#!/bin/bash -e

HOSTNAME="$(echo "$1" | tr '[:upper:]' '[:lower:]')"

if [ "$HOSTNAME" == "" ]; then
    echo "Usage: $0 <hostname>"
    exit 1
fi

if [ "$HOSTNAME" == "localhost" ]; then
    echo "Cannot set hostname to 'localhost'"
    exit 1
fi

if [ "$HOSTNAME" =~ ^.*\.local$ ]; then
    echo "Hostname cannot end with '.local'"
    exit 1
fi

if [[ ! "$HOSTNAME" =~ ^[a-zA-Z][a-zA-Z0-9-]{0,62}$ ]]; then
    echo "Invalid hostname '$HOSTNAME'"
    exit 1
fi

sed -i "s/^127.0.1.1\([[:space:]]*\).*$/127.0.1.1\1$HOSTNAME/" /etc/hosts
echo "$HOSTNAME" > /etc/hostname