#!/usr/bin/env python3
"""obmp-churn-monitor -- decoupled fast-path BGP churn-rate monitor.

Reads openbmp.parsed.unicast_prefix from Kafka with its OWN consumer group and
only COUNTS announcements/withdrawals per (router, peer) -- no relational RIB
maintenance, no per-route DB upserts. Because counting is orders of magnitude
cheaper than psql-app's work, this stays real-time even when the main
ingestion pipeline lags minutes behind during a churn storm.

It does NOT make the bulk DB write faster -- it guarantees churn *visibility*
survives a storm the bulk pipeline cannot keep up with. Aggregates flush every
FLUSH_INTERVAL seconds to churn_metrics (postgres/scripts/010_churn_metrics.sql);
the Live BGP Churn dashboard reads it.

The consumer starts at the topic head (auto.offset.reset=latest, no commits):
on restart it jumps to current churn rather than replaying a stale backlog.
"""
import collections
import os
import time

import psycopg2
from confluent_kafka import Consumer

BROKER = os.environ.get("KAFKA_BROKER", "obmp-kafka:29092")
TOPIC = os.environ.get("CHURN_TOPIC", "openbmp.parsed.unicast_prefix")
PG_DSN = os.environ.get(
    "PG_DSN",
    "host=obmp-psql port=5432 dbname=openbmp user=openbmp password=openbmp",
)
FLUSH_INTERVAL = int(os.environ.get("FLUSH_INTERVAL", "10"))

# Tab-separated field positions in an openbmp.parsed.unicast_prefix data row.
F_ACTION = 0       # "add" (announce) or "del" (withdraw)
F_ROUTER_IP = 4    # BMP router management IP
F_PEER_IP = 7      # BGP peer address
F_PEER_ASN = 8     # BGP peer ASN


def flush(counts, window):
    """Write accumulated per-(router,peer) counts to churn_metrics."""
    if not counts:
        return
    try:
        conn = psycopg2.connect(PG_DSN)
        with conn.cursor() as cur:
            for (router, peer, asn), (adds, dels) in counts.items():
                cur.execute(
                    "INSERT INTO churn_metrics (router_ip, peer_ip, peer_asn, "
                    "adds, dels) VALUES (%s,%s,%s,%s,%s)",
                    (router or None, peer or None, asn, adds, dels))
        conn.commit()
        conn.close()
        tot_a = sum(v[0] for v in counts.values())
        tot_d = sum(v[1] for v in counts.values())
        print(f"flush: {len(counts)} sessions, +{tot_a} -{tot_d} "
              f"({(tot_a + tot_d) / max(window, 1):.0f} msg/s) over "
              f"{window:.0f}s", flush=True)
    except Exception as e:
        print(f"flush failed: {e}", flush=True)


def main():
    print(f"obmp-churn-monitor: topic={TOPIC}, flush={FLUSH_INTERVAL}s", flush=True)
    consumer = Consumer({
        "bootstrap.servers": BROKER,
        "group.id": "obmp-churn-monitor",
        "auto.offset.reset": "latest",
        "enable.auto.commit": False,
    })
    consumer.subscribe([TOPIC])

    counts = collections.defaultdict(lambda: [0, 0])  # key -> [adds, dels]
    last_flush = time.time()
    while True:
        msg = consumer.poll(1.0)
        if msg is not None and not msg.error():
            text = msg.value().decode("utf-8", errors="replace")
            for line in text.split("\n"):
                if not (line.startswith("add\t") or line.startswith("del\t")):
                    continue
                f = line.split("\t")
                if len(f) <= F_PEER_ASN:
                    continue
                try:
                    asn = int(f[F_PEER_ASN])
                except ValueError:
                    asn = None
                key = (f[F_ROUTER_IP], f[F_PEER_IP], asn)
                if f[F_ACTION] == "add":
                    counts[key][0] += 1
                else:
                    counts[key][1] += 1
        now = time.time()
        if now - last_flush >= FLUSH_INTERVAL:
            flush(counts, now - last_flush)
            counts.clear()
            last_flush = now


if __name__ == "__main__":
    main()