from __future__ import annotations

import json
import threading
from pathlib import Path
from typing import Any


class SessionStore:
    def __init__(self, base_dir: Path) -> None:
        self.base_dir = base_dir
        self.base_dir.mkdir(parents=True, exist_ok=True)
        self._lock = threading.Lock()

    def _path(self, session_id: str) -> Path:
        return self.base_dir / f"{session_id}.json"

    def load(self, session_id: str) -> dict[str, Any]:
        path = self._path(session_id)
        if not path.exists():
            return {"session_id": session_id, "messages": []}
        return json.loads(path.read_text(encoding="utf-8"))

    def save(self, session_id: str, payload: dict[str, Any]) -> None:
        with self._lock:
            self._path(session_id).write_text(
                json.dumps(payload, ensure_ascii=False, indent=2),
                encoding="utf-8",
            )

    def append_message(self, session_id: str, message: dict[str, Any]) -> dict[str, Any]:
        with self._lock:
            payload = self.load(session_id)
            payload.setdefault("messages", []).append(message)
            self.save(session_id, payload)
            return payload

    def clear(self, session_id: str) -> None:
        with self._lock:
            path = self._path(session_id)
            if path.exists():
                path.unlink()