"""Nova Outbox Writer — write an evidence event to the DynamoDB outbox.

ARCHITECTURE.md §9: DynamoDB outbox, RPO=0 (synchronous write before
ack). The event is hash-chained (SHA-256 over canonical JSON); the first
event has prev_event_hash="GENESIS". D-P10-3: the spike writes ONE
CONFIDENCE_COMPUTED event.

The outbox table (Phase 08): nova-outbox, PAY_PER_REQUEST, PK contractId,
SK eventType#eventTs, TTL expire_at = now + 365d (D-044).

CLI: outbox_writer.py <event.json>  (uses AWS creds from env)
"""

import datetime
import hashlib
import json
import os
import sys

import boto3


OUTBOX_TABLE = "nova-outbox"
REGION = os.environ.get("AWS_DEFAULT_REGION", "us-east-1")


def _canonical_hash(event):
    """SHA-256 over canonical JSON (sort_keys, compact separators)."""
    canonical = json.dumps(event, sort_keys=True, separators=(",", ":"))
    return hashlib.sha256(canonical.encode("utf-8")).hexdigest()


def write_event(event, outbox_table=OUTBOX_TABLE, region=REGION):
    """Write an evidence event to the DynamoDB outbox. Returns the item dict."""
    contract_id = event["contractId"]
    event_type = event.get("eventType", "CONFIDENCE_COMPUTED")
    event_ts = event.get("ts") or datetime.datetime.now(datetime.timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")
    sk = f"{event_type}#{event_ts}"

    # Chain: first event = GENESIS (D-P10-3 spike writes one event).
    prev_hash = event.get("prev_event_hash", "GENESIS")
    event_hash = _canonical_hash(event)

    item = {
        "contractId": {"S": contract_id},
        "eventType#eventTs": {"S": sk},
        "payload": {"S": json.dumps(event, sort_keys=True)},
        "prev_event_hash": {"S": prev_hash},
        "hash": {"S": event_hash},
        "environment": {"S": str(event.get("environment", ""))},
        "stack": {"S": str(event.get("stack", ""))},
        "score": {"N": str(event.get("score", 0))},
        "band": {"S": str(event.get("band", ""))},
        "expire_at": {"N": str(int((datetime.datetime.now(datetime.timezone.utc) +
                                     datetime.timedelta(days=365)).timestamp()))},
    }

    session = boto3.Session(region_name=region)
    dyn = session.client("dynamodb")
    dyn.put_item(TableName=outbox_table, Item=item)
    return item


if __name__ == "__main__":
    if len(sys.argv) != 2:
        print("usage: outbox_writer.py <event.json>", file=sys.stderr)
        sys.exit(2)
    with open(sys.argv[1], "r") as fh:
        event = json.load(fh)
    item = write_event(event)
    print(json.dumps({k: list(v.values())[0] for k, v in item.items()}, indent=2))