"""Simple in‑memory virtual file system.

The VFS is just a dictionary mapping file names to string content.
It is shared between all tools and can be exported to the real
filesystem when requested.
"""

from __future__ import annotations

from pathlib import Path
from typing import Dict, Iterable


class VirtualFileSystem:
    """In‑memory file system.

    Attributes
    ----------
    files : Dict[str, str]
        Mapping of file names to file content.
    """

    def __init__(self) -> None:
        self.files: Dict[str, str] = {}

    def create_file(self, name: str, content: str) -> None:
        """Create or overwrite a virtual file."""
        self.files[name] = content

    def list_files(self) -> Iterable[str]:
        """Return an iterable of file names."""
        return self.files.keys()

    def read_file(self, name: str) -> str:
        """Return the content of a virtual file.

        Raises ``KeyError`` if the file does not exist.
        """
        return self.files[name]

    def export_to_disk(self, root: str | Path = ".") -> None:
        """Export all virtual files to the real filesystem.

        Parameters
        ----------
        root : str | Path, optional
            Root directory where the virtual files will be written.
            Defaults to the current working directory.
        """
        root_path = Path(root).expanduser().resolve()
        root_path.mkdir(parents=True, exist_ok=True)
        for name, content in self.files.items():
            file_path = root_path / name
            file_path.parent.mkdir(parents=True, exist_ok=True)
            file_path.write_text(content, encoding="utf-8")

    def __repr__(self) -> str:  # pragma: no cover
        return f"VirtualFileSystem({len(self.files)} files)"