"""
WSGI Protocol Linter
====================

This module provides a middleware that performs sanity checks on the
behavior of the WSGI server and application. It checks that the
:pep:`3333` WSGI spec is properly implemented. It also warns on some
common HTTP errors such as non-empty responses for 304 status codes.

.. autoclass:: LintMiddleware

:copyright: 2007 Pallets
:license: BSD-3-Clause
"""
import typing as t
from types import TracebackType
from urllib.parse import urlparse
from warnings import warn

from ..datastructures import Headers
from ..http import is_entity_header
from ..wsgi import FileWrapper

if t.TYPE_CHECKING:
    from _typeshed.wsgi import StartResponse
    from _typeshed.wsgi import WSGIApplication
    from _typeshed.wsgi import WSGIEnvironment


class WSGIWarning(Warning):
    """Warning class for WSGI warnings."""


class HTTPWarning(Warning):
    """Warning class for HTTP warnings."""


def check_type(context: str, obj: object, need: t.Type = str) -> None:
    if type(obj) is not need:
        warn(
            f"{context!r} requires {need.__name__!r}, got {type(obj).__name__!r}.",
            WSGIWarning,
            stacklevel=3,
        )


class InputStream:
    def __init__(self, stream: t.IO[bytes]) -> None:
        self._stream = stream

    def read(self, *args: t.Any) -> bytes:
        if len(args) == 0:
            warn(
                "WSGI does not guarantee an EOF marker on the input stream, thus making"
                " calls to 'wsgi.input.read()' unsafe. Conforming servers may never"
                " return from this call.",
                WSGIWarning,
                stacklevel=2,
            )
        elif len(args) != 1:
            warn(
                "Too many parameters passed to 'wsgi.input.read()'.",
                WSGIWarning,
                stacklevel=2,
            )
        return self._stream.read(*args)

    def readline(self, *args: t.Any) -> bytes:
        if len(args) == 0:
            warn(
                "Calls to 'wsgi.input.readline()' without arguments are unsafe. Use"
                " 'wsgi.input.read()' instead.",
                WSGIWarning,
                stacklevel=2,
            )
        elif len(args) == 1:
            warn(
                "'wsgi.input.readline()' was called with a size hint. WSGI does not"
                " support this, although it's available on all major servers.",
                WSGIWarning,
                stacklevel=2,
            )
        else:
            raise TypeError("Too many arguments passed to 'wsgi.input.readline()'.")
        return self._stream.readline(*args)

    def __iter__(self) -> t.Iterator[bytes]:
        try:
            return iter(self._stream)
        except TypeError:
            warn("'wsgi.input' is not iterable.", WSGIWarning, stacklevel=2)
            return iter(())

    def close(self) -> None:
        warn("The application closed the input stream!", WSGIWarning, stacklevel=2)
        self._stream.close()


class ErrorStream:
    def __init__(self, stream: t.IO[str]) -> None:
        self._stream = stream

    def write(self, s: str) -> None:
        check_type("wsgi.error.write()", s, str)
        self._stream.write(s)

    def flush(self) -> None:
        self._stream.flush()

    def writelines(self, seq: t.Iterable[str]) -> None:
        for line in seq:
            self.write(line)

    def close(self) -> None:
        warn("The application closed the error stream!", WSGIWarning, stacklevel=2)
        self._stream.close()


class GuardedWrite:
    def __init__(self, write: t.Callable[[bytes], None], chunks: t.List[int]) -> None:
        self._write = write
        self._chunks = chunks

    def __call__(self, s: bytes) -> None:
        check_type("write()", s, bytes)
        self._write(s)
        self._chunks.append(len(s))


class GuardedIterator:
    def __init__(
        self,
        iterator: t.Iterable[bytes],
        headers_set: t.Tuple[int, Headers],
        chunks: t.List[int],
    ) -> None:
        self._iterator = iterator
        self._next = iter(iterator).__next__
        self.closed = False
        self.headers_set = headers_set
        self.chunks = chunks

    def __iter__(self) -> "GuardedIterator":
        return self

    def __next__(self) -> bytes:
        if self.closed:
            warn("Iterated over closed 'app_iter'.", WSGIWarning, stacklevel=2)

        rv = self._next()

        if not self.headers_set:
            warn(
                "The application returned before it started the response.",
                WSGIWarning,
                stacklevel=2,
            )

        check_type("application iterator items", rv, bytes)
        self.chunks.append(len(rv))
        return rv

    def close(self) -> None:
        self.closed = True

        if hasattr(self._iterator, "close"):
            self._iterator.close()  # type: ignore

        if self.headers_set:
            status_code, headers = self.headers_set
            bytes_sent = sum(self.chunks)
            content_length = headers.get("content-length", type=int)

            if status_code == 304:
                for key, _value in headers:
                    key = key.lower()
                    if key not in ("expires", "content-location") and is_entity_header(
                        key
                    ):
                        warn(
                            f"Entity header {key!r} found in 304 response.", HTTPWarning
                        )
                if bytes_sent:
                    warn("304 responses must not have a body.", HTTPWarning)
            elif 100 <= status_code < 200 or status_code == 204:
                if content_length != 0:
                    warn(
                        f"{status_code} responses must have an empty content length.",
                        HTTPWarning,
                    )
                if bytes_sent:
                    warn(f"{status_code} responses must not have a body.", HTTPWarning)
            elif content_length is not None and content_length != bytes_sent:
                warn(
                    "Content-Length and the number of bytes sent to the"
                    " client do not match.",
                    WSGIWarning,
                )

    def __del__(self) -> None:
        if not self.closed:
            try:
                warn(
                    "Iterator was garbage collected before it was closed.", WSGIWarning
                )
            except Exception:
                pass


class LintMiddleware:
    """Warns about common errors in the WSGI and HTTP behavior of the
    server and wrapped application. Some of the issues it checks are:

    -   invalid status codes
    -   non-bytes sent to the WSGI server
    -   strings returned from the WSGI application
    -   non-empty conditional responses
    -   unquoted etags
    -   relative URLs in the Location header
    -   unsafe calls to wsgi.input
    -   unclosed iterators

    Error information is emitted using the :mod:`warnings` module.

    :param app: The WSGI application to wrap.

    .. code-block:: python

        from werkzeug.middleware.lint import LintMiddleware
        app = LintMiddleware(app)
    """

    def __init__(self, app: "WSGIApplication") -> None:
        self.app = app

    def check_environ(self, environ: "WSGIEnvironment") -> None:
        if type(environ) is not dict:
            warn(
                "WSGI environment is not a standard Python dict.",
                WSGIWarning,
                stacklevel=4,
            )
        for key in (
            "REQUEST_METHOD",
            "SERVER_NAME",
            "SERVER_PORT",
            "wsgi.version",
            "wsgi.input",
            "wsgi.errors",
            "wsgi.multithread",
            "wsgi.multiprocess",
            "wsgi.run_once",
        ):
            if key not in environ:
                warn(
                    f"Required environment key {key!r} not found",
                    WSGIWarning,
                    stacklevel=3,
                )
        if environ["wsgi.version"] != (1, 0):
            warn("Environ is not a WSGI 1.0 environ.", WSGIWarning, stacklevel=3)

        script_name = environ.get("SCRIPT_NAME", "")
        path_info = environ.get("PATH_INFO", "")

        if script_name and script_name[0] != "/":
            warn(
                f"'SCRIPT_NAME' does not start with a slash: {script_name!r}",
                WSGIWarning,
                stacklevel=3,
            )

        if path_info and path_info[0] != "/":
            warn(
                f"'PATH_INFO' does not start with a slash: {path_info!r}",
                WSGIWarning,
                stacklevel=3,
            )

    def check_start_response(
        self,
        status: str,
        headers: t.List[t.Tuple[str, str]],
        exc_info: t.Optional[
            t.Tuple[t.Type[BaseException], BaseException, TracebackType]
        ],
    ) -> t.Tuple[int, Headers]:
        check_type("status", status, str)
        status_code_str = status.split(None, 1)[0]

        if len(status_code_str) != 3 or not status_code_str.isdigit():
            warn("Status code must be three digits.", WSGIWarning, stacklevel=3)

        if len(status) < 4 or status[3] != " ":
            warn(
                f"Invalid value for status {status!r}. Valid status strings are three"
                " digits, a space and a status explanation.",
                WSGIWarning,
                stacklevel=3,
            )

        status_code = int(status_code_str)

        if status_code < 100:
            warn("Status code < 100 detected.", WSGIWarning, stacklevel=3)

        if type(headers) is not list:
            warn("Header list is not a list.", WSGIWarning, stacklevel=3)

        for item in headers:
            if type(item) is not tuple or len(item) != 2:
                warn("Header items must be 2-item tuples.", WSGIWarning, stacklevel=3)
            name, value = item
            if type(name) is not str or type(value) is not str:
                warn(
                    "Header keys and values must be strings.", WSGIWarning, stacklevel=3
                )
            if name.lower() == "status":
                warn(
                    "The status header is not supported due to"
                    " conflicts with the CGI spec.",
                    WSGIWarning,
                    stacklevel=3,
                )

        if exc_info is not None and not isinstance(exc_info, tuple):
            warn("Invalid value for exc_info.", WSGIWarning, stacklevel=3)

        headers = Headers(headers)
        self.check_headers(headers)

        return status_code, headers

    def check_headers(self, headers: Headers) -> None:
        etag = headers.get("etag")

        if etag is not None:
            if etag.startswith(("W/", "w/")):
                if etag.startswith("w/"):
                    warn(
                        "Weak etag indicator should be upper case.",
                        HTTPWarning,
                        stacklevel=4,
                    )

                etag = etag[2:]

            if not (etag[:1] == etag[-1:] == '"'):
                warn("Unquoted etag emitted.", HTTPWarning, stacklevel=4)

        location = headers.get("location")

        if location is not None:
            if not urlparse(location).netloc:
                warn(
                    "Absolute URLs required for location header.",
                    HTTPWarning,
                    stacklevel=4,
                )

    def check_iterator(self, app_iter: t.Iterable[bytes]) -> None:
        if isinstance(app_iter, bytes):
            warn(
                "The application returned a bytestring. The response will send one"
                " character at a time to the client, which will kill performance."
                " Return a list or iterable instead.",
                WSGIWarning,
                stacklevel=3,
            )

    def __call__(self, *args: t.Any, **kwargs: t.Any) -> t.Iterable[bytes]:
        if len(args) != 2:
            warn("A WSGI app takes two arguments.", WSGIWarning, stacklevel=2)

        if kwargs:
            warn(
                "A WSGI app does not take keyword arguments.", WSGIWarning, stacklevel=2
            )

        environ: "WSGIEnvironment" = args[0]
        start_response: "StartResponse" = args[1]

        self.check_environ(environ)
        environ["wsgi.input"] = InputStream(environ["wsgi.input"])
        environ["wsgi.errors"] = ErrorStream(environ["wsgi.errors"])

        # Hook our own file wrapper in so that applications will always
        # iterate to the end and we can check the content length.
        environ["wsgi.file_wrapper"] = FileWrapper

        headers_set: t.List[t.Any] = []
        chunks: t.List[int] = []

        def checking_start_response(
            *args: t.Any, **kwargs: t.Any
        ) -> t.Callable[[bytes], None]:
            if len(args) not in {2, 3}:
                warn(
                    f"Invalid number of arguments: {len(args)}, expected 2 or 3.",
                    WSGIWarning,
                    stacklevel=2,
                )

            if kwargs:
                warn("'start_response' does not take keyword arguments.", WSGIWarning)

            status: str = args[0]
            headers: t.List[t.Tuple[str, str]] = args[1]
            exc_info: t.Optional[
                t.Tuple[t.Type[BaseException], BaseException, TracebackType]
            ] = (args[2] if len(args) == 3 else None)

            headers_set[:] = self.check_start_response(status, headers, exc_info)
            return GuardedWrite(start_response(status, headers, exc_info), chunks)

        app_iter = self.app(environ, t.cast("StartResponse", checking_start_response))
        self.check_iterator(app_iter)
        return GuardedIterator(
            app_iter, t.cast(t.Tuple[int, Headers], headers_set), chunks
        )
