#! /bin/sh

set -e
. ./dyndns.conf

## Check that the environment is set up properly.
for i in DYNDNS_ZONE DYNDNS_HOST DYNDNS_SERVER DYNDNS_KEY SSH_CLIENT; do
  eval havep=\${$i+t}\${$i-nil}
  case $havep in nil) echo >&2 "$0: variable $i unset"; exit 2 ;; esac
done

## Find the client address.  This may be useful.
set -- $SSH_CLIENT; client=$1

## Parse the commad line.
set -- $SSH_ORIGINAL_COMMAND

fail_usage () {
  cat >&2 <<EOF
usage: $0 COMMAND ARGS...

Commands:
	set [-force] HOST [ADDR]
	unset HOST
EOF
  exit 1
}
getarg='case $# in 0) fail_usage ;; esac; arg=$1; shift'
doneargs='case $# in 0) ;; *) fail_usage ;; esac'

check_current_state () {
  ck_rrty=$1 ck_name=$2
  set -- $(adnshost --config "nameserver $DYNDNS_SERVER" \
	    -Fi -Tt -t$ck_rrty "$ck_name")
  case $1,$2,$3,$5 in
    ";,failed,permfail,nxdomain" | ";,failed,permfail,nodata")
      err=$5
      ;;
    ";,failed,"*)
      shift 8
      echo >&2 "$0: lookup $ck_name ($ck_rrty) failed: $*"
      exit 4
      ;;
    *)
      err=nil cur_ttl=$2 cur_addr=$4
      ;;
  esac
}

checkhost () {
  host=$1

  case "$host" in
    *..* | .* | *. | *[!-_.a-zA-Z0-9]*)
      echo >&2 "$0: invalid hostname"
      exit 2
      ;;
  esac

  matchp=nil
  for pat in $DYNDNS_HOST; do
    case "$host" in $pat) matchp=t ;; esac
  done
  case $matchp in nil) echo >&2 "$0: hostname not permitted"; exit 2 ;; esac
}

doupdate () {
  cmd=$1
  case ${DYNDNS_TESTONLY_P-nil} in
    nil)
      nsupdate -k "$DYNDNS_KEY" <<EOF
server $DYNDNS_SERVER
zone $DYNDNS_ZONE
$cmd
send
EOF
      ;;
    *)
      cat <<EOF
$cmd
EOF
      ;;
  esac
}

eval $getarg; cmd=$arg
case "$cmd" in
  set)
    forcep=nil
    eval $getarg
    case "$arg" in -force) forcep=t; eval $getarg ;; esac
    host=$arg
    case "$#,$forcep,$1" in
      0,nil,*) addr=$client ;;
      0,t,*) fail_usage ;;
      *,nil,"$client" | *,t,*) addr=$1; shift ;;
      *)
	echo >&2 "$0: incorrect address (wanted = $client; found = $1)"
	exit 3
	;;
    esac
    eval $doneargs
    checkhost "$host"
    case $addr in
      *:*) rrtype=AAAA ;;
      *.*) rrtype=A ;;
      *) echo >&2 "$0: failed to parse new address"; exit 2 ;;
    esac
    name=$host.$DYNDNS_ZONE
    check_current_state $(echo $rrtype | tr A-Z a-z) "$name"
    ttl=${DYNDNS_TTL-14400}
    case $err,$cur_ttl,$cur_addr in
      nil,$ttl,$addr) echo >&2 "$0: nothing to do"; exit 0 ;;
    esac
    doupdate "
	update delete $name IN $rrtype
	update add $name $ttl IN $rrtype $addr"
    ;;
  unset)
    eval $getarg; host=$arg
    eval $doneargs
    checkhost "$host"
    name=$host.$DYNDNS_ZONE
    check_current_state a "$name"
    case $err in
      nxdomain) echo >&2 "$0: nothing to do"; exit 0 ;;
    esac
    doupdate "update delete $name IN"
    ;;
  *)
    fail_usage
    ;;
esac