"""Agent credential persistence with restrictive local permissions."""
from __future__ import annotations

import json
import os
from dataclasses import asdict, dataclass
from pathlib import Path
from typing import Any, Dict, Optional


@dataclass(frozen=True)
class AgentState:
    server: str
    agent_id: str
    host_id: str
    token: str
    heartbeat_interval_s: float = 5.0

    @classmethod
    def from_payload(
        cls,
        server: str,
        payload: Dict[str, Any],
    ) -> "AgentState":
        return cls(
            server=server.rstrip("/"),
            agent_id=str(payload["agent_id"]),
            host_id=str(payload["host_id"]),
            token=str(payload["token"]),
            heartbeat_interval_s=float(payload.get("heartbeat_interval_s", 5.0)),
        )


class StateStore:
    def __init__(self, path: Path) -> None:
        self.path = path

    def load(self) -> Optional[AgentState]:
        try:
            raw = json.loads(self.path.read_text(encoding="utf-8"))
            return AgentState(**raw)
        except FileNotFoundError:
            return None
        except (OSError, TypeError, ValueError, json.JSONDecodeError) as exc:
            raise RuntimeError("Agent state 文件无效: {0}".format(self.path)) from exc

    def save(self, state: AgentState) -> None:
        self.path.parent.mkdir(parents=True, exist_ok=True)
        temporary = self.path.with_suffix(self.path.suffix + ".tmp")
        descriptor = os.open(
            str(temporary),
            os.O_WRONLY | os.O_CREAT | os.O_TRUNC,
            0o600,
        )
        try:
            with os.fdopen(descriptor, "w", encoding="utf-8") as handle:
                json.dump(asdict(state), handle, ensure_ascii=False, indent=2)
                handle.write("\n")
                handle.flush()
                os.fsync(handle.fileno())
            os.chmod(temporary, 0o600)
            os.replace(temporary, self.path)
        finally:
            if temporary.exists():
                temporary.unlink()