit 1
}

need_kernel_source() {
	test -r Kbuild -a -r Kconfig || errx "current directory does not contain a kernel source tree, refusing"
}

has_boot_mount() {
	awk '{print $2}' /etc/fstab | grep -q ^/boot$
}

is_boot_mounted() {
	mountpoint -q /boot
}

mount_boot_on_demand() {
	if has_boot_mount && ! is_boot_mounted; then
		sudo mount /boot
	fi
}

get_latest_kernel() {
	eselect --brief kernel list | tail -n1
}

get_selected_kernel() {
	readlink /usr/src/linux
}

get_running_kernel() {
	uname -r
}

set_kernel() {
	kern=${1:-$(get_latest_kernel)}
	selected=$(get_selected_kernel)
	kerndir=/usr/src/$kern

	test -d "$kerndir" || errx "No such file or directory: $kerndir"

	if test "$kern" = "$selected"; then
		err "Warning: Latest kernel already selected: $kern"
		return
	fi

	printf "Selecting kernel: %s\n" "$kern"

	sudo eselect kernel set "$kern"
	sudo chown -R "$(id -un)":"$(id -gn)" "$kerndir"
}

config_kernel() {
	need_kernel_source
	host=${1:-$(hostname)}

	test -d "$KERNFRAG" || errx "No such file or directory: $KERNFRAG"

	printf "Starting merge for %s...\n\n" "$host"

	awk -v prefix="$KERNFRAG/fragments/" '{print prefix $0}' \
		"$KERNFRAG/templates/base" "$KERNFRAG/templates/$host" | xargs scripts/kconfig/merge_config.sh
}

diff_kernel() {
	need_kernel_source
	diff=${1:-$RUNNING_CONFIG}

	if command -v git >/dev/null; then
		git diff --no-index "$diff" .config
	else
		diff -u "$diff" .config
	fi
}

build_kernel() {
	need_kernel_source
	make -j"$(nproc)"
}

install_kernel() {
	need_kernel_source
	mount_boot_on_demand
	sudo make install modules_install
}

post_install_kernel() {
	sudo emerge --ask=n @module-rebuild
}

clean_kernel() {
	sudo eclean-kernel -An3
}

strip_config() {
	sed -nE '/^(# )?CONFIG_.*/p' "$1"
}

test_diff() {
	dt=$(mktemp)
	strip_config "$RUNNING_CONFIG" > "$dt"

	if ! strip_config .config | diff -q "$dt" -; then
		diff_kernel || true
		printf "Continue? [y/N] "
		read -r response
		if test "$response" != "y"; then
			rm "$dt"
			return 1
		fi
	fi
	rm "$dt"
}

all() {
	set_kernel
	cd /usr/src/linux
	config_kernel
	test_diff
	build_kernel
	install_kernel
	post_install_kernel
	clean_kernel
}

if test $# -eq 0; then
	all
	exit 0
fi

cmd=$1
shift

case $cmd in
	set) set_kernel "$@";;
	config) config_kernel "$@";;
	diff) diff_kernel "$@";;
	build) build_kernel;;
	install) install_kernel;;
	postinst) post_install_kernel;;
	clean) clean_kernel;;
	all) all;;
esac