# network_monitor.py
import time
from scapy.sendrecv import AsyncSniffer
from scapy.all import IP, TCP, UDP, DNS

def process_packet(pkt):
    """Processes a Scapy packet into a simple dictionary."""
    d = {"timestamp": pkt.time}
    if pkt.haslayer(IP):
        ip = pkt[IP]
        d.update(src=ip.src, dst=ip.dst, ttl=ip.ttl, length=len(pkt))
        if pkt.haslayer(TCP):
            t = pkt[TCP]
            d.update(
                proto=6, src_port=t.sport, dst_port=t.dport, flags=str(t.flags),
                info=f"TCP {ip.src}:{t.sport} → {ip.dst}:{t.dport}"
            )
        elif pkt.haslayer(UDP):
            u = pkt[UDP]
            d.update(proto=17, src_port=u.sport, dst_port=u.dport, flags="-")
            if pkt.haslayer(DNS) and hasattr(pkt[DNS], 'qd') and pkt[DNS].qd is not None:
                qname = pkt[DNS].qd.qname
                # qname can be bytes, decode safely
                qname_str = qname.decode(errors='ignore') if isinstance(qname, bytes) else str(qname)
                d.update(proto="DNS", info=f"DNS Query for {qname_str}")
            else:
                d.update(info=f"UDP {ip.src}:{u.sport} → {ip.dst}:{u.dport}")
        else:
            d.setdefault("proto", ip.proto)
    else:
        d.update(src="N/A", dst="N/A", proto="Other", length=len(pkt))
    return d

def start_packet_capture(app, socketio, interface=None, filter_expr="ip"):
    """
    Sniffs packets in a background thread, adds them to the app's deque,
    and emits every packet to connected clients.
    """
    def _handle(pkt):
        try:
            data = process_packet(pkt)
        except Exception:
            return  # Ignore packets that cause processing errors

        # 1. Store the packet in the historical backlog
        app.captured_packets.append(data)

        # 2. Emit EVERY packet to the live feed (filter removed)
        socketio.emit("new_packet", data)

    sniffer = AsyncSniffer(
        iface=interface,
        filter=filter_expr,
        prn=_handle,
        store=False
    )
    sniffer.start()