import errno
import logging
import socket
import struct
import sys
from tornado import gen
import weakref

try:
    import ssl
except ImportError:
    ssl = None

import dask
from tornado import netutil
from tornado.iostream import StreamClosedError
from tornado.tcpclient import TCPClient
from tornado.tcpserver import TCPServer

from ..system import MEMORY_LIMIT
from ..threadpoolexecutor import ThreadPoolExecutor
from ..utils import ensure_ip, get_ip, get_ipv6, nbytes, parse_timedelta, shutting_down

from .registry import Backend, backends
from .addressing import parse_host_port, unparse_host_port
from .core import Comm, Connector, Listener, CommClosedError, FatalCommClosedError
from .utils import to_frames, from_frames, get_tcp_server_address, ensure_concrete_host


logger = logging.getLogger(__name__)


MAX_BUFFER_SIZE = MEMORY_LIMIT / 2


def set_tcp_timeout(comm):
    """
    Set kernel-level TCP timeout on the stream.
    """
    if comm.closed():
        return

    timeout = dask.config.get("distributed.comm.timeouts.tcp")
    timeout = int(parse_timedelta(timeout, default="seconds"))

    sock = comm.socket

    # Default (unsettable) value on Windows
    # https://msdn.microsoft.com/en-us/library/windows/desktop/dd877220(v=vs.85).aspx
    nprobes = 10
    assert timeout >= nprobes + 1, "Timeout too low"

    idle = max(2, timeout // 4)
    interval = max(1, (timeout - idle) // nprobes)
    idle = timeout - interval * nprobes
    assert idle > 0

    try:
        if sys.platform.startswith("win"):
            logger.debug("Setting TCP keepalive: idle=%d, interval=%d", idle, interval)
            sock.ioctl(socket.SIO_KEEPALIVE_VALS, (1, idle * 1000, interval * 1000))
        else:
            sock.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
            try:
                TCP_KEEPIDLE = socket.TCP_KEEPIDLE
                TCP_KEEPINTVL = socket.TCP_KEEPINTVL
                TCP_KEEPCNT = socket.TCP_KEEPCNT
            except AttributeError:
                if sys.platform == "darwin":
                    TCP_KEEPIDLE = 0x10  # (named "TCP_KEEPALIVE" in C)
                    TCP_KEEPINTVL = 0x101
                    TCP_KEEPCNT = 0x102
                else:
                    TCP_KEEPIDLE = None

            if TCP_KEEPIDLE is not None:
                logger.debug(
                    "Setting TCP keepalive: nprobes=%d, idle=%d, interval=%d",
                    nprobes,
                    idle,
                    interval,
                )
                sock.setsockopt(socket.SOL_TCP, TCP_KEEPCNT, nprobes)
                sock.setsockopt(socket.SOL_TCP, TCP_KEEPIDLE, idle)
                sock.setsockopt(socket.SOL_TCP, TCP_KEEPINTVL, interval)

        if sys.platform.startswith("linux"):
            logger.debug("Setting TCP user timeout: %d ms", timeout * 1000)
            TCP_USER_TIMEOUT = 18  # since Linux 2.6.37
            sock.setsockopt(socket.SOL_TCP, TCP_USER_TIMEOUT, timeout * 1000)
    except EnvironmentError as e:
        logger.warning("Could not set timeout on TCP stream: %s", e)


def get_stream_address(comm):
    """
    Get a stream's local address.
    """
    if comm.closed():
        return "<closed>"

    try:
        return unparse_host_port(*comm.socket.getsockname()[:2])
    except EnvironmentError:
        # Probably EBADF
        return "<closed>"


def convert_stream_closed_error(obj, exc):
    """
    Re-raise StreamClosedError as CommClosedError.
    """
    if exc.real_error is not None:
        # The stream was closed because of an underlying OS error
        exc = exc.real_error
        if ssl and isinstance(exc, ssl.SSLError):
            if "UNKNOWN_CA" in exc.reason:
                raise FatalCommClosedError(
                    "in %s: %s: %s" % (obj, exc.__class__.__name__, exc)
                )
        raise CommClosedError("in %s: %s: %s" % (obj, exc.__class__.__name__, exc))
    else:
        raise CommClosedError("in %s: %s" % (obj, exc))


def _do_nothing():
    pass


class TCP(Comm):
    """
    An established communication based on an underlying Tornado IOStream.
    """

    def __init__(self, stream, local_addr, peer_addr, deserialize=True):
        Comm.__init__(self)
        self._local_addr = local_addr
        self._peer_addr = peer_addr
        self.stream = stream
        self.deserialize = deserialize
        self._finalizer = weakref.finalize(self, self._get_finalizer())
        self._finalizer.atexit = False
        self._extra = {}

        stream.set_nodelay(True)
        set_tcp_timeout(stream)
        # set a close callback, to make `self.stream.closed()` more reliable.
        # Background: if `stream` is unused (e.g. because it's in `ConnectionPool.available`),
        # the underlying fd is not watched for changes. In this case, even if the
        # connection is actively closed by the remote end, `self.closed()` would still return `False`.
        # Registering a closed callback will make tornado register the underlying fd
        # for changes, and this would be reflected in `self.closed()` even without reading/writing.
        #
        # Use a global method (instead of a lambda) to avoid creating a reference
        # to the local scope.
        stream.set_close_callback(_do_nothing)
        self._read_extra()

    def _read_extra(self):
        pass

    def _get_finalizer(self):
        def finalize(stream=self.stream, r=repr(self)):
            if not stream.closed():
                logger.warning("Closing dangling stream in %s" % (r,))
                stream.close()

        return finalize

    @property
    def local_address(self):
        return self._local_addr

    @property
    def peer_address(self):
        return self._peer_addr

    async def read(self, deserializers=None):
        stream = self.stream
        if stream is None:
            raise CommClosedError

        try:
            n_frames = await stream.read_bytes(8)
            n_frames = struct.unpack("Q", n_frames)[0]
            lengths = await stream.read_bytes(8 * n_frames)
            lengths = struct.unpack("Q" * n_frames, lengths)

            frames = []
            for length in lengths:
                frame = bytearray(length)
                if length:
                    n = await stream.read_into(frame)
                    assert n == length, (n, length)
                frames.append(frame)
        except StreamClosedError as e:
            self.stream = None
            if not shutting_down():
                convert_stream_closed_error(self, e)
        else:
            try:
                msg = await from_frames(
                    frames,
                    deserialize=self.deserialize,
                    deserializers=deserializers,
                    allow_offload=self.allow_offload,
                )
            except EOFError:
                # Frames possibly garbled or truncated by communication error
                self.abort()
                raise CommClosedError("aborted stream on truncated data")
            return msg

    async def write(self, msg, serializers=None, on_error="message"):
        stream = self.stream
        bytes_since_last_yield = 0
        if stream is None:
            raise CommClosedError

        frames = await to_frames(
            msg,
            allow_offload=self.allow_offload,
            serializers=serializers,
            on_error=on_error,
            context={"sender": self._local_addr, "recipient": self._peer_addr},
        )

        try:
            lengths = [nbytes(frame) for frame in frames]
            length_bytes = [struct.pack("Q", len(frames))] + [
                struct.pack("Q", x) for x in lengths
            ]
            if sum(lengths) < 2 ** 17:  # 128kiB
                b = b"".join(length_bytes + frames)  # small enough, send in one go
                stream.write(b)
            else:
                stream.write(b"".join(length_bytes))  # avoid large memcpy, send in many

                for frame, frame_bytes in zip(frames, lengths):
                    # Can't wait for the write() Future as it may be lost
                    # ("If write is called again before that Future has resolved,
                    #   the previous future will be orphaned and will never resolve")
                    future = stream.write(frame)
                    bytes_since_last_yield += frame_bytes
                    if bytes_since_last_yield > 32e6:
                        await future
                        bytes_since_last_yield = 0
        except StreamClosedError as e:
            stream = None
            convert_stream_closed_error(self, e)
        except TypeError as e:
            if stream._write_buffer is None:
                logger.info("tried to write message %s on closed stream", msg)
            else:
                raise

        return sum(lengths)

    @gen.coroutine
    def close(self):
        # We use gen.coroutine here rather than async def to avoid errors like
        # Task was destroyed but it is pending!
        # Triggered by distributed.deploy.tests.test_local::test_silent_startup
        stream, self.stream = self.stream, None
        if stream is not None and not stream.closed():
            try:
                # Flush the stream's write buffer by waiting for a last write.
                if stream.writing():
                    yield stream.write(b"")
                stream.socket.shutdown(socket.SHUT_RDWR)
            except EnvironmentError:
                pass
            finally:
                self._finalizer.detach()
                stream.close()

    def abort(self):
        stream, self.stream = self.stream, None
        if stream is not None and not stream.closed():
            self._finalizer.detach()
            stream.close()

    def closed(self):
        return self.stream is None or self.stream.closed()

    @property
    def extra_info(self):
        return self._extra


class TLS(TCP):
    """
    A TLS-specific version of TCP.
    """

    def _read_extra(self):
        TCP._read_extra(self)
        sock = self.stream.socket
        if sock is not None:
            self._extra.update(peercert=sock.getpeercert(), cipher=sock.cipher())
            cipher, proto, bits = self._extra["cipher"]
            logger.debug(
                "TLS connection with %r: protocol=%s, cipher=%s, bits=%d",
                self._peer_addr,
                proto,
                cipher,
                bits,
            )


def _expect_tls_context(connection_args):
    ctx = connection_args.get("ssl_context")
    if not isinstance(ctx, ssl.SSLContext):
        raise TypeError(
            "TLS expects a `ssl_context` argument of type "
            "ssl.SSLContext (perhaps check your TLS configuration?)"
            "  Instead got %s" % str(ctx)
        )
    return ctx


class RequireEncryptionMixin:
    def _check_encryption(self, address, connection_args):
        if not self.encrypted and connection_args.get("require_encryption"):
            # XXX Should we have a dedicated SecurityError class?
            raise RuntimeError(
                "encryption required by Dask configuration, "
                "refusing communication from/to %r" % (self.prefix + address,)
            )


class BaseTCPConnector(Connector, RequireEncryptionMixin):
    _executor = ThreadPoolExecutor(2, thread_name_prefix="TCP-Executor")
    _resolver = netutil.ExecutorResolver(close_executor=False, executor=_executor)
    client = TCPClient(resolver=_resolver)

    async def connect(self, address, deserialize=True, **connection_args):
        self._check_encryption(address, connection_args)
        ip, port = parse_host_port(address)
        kwargs = self._get_connect_args(**connection_args)

        try:
            stream = await self.client.connect(
                ip, port, max_buffer_size=MAX_BUFFER_SIZE, **kwargs
            )

            # Under certain circumstances tornado will have a closed connnection with an error and not raise
            # a StreamClosedError.
            #
            # This occurs with tornado 5.x and openssl 1.1+
            if stream.closed() and stream.error:
                raise StreamClosedError(stream.error)

        except StreamClosedError as e:
            # The socket connect() call failed
            convert_stream_closed_error(self, e)

        local_address = self.prefix + get_stream_address(stream)
        return self.comm_class(
            stream, local_address, self.prefix + address, deserialize
        )


class TCPConnector(BaseTCPConnector):
    prefix = "tcp://"
    comm_class = TCP
    encrypted = False

    def _get_connect_args(self, **connection_args):
        return {}


class TLSConnector(BaseTCPConnector):
    prefix = "tls://"
    comm_class = TLS
    encrypted = True

    def _get_connect_args(self, **connection_args):
        ctx = _expect_tls_context(connection_args)
        return {"ssl_options": ctx}


class BaseTCPListener(Listener, RequireEncryptionMixin):
    def __init__(
        self,
        address,
        comm_handler,
        deserialize=True,
        allow_offload=True,
        default_port=0,
        **connection_args
    ):
        self._check_encryption(address, connection_args)
        self.ip, self.port = parse_host_port(address, default_port)
        self.comm_handler = comm_handler
        self.deserialize = deserialize
        self.allow_offload = allow_offload
        self.server_args = self._get_server_args(**connection_args)
        self.tcp_server = None
        self.bound_address = None

    async def start(self):
        self.tcp_server = TCPServer(max_buffer_size=MAX_BUFFER_SIZE, **self.server_args)
        self.tcp_server.handle_stream = self._handle_stream
        backlog = int(dask.config.get("distributed.comm.socket-backlog"))
        for i in range(5):
            try:
                # When shuffling data between workers, there can
                # really be O(cluster size) connection requests
                # on a single worker socket, make sure the backlog
                # is large enough not to lose any.
                sockets = netutil.bind_sockets(
                    self.port, address=self.ip, backlog=backlog
                )
            except EnvironmentError as e:
                # EADDRINUSE can happen sporadically when trying to bind
                # to an ephemeral port
                if self.port != 0 or e.errno != errno.EADDRINUSE:
                    raise
                exc = e
            else:
                self.tcp_server.add_sockets(sockets)
                break
        else:
            raise exc
        self.get_host_port()  # trigger assignment to self.bound_address

    def stop(self):
        tcp_server, self.tcp_server = self.tcp_server, None
        if tcp_server is not None:
            tcp_server.stop()

    def _check_started(self):
        if self.tcp_server is None:
            raise ValueError("invalid operation on non-started TCPListener")

    async def _handle_stream(self, stream, address):
        address = self.prefix + unparse_host_port(*address[:2])
        stream = await self._prepare_stream(stream, address)
        if stream is None:
            # Preparation failed
            return
        logger.debug("Incoming connection from %r to %r", address, self.contact_address)
        local_address = self.prefix + get_stream_address(stream)
        comm = self.comm_class(stream, local_address, address, self.deserialize)
        comm.allow_offload = self.allow_offload
        await self.comm_handler(comm)

    def get_host_port(self):
        """
        The listening address as a (host, port) tuple.
        """
        self._check_started()

        if self.bound_address is None:
            self.bound_address = get_tcp_server_address(self.tcp_server)
        # IPv6 getsockname() can return more a 4-len tuple
        return self.bound_address[:2]

    @property
    def listen_address(self):
        """
        The listening address as a string.
        """
        return self.prefix + unparse_host_port(*self.get_host_port())

    @property
    def contact_address(self):
        """
        The contact address as a string.
        """
        host, port = self.get_host_port()
        host = ensure_concrete_host(host)
        return self.prefix + unparse_host_port(host, port)


class TCPListener(BaseTCPListener):
    prefix = "tcp://"
    comm_class = TCP
    encrypted = False

    def _get_server_args(self, **connection_args):
        return {}

    async def _prepare_stream(self, stream, address):
        return stream


class TLSListener(BaseTCPListener):
    prefix = "tls://"
    comm_class = TLS
    encrypted = True

    def _get_server_args(self, **connection_args):
        ctx = _expect_tls_context(connection_args)
        return {"ssl_options": ctx}

    async def _prepare_stream(self, stream, address):
        try:
            await stream.wait_for_handshake()
        except EnvironmentError as e:
            # The handshake went wrong, log and ignore
            logger.warning(
                "Listener on %r: TLS handshake failed with remote %r: %s",
                self.listen_address,
                address,
                getattr(e, "real_error", None) or e,
            )
        else:
            return stream


class BaseTCPBackend(Backend):

    # I/O

    def get_connector(self):
        return self._connector_class()

    def get_listener(self, loc, handle_comm, deserialize, **connection_args):
        return self._listener_class(loc, handle_comm, deserialize, **connection_args)

    # Address handling

    def get_address_host(self, loc):
        return parse_host_port(loc)[0]

    def get_address_host_port(self, loc):
        return parse_host_port(loc)

    def resolve_address(self, loc):
        host, port = parse_host_port(loc)
        return unparse_host_port(ensure_ip(host), port)

    def get_local_address_for(self, loc):
        host, port = parse_host_port(loc)
        host = ensure_ip(host)
        if ":" in host:
            local_host = get_ipv6(host)
        else:
            local_host = get_ip(host)
        return unparse_host_port(local_host, None)


class TCPBackend(BaseTCPBackend):
    _connector_class = TCPConnector
    _listener_class = TCPListener


class TLSBackend(BaseTCPBackend):
    _connector_class = TLSConnector
    _listener_class = TLSListener


backends["tcp"] = TCPBackend()
backends["tls"] = TLSBackend()
