#!/usr/bin/env bash

set -euxo pipefail

ensure_dummy_loaded () {
    if [ -z "$(lsmod | grep dummy)"]
    then
        sudo modprobe dummy
    fi
}

maybe_add_device () {
    DEVICE="${1}"
    if [ -z "$(ip --brief link | grep ${DEVICE})"]
    then
        sudo ip link add ${DEVICE} type dummy
    fi
}

add_address () {
    DEVICE="${1}"
    ADDR="${2}"

    EXISTING="$(ip --brief addr show "${DEVICE}" | awk '{print $3}')"
    if [ ! -z "${EXISTING}" ]
    then
        if [ "${EXISTING}" == "${ADDR}" ]
        then
            return
        fi

        sudo ip addr flush dev "${DEVICE}"
    fi

    sudo ip link set dev "${DEVICE}" up
    sudo ip addr add "${ADDR}" dev "${DEVICE}"
}

flush_device () {
    DEVICE="${1}"

    sudo ip addr flush dev "${DEVICE}"
    sudo ip link set dev "${DEVICE}" down
}

ensure_dummy_loaded
maybe_add_device deveth0
maybe_add_device deveth1
add_address deveth0 192.168.4.250/24
flush_device deveth1