#!/bin/sh
# vim: set ts=4 et:

set -e

PROC="$(basename "$0")[$$]"

DEBUG=

log() {
    [ -z "$DEBUG" ] && [ "$1" = "debug" ] && return
    FACILITY="kern.$1"
    shift
    logger -s -p "$FACILITY" -t "$PROC" "$@"
}

if [ -z "$MDEV" ]; then
    log err "MDEV env not defined"
    exit 1
fi

RTABLE="${MDEV#eth}"
let RTABLE+=1000

IFACE_CFG=/etc/network/interfaces
IFACE_DIR="${IFACE_CFG}.d"

ip() {
    v=-4
    if [ "$1" = '-4' ] || [ "$1" = '-6' ]; then
        v="$1"
        shift
    fi
    OP="$2"
    [ "$OP" = show ] && LEV=debug || LEV=info
    if /sbin/ip "$v" "$@" || [ -n "$FAIL_OK" ]; then
        log "$LEV" "OK: ip $v $*"
    else
        log err "FAIL: ip $v $*"
    fi
}

assemble_interfaces() {
    log info "Rebuilding $IFACE_CFG"
    cd "$IFACE_DIR"
    cat lo > "$IFACE_CFG.new"
    for i in /sys/class/net/eth*; do
        IFACE="$(basename "$i")"
        [ ! -f "$IFACE" ] && sed -e "s/%%/$IFACE/g" DEFAULT > "$IFACE"
        cat "$IFACE" >> "$IFACE_CFG.new"
    done
    cp -a "$IFACE_CFG" "$IFACE_CFG.bak"
    mv "$IFACE_CFG.new" "$IFACE_CFG"
}

interface_up() {
    log info "Bringing up $MDEV"
    ifup "$MDEV"
}

cleanup_interface() {
    log info "Cleaning up $MDEV"

    # kill related udhcpc
    kill "$(cat "/run/udhcpc.$MDEV.pid")"

    # tidy up /run/ifstate, if it exists
    [ -f /run/ifstate ] && sed -i -e "/^$MDEV=/d" /run/ifstate

    # remove related rules
    for V in 4 6; do
        for P in $(ip -"$V" rule show table "$RTABLE" | cut -d: -f1); do
            ip -"$V" rule del pref "$P"
        done
    done
}

log info "STARTING: $ACTION $MDEV"

if exec 200>>"$IFACE_CFG"; then
    if flock 200; then
        case $ACTION in
            add|"")
                assemble_interfaces
                interface_up
                ;;
            remove)
                assemble_interfaces
                cleanup_interface
                ;;
            *)
                log err "Unknown action '$ACTION'"
                exit 1
                ;;
        esac
    else
        log err "Unable to flock $IFACE_CFG"
        exit 1
    fi
else
    log err "Unable to assign fd 200 to flock $IFACE_CFG"
    exit 1
fi

log info "FINISHED: $ACTION $MDEV"