import subprocess
import time
import os
import sys
import logging

# Configuration
primary_gateway = "172.30.1.1"
backup_gateway = "172.30.2.1"
host_to_ping = "8.8.8.8"
dhcp_config_file = "/etc/dnsmasq.d/02-pihole-dhcp.conf"  # Path to the DHCP config file
dhcp_service_name = "pihole-FTL.service"
ping_timeout = 3  # in seconds
ping_interval = 10  # in seconds
failure_threshold = 3  # Number of consecutive ping failures before switching

# Set up logging
logging.basicConfig(filename='/var/log/gateway_failover.log', level=logging.INFO,
                    format='%(asctime)s - %(message)s')

def log_message(message):
    logging.info(message)

# Check for root privileges
if os.geteuid() != 0:
    print("This script requires root privileges.")
    sys.exit(1)

def change_gateway(gateway):
    """
    Changes the default gateway for the server and updates the DHCP configuration
    for all network clients.
    """
    try:
        subprocess.run(["ip", "route", "del", "default"], check=True)
        subprocess.run(["ip", "route", "add", "default", "via", gateway], check=True)
        log_message(f"Server gateway changed to {gateway}")
        update_dhcp_gateway(gateway)
        restart_dhcp_server()
    except subprocess.CalledProcessError as e:
        log_message(f"Error changing gateway: {e}")

def update_dhcp_gateway(gateway):
    """
    Updates the DHCP configuration file to change the default gateway for clients.
    """
    try:
        with open(dhcp_config_file, 'r') as file:
            config = file.readlines()

        with open(dhcp_config_file, 'w') as file:
            for line in config:
                if "dhcp-option=option:router" in line:
                    file.write(f"dhcp-option=option:router,{gateway}\n")
                else:
                    file.write(line)

        log_message(f"DHCP configuration updated with gateway {gateway}")
    except Exception as e:
        log_message(f"Error updating DHCP config: {e}")

def restart_dhcp_server():
    """
    Restarts the DHCP server to apply the new gateway settings to all clients.
    """
    try:
        subprocess.run(["systemctl", "restart", dhcp_service_name], check=True)
        log_message("DHCP server restarted successfully.")
    except subprocess.CalledProcessError as e:
        log_message(f"Error restarting DHCP server: {e}")

def ping_host_via_wlan(host):
    """
    Pings the specified host using the Raspberry Pi's wlan0 interface.
    """
    result = subprocess.run(
        ["ping", "-I", "wlan0", "-c", "1", "-W", str(ping_timeout), host],
        stdout=subprocess.DEVNULL
    )
    return result.returncode == 0

def ping_host(host):
    """
    Pings the specified host via current default interface.
    """
    result = subprocess.run(
        ["ping", "-c", "1", "-W", str(ping_timeout), host],
        stdout=subprocess.DEVNULL
    )
    return result.returncode == 0

def main():
    current_gateway = primary_gateway
    consecutive_failures = 0
    wlan_successes = 0

    try:
        while True:
            if current_gateway == primary_gateway:
                if ping_host(host_to_ping):
                    consecutive_failures = 0
                else:
                    consecutive_failures += 1
                    if consecutive_failures >= failure_threshold:
                        change_gateway(backup_gateway)
                        current_gateway = backup_gateway
                        log_message("Switched to backup gateway.")
                        wlan_successes = 0  # reset counter for recovery
            else:
                # On backup, check if we can reach via wlan0
                if ping_host_via_wlan(host_to_ping):
                    wlan_successes += 1
                    if wlan_successes >= 3:
                        change_gateway(primary_gateway)
                        current_gateway = primary_gateway
                        log_message("Switched back to primary gateway.")
                        consecutive_failures = 0
                else:
                    wlan_successes = 0

            time.sleep(ping_interval)

    except KeyboardInterrupt:
        log_message("Script terminated by user.")

if __name__ == "__main__":
    main()