#!/usr/bin/env bash
# This script boots the first linux it finds in a grub config on any available mount point
# using kexec

DEBIAN_FRONTEND=noninteractive sudo apt-get -q -y install kexec-tools

set -euvo pipefail

parts=$(sudo blkid | grep -v /dev/loop | sort | cut -d: -f 1)
grub_paths="/boot/grub/grub.cfg /grub/grub.cfg /boot/grub.cfg"
echo $parts

for device in $parts; do
	mntpnt="/bootmount/$device"
	sudo mkdir -p "$mntpnt"
	sudo mount -o ro "$device" "$mntpnt" || true
	for grub_path in $grub_paths; do
		path="${mntpnt}${grub_path}"
		if [ -f "$path" ]; then
			echo "Found grub cfg at $path"
			menu=$(grep '^\s*menuentry\s\s*["'\'']' < "$path" | head -n 1 | sed 's/^\s*//g' || true)
			linux=$(grep '^\s*linux' < "$path" | head -n 1 | sed 's/^\s*linux\s*//' | sed 's/\s*$//' || true)
			initrd=$(grep '^\s*initrd' < "$path" | head -n 1 | sed 's/^\s*initrd\s*//' | sed 's/\s*$//' || true)

			kernel=$(echo "$linux" | awk -F '[\t ]' '{print $1}')
			command=$(echo "$linux" | awk -F '[\t ]' '{s = ""; for (i = 2; i <= NF; i++) s = s $i " "; print s}')

			echo "config: $menu $linux"
			echo "kernel: $kernel"
			echo "kernel command: $command"
			echo "initrd: $initrd"
			sudo kexec -l "$mntpnt/$kernel" --initrd="$mntpnt/$initrd" --command-line="$command"
			sudo kexec -e
			exit 1
		fi
	done
done