#!/bin/sh -e

# this variable is only set if the usepeerdns pppd option is being used
[ "$USEPEERDNS" ] || exit 0

# exit if the resolvconf package is installed
[ -x /sbin/resolvconf ] && exit 0

# exit if systemd-resolved is running
[ -e /run/systemd/system ] && \
  systemctl is-active --quiet systemd-resolved.service &&
  exit 0

case "$6" in
  nm-*-service-*|/org/freedesktop/NetworkManager/PPP/*)
        # NetworkManager handles it
        exit 0
        ;;
esac

# create the file if it does not exist
if [ ! -e /etc/resolv.conf ]; then
  : > /etc/resolv.conf
fi

# follow any symlink to find the real file
REALRESOLVCONF=$(readlink --canonicalize /etc/resolv.conf)

# merge the new nameservers with the other options from the old configuration
{
  echo '# PPP: This file was written by /etc/ppp/ip-up.d/0000usepeerdns.'
  echo '# PPP: The following entries were obtained using PPP:'
  cat /etc/ppp/resolv.conf
  echo '# PPP: End of section rewritten by 0000usepeerdns.'
  grep -vE "^(nameserver[[:space:]]|# PPP: )" "$REALRESOLVCONF" || true
} > "$REALRESOLVCONF.tmp"

# backup the old configuration and install the new one
cp -a "$REALRESOLVCONF" "$REALRESOLVCONF.pppd-backup.$PPP_IFACE"
mv -f "$REALRESOLVCONF.tmp" "$REALRESOLVCONF"

# restart nscd because resolv.conf has changed
if [ -e /var/run/nscd.pid ]; then
  /etc/init.d/nscd restart || true
fi

exit 0