"""Defines private helper functions for the Request class.

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.

"""

import re


QS_PATTERN = re.compile(r'(?<![0-9])([a-zA-Z][a-zA-Z_0-9\-.]*)=([^&]+)')
"""Match query string fields that have names which start with a letter."""


def parse_query_string(query_string):
    """Parse a query string into a dict

    Query string parameters are assumed to use standard form-encoding. Only
    parameters with values are parsed. for example, given "foo=bar&flag",
    this function would ignore "flag".

    Args:
        query_string: The query string to parse

    Returns:
        A dict containing (name, value) pairs, one per query parameter. Note
        that value will be a string, and that name is case-sensitive, both
        copied directly from the query string.

    Raises:
        TypeError: query_string was not a string or buffer

    """

    # PERF: use for loop in lieu of the dict constructor
    params = {}
    for k, v in QS_PATTERN.findall(query_string):
        params[k] = v

    return params


def parse_headers(env):
    """Parse HTTP headers out of a WSGI environ dictionary

    Args:
        env: A WSGI environ dictionary

    Returns:
        A dict containing (name, value) pairs, one per HTTP header

    Raises:
        KeyError: The env dictionary did not contain a key that is required by
            PEP-333.
        TypeError: env is not dictionary-like. In other words, it has no
            attribute '__getitem__'.


    """

    # Parse HTTP_*
    headers = {}
    for key in env:
        if key.startswith('HTTP_'):
            headers[key[5:]] = env[key]

    # Per the WSGI spec, Content-Type is not under HTTP_*
    if 'CONTENT_TYPE' in env:
        headers['CONTENT_TYPE'] = env['CONTENT_TYPE']

    # Per the WSGI spec, Content-Length is not under HTTP_*
    if 'CONTENT_LENGTH' in env:
        headers['CONTENT_LENGTH'] = env['CONTENT_LENGTH']

    # Fallback to SERVER_* vars if the Host header isn't specified
    if 'HOST' not in headers:
        host = env['SERVER_NAME']
        port = env['SERVER_PORT']

        if port != '80':
            host = ''.join([host, ':', port])

        headers['HOST'] = host

    return headers


class Body(object):
    """Wrap wsgi.input streams to make them more robust.

    The 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.
    """

    def __init__(self, stream, stream_len):
        """Initialize the request body instance.

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

        self.stream = stream
        self.stream_len = stream_len

        def _make_stream_reader(func):
            def read(size=None):
                if size is None or size > self.stream_len:
                    size = self.stream_len

                return func(size)

            return read

        # NOTE(kgriffs): All of the wrapped methods take a single argument,
        # which is a size AKA length AKA limit, always in bytes/characters.
        # This is consistent with Gunicorn's "Body" class.
        for attr in ('read', 'readline', 'readlines'):
            target = getattr(self.stream, attr)
            setattr(self, attr, _make_stream_reader(target))

    def __iter__(self):
        return self

    def __next__(self):
        return next(self.stream)

    next = __next__