import hashlib
import json
from dataclasses import dataclass
from datetime import datetime
from typing import Any

from django.db import transaction

from commerce.models import SourceRecord, SourceSystem


@dataclass(frozen=True)
class IngestResult:
    record: SourceRecord
    created: bool
    changed: bool


def payload_hash(payload: dict[str, Any]) -> str:
    canonical = json.dumps(
        payload,
        ensure_ascii=False,
        sort_keys=True,
        separators=(",", ":"),
        default=str,
    )
    return hashlib.sha256(canonical.encode("utf-8")).hexdigest()


@transaction.atomic
def ingest_source_record(
    *,
    source: SourceSystem,
    entity_type: str,
    external_id: str,
    payload: dict[str, Any],
    source_updated_at: datetime | None = None,
) -> IngestResult:
    """Idempotently retain the latest payload and report whether it changed."""

    digest = payload_hash(payload)
    existing = (
        SourceRecord.objects.select_for_update()
        .filter(
            source=source,
            entity_type=entity_type,
            external_id=str(external_id),
        )
        .first()
    )
    if existing is not None:
        changed = (
            existing.payload_hash != digest
            or existing.source_updated_at != source_updated_at
        )
        if changed:
            existing.payload = payload
            existing.payload_hash = digest
            existing.source_updated_at = source_updated_at
            existing.save(
                update_fields=[
                    "payload",
                    "payload_hash",
                    "source_updated_at",
                    "received_at",
                ]
            )
        else:
            existing.save(update_fields=["received_at"])
        return IngestResult(record=existing, created=False, changed=changed)

    record = SourceRecord.objects.create(
        source=source,
        entity_type=entity_type,
        external_id=str(external_id),
        payload=payload,
        payload_hash=digest,
        source_updated_at=source_updated_at,
    )
    return IngestResult(record=record, created=True, changed=True)