#!/bin/bash
set -e

INTERFACE="wg0"
MOUNT_CONFIG="/etc/wireguard/${INTERFACE}.conf"
CONFIG_DIR="/run/wireguard"
CONFIG_FILE="${CONFIG_DIR}/${INTERFACE}.conf"
CHECK_INTERVAL="${HEALTH_CHECK_INTERVAL:-10}"
CHECK_HOST="${HEALTH_CHECK_HOST:-1.1.1.1}"

# ──────────────────────────────────────────────
# Validate config exists, copy to writable location
# ──────────────────────────────────────────────
if [ ! -f "$MOUNT_CONFIG" ]; then
    echo "[error] WireGuard config not found at ${MOUNT_CONFIG}"
    echo "[error] Mount your config file: -v /path/to/your.conf:/etc/wireguard/wg0.conf:ro"
    exit 1
fi

mkdir -p "$CONFIG_DIR"
cp "$MOUNT_CONFIG" "$CONFIG_FILE"
chmod 600 "$CONFIG_FILE"

# Extract endpoint IP and port from the config
VPN_ENDPOINT=$(grep -i '^Endpoint' "$CONFIG_FILE" | head -1 | sed 's/.*= *//;s/:.*//;s/ //g')
VPN_PORT=$(grep -i '^Endpoint' "$CONFIG_FILE" | head -1 | sed 's/.*://;s/ //g')
# Extract address
VPN_ADDRESS=$(grep -i '^Address' "$CONFIG_FILE" | head -1 | sed 's/.*= *//;s/ //g')

if [ -z "$VPN_ENDPOINT" ] || [ -z "$VPN_PORT" ]; then
    echo "[error] Could not parse Endpoint from ${CONFIG_FILE}"
    exit 1
fi

echo "[init] Config: ${CONFIG_FILE}"
echo "[init] Endpoint: ${VPN_ENDPOINT}:${VPN_PORT}"
echo "[init] Address: ${VPN_ADDRESS}"

# ──────────────────────────────────────────────
# Kill switch: only allow traffic through wg0
# ──────────────────────────────────────────────
setup_killswitch() {
    echo "[killswitch] Setting up iptables kill switch..."

    # Flush existing rules
    iptables -F
    iptables -X
    iptables -t nat -F

    # Default policy: DROP everything
    iptables -P INPUT DROP
    iptables -P FORWARD DROP
    iptables -P OUTPUT DROP

    # Allow loopback
    iptables -A INPUT  -i lo -j ACCEPT
    iptables -A OUTPUT -o lo -j ACCEPT

    # Allow traffic to/from VPN endpoint (needed to establish tunnel)
    iptables -A OUTPUT -d "$VPN_ENDPOINT" -p udp --dport "$VPN_PORT" -j ACCEPT
    iptables -A INPUT  -s "$VPN_ENDPOINT" -p udp --sport "$VPN_PORT" -j ACCEPT

    # Allow all traffic through the WireGuard interface
    iptables -A INPUT  -i "$INTERFACE" -j ACCEPT
    iptables -A OUTPUT -o "$INTERFACE" -j ACCEPT

    # Allow DNS to the VPN DNS server (through wg0)
    iptables -A OUTPUT -o "$INTERFACE" -p udp --dport 53 -j ACCEPT
    iptables -A OUTPUT -o "$INTERFACE" -p tcp --dport 53 -j ACCEPT

    # Allow DHCP (for container networking)
    iptables -A OUTPUT -p udp --dport 67:68 -j ACCEPT
    iptables -A INPUT  -p udp --sport 67:68 -j ACCEPT

    # Allow established/related connections
    iptables -A INPUT  -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
    iptables -A OUTPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT

    # ── Allow incoming connections to exposed service ports (e.g. app on 8000) ──
    # LOCAL_PORTS can be set as env var, e.g. "8000,8080,3000"
    if [ -n "${LOCAL_PORTS:-}" ]; then
        for port in $(echo "$LOCAL_PORTS" | tr ',' ' '); do
            echo "[killswitch] Allowing incoming traffic on port ${port}"
            iptables -A INPUT  -p tcp --dport "$port" -j ACCEPT
            iptables -A OUTPUT -p tcp --sport "$port" -j ACCEPT
        done
    fi

    # ── FORWARDING (so other containers can use this VPN) ──
    iptables -A FORWARD -i eth0 -o "$INTERFACE" -j ACCEPT
    iptables -A FORWARD -i "$INTERFACE" -o eth0 -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT

    # NAT: masquerade traffic from other containers going out through wg0
    iptables -t nat -A POSTROUTING -o "$INTERFACE" -j MASQUERADE

    echo "[killswitch] Kill switch active. Traffic blocked if VPN drops."
}

# ──────────────────────────────────────────────
# Enable IP forwarding so other containers can route through us
# ──────────────────────────────────────────────
enable_forwarding() {
    echo "[init] Enabling IP forwarding..."
    if cat /proc/sys/net/ipv4/ip_forward 2>/dev/null | grep -q 1; then
        echo "[init] IP forwarding already enabled."
    elif echo 1 > /proc/sys/net/ipv4/ip_forward 2>/dev/null; then
        echo "[init] IP forwarding enabled via /proc."
    else
        echo "[init] /proc read-only — relying on --sysctl net.ipv4.ip_forward=1"
    fi
}

# ──────────────────────────────────────────────
# Start WireGuard manually (no wg-quick, avoids sysctl issues)
# ──────────────────────────────────────────────
start_vpn() {
    echo "[vpn] Starting WireGuard interface ${INTERFACE}..."

    # Create the interface
    ip link add "$INTERFACE" type wireguard

    # Apply the WireGuard config (keys, peer, endpoint)
    wg setconf "$INTERFACE" <(grep -v -i '^\(Address\|DNS\|MTU\|Table\|PreUp\|PostUp\|PreDown\|PostDown\|SaveConfig\)' "$CONFIG_FILE")

    # Assign the address
    ip -4 address add "$VPN_ADDRESS" dev "$INTERFACE"

    # Set MTU
    ip link set mtu 1420 up dev "$INTERFACE"

    # Find default gateway/interface for the endpoint route
    DEFAULT_GW=$(ip route | grep '^default' | head -1 | awk '{print $3}')
    DEFAULT_IF=$(ip route | grep '^default' | head -1 | awk '{print $5}')

    # Route VPN endpoint through the container's default gateway
    if [ -n "$DEFAULT_GW" ] && [ -n "$DEFAULT_IF" ]; then
        ip route add "$VPN_ENDPOINT/32" via "$DEFAULT_GW" dev "$DEFAULT_IF" 2>/dev/null || true
    fi

    # Route all traffic through the WireGuard tunnel
    ip route add 0.0.0.0/1 dev "$INTERFACE"
    ip route add 128.0.0.0/1 dev "$INTERFACE"

    # ── Policy routing: ensure responses to incoming LAN traffic go back via eth0 ──
    if [ -n "$DEFAULT_GW" ] && [ -n "$DEFAULT_IF" ]; then
        # Get the container's eth0 IP address (BusyBox-compatible, no grep -P)
        ETH0_IP=$(ip -4 addr show "$DEFAULT_IF" | awk '/inet / {split($2, a, "/"); print a[1]}' | head -1)
        ETH0_SUBNET=$(ip -4 route show dev "$DEFAULT_IF" | grep -v default | head -1 | awk '{print $1}')
        if [ -n "$ETH0_IP" ] && [ -n "$ETH0_SUBNET" ]; then
            echo "[vpn] Setting up policy routing for incoming traffic (${ETH0_IP} on ${DEFAULT_IF})"
            ip route add default via "$DEFAULT_GW" dev "$DEFAULT_IF" table 100 2>/dev/null || true
            ip route add "$ETH0_SUBNET" dev "$DEFAULT_IF" table 100 2>/dev/null || true
            ip rule add from "$ETH0_IP" table 100 priority 100 2>/dev/null || true
            echo "[vpn] Policy routing active — incoming connections will be routed back via ${DEFAULT_IF}"
        fi
    fi

    # Set up DNS
    VPN_DNS=$(grep -i '^DNS' "$CONFIG_FILE" | head -1 | sed 's/.*= *//;s/ //g')
    if [ -n "$VPN_DNS" ]; then
        echo "nameserver $VPN_DNS" > /etc/resolv.conf
        echo "[vpn] DNS set to ${VPN_DNS}"
    fi

    echo "[vpn] WireGuard interface ${INTERFACE} is up."
}

# ──────────────────────────────────────────────
# Stop WireGuard manually
# ──────────────────────────────────────────────
stop_vpn() {
    echo "[vpn] Stopping WireGuard interface ${INTERFACE}..."
    ip link del "$INTERFACE" 2>/dev/null || true
}

# ──────────────────────────────────────────────
# Health check loop — restarts VPN if tunnel dies
# ──────────────────────────────────────────────
health_loop() {
    local failures=0
    local max_failures=3

    echo "[health] Starting health check (every ${CHECK_INTERVAL}s, target ${CHECK_HOST})..."

    while true; do
        sleep "$CHECK_INTERVAL"

        if curl -sf --max-time 5 "http://$CHECK_HOST" > /dev/null 2>&1; then
            if [ "$failures" -gt 0 ]; then
                echo "[health] VPN recovered."
                failures=0
            fi
        else
            failures=$((failures + 1))
            echo "[health] Ping failed ($failures/$max_failures)"

            if [ "$failures" -ge "$max_failures" ]; then
                echo "[health] VPN appears down. Restarting WireGuard..."
                stop_vpn
                sleep 2
                start_vpn
                failures=0
                echo "[health] WireGuard restarted."
            fi
        fi
    done
}

# ──────────────────────────────────────────────
# Graceful shutdown
# ──────────────────────────────────────────────
cleanup() {
    echo "[shutdown] Stopping WireGuard..."
    stop_vpn
    echo "[shutdown] Flushing iptables..."
    iptables -F
    iptables -t nat -F
    echo "[shutdown] Done."
    exit 0
}

trap cleanup SIGTERM SIGINT

# ── Main ──
enable_forwarding
setup_killswitch
start_vpn
health_loop