#
# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements. See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership. The ASF licenses this file
# to you 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.
#

from __future__ import absolute_import
import logging
import socket
import struct

from .transport.TTransport import TTransportException, TTransportBase, TMemoryBuffer

from io import BytesIO
from collections import deque
from contextlib import contextmanager
from tornado import gen, iostream, ioloop, tcpserver, concurrent

__all__ = ['TTornadoServer', 'TTornadoStreamTransport']

logger = logging.getLogger(__name__)


class _Lock(object):
    def __init__(self):
        self._waiters = deque()

    def acquired(self):
        return len(self._waiters) > 0

    @gen.coroutine
    def acquire(self):
        blocker = self._waiters[-1] if self.acquired() else None
        future = concurrent.Future()
        self._waiters.append(future)
        if blocker:
            yield blocker

        raise gen.Return(self._lock_context())

    def release(self):
        assert self.acquired(), 'Lock not aquired'
        future = self._waiters.popleft()
        future.set_result(None)

    @contextmanager
    def _lock_context(self):
        try:
            yield
        finally:
            self.release()


class TTornadoStreamTransport(TTransportBase):
    """a framed, buffered transport over a Tornado stream"""
    def __init__(self, host, port, stream=None, io_loop=None):
        self.host = host
        self.port = port
        self.io_loop = io_loop or ioloop.IOLoop.current()
        self.__wbuf = BytesIO()
        self._read_lock = _Lock()

        # servers provide a ready-to-go stream
        self.stream = stream

    def with_timeout(self, timeout, future):
        return gen.with_timeout(timeout, future, self.io_loop)

    @gen.coroutine
    def open(self, timeout=None):
        logger.debug('socket connecting')
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)
        self.stream = iostream.IOStream(sock)

        try:
            connect = self.stream.connect((self.host, self.port))
            if timeout is not None:
                yield self.with_timeout(timeout, connect)
            else:
                yield connect
        except (socket.error, IOError, ioloop.TimeoutError) as e:
            message = 'could not connect to {}:{} ({})'.format(self.host, self.port, e)
            raise TTransportException(
                type=TTransportException.NOT_OPEN,
                message=message)

        raise gen.Return(self)

    def set_close_callback(self, callback):
        """
        Should be called only after open() returns
        """
        self.stream.set_close_callback(callback)

    def close(self):
        # don't raise if we intend to close
        self.stream.set_close_callback(None)
        self.stream.close()

    def read(self, _):
        # The generated code for Tornado shouldn't do individual reads -- only
        # frames at a time
        assert False, "you're doing it wrong"

    @contextmanager
    def io_exception_context(self):
        try:
            yield
        except (socket.error, IOError) as e:
            raise TTransportException(
                type=TTransportException.END_OF_FILE,
                message=str(e))
        except iostream.StreamBufferFullError as e:
            raise TTransportException(
                type=TTransportException.UNKNOWN,
                message=str(e))

    @gen.coroutine
    def readFrame(self):
        # IOStream processes reads one at a time
        with (yield self._read_lock.acquire()):
            with self.io_exception_context():
                frame_header = yield self.stream.read_bytes(4)
                if len(frame_header) == 0:
                    raise iostream.StreamClosedError('Read zero bytes from stream')
                frame_length, = struct.unpack('!i', frame_header)
                frame = yield self.stream.read_bytes(frame_length)
                raise gen.Return(frame)

    def write(self, buf):
        self.__wbuf.write(buf)

    def flush(self):
        frame = self.__wbuf.getvalue()
        # reset wbuf before write/flush to preserve state on underlying failure
        frame_length = struct.pack('!i', len(frame))
        self.__wbuf = BytesIO()
        with self.io_exception_context():
            return self.stream.write(frame_length + frame)


class TTornadoServer(tcpserver.TCPServer):
    def __init__(self, processor, iprot_factory, oprot_factory=None,
                 *args, **kwargs):
        super(TTornadoServer, self).__init__(*args, **kwargs)

        self._processor = processor
        self._iprot_factory = iprot_factory
        self._oprot_factory = (oprot_factory if oprot_factory is not None
                               else iprot_factory)

    @gen.coroutine
    def handle_stream(self, stream, address):
        host, port = address[:2]
        trans = TTornadoStreamTransport(host=host, port=port, stream=stream,
                                        io_loop=self.io_loop)
        oprot = self._oprot_factory.getProtocol(trans)

        try:
            while not trans.stream.closed():
                try:
                    frame = yield trans.readFrame()
                except TTransportException as e:
                    if e.type == TTransportException.END_OF_FILE:
                        break
                    else:
                        raise
                tr = TMemoryBuffer(frame)
                iprot = self._iprot_factory.getProtocol(tr)
                yield self._processor.process(iprot, oprot)
        except Exception:
            logger.exception('thrift exception in handle_stream')
            trans.close()

        logger.info('client disconnected %s:%d', host, port)