"""
SecureTranport support for urllib3 via ctypes.

This makes platform-native TLS available to urllib3 users on macOS without the
use of a compiler. This is an important feature because the Python Package
Index is moving to become a TLSv1.2-or-higher server, and the default OpenSSL
that ships with macOS is not capable of doing TLSv1.2. The only way to resolve
this is to give macOS users an alternative solution to the problem, and that
solution is to use SecureTransport.

We use ctypes here because this solution must not require a compiler. That's
because pip is not allowed to require a compiler either.

This is not intended to be a seriously long-term solution to this problem.
The hope is that PEP 543 will eventually solve this issue for us, at which
point we can retire this contrib module. But in the short term, we need to
solve the impending tire fire that is Python on Mac without this kind of
contrib module. So...here we are.

To use this module, simply import and inject it::

    import urllib3.contrib.securetransport
    urllib3.contrib.securetransport.inject_into_urllib3()

Happy TLSing!
"""
from __future__ import absolute_import

import contextlib
import ctypes
import errno
import os.path
import shutil
import socket
import ssl
import threading
import weakref

from .. import util
from ._securetransport.bindings import (
    Security, SecurityConst, CoreFoundation
)
from ._securetransport.low_level import (
    _assert_no_error, _cert_array_from_pem, _temporary_keychain,
    _load_client_cert_chain
)

try:  # Platform-specific: Python 2
    from socket import _fileobject
except ImportError:  # Platform-specific: Python 3
    _fileobject = None
    from ..packages.backports.makefile import backport_makefile

__all__ = ['inject_into_urllib3', 'extract_from_urllib3']

# SNI always works
HAS_SNI = True

orig_util_HAS_SNI = util.HAS_SNI
orig_util_SSLContext = util.ssl_.SSLContext

# This dictionary is used by the read callback to obtain a handle to the
# calling wrapped socket. This is a pretty silly approach, but for now it'll
# do. I feel like I should be able to smuggle a handle to the wrapped socket
# directly in the SSLConnectionRef, but for now this approach will work I
# guess.
#
# We need to lock around this structure for inserts, but we don't do it for
# reads/writes in the callbacks. The reasoning here goes as follows:
#
#    1. It is not possible to call into the callbacks before the dictionary is
#       populated, so once in the callback the id must be in the dictionary.
#    2. The callbacks don't mutate the dictionary, they only read from it, and
#       so cannot conflict with any of the insertions.
#
# This is good: if we had to lock in the callbacks we'd drastically slow down
# the performance of this code.
_connection_refs = weakref.WeakValueDictionary()
_connection_ref_lock = threading.Lock()

# Limit writes to 16kB. This is OpenSSL's limit, but we'll cargo-cult it over
# for no better reason than we need *a* limit, and this one is right there.
SSL_WRITE_BLOCKSIZE = 16384

# This is our equivalent of util.ssl_.DEFAULT_CIPHERS, but expanded out to
# individual cipher suites. We need to do this because this is how
# SecureTransport wants them.
CIPHER_SUITES = [
    SecurityConst.TLS_AES_256_GCM_SHA384,
    SecurityConst.TLS_CHACHA20_POLY1305_SHA256,
    SecurityConst.TLS_AES_128_GCM_SHA256,
    SecurityConst.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
    SecurityConst.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
    SecurityConst.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
    SecurityConst.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
    SecurityConst.TLS_DHE_DSS_WITH_AES_256_GCM_SHA384,
    SecurityConst.TLS_DHE_RSA_WITH_AES_256_GCM_SHA384,
    SecurityConst.TLS_DHE_DSS_WITH_AES_128_GCM_SHA256,
    SecurityConst.TLS_DHE_RSA_WITH_AES_128_GCM_SHA256,
    SecurityConst.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384,
    SecurityConst.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384,
    SecurityConst.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,
    SecurityConst.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,
    SecurityConst.TLS_DHE_RSA_WITH_AES_256_CBC_SHA256,
    SecurityConst.TLS_DHE_DSS_WITH_AES_256_CBC_SHA256,
    SecurityConst.TLS_DHE_RSA_WITH_AES_256_CBC_SHA,
    SecurityConst.TLS_DHE_DSS_WITH_AES_256_CBC_SHA,
    SecurityConst.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256,
    SecurityConst.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256,
    SecurityConst.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,
    SecurityConst.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,
    SecurityConst.TLS_DHE_RSA_WITH_AES_128_CBC_SHA256,
    SecurityConst.TLS_DHE_DSS_WITH_AES_128_CBC_SHA256,
    SecurityConst.TLS_DHE_RSA_WITH_AES_128_CBC_SHA,
    SecurityConst.TLS_DHE_DSS_WITH_AES_128_CBC_SHA,
    SecurityConst.TLS_RSA_WITH_AES_256_GCM_SHA384,
    SecurityConst.TLS_RSA_WITH_AES_128_GCM_SHA256,
    SecurityConst.TLS_RSA_WITH_AES_256_CBC_SHA256,
    SecurityConst.TLS_RSA_WITH_AES_128_CBC_SHA256,
    SecurityConst.TLS_RSA_WITH_AES_256_CBC_SHA,
    SecurityConst.TLS_RSA_WITH_AES_128_CBC_SHA,
]

# Basically this is simple: for PROTOCOL_SSLv23 we turn it into a low of
# TLSv1 and a high of TLSv1.2. For everything else, we pin to that version.
_protocol_to_min_max = {
    ssl.PROTOCOL_SSLv23: (SecurityConst.kTLSProtocol1, SecurityConst.kTLSProtocol12),
}

if hasattr(ssl, "PROTOCOL_SSLv2"):
    _protocol_to_min_max[ssl.PROTOCOL_SSLv2] = (
        SecurityConst.kSSLProtocol2, SecurityConst.kSSLProtocol2
    )
if hasattr(ssl, "PROTOCOL_SSLv3"):
    _protocol_to_min_max[ssl.PROTOCOL_SSLv3] = (
        SecurityConst.kSSLProtocol3, SecurityConst.kSSLProtocol3
    )
if hasattr(ssl, "PROTOCOL_TLSv1"):
    _protocol_to_min_max[ssl.PROTOCOL_TLSv1] = (
        SecurityConst.kTLSProtocol1, SecurityConst.kTLSProtocol1
    )
if hasattr(ssl, "PROTOCOL_TLSv1_1"):
    _protocol_to_min_max[ssl.PROTOCOL_TLSv1_1] = (
        SecurityConst.kTLSProtocol11, SecurityConst.kTLSProtocol11
    )
if hasattr(ssl, "PROTOCOL_TLSv1_2"):
    _protocol_to_min_max[ssl.PROTOCOL_TLSv1_2] = (
        SecurityConst.kTLSProtocol12, SecurityConst.kTLSProtocol12
    )
if hasattr(ssl, "PROTOCOL_TLS"):
    _protocol_to_min_max[ssl.PROTOCOL_TLS] = _protocol_to_min_max[ssl.PROTOCOL_SSLv23]


def inject_into_urllib3():
    """
    Monkey-patch urllib3 with SecureTransport-backed SSL-support.
    """
    util.ssl_.SSLContext = SecureTransportContext
    util.HAS_SNI = HAS_SNI
    util.ssl_.HAS_SNI = HAS_SNI
    util.IS_SECURETRANSPORT = True
    util.ssl_.IS_SECURETRANSPORT = True


def extract_from_urllib3():
    """
    Undo monkey-patching by :func:`inject_into_urllib3`.
    """
    util.ssl_.SSLContext = orig_util_SSLContext
    util.HAS_SNI = orig_util_HAS_SNI
    util.ssl_.HAS_SNI = orig_util_HAS_SNI
    util.IS_SECURETRANSPORT = False
    util.ssl_.IS_SECURETRANSPORT = False


def _read_callback(connection_id, data_buffer, data_length_pointer):
    """
    SecureTransport read callback. This is called by ST to request that data
    be returned from the socket.
    """
    wrapped_socket = None
    try:
        wrapped_socket = _connection_refs.get(connection_id)
        if wrapped_socket is None:
            return SecurityConst.errSSLInternal
        base_socket = wrapped_socket.socket

        requested_length = data_length_pointer[0]

        timeout = wrapped_socket.gettimeout()
        error = None
        read_count = 0

        try:
            while read_count < requested_length:
                if timeout is None or timeout >= 0:
                    if not util.wait_for_read(base_socket, timeout):
                        raise socket.error(errno.EAGAIN, 'timed out')

                remaining = requested_length - read_count
                buffer = (ctypes.c_char * remaining).from_address(
                    data_buffer + read_count
                )
                chunk_size = base_socket.recv_into(buffer, remaining)
                read_count += chunk_size
                if not chunk_size:
                    if not read_count:
                        return SecurityConst.errSSLClosedGraceful
                    break
        except (socket.error) as e:
            error = e.errno

            if error is not None and error != errno.EAGAIN:
                data_length_pointer[0] = read_count
                if error == errno.ECONNRESET or error == errno.EPIPE:
                    return SecurityConst.errSSLClosedAbort
                raise

        data_length_pointer[0] = read_count

        if read_count != requested_length:
            return SecurityConst.errSSLWouldBlock

        return 0
    except Exception as e:
        if wrapped_socket is not None:
            wrapped_socket._exception = e
        return SecurityConst.errSSLInternal


def _write_callback(connection_id, data_buffer, data_length_pointer):
    """
    SecureTransport write callback. This is called by ST to request that data
    actually be sent on the network.
    """
    wrapped_socket = None
    try:
        wrapped_socket = _connection_refs.get(connection_id)
        if wrapped_socket is None:
            return SecurityConst.errSSLInternal
        base_socket = wrapped_socket.socket

        bytes_to_write = data_length_pointer[0]
        data = ctypes.string_at(data_buffer, bytes_to_write)

        timeout = wrapped_socket.gettimeout()
        error = None
        sent = 0

        try:
            while sent < bytes_to_write:
                if timeout is None or timeout >= 0:
                    if not util.wait_for_write(base_socket, timeout):
                        raise socket.error(errno.EAGAIN, 'timed out')
                chunk_sent = base_socket.send(data)
                sent += chunk_sent

                # This has some needless copying here, but I'm not sure there's
                # much value in optimising this data path.
                data = data[chunk_sent:]
        except (socket.error) as e:
            error = e.errno

            if error is not None and error != errno.EAGAIN:
                data_length_pointer[0] = sent
                if error == errno.ECONNRESET or error == errno.EPIPE:
                    return SecurityConst.errSSLClosedAbort
                raise

        data_length_pointer[0] = sent

        if sent != bytes_to_write:
            return SecurityConst.errSSLWouldBlock

        return 0
    except Exception as e:
        if wrapped_socket is not None:
            wrapped_socket._exception = e
        return SecurityConst.errSSLInternal


# We need to keep these two objects references alive: if they get GC'd while
# in use then SecureTransport could attempt to call a function that is in freed
# memory. That would be...uh...bad. Yeah, that's the word. Bad.
_read_callback_pointer = Security.SSLReadFunc(_read_callback)
_write_callback_pointer = Security.SSLWriteFunc(_write_callback)


class WrappedSocket(object):
    """
    API-compatibility wrapper for Python's OpenSSL wrapped socket object.

    Note: _makefile_refs, _drop(), and _reuse() are needed for the garbage
    collector of PyPy.
    """
    def __init__(self, socket):
        self.socket = socket
        self.context = None
        self._makefile_refs = 0
        self._closed = False
        self._exception = None
        self._keychain = None
        self._keychain_dir = None
        self._client_cert_chain = None

        # We save off the previously-configured timeout and then set it to
        # zero. This is done because we use select and friends to handle the
        # timeouts, but if we leave the timeout set on the lower socket then
        # Python will "kindly" call select on that socket again for us. Avoid
        # that by forcing the timeout to zero.
        self._timeout = self.socket.gettimeout()
        self.socket.settimeout(0)

    @contextlib.contextmanager
    def _raise_on_error(self):
        """
        A context manager that can be used to wrap calls that do I/O from
        SecureTransport. If any of the I/O callbacks hit an exception, this
        context manager will correctly propagate the exception after the fact.
        This avoids silently swallowing those exceptions.

        It also correctly forces the socket closed.
        """
        self._exception = None

        # We explicitly don't catch around this yield because in the unlikely
        # event that an exception was hit in the block we don't want to swallow
        # it.
        yield
        if self._exception is not None:
            exception, self._exception = self._exception, None
            self.close()
            raise exception

    def _set_ciphers(self):
        """
        Sets up the allowed ciphers. By default this matches the set in
        util.ssl_.DEFAULT_CIPHERS, at least as supported by macOS. This is done
        custom and doesn't allow changing at this time, mostly because parsing
        OpenSSL cipher strings is going to be a freaking nightmare.
        """
        ciphers = (Security.SSLCipherSuite * len(CIPHER_SUITES))(*CIPHER_SUITES)
        result = Security.SSLSetEnabledCiphers(
            self.context, ciphers, len(CIPHER_SUITES)
        )