#!/bin/sh

LOGGER_TAG="fixwgmtu"
GOOGLE_TARGET="8.8.8.8"

START_MTU=1500
MIN_OUTER_MTU=1000
WG_MIN_MTU=1280
WG_OVERHEAD=80

SLEEP_SECS=5

log_msg() {
    logger -t "$LOGGER_TAG" "$*"
}

get_asn_org() {
    curl -fsS --max-time 5 https://ipconfig.io/json 2>/dev/null \
        | sed -n 's/.*"asn_org"[[:space:]]*:[[:space:]]*"\([^"]*\)".*/\1/p' \
        | head -n 1
}

mtu_to_payload() {
    echo $(( $1 - 28 ))
}

test_normal_ping() {
    target="$1"
    ping -c 1 -W 3 "$target" >/dev/null 2>&1
}

test_ping_mtu() {
    target="$1"
    mtu="$2"
    payload="$(mtu_to_payload "$mtu")"

    [ -z "$payload" ] && return 1
    [ "$payload" -le 0 ] && return 1

    ping -c 1 -W 3 -s "$payload" "$target" >/dev/null 2>&1
    return $?
}

find_good_mtu() {
    target="$1"

    low="$MIN_OUTER_MTU"
    high="$START_MTU"
    best="$MIN_OUTER_MTU"

    while [ "$low" -le "$high" ]; do
        mid=$(( (low + high) / 2 ))
        mid=$(( mid - (mid % 20) ))

        [ "$mid" -lt "$MIN_OUTER_MTU" ] && mid="$MIN_OUTER_MTU"

        if test_ping_mtu "$target" "$mid"; then
            best="$mid"
            low=$((mid + 20))
        else
            high=$((mid - 20))
        fi
    done

    start=$((best - 30))
    end=$((best + 30))

    [ "$start" -lt "$MIN_OUTER_MTU" ] && start="$MIN_OUTER_MTU"
    [ "$end" -gt "$START_MTU" ] && end="$START_MTU"

    fine_best="$MIN_OUTER_MTU"
    i="$start"
    while [ "$i" -le "$end" ]; do
        probe=$(( i - (i % 10) ))

        if test_ping_mtu "$target" "$probe"; then
            fine_best="$probe"
        fi

        i=$((i + 10))
    done

    echo "$fine_best"
    return 0
}

get_real_dev() {
    iface="$1"

    # Hardcode common OpenWrt/AREDN logical WAN bridge
    if [ "$iface" = "wan" ] && [ -d /sys/class/net/br-wan ]; then
        echo "br-wan"
        return 0
    fi

    if [ -d "/sys/class/net/$iface" ]; then
        echo "$iface"
        return 0
    fi

    dev="$(ifstatus "$iface" 2>/dev/null | sed -n 's/.*"l3_device"[[:space:]]*:[[:space:]]*"\([^"]*\)".*/\1/p' | head -n 1)"
    [ -n "$dev" ] && [ -d "/sys/class/net/$dev" ] && { echo "$dev"; return 0; }

    dev="$(ifstatus "$iface" 2>/dev/null | sed -n 's/.*"device"[[:space:]]*:[[:space:]]*"\([^"]*\)".*/\1/p' | head -n 1)"
    [ -n "$dev" ] && [ -d "/sys/class/net/$dev" ] && { echo "$dev"; return 0; }

    return 1
}

get_iface_current_mtu() {
    iface="$1"
    realdev="$(get_real_dev "$iface")" || return 1
    cat "/sys/class/net/$realdev/mtu" 2>/dev/null
}

set_iface_mtu_if_needed() {
    iface="$1"
    new_mtu="$2"

    case "$new_mtu" in
        ''|*[!0-9]*)
            return 1
            ;;
    esac

    realdev="$(get_real_dev "$iface")" || return 1
    current_mtu="$(cat "/sys/class/net/$realdev/mtu" 2>/dev/null)"

    if [ "$current_mtu" = "$new_mtu" ]; then
        return 0
    fi

    ip link set dev "$realdev" mtu "$new_mtu" >/dev/null 2>&1
    return $?
}

get_wg_endpoint_host() {
    iface="$1"

    host="$(uci -q get "network.wireguard_${iface}.endpoint_host" 2>/dev/null)"
    if [ -n "$host" ]; then
        echo "$host"
        return 0
    fi

    host="$(uci show network 2>/dev/null \
        | grep "\.endpoint_host=" \
        | grep "$iface" \
        | sed -n "s/.*endpoint_host='\([^']*\)'.*/\1/p" \
        | head -n 1)"

    if [ -n "$host" ]; then
        echo "$host"
        return 0
    fi

    return 1
}

handle_wan() {
    iface="$1"
    target="$GOOGLE_TARGET"

    good_mtu="$(find_good_mtu "$target")"
    case "$good_mtu" in
        ''|*[!0-9]*)
            log_msg "$iface up, failed to determine WAN MTU using $target"
            return 1
            ;;
    esac

    if [ "$good_mtu" -lt 1500 ]; then
        asn_org="$(get_asn_org)"
        [ -z "$asn_org" ] && asn_org="unknown"
        realdev="$(get_real_dev "$iface")"
        [ -z "$realdev" ] && realdev="unknown"

        if set_iface_mtu_if_needed "$iface" "$good_mtu"; then
            log_msg "$iface up, WAN via $asn_org, target $target, path MTU $good_mtu, set device $realdev MTU to $good_mtu"
        else
            log_msg "$iface up, WAN via $asn_org, target $target, path MTU $good_mtu, failed to set device $realdev MTU"
        fi
    else
        log_msg "$iface up, WAN path supports 1500 via $target"
    fi

    return 0
}

handle_wgs() {
    iface="$1"
    endpoint_host="$(get_wg_endpoint_host "$iface")"

    if [ -z "$endpoint_host" ]; then
        wg_mtu="$WG_MIN_MTU"
        if set_iface_mtu_if_needed "$iface" "$wg_mtu"; then
            log_msg "$iface up, no endpoint_host found in UCI, set $iface MTU to safe minimum $wg_mtu"
        else
            log_msg "$iface up, no endpoint_host found in UCI, failed to set $iface MTU to safe minimum $wg_mtu"
        fi
        return 0
    fi

    if test_normal_ping "$endpoint_host"; then
        outer_mtu="$(find_good_mtu "$endpoint_host")"
        case "$outer_mtu" in
            ''|*[!0-9]*)
                wg_mtu="$WG_MIN_MTU"
                ;;
            *)
                wg_mtu=$((outer_mtu - WG_OVERHEAD))
                if [ "$wg_mtu" -lt "$WG_MIN_MTU" ]; then
                    wg_mtu="$WG_MIN_MTU"
                fi
                ;;
        esac

        if set_iface_mtu_if_needed "$iface" "$wg_mtu"; then
            log_msg "$iface up, endpoint $endpoint_host reachable, outer MTU $outer_mtu, set $iface MTU to $wg_mtu"
        else
            log_msg "$iface up, endpoint $endpoint_host reachable, outer MTU $outer_mtu, failed to set $iface MTU to $wg_mtu"
        fi
    else
        wg_mtu="$WG_MIN_MTU"
        if set_iface_mtu_if_needed "$iface" "$wg_mtu"; then
            log_msg "$iface up, endpoint $endpoint_host did not respond to ping, set $iface MTU to safe minimum $wg_mtu"
        else
            log_msg "$iface up, endpoint $endpoint_host did not respond to ping, failed to set $iface MTU to safe minimum $wg_mtu"
        fi
    fi

    return 0
}

if [ "$ACTION" = "ifup" ]; then
    case "$INTERFACE" in
        wan|wgs[0-9]*)
            sleep "$SLEEP_SECS"

            case "$INTERFACE" in
                wan)
                    handle_wan "$INTERFACE"
                    ;;
                wgs[0-9]*)
                    handle_wgs "$INTERFACE"
                    ;;
            esac
            ;;
    esac
fi

exit 0