"""本地文件系统存储实现（MVP）。"""

from pathlib import Path

from app.core.config import get_settings
from app.core.logging import get_logger

logger = get_logger(__name__)


class LocalStorageService:
    """文件存储到服务器本地 data/ 目录。

    key 格式示例：
      users/{uid}/kbs/{kb_id}/original/{rand}_{safe_name}
      users/{uid}/kbs/{kb_id}/markdown/{rand}.md

    实际路径 = storage_root / key
    """

    def __init__(self) -> None:
        settings = get_settings()
        self._root = settings.storage_root_path
        self._root.mkdir(parents=True, exist_ok=True)

    def _resolve(self, key: str) -> Path:
        """解析 key 为绝对路径，同时防路径穿越。"""
        path = (self._root / key).resolve()
        # 安全：确保解析后路径仍在 root 内
        if not str(path).startswith(str(self._root)):
            raise ValueError(f"路径穿越检测：key={key}")
        return path

    def save(self, key: str, data: bytes) -> str:
        path = self._resolve(key)
        path.parent.mkdir(parents=True, exist_ok=True)
        path.write_bytes(data)
        logger.debug("Saved file: %s (%d bytes)", key, len(data))
        return key

    def read(self, key: str) -> bytes:
        path = self._resolve(key)
        return path.read_bytes()

    def delete(self, key: str) -> None:
        path = self._resolve(key)
        if path.exists():
            path.unlink()
            logger.debug("Deleted file: %s", key)

    def exists(self, key: str) -> bool:
        return self._resolve(key).exists()

    def get_size(self, key: str) -> int:
        path = self._resolve(key)
        return path.stat().st_size


# 单例
_instance: LocalStorageService | None = None


def get_storage() -> LocalStorageService:
    global _instance
    if _instance is None:
        _instance = LocalStorageService()
    return _instance