# Copyright 2013 by Rackspace Hosting, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""WSGI BoundedStream class."""

from __future__ import annotations

import io
from typing import BinaryIO, Callable, List, Optional, TypeVar, Union

from falcon.util import deprecated

__all__ = ('BoundedStream',)


Result = TypeVar('Result', bound=Union[bytes, List[bytes]])


class BoundedStream(io.IOBase):
    """Wrap *wsgi.input* streams to make them more robust.

    ``socket._fileobject`` and ``io.BufferedReader`` are sometimes used
    to implement *wsgi.input*. However, app developers are often burned
    by the fact that the `read()` method for these objects block
    indefinitely if either no size is passed, or a size greater than
    the request's content length is passed to the method.

    This class normalizes *wsgi.input* behavior between WSGI servers
    by implementing non-blocking behavior for the cases mentioned
    above. The caller is not allowed to read more than the number of
    bytes specified by the Content-Length header in the request.

    Args:
        stream: Instance of ``socket._fileobject`` from
            ``environ['wsgi.input']``
        stream_len: Expected content length of the stream.
    """

    def __init__(self, stream: BinaryIO, stream_len: int) -> None:
        self.stream = stream
        self.stream_len = stream_len

        self._bytes_remaining = self.stream_len

    def __iter__(self) -> BoundedStream:
        return self

    def __next__(self) -> bytes:
        return next(self.stream)

    next = __next__

    def _read(self, size: Optional[int], target: Callable[[int], Result]) -> Result:
        """Proxy reads to the underlying stream.

        Args:
            size (int): Maximum number of bytes to read. Will be
                coerced, if None or -1, to the number of remaining bytes
                in the stream. Will likewise be coerced if greater than
                the number of remaining bytes, to avoid making a
                blocking call to the wrapped stream.
            target (callable): Once `size` has been fixed up, this function
                will be called to actually do the work.

        Returns:
            bytes: Data read from the stream, as returned by `target`.

        """

        # NOTE(kgriffs): Default to reading all remaining bytes if the
        # size is not specified or is out of bounds. This behaves
        # similarly to the IO streams passed in by non-wsgiref servers.
        if size is None or size == -1 or size > self._bytes_remaining:
            size = self._bytes_remaining

        self._bytes_remaining -= size
        return target(size)

    def readable(self) -> bool:
        """Return ``True`` always."""
        return True

    def seekable(self) -> bool:
        """Return ``False`` always."""
        return False

    def writable(self) -> bool:
        """Return ``False`` always."""
        return False

    def read(self, size: Optional[int] = None) -> bytes:
        """Read from the stream.

        Args:
            size (int): Maximum number of bytes/characters to read.
                Defaults to reading until EOF.

        Returns:
            bytes: Data read from the stream.

        """

        return self._read(size, self.stream.read)

    def readline(self, limit: Optional[int] = None) -> bytes:
        """Read a line from the stream.

        Args:
            limit (int): Maximum number of bytes/characters to read.
                Defaults to reading until EOF.

        Returns:
            bytes: Data read from the stream.

        """

        return self._read(limit, self.stream.readline)

    def readlines(self, hint: Optional[int] = None) -> List[bytes]:
        """Read lines from the stream.

        Args:
            hint (int): Maximum number of bytes/characters to read.
                Defaults to reading until EOF.

        Returns:
            bytes: Data read from the stream.

        """

        return self._read(hint, self.stream.readlines)

    def write(self, data: bytes) -> None:
        """Raise IOError always; writing is not supported."""

        raise IOError('Stream is not writeable')

    def exhaust(self, chunk_size: int = 64 * 1024) -> None:
        """Exhaust the stream.

        This consumes all the data left until the limit is reached.

        Args:
            chunk_size (int): The size for a chunk (default: 64 KB).
                It will read the chunk until the stream is exhausted.
        """
        while True:
            chunk = self.read(chunk_size)
            if not chunk:
                break

    @property
    def eof(self) -> bool:
        """``True`` if there is no more data to read from the stream,
        otherwise ``False``.
        """  # noqa: D205
        return self._bytes_remaining <= 0

    @property
    # NOTE(caselit): Deprecated long ago. Warns since 4.0.
    @deprecated(
        'Use `eof` instead. '
        '(This compatibility alias will be removed in Falcon 5.0.)',
        is_property=True,
    )
    def is_exhausted(self) -> bool:
        """Deprecated alias for `eof`."""
        return self.eof


# NOTE(kgriffs): Alias for backwards-compat
Body = BoundedStream