"""Create a new, valid Obsidian vault on disk."""

import json
import os


def create_obsidian_vault(parent_dir: str, name: str) -> str:
    """Create a new Obsidian vault under ``parent_dir`` and return its path.

    Creates ``parent_dir/name/`` together with a minimal but valid Obsidian
    configuration: ``parent_dir/name/.obsidian/app.json`` containing ``{}``.
    The presence of an ``.obsidian/`` directory is what Obsidian uses to
    recognise a folder as a vault, so the result opens cleanly in Obsidian.

    Impure: it writes to the filesystem. If the target already looks like a
    vault (it already has an ``.obsidian/`` directory) a ``FileExistsError`` is
    raised so an existing vault is never silently overwritten. A
    ``ValueError`` is raised for an empty ``name`` or one containing a path
    separator.

    Args:
        parent_dir: Directory under which the new vault folder is created. It is
            created if it does not exist yet.
        name: Name of the new vault folder (a single path segment, no
            separators).

    Returns:
        The absolute path of the created vault directory.
    """
    if not name or os.sep in name or (os.altsep and os.altsep in name):
        raise ValueError(f"invalid vault name: {name!r}")

    vault_path = os.path.abspath(os.path.join(parent_dir, name))
    obsidian_dir = os.path.join(vault_path, ".obsidian")

    if os.path.isdir(obsidian_dir):
        raise FileExistsError(f"vault already exists: {vault_path}")

    os.makedirs(obsidian_dir, exist_ok=True)
    app_json = os.path.join(obsidian_dir, "app.json")
    with open(app_json, "w", encoding="utf-8") as handle:
        json.dump({}, handle)

    return vault_path


if __name__ == "__main__":
    import tempfile

    with tempfile.TemporaryDirectory() as tmp:
        path = create_obsidian_vault(tmp, "MyVault")
        assert os.path.isdir(path), path
        assert os.path.isfile(os.path.join(path, ".obsidian", "app.json"))
        with open(os.path.join(path, ".obsidian", "app.json")) as f:
            assert json.load(f) == {}

        # Re-creating the same vault must fail.
        try:
            create_obsidian_vault(tmp, "MyVault")
            raise AssertionError("expected FileExistsError")
        except FileExistsError:
            pass

        # Invalid name must fail.
        try:
            create_obsidian_vault(tmp, "bad/name")
            raise AssertionError("expected ValueError")
        except ValueError:
            pass

    print("OK")