import os
from pathlib import Path

class VirtualFileSystem:
    """
    A simple in-memory virtual file system that stores files as a dictionary.
    Provides methods to write, read, list, and export files to the real filesystem.
    """
    def __init__(self):
        self.files = {}  # dict of filename -> content

    def write_file(self, name: str, content: str):
        """
        Write content to a virtual file. Overwrites if the file already exists.
        """
        self.files[name] = content

    def read_file(self, name: str) -> str:
        """
        Read content from a virtual file. Returns empty string if file does not exist.
        """
        return self.files.get(name, "")

    def list_files(self):
        """
        Return a list of all virtual file names.
        """
        return list(self.files.keys())

    def export_to_disk(self, base_path: str):
        """
        Export all virtual files to the real filesystem under the given base_path.
        Creates directories as needed.
        """
        os.makedirs(base_path, exist_ok=True)
        for name, content in self.files.items():
            file_path = os.path.join(base_path, name)
            os.makedirs(os.path.dirname(file_path), exist_ok=True)
            with open(file_path, "w", encoding="utf-8") as f:
                f.write(content)