#!/bin/bash

USAGE="
Usage:
    ipv6 [-p] enable
    ipv6 [-p] disable
    ipv6 status

    -p: enable/disable ipv6 permanently in grub
"

if [ "$#" -gt 2 -o "$#" -lt 1 -o "$1" == "-h" -o "$1" == "--help" ]; then
    echo "$USAGE"
    exit 0
fi

indent() { sed 's/^/   /'; }

show_status() {
    echo "--"
    if test -f /proc/net/if_inet6; then
        # IPv6 enabled in kernel
        if ls /proc/sys/net/ipv6/conf/all/disable_ipv6 > /dev/null 2>&1; then 
            if [ $( sysctl -n net.ipv6.conf.all.disable_ipv6 ) -eq 1 ]; then 
                echo -n "-- IPv6 status:  ENABLED in kernel but DISABLED temporarily"
            else
                echo -n "-- IPv6 status:  ENABLED"
            fi
        else
            echo -n "-- IPv6 status:  ENABLED"
        fi
    else
        echo -n "-- IPv6 status:  DISABLED in kernel"
    fi

    IPV6DISABLED=$( sudo bash -c "cat /etc/default/grub |grep 'ipv6.disable=1'" )
    if [ "$IPV6DISABLED" ]; then
        echo " (disabled for next startup)"
    else
        echo " (enabled for next startup)"
    fi
    echo "--"
    #cat /etc/sysctl.conf | grep disable_ipv6 | indent
    #echo "-- Values in /etc/sysctl.conf set to:"
    #cat /etc/sysctl.conf | grep disable_ipv6 | indent
}

NAMES='all default eth0 lo'

if [ "$1" == "-p" ]; then 
    PERSISTENT=true
    shift
fi

DIST=$( lsb_release -cs )

case $1 in

enable)
    if [ "$PERSISTENT" ]; then
        #echo "-- IPv6 status:  ENABLED permanently"
        sudo sed -i -e "s/GRUB_CMDLINE_LINUX_DEFAULT=\"ipv6.disable=1 /GRUB_CMDLINE_LINUX_DEFAULT=\"/" /etc/default/grub
        sudo update-grub
        if [ "$DIST" == 'focal' ]; then 
            sudo sed -i -e '/ServerArguments=-listen/d' -e '/[X11]/a ServerArguments=-listen tcp' /etc/sddm.conf
        fi
        echo "-- IPv6 permanently enabled in grub. Reboot for the changes to take efect."
    else 
        if  test -f /proc/net/if_inet6; then 
            for s in $NAMES; do
                sudo sysctl -w net.ipv6.conf.${s}.disable_ipv6=0
                #sudo sed -i -e "/net.ipv6.conf.${s}.disable_ipv6/d" /etc/sysctl.conf
                #sudo bash -c "echo 'net.ipv6.conf.${s}.disable_ipv6=0' >> /etc/sysctl.conf"
            done
        else
            echo "--"
            echo "-- ERROR: IPv6 not active in kernel. Enable it at startup and reboot."
        fi
    fi
    show_status
    #echo "-- Values in /etc/sysctl.conf set to:"
    #cat /etc/sysctl.conf | grep disable_ipv6 | indent
    ;;

disable)
    if [ "$PERSISTENT" ]; then
        #echo "-- IPv6 status:  DISABLED permanently"
        sudo sed -i -e "s/GRUB_CMDLINE_LINUX_DEFAULT=\"/GRUB_CMDLINE_LINUX_DEFAULT=\"ipv6.disable=1 /" /etc/default/grub
        sudo update-grub
        if [ "$DIST" == 'focal' ]; then 
            sudo sed -i -e '/ServerArguments=-listen/d' -e '/[X11]/a #ServerArguments=-listen tcp' /etc/sddm.conf
        fi
        echo "-- IPv6 permanently disabled in grub. Reboot for the changes to take efect."
        echo "--   Note: Xorg option '-listen tcp' deleted to avoid a bug that prevents Xorg to "
        echo "--   start when ipv6 is disabled (https://bugzilla.redhat.com/show_bug.cgi?id=2075132)."
    else 
        if ls /proc/sys/net/ipv6/conf/all/disable_ipv6 > /dev/null 2>&1; then 
            for s in $NAMES; do
                sudo sysctl -w net.ipv6.conf.${s}.disable_ipv6=1
                #sudo sed -i -e "/net.ipv6.conf.${s}.disable_ipv6/d" /etc/sysctl.conf
                #sudo bash -c "echo 'net.ipv6.conf.${s}.disable_ipv6=1' >> /etc/sysctl.conf"
            done
        fi
    fi
    show_status
    #echo "-- Values in /etc/sysctl.conf set to:"
    #cat /etc/sysctl.conf | grep disable_ipv6 | indent
    ;;

status)
    show_status
    ;;

*)
    echo ""
    echo "ERROR: Invalid argument value '$1'" >&2
    echo "$USAGE"
    exit 1
    ;;

esac