#!/bin/bash
###
### kexec wrapper for faster reboots.
###
version_sort() {
    # tldr of this awk:
    # if a digit in a version string isnt a number, assume .0.
    # i.e. 4.18.0-553.69.1.lve > 4.18.0-553.lve.el8
    awk -F'[-.]' '{ printf "%s.%s.%s.%s.%s.%s: %s\n", 
    $2, $3, $4, $5, $6 ~ /^[0-9]+$/ ? $6 : 0, $7  ~ /^[0-9]+$/ ? $7 : 0, $0
    }' | sort -V | tail -1 | awk -F': ' '{print $2}'
}
kernel=""
for arg in "$@"; do
    case "$arg" in
        "latest" )
            kernel="latest"
        ;;
        "current" )
            kernel="current"
        ;;
        --help | -h)
            echo "kreboot: Immediately sync then reinitialize the current or latest kernel using kexec instead of a hardware reboot"
            echo "usage: kreboot [current|latest]"
            echo "The purpose of this tool is to provide the option of faster recovery in reboots unrelated to hardware issues"
        ;;
        * )
            echo "usage: kreboot [current|latest]"
        ;;
   esac
done

if [[ -z $kernel ]]; then
    echo "Please select a kernel between \"current\" or \"latest\"."
else
    echo "Loading $kernel kernel"
    if [[ $kernel == "current" ]]; then
        set -x
        kexec -l /boot/vmlinuz-$(uname -r) --initrd=/boot/initramfs-$(uname -r).img --reuse-cmdline && sync && kexec -e
    elif [[ $kernel == "latest" ]]; then
        set -x
        kexec -l $(find /boot/vmlinuz-* -not -name '*rescue*' | version_sort) --initrd=$(find /boot/initramfs-*.img -not -name "*kdump.img" | version_sort) --reuse-cmdline && sync && kexec -e
    fi
fi