#!/usr/bin/env bash
# net-setup.sh -- create the tap + bridge the VT1200 harness needs on the host.
#
# Idempotent: safe to re-run, and NEEDS re-running after a reboot, because both
# the tap and the bridge are runtime kernel state and do not survive one.
#
#   ./harness/net-setup.sh
#
# The tap is owned by your user, which is what lets MAME attach to it with no
# sudo and no capabilities of its own.  The bridge gets an address so the host
# can serve BOOTP and TFTP to the terminal.
#
# IMPORTANT: both interfaces will still show DOWN until MAME opens the tap.  A
# tap has carrier only while a process holds it open, and a bridge whose only
# port has no carrier reports down.  That is correct, not a failure.

set -euo pipefail

UID_="$(id -u)"
USER_="$(id -un)"
TAP="tap-mess-${UID_}-0"          # MAME's own naming: taptun.cpp, "tap-mess-%d-0"
BRIDGE="vt1200"
ADDR="192.168.99.1/24"

if ! sudo -n true 2>/dev/null; then
    echo "net-setup: needs passwordless sudo (or run these by hand):" >&2
    echo "  ip tuntap add dev $TAP mode tap user $USER_" >&2
    echo "  ip link add dev $BRIDGE type bridge" >&2
    exit 1
fi

if ip link show "$TAP" >/dev/null 2>&1; then
    echo "net-setup: $TAP exists, leaving it"
else
    sudo -n ip tuntap add dev "$TAP" mode tap user "$USER_"
    echo "net-setup: created $TAP (owned by $USER_)"
fi

if ip link show "$BRIDGE" >/dev/null 2>&1; then
    echo "net-setup: $BRIDGE exists, leaving it"
else
    sudo -n ip link add dev "$BRIDGE" type bridge
    echo "net-setup: created $BRIDGE"
fi

sudo -n ip link set "$TAP" master "$BRIDGE"
sudo -n ip link set "$TAP" up
sudo -n ip link set "$BRIDGE" up
# single-member bridge: no STP, so it forwards immediately instead of after ~30s
sudo -n ip link set "$BRIDGE" type bridge stp_state 0
sudo -n ip addr replace "$ADDR" dev "$BRIDGE"

echo
echo "host side now:"
ip -brief addr show "$BRIDGE" | sed 's/^/  /'
ip -brief link show "$TAP" | sed 's/^/  /'
echo
echo "reminder: both read DOWN until MAME holds the tap. Then run, in another shell:"
echo "  sudo python3 -u harness/serve.py 192.168.99.1 --bootp"
echo "  ./run.sh net"