#!/bin/bash
# Setup TAP/Bridge networking for QEMU VM
# Defaults:
#   BRIDGE_NAME=br-rego-vpn
#   TAP_NAME=tap0
#   BRIDGE_CIDR=100.100.0.1/24
#   VM_NET_IP=100.100.0.2
#   VM_SUBNET=100.100.0.0/24

set -e

BRIDGE_NAME="${BRIDGE_NAME:-br-rego-vpn}"
TAP_NAME="${TAP_NAME:-tap0}"
BRIDGE_CIDR="${BRIDGE_CIDR:-100.100.0.1}"
VM_NET_IP="${VM_NET_IP:-100.100.0.2}"
VM_SUBNET="${VM_SUBNET:-100.100.0.0}"
TARGET_IP="${TARGET_IP:-10.35.33.230}"

if [[ "$BRIDGE_CIDR" != */* ]]; then
    BRIDGE_CIDR="$BRIDGE_CIDR/24"
fi

if [[ "$VM_SUBNET" != */* ]]; then
    VM_SUBNET="$VM_SUBNET/24"
fi

# Pick the outbound interface based on the container's default route.
# (In Docker, this is not always eth1 when multiple networks are attached.)
WAN_IF="$(ip route show default 0.0.0.0/0 2>/dev/null | awk '{for(i=1;i<=NF;i++) if($i=="dev"){print $(i+1); exit}}')"
if [ -z "${WAN_IF}" ]; then
    WAN_IF="eth1"
fi

# Ensure bridge exists
if ! ip link show "$BRIDGE_NAME" &>/dev/null; then
    ip link add "$BRIDGE_NAME" type bridge
fi

# Ensure bridge has address and is up
ip addr show dev "$BRIDGE_NAME" | grep -qF "$BRIDGE_CIDR" || ip addr add "$BRIDGE_CIDR" dev "$BRIDGE_NAME" 2>/dev/null || true
ip link set "$BRIDGE_NAME" up

# Ensure TAP exists
if ! ip link show "$TAP_NAME" &>/dev/null; then
    ip tuntap add "$TAP_NAME" mode tap
fi

# Ensure TAP is attached and up
ip link set "$TAP_NAME" master "$BRIDGE_NAME" 2>/dev/null || true
ip link set "$TAP_NAME" up

# Enable IP forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward

# Setup NAT/masquerade for outbound traffic from VM
iptables -t nat -C POSTROUTING -s "$VM_SUBNET" -o "$WAN_IF" -j MASQUERADE 2>/dev/null || \
    iptables -t nat -A POSTROUTING -s "$VM_SUBNET" -o "$WAN_IF" -j MASQUERADE

# Ensure forwarding between the VM bridge and outbound interface
iptables -C FORWARD -i "$BRIDGE_NAME" -o "$WAN_IF" -j ACCEPT 2>/dev/null || \
    iptables -A FORWARD -i "$BRIDGE_NAME" -o "$WAN_IF" -j ACCEPT
iptables -C FORWARD -i "$WAN_IF" -o "$BRIDGE_NAME" -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT 2>/dev/null || \
    iptables -A FORWARD -i "$WAN_IF" -o "$BRIDGE_NAME" -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT

# Forward traffic destined for VPN networks to VM (TARGET_IP defaults to IBM i)
# The VM will route this through its VPN tunnel
iptables -C FORWARD -d "$TARGET_IP" -j ACCEPT 2>/dev/null ||     iptables -A FORWARD -d "$TARGET_IP" -j ACCEPT
iptables -C FORWARD -s "$TARGET_IP" -j ACCEPT 2>/dev/null ||     iptables -A FORWARD -s "$TARGET_IP" -j ACCEPT

# Route to TARGET_IP through VM
ip route add "$TARGET_IP" via "$VM_NET_IP" 2>/dev/null || true

echo "Network setup complete"
echo "Bridge: $BRIDGE_NAME = $BRIDGE_CIDR"
echo "TAP: $TAP_NAME attached to $BRIDGE_NAME"
echo "Route: $TARGET_IP via $VM_NET_IP (VM)"
echo "Outbound interface: ${WAN_IF}"