"""Retention minimization for governed provider-report results."""

from __future__ import annotations

from datetime import UTC, datetime

from sqlalchemy.orm import Session

from govoplan_reporting.backend.db.models import ReportingProviderExecution


class ReportingRetentionService:
    def apply_retention(
        self,
        session: object,
        *,
        dry_run: bool,
        now: datetime,
        limit: int = 500,
    ) -> dict[str, int]:
        if not isinstance(session, Session):
            raise TypeError("Reporting retention requires a SQLAlchemy Session")
        observed_at = _aware(now)
        rows = (
            session.query(ReportingProviderExecution)
            .filter(
                ReportingProviderExecution.expires_at.is_not(None),
                ReportingProviderExecution.expires_at <= observed_at,
                ReportingProviderExecution.retention_redacted_at.is_(None),
            )
            .order_by(
                ReportingProviderExecution.expires_at.asc(),
                ReportingProviderExecution.id.asc(),
            )
            .limit(max(1, min(int(limit), 5_000)))
            .all()
        )
        counts = {
            "eligible": len(rows),
            "redacted": 0,
            "remaining_in_batch": 0,
        }
        if dry_run:
            return counts
        for row in rows:
            # Keep immutable request/output hashes and provenance as audit
            # evidence while removing the retained report detail itself.
            row.result_payload = {}
            row.retention_redacted_at = observed_at
            counts["redacted"] += 1
        session.flush()
        counts["remaining_in_batch"] = (
            session.query(ReportingProviderExecution.id)
            .filter(
                ReportingProviderExecution.expires_at.is_not(None),
                ReportingProviderExecution.expires_at <= observed_at,
                ReportingProviderExecution.retention_redacted_at.is_(None),
            )
            .limit(1)
            .count()
        )
        return counts


def _aware(value: datetime) -> datetime:
    return value if value.tzinfo is not None else value.replace(tzinfo=UTC)


__all__ = ["ReportingRetentionService"]