#!/bin/bash
# Script to detect the host machine's IP address
# This is useful for Docker containers that need to connect back to services on the host

# Method 1: Try to get IP from default gateway (works in most Docker setups)
# The default gateway in a Docker container is typically the host machine
get_ip_from_gateway() {
    # Try to get the default gateway IP
    if command -v ip >/dev/null 2>&1; then
        ip route show default | awk '/default/ {print $3}' 2>/dev/null | head -1
    elif command -v route >/dev/null 2>&1; then
        route -n | awk '/^0.0.0.0/ {print $2}' 2>/dev/null | head -1
    fi
}

# Method 2: Try host.docker.internal (works on Docker Desktop and with extra_hosts)
get_ip_from_host_docker_internal() {
    if command -v getent >/dev/null 2>&1; then
        getent hosts host.docker.internal 2>/dev/null | awk '{print $1}' | head -1
    elif command -v nslookup >/dev/null 2>&1; then
        nslookup host.docker.internal 2>/dev/null | grep -A1 "Name:" | grep "Address:" | awk '{print $2}' | head -1
    fi
}

# Method 3: Get IP from network interface (for host machine)
get_ip_from_interface() {
    # Try common network interfaces
    for interface in eth0 enp0s8 enp0s3 ens33; do
        if command -v ip >/dev/null 2>&1; then
            ip addr show "$interface" 2>/dev/null | grep -oP 'inet \K[\d.]+' | head -1
        elif command -v ifconfig >/dev/null 2>&1; then
            ifconfig "$interface" 2>/dev/null | grep -oP 'inet \K[\d.]+' | head -1
        fi
    done
}

# Method 4: Get IP from hostname (if hostname resolves to an IP)
get_ip_from_hostname() {
    # Try to resolve the hostname
    if command -v hostname >/dev/null 2>&1; then
        hostname -I 2>/dev/null | awk '{print $1}'
    fi
}

# Main logic: Try methods in order of reliability
detect_host_ip() {
    local ip=""
    
    # If running inside Docker, try gateway method first
    if [ -f /.dockerenv ] || [ -n "${DOCKER_CONTAINER:-}" ]; then
        ip=$(get_ip_from_gateway)
        if [ -n "$ip" ] && [ "$ip" != "127.0.0.1" ]; then
            echo "$ip"
            return 0
        fi
        
        # Try host.docker.internal
        ip=$(get_ip_from_host_docker_internal)
        if [ -n "$ip" ] && [ "$ip" != "127.0.0.1" ]; then
            echo "$ip"
            return 0
        fi
    fi
    
    # Try interface method (works on host machine)
    ip=$(get_ip_from_interface)
    if [ -n "$ip" ] && [ "$ip" != "127.0.0.1" ]; then
        echo "$ip"
        return 0
    fi
    
    # Try hostname method
    ip=$(get_ip_from_hostname)
    if [ -n "$ip" ] && [ "$ip" != "127.0.0.1" ]; then
        echo "$ip"
        return 0
    fi
    
    # Fallback: return localhost (not ideal but better than nothing)
    echo "127.0.0.1"
    return 1
}

# Execute and output the IP
detect_host_ip