#!/bin/sh
#
# Copyright (c) Brian Tarricone <brian@tarricone.org>
# Released under the terms of the BSD 3-clause license.
# See https://opensource.org/licenses/BSD-3-Clause for details.

set -e

default_check_interval=5
default_health_ips="8.8.8.8 1.1.1.1"
default_ping_count=5
default_health_quorum=1
default_up_successes=5
default_down_failures=3
default_active_metric=10
default_inactive_metric=20

log() {
    logger -t wan-failover -p daemon.notice "$1"
}

dlog() {
    if [ "$debug" ]; then
        logger -t wan-failover -p daemon.debug "$1"
    fi
}

elog() {
	logger -t wan-failover -p daemon.err "$1"
}

cfg() {
    uci get "$1" 2>/dev/null
}

cfg_set() {
    uci set "$1"="$2"
}

cfg_commit() {
    uci commit "$1"
}

ourcfg() {
    cfg "wan-failover.$1"
}

cfg_init() {
    [ "$(ourcfg globals.debug || echo 'false')" = "true" ] && debug=1 || debug=
	check_interval=$(ourcfg globals.check_interval || echo $default_check_interval)

    primary_iface=$(ourcfg globals.primary || echo '')
    primary_ifname=$(ourcfg wan.ifname || cfg network.$primary_iface.ifname || cfg network.$primary_iface.device || echo '')
    fallback_iface=$(ourcfg globals.fallback || echo '')
    fallback_ifname=$(ourcfg wwan.ifname || cfg network.$fallback_iface.ifname || cfg network.$fallback_iface.device || echo '')

    primary_health_ips=$(ourcfg $primary_iface.ip || echo $default_health_ips)
    primary_ping_count=$(ourcfg $primary_iface.count || echo $default_ping_count)
    primary_health_quorum=$(ourcfg $primary_iface.quorum || echo $default_health_quorum)
    primary_up_successes=$(ourcfg $primary_iface.up || echo $default_up_successes)
    primary_down_failures=$(ourcfg $primary_iface.down || echo $default_down_failures)
    
    fallback_health_ips=$(ourcfg $fallback_iface.ip || echo $default_health_ips)
    fallback_ping_count=$(ourcfg $fallback_iface.count || echo $default_ping_count)
    fallback_health_quorum=$(ourcfg $fallback_iface.quorum || echo $default_health_quorum)
    fallback_up_successes=$(ourcfg $fallback_iface.up || echo $default_up_successes)
    fallback_down_failures=$(ourcfg $fallback_iface.down || echo $default_down_failures)

    active_metric=$(ourcfg globals.active_metric || echo $default_active_metric)
    inactive_metric=$(ourcfg globals.inactive_metric || echo $default_inactive_metric)

    if [ -z "$primary_iface" ]; then
    	elog "Must set wan-failover.globals.primary to the primary interface"
    	exit 1
	fi
	if [ -z "$primary_ifname" ]; then
		elog "Can't figure out interface device name for interface $primary_iface" >&2
		exit 1
	fi
    if [ -z "$fallback_iface" ]; then
    	elog "Must set wan-failover.globals.fallback to the fallback interface"
    	exit 1
	fi
	if [ -z "$fallback_ifname" ]; then
		elog "Can't figure out interface device name for interface $fallback_iface" >&2
		exit 1
	fi

	log "initialized with primary interface $primary_iface ($primary_ifname), fallback interface $fallback_iface ($fallback_ifname); will wait $check_interval second(s) between each check"
    log "will check primary using $primary_health_ips ($primary_health_quorum must work) with $primary_ping_count ping(s), and will require $primary_up_successes successes to be up, $primary_down_failures to be down"
    log "will check fallback using $fallback_health_ips ($fallback_health_quorum must work) with $fallback_ping_count ping(s), and will require $fallback_up_successes successes to be up, $fallback_down_failures to be down"
    log "active interface metric will be set to $active_metric, inactive to $inactive_metric"
}

get_active_iface() {
    local primary=$(cfg network.$primary_iface.metric)
    local fallback=$(cfg network.$fallback_iface.metric)
    dlog "current primary metric is $primary, fallback metric is $fallback"
    [ $primary -gt $fallback ] && echo $fallback_iface || echo $primary_iface
}

set_active_iface() {
    local active=$1
    local inactive=$2
    dlog "setting interface $active active, $inactive inactive"
    cfg_set network.$active.metric $active_metric
    cfg_set network.$inactive.metric $inactive_metric
    cfg_commit network
    /etc/init.d/network reload
}

ping_target() {
    local ifname=$1
    local count=$2
    local ip=$3

    echo "$ip" | grep -q ':' && ping=ping6 || ping=ping

    local successes=0
    local failures=0
    while [ $count -gt 0 ]; do
        dlog "[$ifname,$ip] ping"
        $ping -n -q -I $ifname -c 1 -w 2 $ip >/dev/null 2>&1 &&
            successes=$(expr $successes + 1) ||
            failures=$(expr $failures + 1)
        dlog "[$ifname,$ip] ping successes: $successes, failures: $failures"
        count=$(expr $count - 1 || true)
    done

    [ $successes -gt $failures ] && return 0 || return 1
}

check_health() {
    local ifname=$1
    shift
    local count=$1
    shift
    local quorum=$1
    shift
    local ips="$@"

    local pids=
    local ip
    for ip in $ips; do
        ping_target $ifname $count $ip &
        pids="$pids $!"
    done

    local successes=0
    local failures=0
    local pid
    for pid in $pids; do
        wait $pid && {
        	dlog "[$pid] got success"
            successes=$(expr $successes + 1)
        } || {
        	dlog "[$pid] got failure"
            failures=$(expr $failures + 1)
		}
    done

    [ $successes -ge $quorum ] && return 0 || return 1
}

cfg_init

primary_successes=0
primary_failures=0
fallback_failures=0
fallback_successes=0

while true; do
	sleep $check_interval

    active=$(get_active_iface)
    dlog "currently active: $active"

    dlog "checking health"
    check_health $primary_ifname $primary_ping_count $primary_health_quorum $primary_health_ips &
    primary_pid=$!
    check_health $fallback_ifname $fallback_ping_count $fallback_health_quorum $fallback_health_ips &
    fallback_pid=$!

    wait $primary_pid && {
        primary_successes=$(expr $primary_successes + 1)
        primary_failures=0
    } || {
        primary_successes=0
        primary_failures=$(expr $primary_failures + 1)
    }
    dlog "[$primary_iface] health check done; successes: $primary_successes, failures: $primary_failures"

    wait $fallback_pid && {
        fallback_successes=$(expr $fallback_successes + 1)
        fallback_failures=0
    } || {
        fallback_successes=0
        fallback_failures=$(expr $fallback_failures + 1)
    }
    dlog "[$fallback_iface] health check done; successes: $fallback_successes, failures: $fallback_failures"

    if [ "$active" = "$primary_iface" ]; then
        if [ $primary_failures -ge $primary_down_failures ]; then
            if [ $fallback_failures -ge $fallback_down_failures ]; then
                elog "primary is down, but fallback is as well"
            else
                log "$primary_iface is down, setting $fallback_iface active"
                set_active_iface $fallback_iface $primary_iface
            fi
        fi
    else
        if [ $primary_successes -ge $primary_up_successes ]; then
            log "$primary_iface is back up; setting active"
            set_active_iface $primary_iface $fallback_iface
		elif [ $primary_successes -gt 0 ]; then
			dlog "$primary_iface is coming back up; sticking with $fallback_iface until certain"
        else
            dlog "$primary_iface is still down; sticking with $fallback_iface"
        fi
    fi
done