"""Repository asset resolution shared by BMC tutorial notebooks.

When opening an individual notebook, save this file beside its Python source.
"""


def repo_file(path, *, base_url="https://raw.githubusercontent.com/BMClab/BMC/master/"):
    """Find a repository file beside this notebook, or fetch a temporary copy.

    Local files take precedence. Only file acquisition falls back to GitHub;
    parsing errors remain visible to the calling notebook. urllib3 selects its
    browser transport automatically without platform-specific imports.
    """
    import hashlib
    import tempfile
    from pathlib import Path, PurePosixPath
    from urllib.parse import quote

    import marimo as mo
    import urllib3

    relative = PurePosixPath(path)
    if relative.is_absolute() or ".." in relative.parts or "\\" in str(path):
        raise ValueError("Use a repository-relative path such as data/walk.trc")
    location = mo.notebook_dir()
    if location is not None:
        directory = Path(location).resolve()
        for base in (directory, *directory.parents):
            local = base.joinpath(*relative.parts)
            if local.is_file():
                return local
    url = base_url.rstrip("/") + "/" + quote(relative.as_posix(), safe="/")
    key = hashlib.sha256(base_url.rstrip("/").encode()).hexdigest()[:16]
    cached = (Path(tempfile.gettempdir()) / "bmc-notebooks-v2" / key).joinpath(*relative.parts)
    if not cached.is_file():
        response = urllib3.request("GET", url, timeout=30.0, retries=2)
        if response.status != 200:
            raise OSError(f"Cannot load {path}: HTTP {response.status} from {url}")
        cached.parent.mkdir(parents=True, exist_ok=True)
        with tempfile.NamedTemporaryFile(dir=cached.parent, delete=False) as download:
            temporary = Path(download.name)
            download.write(response.data)
        try:
            temporary.replace(cached)
        finally:
            temporary.unlink(missing_ok=True)
    return cached