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

set -e

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

cd "$IFACE_DIR"

cat > "$IFACE_CFG.new" <<EOT
# NOTE: /etc/network/assemble-interfaces rewrites this file.  Edit files in
#       /etc/network/interfaces.d/ to persist any customizations.

EOT

# loopback first
cat lo >> "$IFACE_CFG.new"

# existing eths
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

# all the rest
for i in "$IFACE_DIR"/*; do
    IFACE="$(basename "$i")"
    case $IFACE in
        DEFAULT|lo|eth*)
            continue
            ;;
        *)
            cat "$IFACE" >> "$IFACE_CFG.new"
            ;;
    esac
done

# install new interfaces config
cp -a "$IFACE_CFG" "$IFACE_CFG.bak"
mv "$IFACE_CFG.new" "$IFACE_CFG"