"""Lightweight change-event emitter to Kafka for sources without a native
Debezium connector (Cassandra 4.1 with cdc disabled, Neo4j 4.4 Community).

This performs an application-level dual-write: as the generators insert data,
each new record is also published to Kafka as a Debezium-style change event.
The platform's all-topics S3 consumer then archives these to object storage,
so Cassandra/Neo4j changes flow DB -> Kafka -> S3 just like the CDC sources.

Best-effort: never raises, so data generation cannot be broken by Kafka issues.
"""
import json
import os
import time

KAFKA_BOOTSTRAP = os.getenv("CDC_KAFKA_BOOTSTRAP", "10.0.21.36:9092")

_producer = None


def _default(o):
    # make datetimes / uuids / Decimals JSON-serializable
    try:
        import datetime
        if isinstance(o, (datetime.datetime, datetime.date)):
            return o.isoformat()
    except Exception:
        pass
    return str(o)


def _get_producer():
    global _producer
    if _producer is None:
        from kafka import KafkaProducer
        _producer = KafkaProducer(
            bootstrap_servers=KAFKA_BOOTSTRAP,
            value_serializer=lambda v: json.dumps(v, default=_default).encode("utf-8"),
            linger_ms=50,
            acks=1,
            retries=3,
            request_timeout_ms=20000,
        )
    return _producer


def emit_changes(topic, db, table, records):
    """Publish a list of dict records as change events. Returns count sent."""
    if not records:
        return 0
    try:
        p = _get_producer()
        now = int(time.time() * 1000)
        for r in records:
            evt = {
                "op": "c",
                "ts_ms": now,
                "source": {"connector": "app-cdc", "db": db, "table": table},
                "after": r,
            }
            p.send(topic, evt)
        p.flush(timeout=30)
        print(f"[cdc] emitted {len(records)} change events -> {topic}")
        return len(records)
    except Exception as e:
        print(f"[cdc] emit warning ({topic}): {str(e)[:200]}")
        return 0