path: root/contrib/python/Flask/py3/flask/scaffold.py

import importlib.util
import mimetypes
import os
import pkgutil
import sys
import typing as t
from collections import defaultdict
from functools import update_wrapper
from json import JSONDecoder
from json import JSONEncoder

from jinja2 import ChoiceLoader, FileSystemLoader, ResourceLoader
from werkzeug.exceptions import default_exceptions
from werkzeug.exceptions import HTTPException

from .cli import AppGroup
from .globals import current_app
from .helpers import get_root_path
from .helpers import locked_cached_property
from .helpers import send_file
from .helpers import send_from_directory
from .templating import _default_template_ctx_processor
from .typing import AfterRequestCallable
from .typing import AppOrBlueprintKey
from .typing import BeforeRequestCallable
from .typing import GenericException
from .typing import TeardownCallable
from .typing import TemplateContextProcessorCallable
from .typing import URLDefaultCallable
from .typing import URLValuePreprocessorCallable

if t.TYPE_CHECKING:
    from .wrappers import Response
    from .typing import ErrorHandlerCallable

# a singleton sentinel value for parameter defaults
_sentinel = object()

F = t.TypeVar("F", bound=t.Callable[..., t.Any])


def setupmethod(f: F) -> F:
    """Wraps a method so that it performs a check in debug mode if the
    first request was already handled.
    """

    def wrapper_func(self, *args: t.Any, **kwargs: t.Any) -> t.Any:
        if self._is_setup_finished():
            raise AssertionError(
                "A setup function was called after the first request "
                "was handled. This usually indicates a bug in the"
                " application where a module was not imported and"
                " decorators or other functionality was called too"
                " late.\nTo fix this make sure to import all your view"
                " modules, database models, and everything related at a"
                " central place before the application starts serving"
                " requests."
            )
        return f(self, *args, **kwargs)

    return t.cast(F, update_wrapper(wrapper_func, f))


class Scaffold:
    """Common behavior shared between :class:`~flask.Flask` and
    :class:`~flask.blueprints.Blueprint`.

    :param import_name: The import name of the module where this object
        is defined. Usually :attr:`__name__` should be used.
    :param static_folder: Path to a folder of static files to serve.
        If this is set, a static route will be added.
    :param static_url_path: URL prefix for the static route.
    :param template_folder: Path to a folder containing template files.
        for rendering. If this is set, a Jinja loader will be added.
    :param root_path: The path that static, template, and resource files
        are relative to. Typically not set, it is discovered based on
        the ``import_name``.

    .. versionadded:: 2.0
    """

    name: str
    _static_folder: t.Optional[str] = None
    _static_url_path: t.Optional[str] = None

    #: JSON encoder class used by :func:`flask.json.dumps`. If a
    #: blueprint sets this, it will be used instead of the app's value.
    json_encoder: t.Optional[t.Type[JSONEncoder]] = None

    #: JSON decoder class used by :func:`flask.json.loads`. If a
    #: blueprint sets this, it will be used instead of the app's value.
    json_decoder: t.Optional[t.Type[JSONDecoder]] = None

    def __init__(
        self,
        import_name: str,
        static_folder: t.Optional[t.Union[str, os.PathLike]] = None,
        static_url_path: t.Optional[str] = None,
        template_folder: t.Optional[str] = None,
        root_path: t.Optional[str] = None,
    ):
        #: The name of the package or module that this object belongs
        #: to. Do not change this once it is set by the constructor.
        self.import_name = import_name

        self.static_folder = static_folder  # type: ignore
        self.static_url_path = static_url_path

        package_name = import_name
        self.module_loader = pkgutil.find_loader(import_name)
        if self.module_loader and not self.module_loader.is_package(import_name):
            package_name = package_name.rsplit('.', 1)[0]
        self._builtin_resource_prefix = package_name.replace('.', '/')

        #: The path to the templates folder, relative to
        #: :attr:`root_path`, to add to the template loader. ``None`` if
        #: templates should not be added.
        self.template_folder = template_folder

        if root_path is None:
            root_path = get_root_path(self.import_name)

        #: Absolute path to the package on the filesystem. Used to look
        #: up resources contained in the package.
        self.root_path = root_path

        #: The Click command group for registering CLI commands for this
        #: object. The commands are available from the ``flask`` command
        #: once the application has been discovered and blueprints have
        #: been registered.
        self.cli = AppGroup()

        #: A dictionary mapping endpoint names to view functions.
        #:
        #: To register a view function, use the :meth:`route` decorator.
        #:
        #: This data structure is internal. It should not be modified
        #: directly and its format may change at any time.
        self.view_functions: t.Dict[str, t.Callable] = {}

        #: A data structure of registered error handlers, in the format
        #: ``{scope: {code: {class: handler}}}```. The ``scope`` key is
        #: the name of a blueprint the handlers are active for, or
        #: ``None`` for all requests. The ``code`` key is the HTTP
        #: status code for ``HTTPException``, or ``None`` for
        #: other exceptions. The innermost dictionary maps exception
        #: classes to handler functions.
        #:
        #: To register an error handler, use the :meth:`errorhandler`
        #: decorator.
        #:
        #: This data structure is internal. It should not be modified
        #: directly and its format may change at any time.
        self.error_handler_spec: t.Dict[
            AppOrBlueprintKey,
            t.Dict[
                t.Optional[int],
                t.Dict[t.Type[Exception], "ErrorHandlerCallable[Exception]"],
            ],
        ] = defaultdict(lambda: defaultdict(dict))

        #: A data structure of functions to call at the beginning of
        #: each request, in the format ``{scope: [functions]}``. The
        #: ``scope`` key is the name of a blueprint the functions are
        #: active for, or ``None`` for all requests.
        #:
        #: To register a function, use the :meth:`before_request`
        #: decorator.
        #:
        #: This data structure is internal. It should not be modified
        #: directly and its format may change at any time.
        self.before_request_funcs: t.Dict[
            AppOrBlueprintKey, t.List[BeforeRequestCallable]
        ] = defaultdict(list)

        #: A data structure of functions to call at the end of each
        #: request, in the format ``{scope: [functions]}``. The
        #: ``scope`` key is the name of a blueprint the functions are
        #: active for, or ``None`` for all requests.
        #:
        #: To register a function, use the :meth:`after_request`
        #: decorator.
        #:
        #: This data structure is internal. It should not be modified
        #: directly and its format may change at any time.
        self.after_request_funcs: t.Dict[
            AppOrBlueprintKey, t.List[AfterRequestCallable]
        ] = defaultdict(list)

        #: A data structure of functions to call at the end of each
        #: request even if an exception is raised, in the format
        #: ``{scope: [functions]}``. The ``scope`` key is the name of a
        #: blueprint the functions are active for, or ``None`` for all
        #: requests.
        #:
        #: To register a function, use the :meth:`teardown_request`
        #: decorator.
        #:
        #: This data structure is internal. It should not be modified
        #: directly and its format may change at any time.
        self.teardown_request_funcs: t.Dict[
            AppOrBlueprintKey, t.List[TeardownCallable]
        ] = defaultdict(list)

        #: A data structure of functions to call to pass extra context
        #: values when rendering templates, in the format
        #: ``{scope: [functions]}``. The ``scope`` key is the name of a
        #: blueprint the functions are active for, or ``None`` for all
        #: requests.
        #:
        #: To register a function, use the :meth:`context_processor`
        #: decorator.
        #:
        #: This data structure is internal. It should not be modified
        #: directly and its format may change at any time.
        self.template_context_processors: t.Dict[
            AppOrBlueprintKey, t.List[TemplateContextProcessorCallable]
        ] = defaultdict(list, {None: [_default_template_ctx_processor]})

        #: A data structure of functions to call to modify the keyword
        #: arguments passed to the view function, in the format
        #: ``{scope: [functions]}``. The ``scope`` key is the name of a
        #: blueprint the functions are active for, or ``None`` for all
        #: requests.
        #:
        #: To register a function, use the
        #: :meth:`url_value_preprocessor` decorator.
        #:
        #: This data structure is internal. It should not be modified
        #: directly and its format may change at any time.
        self.url_value_preprocessors: t.Dict[
            AppOrBlueprintKey,
            t.List[URLValuePreprocessorCallable],
        ] = defaultdict(list)

        #: A data structure of functions to call to modify the keyword
        #: arguments when generating URLs, in the format
        #: ``{scope: [functions]}``. The ``scope`` key is the name of a
        #: blueprint the functions are active for, or ``None`` for all
        #: requests.
        #:
        #: To register a function, use the :meth:`url_defaults`
        #: decorator.
        #:
        #: This data structure is internal. It should not be modified
        #: directly and its format may change at any time.
        self.url_default_functions: t.Dict[
            AppOrBlueprintKey, t.List[URLDefaultCallable]
        ] = defaultdict(list)

    def __repr__(self) -> str:
        return f"<{type(self).__name__} {self.name!r}>"

    def _is_setup_finished(self) -> bool:
        raise NotImplementedError

    @property
    def static_folder(self) -> t.Optional[str]:
        """The absolute path to the configured static folder. ``None``
        if no static folder is set.
        """
        if self._static_folder is not None:
            return os.path.join(self.root_path, self._static_folder)
        else:
            return None

    @static_folder.setter
    def static_folder(self, value: t.Optional[t.Union[str, os.PathLike]]) -> None:
        if value is not None:
            value = os.fspath(value).rstrip(r"\/")

        self._static_folder = value

    @property
    def has_static_folder(self) -> bool:
        """``True`` if :attr:`static_folder` is set.

        .. versionadded:: 0.5
        """
        return self.static_folder is not None

    @property
    def static_url_path(self) -> t.Optional[str]:
        """The URL prefix that the static route will be accessible from.

        If it was not configured during init, it is derived from
        :attr:`static_folder`.
        """
        if self._static_url_path is not None:
            return self._static_url_path

        if self.static_folder is not None:
            basename = os.path.basename(self.static_folder)
            return f"/{basename}".rstrip("/")

        return None

    @static_url_path.setter
    def static_url_path(self, value: t.Optional[str]) -> None:
        if value is not None:
            value = value.rstrip("/")

        self._static_url_path = value

    def get_send_file_max_age(self, filename: t.Optional[str]) -> t.Optional[int]:
        """Used by :func:`send_file` to determine the ``max_age`` cache
        value for a given file path if it wasn't passed.

        By default, this returns :data:`SEND_FILE_MAX_AGE_DEFAULT` from
        the configuration of :data:`~flask.current_app`. This defaults
        to ``None``, which tells the browser to use conditional requests
        instead of a timed cache, which is usually preferable.

        .. versionchanged:: 2.0
            The default configuration is ``None`` instead of 12 hours.

        .. versionadded:: 0.9
        """
        value = current_app.send_file_max_age_default

        if value is None:
            return None

        return int(value.total_seconds())

    def send_static_file(self, filename: str) -> "Response":
        """The view function used to serve files from
        :attr:`static_folder`. A route is automatically registered for
        this view at :attr:`static_url_path` if :attr:`static_folder` is
        set.

        .. versionadded:: 0.5
        """

        if self.module_loader is not None:
            from io import BytesIO
            path = os.path.join(self._builtin_resource_prefix, self._static_folder, filename)
            try:
                data = self.module_loader.get_data(path)
            except IOError:
                data = None
            if data:
                mimetype = mimetypes.guess_type(filename)[0]
                max_age = self.get_send_file_max_age(filename)
                fobj = BytesIO(data)
                # Note: in case of uWSGI, might also need to set
                # `wsgi-disable-file-wrapper = true`
                # because, otherwise, uwsgi expects a `fileno` on it.
                return send_file(fobj, mimetype=mimetype, max_age=max_age, conditional=True)

        if not self.has_static_folder:
            raise RuntimeError("'static_folder' must be set to serve static_files.")

        # send_file only knows to call get_send_file_max_age on the app,
        # call it here so it works for blueprints too.
        max_age = self.get_send_file_max_age(filename)
        return send_from_directory(
            t.cast(str, self.static_folder), filename, max_age=max_age
        )

    @locked_cached_property
    def jinja_loader(self) -> t.Optional[FileSystemLoader]:
        """The Jinja loader for this object's templates. By default this
        is a class :class:`jinja2.loaders.FileSystemLoader` to
        :attr:`template_folder` if it is set.

        .. versionadded:: 0.5
        """
        if self.template_folder is not None:
            return ChoiceLoader([
                FileSystemLoader(os.path.join(self.root_path, self.template_folder)),
                ResourceLoader(os.path.join(self._builtin_resource_prefix, self.template_folder), self.module_loader),
            ])
        else:
            return None

    def open_resource(self, resource: str, mode: str = "rb") -> t.IO[t.AnyStr]:
        """Open a resource file relative to :attr:`root_path` for
        reading.

        For example, if the file ``schema.sql`` is next to the file
        ``app.py`` where the ``Flask`` app is defined, it can be opened
        with:

        .. code-block:: python

            with app.open_resource("schema.sql") as f:
                conn.executescript(f.read())

        :param resource: Path to the resource relative to
            :attr:`root_path`.
        :param mode: Open the file in this mode. Only reading is
            supported, valid values are "r" (or "rt") and "rb".
        """
        if mode not in {"r", "rt", "rb"}:
            raise ValueError("Resources can only be opened for reading.")

        return open(os.path.join(self.root_path, resource), mode)

    def _method_route(self, method: str, rule: str, options: dict) -> t.Callable:
        if "methods" in options:
            raise TypeError("Use the 'route' decorator to use the 'methods' argument.")

        return self.route(rule, methods=[method], **options)

    def get(self, rule: str, **options: t.Any) -> t.Callable:
        """Shortcut for :meth:`route` with ``methods=["GET"]``.

        .. versionadded:: 2.0
        """
        return self._method_route("GET", rule, options)

    def post(self, rule: str, **options: t.Any) -> t.Callable:
        """Shortcut for :meth:`route` with ``methods=["POST"]``.

        .. versionadded:: 2.0
        """
        return self._method_route("POST", rule, options)

    def put(self, rule: str, **options: t.Any) -> t.Callable:
        """Shortcut for :meth:`route` with ``methods=["PUT"]``.

        .. versionadded:: 2.0
        """
        return self._method_route("PUT", rule, options)

    def delete(self, rule: str, **options: t.Any) -> t.Callable:
        """Shortcut for :meth:`route` with ``methods=["DELETE"]``.

        .. versionadded:: 2.0
        """
        return self._method_route("DELETE", rule, options)

    def patch(self, rule: str, **options: t.Any) -> t.Callable:
        """Shortcut for :meth:`route` with ``methods=["PATCH"]``.

        .. versionadded:: 2.0
        """
        return self._method_route("PATCH", rule, options)

    def route(self, rule: str, **options: t.Any) -> t.Callable:
        """Decorate a view function to register it with the given URL
        rule and options. Calls :meth:`add_url_rule`, which has more
        details about the implementation.

        .. code-block:: python

            @app.route("/")
            def index():
                return "Hello, World!"

        See :ref:`url-route-registrations`.

        The endpoint name for the route defaults to the name of the view
        function if the ``endpoint`` parameter isn't passed.

        The ``methods`` parameter defaults to ``["GET"]``. ``HEAD`` and
        ``OPTIONS`` are added automatically.

        :param rule: The URL rule string.
        :param options: Extra options passed to the
            :class:`~werkzeug.routing.Rule` object.
        """

        def decorator(f: t.Callable) -> t.Callable:
            endpoint = options.pop("endpoint", None)
            self.add_url_rule(rule, endpoint, f, **options)
            return f

        return decorator

    @setupmethod
    def add_url_rule(
        self,
        rule: str,
        endpoint: t.Optional[str] = None,
        view_func: t.Optional[t.Callable] = None,
        provide_automatic_options: t.Optional[bool] = None,
        **options: t.Any,
    ) -> None:
        """Register a rule for routing incoming requests and building
        URLs. The :meth:`route` decorator is a shortcut to call this
        with the ``view_func`` argument. These are equivalent:

        .. code-block:: python

            @app.route("/")
            def index():
                ...

        .. code-block:: python

            def index():
                ...

            app.add_url_rule("/", view_func=index)

        See :ref:`url-route-registrations`.

        The endpoint name for the route defaults to the name of the view
        function if the ``endpoint`` parameter isn't passed. An error
        will be raised if a function has already been registered for the
        endpoint.

        The ``methods`` parameter defaults to ``["GET"]``. ``HEAD`` is
        always added automatically, and ``OPTIONS`` is added
        automatically by default.

        ``view_func`` does not necessarily need to be passed, but if the
        rule should participate in routing an endpoint name must be
        associated with a view function at some point with the
        :meth:`endpoint` decorator.

        .. code-block:: python

            app.add_url_rule("/", endpoint="index")

            @app.endpoint("index")
            def index():
                ...

        If ``view_func`` has a ``required_methods`` attribute, those
        methods are added to the passed and automatic methods. If it
        has a ``provide_automatic_methods`` attribute, it is used as the
        default if the parameter is not passed.

        :param rule: The URL rule string.
        :param endpoint: The endpoint name to associate with the rule
            and view function. Used when routing and building URLs.
            Defaults to ``view_func.__name__``.
        :param view_func: The view function to associate with the
            endpoint name.
        :param provide_automatic_options: Add the ``OPTIONS`` method and
            respond to ``OPTIONS`` requests automatically.
        :param options: Extra options passed to the
            :class:`~werkzeug.routing.Rule` object.
        """
        raise NotImplementedError

    def endpoint(self, endpoint: str) -> t.Callable:
        """Decorate a view function to register it for the given
        endpoint. Used if a rule is added without a ``view_func`` with
        :meth:`add_url_rule`.

        .. code-block:: python

            app.add_url_rule("/ex", endpoint="example")

            @app.endpoint("example")
            def example():
                ...

        :param endpoint: The endpoint name to associate with the view
            function.
        """

        def decorator(f):
            self.view_functions[endpoint] = f
            return f

        return decorator

    @setupmethod
    def before_request(self, f: BeforeRequestCallable) -> BeforeRequestCallable:
        """Register a function to run before each request.

        For example, this can be used to open a database connection, or
        to load the logged in user from the session.

        .. code-block:: python

            @app.before_request
            def load_user():
                if "user_id" in session:
                    g.user = db.session.get(session["user_id"])

        The function will be called without any arguments. If it returns
        a non-``None`` value, the value is handled as if it was the
        return value from the view, and further request handling is
        stopped.
        """
        self.before_request_funcs.setdefault(None, []).append(f)
        return f

    @setupmethod
    def after_request(self, f: AfterRequestCallable) -> AfterRequestCallable:
        """Register a function to run after each request to this object.

        The function is called with the response object, and must return
        a response object. This allows the functions to modify or
        replace the response before it is sent.

        If a function raises an exception, any remaining
        ``after_request`` functions will not be called. Therefore, this
        should not be used for actions that must execute, such as to
        close resources. Use :meth:`teardown_request` for that.
        """
        self.after_request_funcs.setdefault(None, []).append(f)
        return f

    @setupmethod
    def teardown_request(self, f: TeardownCallable) -> TeardownCallable:
        """Register a function to be run at the end of each request,
        regardless of whether there was an exception or not.  These functions
        are executed when the request context is popped, even if not an
        actual request was performed.

        Example::

            ctx = app.test_request_context()
            ctx.push()
            ...
            ctx.pop()

        When ``ctx.pop()`` is executed in the above example, the teardown
        functions are called just before the request context moves from the
        stack of active contexts.  This becomes relevant if you are using
        such constructs in tests.

        Teardown functions must avoid raising exceptions, since they . If they
        execute code that might fail they
        will have to surround the execution of these code by try/except
        statements and log occurring errors.

        When a teardown function was called because of an exception it will
        be passed an error object.

        The return values of teardown functions are ignored.

        .. admonition:: Debug Note

           In debug mode Flask will not tear down a request on an exception
           immediately.  Instead it will keep it alive so that the interactive
           debugger can still access it.  This behavior can be controlled
           by the ``PRESERVE_CONTEXT_ON_EXCEPTION`` configuration variable.
        """
        self.teardown_request_funcs.setdefault(None, []).append(f)
        return f

    @setupmethod
    def context_processor(
        self, f: TemplateContextProcessorCallable
    ) -> TemplateContextProcessorCallable:
        """Registers a template context processor function."""
        self.template_context_processors[None].append(f)
        return f

    @setupmethod
    def url_value_preprocessor(
        self, f: URLValuePreprocessorCallable
    ) -> URLValuePreprocessorCallable:
        """Register a URL value preprocessor function for all view
        functions in the application. These functions will be called before the
        :meth:`before_request` functions.

        The function can modify the values captured from the matched url before
        they are passed to the view. For example, this can be used to pop a
        common language code value and place it in ``g`` rather than pass it to
        every view.

        The function is passed the endpoint name and values dict. The return
        value is ignored.
        """
        self.url_value_preprocessors[None].append(f)
        return f

    @setupmethod
    def url_defaults(self, f: URLDefaultCallable) -> URLDefaultCallable:
        """Callback function for URL defaults for all view functions of the
        application.  It's called with the endpoint and values and should
        update the values passed in place.
        """
        self.url_default_functions[None].append(f)
        return f

    @setupmethod
    def errorhandler(
        self, code_or_exception: t.Union[t.Type[GenericException], int]
    ) -> t.Callable[
        ["ErrorHandlerCallable[GenericException]"],
        "ErrorHandlerCallable[GenericException]",
    ]:
        """Register a function to handle errors by code or exception class.

        A decorator that is used to register a function given an
        error code.  Example::

            @app.errorhandler(404)
            def page_not_found(error):
                return 'This page does not exist', 404

        You can also register handlers for arbitrary exceptions::

            @app.errorhandler(DatabaseError)
            def special_exception_handler(error):
                return 'Database connection failed', 500

        .. versionadded:: 0.7
            Use :meth:`register_error_handler` instead of modifying
            :attr:`error_handler_spec` directly, for application wide error
            handlers.

        .. versionadded:: 0.7
           One can now additionally also register custom exception types
           that do not necessarily have to be a subclass of the
           :class:`~werkzeug.exceptions.HTTPException` class.

        :param code_or_exception: the code as integer for the handler, or
                                  an arbitrary exception
        """

        def decorator(
            f: "ErrorHandlerCallable[GenericException]",
        ) -> "ErrorHandlerCallable[GenericException]":
            self.register_error_handler(code_or_exception, f)
            return f

        return decorator

    @setupmethod
    def register_error_handler(
        self,
        code_or_exception: t.Union[t.Type[GenericException], int],
        f: "ErrorHandlerCallable[GenericException]",
    ) -> None:
        """Alternative error attach function to the :meth:`errorhandler`
        decorator that is more straightforward to use for non decorator
        usage.

        .. versionadded:: 0.7
        """
        if isinstance(code_or_exception, HTTPException):  # old broken behavior
            raise ValueError(
                "Tried to register a handler for an exception instance"
                f" {code_or_exception!r}. Handlers can only be"
                " registered for exception classes or HTTP error codes."
            )

        try:
            exc_class, code = self._get_exc_class_and_code(code_or_exception)
        except KeyError:
            raise KeyError(
                f"'{code_or_exception}' is not a recognized HTTP error"
                " code. Use a subclass of HTTPException with that code"
                " instead."
            ) from None

        self.error_handler_spec[None][code][exc_class] = t.cast(
            "ErrorHandlerCallable[Exception]", f
        )

    @staticmethod
    def _get_exc_class_and_code(
        exc_class_or_code: t.Union[t.Type[Exception], int]
    ) -> t.Tuple[t.Type[Exception], t.Optional[int]]:
        """Get the exception class being handled. For HTTP status codes
        or ``HTTPException`` subclasses, return both the exception and
        status code.

        :param exc_class_or_code: Any exception class, or an HTTP status
            code as an integer.
        """
        exc_class: t.Type[Exception]
        if isinstance(exc_class_or_code, int):
            exc_class = default_exceptions[exc_class_or_code]
        else:
            exc_class = exc_class_or_code

        assert issubclass(
            exc_class, Exception
        ), "Custom exceptions must be subclasses of Exception."

        if issubclass(exc_class, HTTPException):
            return exc_class, exc_class.code
        else:
            return exc_class, None


def _endpoint_from_view_func(view_func: t.Callable) -> str:
    """Internal helper that returns the default endpoint for a given
    function.  This always is the function name.
    """
    assert view_func is not None, "expected view func if endpoint is not provided."
    return view_func.__name__


def _matching_loader_thinks_module_is_package(loader, mod_name):
    """Attempt to figure out if the given name is a package or a module.

    :param: loader: The loader that handled the name.
    :param mod_name: The name of the package or module.
    """
    # Use loader.is_package if it's available.
    if hasattr(loader, "is_package"):
        return loader.is_package(mod_name)

    cls = type(loader)

    # NamespaceLoader doesn't implement is_package, but all names it
    # loads must be packages.
    if cls.__module__ == "_frozen_importlib" and cls.__name__ == "NamespaceLoader":
        return True

    # Otherwise we need to fail with an error that explains what went
    # wrong.
    raise AttributeError(
        f"'{cls.__name__}.is_package()' must be implemented for PEP 302"
        f" import hooks."
    )


def _find_package_path(root_mod_name):
    """Find the path that contains the package or module."""
    try:
        spec = importlib.util.find_spec(root_mod_name)

        if spec is None:
            raise ValueError("not found")
    # ImportError: the machinery told us it does not exist
    # ValueError:
    #    - the module name was invalid
    #    - the module name is __main__
    #    - *we* raised `ValueError` due to `spec` being `None`
    except (ImportError, ValueError):
        pass  # handled below
    else:
        # namespace package
        if spec.origin in {"namespace", None}:
            return os.path.dirname(next(iter(spec.submodule_search_locations)))
        # a package (with __init__.py)
        elif spec.submodule_search_locations:
            return os.path.dirname(os.path.dirname(spec.origin))
        # just a normal module
        else:
            return os.path.dirname(spec.origin)

    # we were unable to find the `package_path` using PEP 451 loaders
    loader = pkgutil.get_loader(root_mod_name)

    if loader is None or root_mod_name == "__main__":
        # import name is not found, or interactive/main module
        return os.getcwd()

    if hasattr(loader, "get_filename"):
        filename = loader.get_filename(root_mod_name)
    elif hasattr(loader, "archive"):
        # zipimporter's loader.archive points to the .egg or .zip file.
        filename = loader.archive
    else:
        # At least one loader is missing both get_filename and archive:
        # Google App Engine's HardenedModulesHook, use __file__.
        filename = importlib.import_module(root_mod_name).__file__

    package_path = os.path.abspath(os.path.dirname(filename))

    # If the imported name is a package, filename is currently pointing
    # to the root of the package, need to get the current directory.
    if _matching_loader_thinks_module_is_package(loader, root_mod_name):
        package_path = os.path.dirname(package_path)

    return package_path


def find_package(import_name: str):
    """Find the prefix that a package is installed under, and the path
    that it would be imported from.

    The prefix is the directory containing the standard directory
    hierarchy (lib, bin, etc.). If the package is not installed to the
    system (:attr:`sys.prefix`) or a virtualenv (``site-packages``),
    ``None`` is returned.

    The path is the entry in :attr:`sys.path` that contains the package
    for import. If the package is not installed, it's assumed that the
    package was imported from the current working directory.
    """
    root_mod_name, _, _ = import_name.partition(".")
    package_path = _find_package_path(root_mod_name)
    py_prefix = os.path.abspath(sys.prefix)

    # installed to the system
    if package_path.startswith(py_prefix):
        return py_prefix, package_path

    site_parent, site_folder = os.path.split(package_path)

    # installed to a virtualenv
    if site_folder.lower() == "site-packages":
        parent, folder = os.path.split(site_parent)

        # Windows (prefix/lib/site-packages)
        if folder.lower() == "lib":
            return parent, package_path

        # Unix (prefix/lib/pythonX.Y/site-packages)
        if os.path.basename(parent).lower() == "lib":
            return os.path.dirname(parent), package_path

        # something else (prefix/site-packages)
        return site_parent, package_path

    # not installed
    return None, package_path