#!/bin/sh
#
# $Id: checkdns.backup,v 1.7 2006/09/30 04:13:12 kadmos Exp $
#
# Point the DNS for a domain to this server (the backup server)
# if this server can't access the primary server.
#
# This script should be run periodically on the backup host.
#
# Which DNS records are updated is determined by the ddclient
# configuration file (e.g. $HOME/.ddclient.<domain>.conf).
#
# You must set the following variables in ~/.checkdns
# domain    name of A record to redirect
# primary   public host name of server that should serve domain by default
# backup    public host name of server that should serve domain if primary is down

###
# FUNCTIONS

# Import the common shell functions.
if test -f "$HOME/bin/functions"
then
    . "$HOME/bin/functions"
else
    echo "${0##/*/}: Cannot find function library, exiting"
    exit 1
fi


###
# CONFIGURATION

# DEFAULTS
# Device name of the internet interface.
interface=ppp0

# Whether to print debug messages to stderr.
debug=
quiet=
sms=true
syslog=true

while getopts "c:dq" flag
do
    case $flag in
    d)
        debug=true
        quiet=
        ;;
    q)
        quiet=true
        debug=
        ;;
    *)
        error "Invalid option -$flag"
        exit 2
    esac
done

# Read local configuration.
if test -f "$HOME/.checkdns"
then
    . "$HOME/.checkdns"
else
    error "Cannot find configuration file $HOME/.checkdns, exiting"
    exit 1
fi

# Configuration file for ddclient.
conf=$HOME/.ddclient.$domain.conf

# Cache file for ddclient.
cache=$HOME/.ddclient.$domain.cache

# must always call this function at the start of the script
get_addresses()
{
	primaryaddress=$(get_address_of ${primary})
	if test $? -eq 0
	then
		backupaddress=$(get_address_of ${backup})
		if test $? -eq 0
		then
			domainaddress=$(get_address_of ${domain})
			if test $? -eq 0
			then
				return 0
			else
				return 1
			fi
		else
			return 1
		fi
	else
		return 1
	fi
}

primary_down()
{
    ! host_up ${primary}
}

redirected()
{
    if test "${domainaddress}" = "${backupaddress}"
    then
        return 0
    else
        return 1
    fi
}

redirect_to_backup()
{
	notice "Primary server for ${domain} is down, redirecting to ${backup} (${backupaddress})"
	run /usr/sbin/ddclient -file "${conf}" -cache /dev/null -use=ip -ip "${backupaddress}"
	if test $? -eq 0
	then
		info "Redirected ${domain} to ${backup}"
		return 0
	else
		error "Error redirecting ${domain} to ${backup}"
		return 1
	fi
}

get_addresses

if internet_reachable
then
    if primary_down
    then
        info "Cannot reach ${primary}"
        if ! redirected
        then
			if redirect_to_backup
			then
				info "Redirection complete"
				exit 0
			else
				error "Cannot redirect ${domain}"
				exit 1
			fi
        else
            debug "Backup server for ${domain} is already in charge, not redirecting"
			exit 0
        fi
    else
        debug "Primary server for ${domain} is up, not redirecting"
		exit 0
    fi
else
	error "Cannot reach the internet"
	exit 1
fi