#!/bin/bash

CONFIG_FILE="/etc/sysconfig/network"

function set_hostname() {
    NAME=$1

    [ -n "$NAME" ] || exit 0

    sed -i '/^HOSTNAME=.*$/d' $CONFIG_FILE
    echo "HOSTNAME=$NAME" >> $CONFIG_FILE
    [[ $(awk -F= '/^VERSION_ID/ {gsub("\"","");print $2}' /etc/os-release) -ge 7 ]] && echo $NAME > /etc/hostname
        
    hostname $NAME
}

function get_dns_name() {
    first_ip=$(hostname -I | cut -d' ' -f1)
    text=$(host $first_ip)
    [ $? = 0 ] || exit 0
    [[ $text == *"has no PTR record" ]] && exit 0
    name=$(echo "$text" | awk '{print $(NF)}' | sed 's/\.$//')
    echo $name
}

if [ -n "$SET_HOSTNAME" ]; then
    set_hostname $(echo "$SET_HOSTNAME" | sed -e 's/[^-a-zA-Z0-9]/-/g' -e 's/^-*//g' -e 's/-*$//g')
elif [ -n "$DNS_HOSTNAME" ]; then
    set_hostname $(get_dns_name)
fi