from __future__ import annotations

import json
import os
from pathlib import Path
from uuid import uuid4

from cloud.internal_api.models import HostGovernancePolicyModel


class HostPolicyCacheError(RuntimeError):
    """Raised when the locally cached non-secret Host policy is invalid."""


class HostPolicyCacheStore:
    """Atomically persists only the Cloud-supplied, non-secret policy cache."""

    def __init__(self, path: str | Path) -> None:
        self.path = Path(path)

    def load(self) -> HostGovernancePolicyModel | None:
        if not self.path.exists():
            return None
        try:
            payload = json.loads(self.path.read_text(encoding="utf-8"))
            return HostGovernancePolicyModel.model_validate(payload)
        except (OSError, ValueError, json.JSONDecodeError) as exc:
            raise HostPolicyCacheError("Host policy cache is invalid") from exc

    def save(self, policy: HostGovernancePolicyModel) -> None:
        self.path.parent.mkdir(parents=True, exist_ok=True)
        temporary = self.path.with_name(f".{self.path.name}.{uuid4().hex}.tmp")
        try:
            temporary.write_text(
                policy.model_dump_json(indent=2) + "\n",
                encoding="utf-8",
            )
            os.replace(temporary, self.path)
        finally:
            if temporary.exists():
                temporary.unlink()

    def clear(self) -> None:
        try:
            self.path.unlink()
        except FileNotFoundError:
            return