from urllib.parse import urljoin


def patch_transformers_relative_redirects():
    """Patch old transformers download code to handle relative HF redirects."""
    try:
        from transformers import file_utils as transformers_file_utils
    except Exception:
        return

    original_head = transformers_file_utils.requests.head
    if getattr(original_head, "_xplainer_relative_redirect_patch", False):
        return

    def patched_head(url, *args, **kwargs):
        response = original_head(url, *args, **kwargs)
        location = response.headers.get("Location")
        if location and not location.startswith(("http://", "https://")):
            response.headers["Location"] = urljoin(url, location)
        return response

    patched_head._xplainer_relative_redirect_patch = True
    transformers_file_utils.requests.head = patched_head