#!/usr/bin/env bash
set -euo pipefail

TPROXY_PORT="${TPROXY_PORT:-7895}"
TPROXY_MARK="${TPROXY_MARK:-1}"
TPROXY_TABLE="${TPROXY_TABLE:-100}"
TPROXY_CHAIN="${TPROXY_CHAIN:-VPN_PROXY_TPROXY}"
GATEWAY_FORWARD_CHAIN="${GATEWAY_FORWARD_CHAIN:-VPN_PROXY_FORWARD}"
GATEWAY_NAT_CHAIN="${GATEWAY_NAT_CHAIN:-VPN_PROXY_NAT}"
GATEWAY_CLIENT_CIDRS="${GATEWAY_CLIENT_CIDRS:-10.0.0.0/8 172.16.0.0/12 192.168.0.0/16}"
PROXY_PORT="${PROXY_PORT:-8080}"
PROXY_BIND_IP="${PROXY_BIND_IP:-0.0.0.0}"
PROXY_INPUT_CHAIN="${PROXY_INPUT_CHAIN:-VPN_PROXY_INPUT}"
PROXY_FIREWALL="${PROXY_FIREWALL:-true}"
PROXY_ALLOWED_CIDRS="${PROXY_ALLOWED_CIDRS:-10.0.0.0/8 172.16.0.0/12 192.168.0.0/16}"
BYPASS_CIDRS="${BYPASS_CIDRS:-0.0.0.0/8 10.0.0.0/8 100.64.0.0/10 127.0.0.0/8 169.254.0.0/16 172.16.0.0/12 192.168.0.0/16 224.0.0.0/4 240.0.0.0/4}"

log() {
  printf '[gateway-entrypoint] %s\n' "$*"
}

ipt() {
  iptables -w "$@"
}

cleanup_proxy_firewall() {
  ipt -D INPUT -p tcp --dport "$PROXY_PORT" -j "$PROXY_INPUT_CHAIN" 2>/dev/null || true
  ipt -D INPUT -p udp --dport "$PROXY_PORT" -j "$PROXY_INPUT_CHAIN" 2>/dev/null || true
  ipt -F "$PROXY_INPUT_CHAIN" 2>/dev/null || true
  ipt -X "$PROXY_INPUT_CHAIN" 2>/dev/null || true
}

cleanup_tproxy() {
  ipt -t mangle -D PREROUTING -j "$TPROXY_CHAIN" 2>/dev/null || true
  ipt -t mangle -F "$TPROXY_CHAIN" 2>/dev/null || true
  ipt -t mangle -X "$TPROXY_CHAIN" 2>/dev/null || true
  ip rule del fwmark "$TPROXY_MARK" table "$TPROXY_TABLE" 2>/dev/null || true
  ip route flush table "$TPROXY_TABLE" 2>/dev/null || true
}

cleanup_gateway_forwarding() {
  ipt -D FORWARD -j "$GATEWAY_FORWARD_CHAIN" 2>/dev/null || true
  ipt -t nat -D POSTROUTING -j "$GATEWAY_NAT_CHAIN" 2>/dev/null || true
  ipt -F "$GATEWAY_FORWARD_CHAIN" 2>/dev/null || true
  ipt -X "$GATEWAY_FORWARD_CHAIN" 2>/dev/null || true
  ipt -t nat -F "$GATEWAY_NAT_CHAIN" 2>/dev/null || true
  ipt -t nat -X "$GATEWAY_NAT_CHAIN" 2>/dev/null || true
}

enable_ip_forwarding() {
  if [[ -w /proc/sys/net/ipv4/ip_forward ]]; then
    printf '1' > /proc/sys/net/ipv4/ip_forward || true
  elif command -v sysctl >/dev/null 2>&1; then
    sysctl -w net.ipv4.ip_forward=1 >/dev/null 2>&1 || true
  fi
}

setup_proxy_firewall() {
  if [[ "$PROXY_FIREWALL" != "true" || "$PROXY_BIND_IP" == "127.0.0.1" || "$PROXY_BIND_IP" == "::1" ]]; then
    return
  fi

  cleanup_proxy_firewall
  ipt -N "$PROXY_INPUT_CHAIN"
  for cidr in $PROXY_ALLOWED_CIDRS; do
    ipt -A "$PROXY_INPUT_CHAIN" -s "$cidr" -j RETURN
  done
  ipt -A "$PROXY_INPUT_CHAIN" -j DROP
  ipt -I INPUT -p tcp --dport "$PROXY_PORT" -j "$PROXY_INPUT_CHAIN"
  ipt -I INPUT -p udp --dport "$PROXY_PORT" -j "$PROXY_INPUT_CHAIN"
}

setup_gateway_forwarding() {
  log "setup direct gateway forwarding"
  cleanup_gateway_forwarding
  enable_ip_forwarding

  ipt -N "$GATEWAY_FORWARD_CHAIN"
  ipt -t nat -N "$GATEWAY_NAT_CHAIN"
  for cidr in $GATEWAY_CLIENT_CIDRS; do
    ipt -A "$GATEWAY_FORWARD_CHAIN" -s "$cidr" -j ACCEPT
    ipt -A "$GATEWAY_FORWARD_CHAIN" -d "$cidr" -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
    ipt -t nat -A "$GATEWAY_NAT_CHAIN" -s "$cidr" -m addrtype ! --dst-type LOCAL -j MASQUERADE
  done
  ipt -I FORWARD 1 -j "$GATEWAY_FORWARD_CHAIN"
  ipt -t nat -I POSTROUTING 1 -j "$GATEWAY_NAT_CHAIN"
}

setup_tproxy() {
  log "setup tproxy on port ${TPROXY_PORT}"
  cleanup_tproxy
  enable_ip_forwarding

  ip rule add fwmark "$TPROXY_MARK" table "$TPROXY_TABLE" 2>/dev/null || true
  ip route replace local 0.0.0.0/0 dev lo table "$TPROXY_TABLE"
  ipt -t mangle -N "$TPROXY_CHAIN"
  ipt -t mangle -A "$TPROXY_CHAIN" -m addrtype --dst-type LOCAL -j RETURN
  ipt -t mangle -A "$TPROXY_CHAIN" -m mark --mark "$TPROXY_MARK" -j RETURN

  # Private/local destinations stay reachable; every intercepted public packet goes to VPN.
  for cidr in $BYPASS_CIDRS; do
    ipt -t mangle -A "$TPROXY_CHAIN" -d "$cidr" -j RETURN
  done

  ipt -t mangle -A "$TPROXY_CHAIN" -p tcp -j TPROXY --on-port "$TPROXY_PORT" --tproxy-mark "$TPROXY_MARK/$TPROXY_MARK"
  ipt -t mangle -A "$TPROXY_CHAIN" -p udp -j TPROXY --on-port "$TPROXY_PORT" --tproxy-mark "$TPROXY_MARK/$TPROXY_MARK"
}

setup_gateway_forwarding
setup_tproxy
setup_proxy_firewall

node /app/src/server/index.js &
APP_PID=$!

shutdown() {
  kill "$APP_PID" 2>/dev/null || true
  wait "$APP_PID" 2>/dev/null || true
  cleanup_proxy_firewall
  cleanup_tproxy
  cleanup_gateway_forwarding
}

trap 'shutdown; exit 0' SIGTERM SIGINT
wait "$APP_PID"
STATUS=$?
cleanup_proxy_firewall
cleanup_tproxy
cleanup_gateway_forwarding
exit "$STATUS"