from __future__ import absolute_import
import collections
import functools
import logging

from ._collections import HTTPHeaderDict, RecentlyUsedContainer
from .connectionpool import HTTPConnectionPool, HTTPSConnectionPool
from .connectionpool import port_by_scheme
from .exceptions import LocationValueError, MaxRetryError, ProxySchemeUnknown
import six
from six.moves.urllib.parse import urljoin
from .request import RequestMethods
from .util.url import parse_url
from .util.retry import Retry


__all__ = ['PoolManager', 'ProxyManager', 'proxy_from_url']


log = logging.getLogger(__name__)

SSL_KEYWORDS = ('key_file', 'cert_file', 'cert_reqs', 'ca_certs',
                'ssl_version', 'ca_cert_dir', 'ssl_context')

# All known keyword arguments that could be provided to the pool manager, its
# pools, or the underlying connections. This is used to construct a pool key.
_key_fields = (
    'key_scheme',  # str
    'key_host',  # str
    'key_port',  # int
    'key_timeout',  # int or float or Timeout
    'key_retries',  # int or Retry
    'key_strict',  # bool
    'key_block',  # bool
    'key_source_address',  # str
    'key_key_file',  # str
    'key_cert_file',  # str
    'key_cert_reqs',  # str
    'key_ca_certs',  # str
    'key_ssl_version',  # str
    'key_ca_cert_dir',  # str
    'key_ssl_context',  # instance of ssl.SSLContext or urllib3.util.ssl_.SSLContext
    'key_maxsize',  # int
    'key_headers',  # dict
    'key__proxy',  # parsed proxy url
    'key__proxy_headers',  # dict
    'key_socket_options',  # list of (level (int), optname (int), value (int or str)) tuples
    'key__socks_options',  # dict
    'key_assert_hostname',  # bool or string
    'key_assert_fingerprint',  # str
    'key_server_hostname', #str
)

#: The namedtuple class used to construct keys for the connection pool.
#: All custom key schemes should include the fields in this key at a minimum.
PoolKey = collections.namedtuple('PoolKey', _key_fields)


def _default_key_normalizer(key_class, request_context):
    """
    Create a pool key out of a request context dictionary.

    According to RFC 3986, both the scheme and host are case-insensitive.
    Therefore, this function normalizes both before constructing the pool
    key for an HTTPS request. If you wish to change this behaviour, provide
    alternate callables to ``key_fn_by_scheme``.

    :param key_class:
        The class to use when constructing the key. This should be a namedtuple
        with the ``scheme`` and ``host`` keys at a minimum.
    :type  key_class: namedtuple
    :param request_context:
        A dictionary-like object that contain the context for a request.
    :type  request_context: dict

    :return: A namedtuple that can be used as a connection pool key.
    :rtype:  PoolKey
    """
    # Since we mutate the dictionary, make a copy first
    context = request_context.copy()
    context['scheme'] = context['scheme'].lower()
    context['host'] = context['host'].lower()

    # These are both dictionaries and need to be transformed into frozensets
    for key in ('headers', '_proxy_headers', '_socks_options'):
        if key in context and context[key] is not None:
            context[key] = frozenset(context[key].items())

    # The socket_options key may be a list and needs to be transformed into a
    # tuple.
    socket_opts = context.get('socket_options')
    if socket_opts is not None:
        context['socket_options'] = tuple(socket_opts)

    # Map the kwargs to the names in the namedtuple - this is necessary since
    # namedtuples can't have fields starting with '_'.
    for key in list(context.keys()):
        context['key_' + key] = context.pop(key)

    # Default to ``None`` for keys missing from the context
    for field in key_class._fields:
        if field not in context:
            context[field] = None

    return key_class(**context)


#: A dictionary that maps a scheme to a callable that creates a pool key.
#: This can be used to alter the way pool keys are constructed, if desired.
#: Each PoolManager makes a copy of this dictionary so they can be configured
#: globally here, or individually on the instance.
key_fn_by_scheme = {
    'http': functools.partial(_default_key_normalizer, PoolKey),
    'https': functools.partial(_default_key_normalizer, PoolKey),
}

pool_classes_by_scheme = {
    'http': HTTPConnectionPool,
    'https': HTTPSConnectionPool,
}


class PoolManager(RequestMethods):
    """
    Allows for arbitrary requests while transparently keeping track of
    necessary connection pools for you.

    :param num_pools:
        Number of connection pools to cache before discarding the least
        recently used pool.

    :param headers:
        Headers to include with all requests, unless other headers are given
        explicitly.

    :param \\**connection_pool_kw:
        Additional parameters are used to create fresh
        :class:`urllib3.connectionpool.ConnectionPool` instances.

    Example::

        >>> manager = PoolManager(num_pools=2)
        >>> r = manager.request('GET', 'http://google.com/')
        >>> r = manager.request('GET', 'http://google.com/mail')
        >>> r = manager.request('GET', 'http://yahoo.com/')
        >>> len(manager.pools)
        2

    """

    proxy = None

    def __init__(self, num_pools=10, headers=None, **connection_pool_kw):
        RequestMethods.__init__(self, headers)
        self.connection_pool_kw = connection_pool_kw
        self.pools = RecentlyUsedContainer(num_pools,
                                           dispose_func=lambda p: p.close())

        # Locally set the pool classes and keys so other PoolManagers can
        # override them.
        self.pool_classes_by_scheme = pool_classes_by_scheme
        self.key_fn_by_scheme = key_fn_by_scheme.copy()

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.clear()
        # Return False to re-raise any potential exceptions
        return False

    def _new_pool(self, scheme, host, port, request_context=None):
        """
        Create a new :class:`ConnectionPool` based on host, port, scheme, and
        any additional pool keyword arguments.

        If ``request_context`` is provided, it is provided as keyword arguments
        to the pool class used. This method is used to actually create the
        connection pools handed out by :meth:`connection_from_url` and
        companion methods. It is intended to be overridden for customization.
        """
        pool_cls = self.pool_classes_by_scheme[scheme]
        if request_context is None:
            request_context = self.connection_pool_kw.copy()

        # Although the context has everything necessary to create the pool,
        # this function has historically only used the scheme, host, and port
        # in the positional args. When an API change is acceptable these can
        # be removed.
        for key in ('scheme', 'host', 'port'):
            request_context.pop(key, None)

        if scheme == 'http':
            for kw in SSL_KEYWORDS:
                request_context.pop(kw, None)

        return pool_cls(host, port, **request_context)

    def clear(self):
        """
        Empty our store of pools and direct them all to close.

        This will not affect in-flight connections, but they will not be
        re-used after completion.
        """
        self.pools.clear()

    def connection_from_host(self, host, port=None, scheme='http', pool_kwargs=None):
        """
        Get a :class:`ConnectionPool` based on the host, port, and scheme.

        If ``port`` isn't given, it will be derived from the ``scheme`` using
        ``urllib3.connectionpool.port_by_scheme``. If ``pool_kwargs`` is
        provided, it is merged with the instance's ``connection_pool_kw``
        variable and used to create the new connection pool, if one is
        needed.
        """

        if not host:
            raise LocationValueError("No host specified.")

        request_context = self._merge_pool_kwargs(pool_kwargs)
        request_context['scheme'] = scheme or 'http'
        if not port:
            port = port_by_scheme.get(request_context['scheme'].lower(), 80)
        request_context['port'] = port
        request_context['host'] = host

        return self.connection_from_context(request_context)

    def connection_from_context(self, request_context):
        """
        Get a :class:`ConnectionPool` based on the request context.

        ``request_context`` must at least contain the ``scheme`` key and its
        value must be a key in ``key_fn_by_scheme`` instance variable.
        """
        scheme = request_context['scheme'].lower()
        pool_key_constructor = self.key_fn_by_scheme[scheme]
        pool_key = pool_key_constructor(request_context)

        return self.connection_from_pool_key(pool_key, request_context=request_context)

    def connection_from_pool_key(self, pool_key, request_context=None):
        """
        Get a :class:`ConnectionPool` based on the provided pool key.

        ``pool_key`` should be a namedtuple that only contains immutable
        objects. At a minimum it must have the ``scheme``, ``host``, and
        ``port`` fields.
        """
        with self.pools.lock:
            # If the scheme, host, or port doesn't match existing open
            # connections, open a new ConnectionPool.
            pool = self.pools.get(pool_key)
            if pool:
                return pool

            # Make a fresh ConnectionPool of the desired type
            scheme = request_context['scheme']
            host = request_context['host']
            port = request_context['port']
            pool = self._new_pool(scheme, host, port, request_context=request_context)
            self.pools[pool_key] = pool

        return pool

    def connection_from_url(self, url, pool_kwargs=None):
        """
        Similar to :func:`urllib3.connectionpool.connection_from_url`.

        If ``pool_kwargs`` is not provided and a new pool needs to be
        constructed, ``self.connection_pool_kw`` is used to initialize
        the :class:`urllib3.connectionpool.ConnectionPool`. If ``pool_kwargs``
        is provided, it is used instead. Note that if a new pool does not
        need to be created for the request, the provided ``pool_kwargs`` are
        not used.
        """
        u = parse_url(url)
        return self.connection_from_host(u.host, port=u.port, scheme=u.scheme,
                                         pool_kwargs=pool_kwargs)

    def _merge_pool_kwargs(self, override):
        """
        Merge a dictionary of override values for self.connection_pool_kw.

        This does not modify self.connection_pool_kw and returns a new dict.
        Any keys in the override dictionary with a value of ``None`` are
        removed from the merged dictionary.
        """
        base_pool_kwargs = self.connection_pool_kw.copy()
        if override:
            for key, value in override.items():
                if value is None:
                    try:
                        del base_pool_kwargs[key]
                    except KeyError:
                        pass
                else:
                    base_pool_kwargs[key] = value
        return base_pool_kwargs

    def urlopen(self, method, url, redirect=True, **kw):
        """
        Same as :meth:`urllib3.connectionpool.HTTPConnectionPool.urlopen`
        with custom cross-host redirect logic and only sends the request-uri
        portion of the ``url``.

        The given ``url`` parameter must be absolute, such that an appropriate
        :class:`urllib3.connectionpool.ConnectionPool` can be chosen for it.
        """
        u = parse_url(url)
        conn = self.connection_from_host(u.host, port=u.port, scheme=u.scheme)

        kw['assert_same_host'] = False
        kw['redirect'] = False

        if 'headers' not in kw:
            kw['headers'] = self.headers.copy()

        if self.proxy is not None and u.scheme == "http":
            response = conn.urlopen(method, url, **kw)
        else:
            response = conn.urlopen(method, u.request_uri, **kw)

        redirect_location = redirect and response.get_redirect_location()
        if not redirect_location:
            return response

        # Support relative URLs for redirecting.
        redirect_location = urljoin(url, redirect_location)

        if response.status == 303:
            # Change the method according to RFC 9110, Section 15.4.4.
            method = 'GET'
            # And lose the body not to transfer anything sensitive.
            kw["body"] = None
            kw["headers"] = HTTPHeaderDict(kw["headers"])._prepare_for_method_change()

        retries = kw.get('retries')
        if not isinstance(retries, Retry):
            retries = Retry.from_int(retries, redirect=redirect)

        # Strip headers marked as unsafe to forward to the redirected location.
        # Check remove_headers_on_redirect to avoid a potential network call within
        # conn.is_same_host() which may use socket.gethostbyname() in the future.
        if (retries.remove_headers_on_redirect
                and not conn.is_same_host(redirect_location)):
            headers = list(six.iterkeys(kw['headers']))
            for header in headers:
                if header.lower() in retries.remove_headers_on_redirect:
                    kw['headers'].pop(header, None)

        try:
            retries = retries.increment(method, url, response=response, _pool=conn)
        except MaxRetryError:
            if retries.raise_on_redirect:
                raise
            return response

        kw['retries'] = retries
        kw['redirect'] = redirect

        log.info("Redirecting %s -> %s", url, redirect_location)
        return self.urlopen(method, redirect_location, **kw)


class ProxyManager(PoolManager):
    """
    Behaves just like :class:`PoolManager`, but sends all requests through
    the defined proxy, using the CONNECT method for HTTPS URLs.

    :param proxy_url:
        The URL of the proxy to be used.

    :param proxy_headers:
        A dictionary containing headers that will be sent to the proxy. In case
        of HTTP they are being sent with each request, while in the
        HTTPS/CONNECT case they are sent only once. Could be used for proxy
        authentication.

    Example:
        >>> proxy = urllib3.ProxyManager('http://localhost:3128/')
        >>> r1 = proxy.request('GET', 'http://google.com/')
        >>> r2 = proxy.request('GET', 'http://httpbin.org/')
        >>> len(proxy.pools)
        1
        >>> r3 = proxy.request('GET', 'https://httpbin.org/')
        >>> r4 = proxy.request('GET', 'https://twitter.com/')
        >>> len(proxy.pools)
        3

    """

    def __init__(self, proxy_url, num_pools=10, headers=None,
                 proxy_headers=None, **connection_pool_kw):

        if isinstance(proxy_url, HTTPConnectionPool):
            proxy_url = '%s://%s:%i' % (proxy_url.scheme, proxy_url.host,
                                        proxy_url.port)
        proxy = parse_url(proxy_url)
        if not proxy.port:
            port = port_by_scheme.get(proxy.scheme, 80)
            proxy = proxy._replace(port=port)

        if proxy.scheme not in ("http", "https"):
            raise ProxySchemeUnknown(proxy.scheme)

        self.proxy = proxy
        self.proxy_headers = proxy_headers or {}

        connection_pool_kw['_proxy'] = self.proxy
        connection_pool_kw['_proxy_headers'] = self.proxy_headers

        super(ProxyManager, self).__init__(
            num_pools, headers, **connection_pool_kw)

    def connection_from_host(self, host, port=None, scheme='http', pool_kwargs=None):
        if scheme == "https":
            return super(ProxyManager, self).connection_from_host(
                host, port, scheme, pool_kwargs=pool_kwargs)

        return super(ProxyManager, self).connection_from_host(
            self.proxy.host, self.proxy.port, self.proxy.scheme, pool_kwargs=pool_kwargs)

    def _set_proxy_headers(self, url, headers=None):
        """
        Sets headers needed by proxies: specifically, the Accept and Host
        headers. Only sets headers not provided by the user.
        """
        headers_ = {'Accept': '*/*'}

        netloc = parse_url(url).netloc
        if netloc:
            headers_['Host'] = netloc

        if headers:
            headers_.update(headers)
        return headers_

    def urlopen(self, method, url, redirect=True, **kw):
        "Same as HTTP(S)ConnectionPool.urlopen, ``url`` must be absolute."
        u = parse_url(url)

        if u.scheme == "http":
            # For proxied HTTPS requests, httplib sets the necessary headers
            # on the CONNECT to the proxy. For HTTP, we'll definitely
            # need to set 'Host' at the very least.
            headers = kw.get('headers', self.headers)
            kw['headers'] = self._set_proxy_headers(url, headers)

        return super(ProxyManager, self).urlopen(method, url, redirect=redirect, **kw)


def proxy_from_url(url, **kw):
    return ProxyManager(proxy_url=url, **kw)
