#!/usr/bin/env bash

get_vmlinuz_start_postion()
{
        local vmlinuz=$1

        # '1f 8b 08' - https://www.filesignatures.net/index.php?page=search&search=1F8B08&mode=SIG
        local vmlinuz_start_line=$(od -A d -t x1 ${vmlinuz} | grep "1f 8b 08")
        local vmlinuz_start_postion=${vmlinuz_start_line%% *}

        [ -z ${vmlinuz_start_postion} ] && die "identify vmlinuz failed"

        [ "${vmlinuz_start_postion}" == "0000000" ] || {
                local vmlinuz_start_postion_tmp=$(echo ${vmlinuz_start_line} | awk '{for(i=1;i<=NF;i++)if($i=="1f")print i-1}')
                vmlinuz_start_postion=$((${vmlinuz_start_postion} + ${vmlinuz_start_postion_tmp} -1))
        }

        echo ${vmlinuz_start_postion}
}

unzip_vmlinuz()
{
        local vmlinuz=$1

        [ -f "$vmlinuz" ] || die "cannot find vmlinuz: $vmlinuz"

        file ${vmlinuz} | grep -q gzip || return

        local vmlinuz_start_postion=$(get_vmlinuz_start_postion ${vmlinuz})

        if [ $vmlinuz_start_postion -eq 0 ]; then
                dd if=$vmlinuz bs=1 | zcat > $vmlinuz.tmp
        else
                dd if=$vmlinuz bs=1 skip=$vmlinuz_start_postion | zcat > $vmlinuz.tmp
        fi

        mv $vmlinuz.tmp $vmlinuz
}

unzip_vmlinuz $1