import hashlib
import logging
import time
import threading

from scapy.config import conf
from scapy.layers.inet import TCP, IP
from scapy.packet import Packet
from scapy.sendrecv import send, sniff

from random import randrange

log = logging.getLogger(__name__)

SERVER_IP = "127.0.0.1"
SERVER_PORT = 20102
COOKIE_SECRET = "TASTY_COOKIES123"
SRC_PORT = randrange(10000, 50000)


def generate_syn_cookie(client_ip: str, client_port: int, server_secret: str):
    hash_input = f"{client_ip}{client_port}{server_secret}".encode()
    return int(hashlib.sha256(hash_input).hexdigest(), 16) % (2**32)


def handle_packet(packet: Packet):
    if (
        packet.haslayer(TCP)
        and packet[TCP].dport == SRC_PORT
        and "A" in packet[TCP].flags
    ):
        print("Flag found in payload:", packet[TCP].payload)
        exit()


# Function to start the packet sniffing
def start_sniffing():
    sniff(
        filter=f"tcp port {SERVER_PORT}",
        prn=handle_packet,
        store=False,
        monitor=True,
        iface="lo",
    )


# Run the server in a separate thread
def main():
    conf.use_pcap = True
    server_thread = threading.Thread(target=start_sniffing)
    server_thread.start()

    time.sleep(1)  # wait for the sniffer to start.

    # Calculate the SYN cookie to send
    cookie = generate_syn_cookie(SERVER_IP, SERVER_PORT, COOKIE_SECRET)

    # Send SYN packet with correct cookie
    syn_packet = IP(dst=SERVER_IP) / TCP(
        sport=SRC_PORT, dport=SERVER_PORT, flags="S", seq=cookie
    )
    send(syn_packet)


if __name__ == "__main__":
    logging.basicConfig(
        level=logging.INFO,
        format="%(asctime)s %(levelname)s [%(module)s:%(lineno)d] %(message)s",
    )
    logging.getLogger("asyncio").setLevel(logging.WARNING)
    main()