"""Abstract Transport class."""

__all__ = ['ReadTransport', 'WriteTransport', 'Transport']


class BaseTransport:
    """Base ABC for transports."""

    def __init__(self, extra=None):
        if extra is None:
            extra = {}
        self._extra = extra

    def get_extra_info(self, name, default=None):
        """Get optional transport information."""
        return self._extra.get(name, default)

    def close(self):
        """Close the transport.

        Buffered data will be flushed asynchronously.  No more data
        will be received.  After all buffered data is flushed, the
        protocol's connection_lost() method will (eventually) called
        with None as its argument.
        """
        raise NotImplementedError


class ReadTransport(BaseTransport):
    """ABC for read-only transports."""

    def pause_reading(self):
        """Pause the receiving end.

        No data will be passed to the protocol's data_received()
        method until resume_reading() is called.
        """
        raise NotImplementedError

    def resume_reading(self):
        """Resume the receiving end.

        Data received will once again be passed to the protocol's
        data_received() method.
        """
        raise NotImplementedError


class WriteTransport(BaseTransport):
    """ABC for write-only transports."""

    def set_write_buffer_limits(self, high=None, low=None):
        """Set the high- and low-water limits for write flow control.

        These two values control when to call the protocol's
        pause_writing() and resume_writing() methods.  If specified,
        the low-water limit must be less than or equal to the
        high-water limit.  Neither value can be negative.

        The defaults are implementation-specific.  If only the
        high-water limit is given, the low-water limit defaults to a
        implementation-specific value less than or equal to the
        high-water limit.  Setting high to zero forces low to zero as
        well, and causes pause_writing() to be called whenever the
        buffer becomes non-empty.  Setting low to zero causes
        resume_writing() to be called only once the buffer is empty.
        Use of zero for either limit is generally sub-optimal as it
        reduces opportunities for doing I/O and computation
        concurrently.
        """
        raise NotImplementedError

    def get_write_buffer_size(self):
        """Return the current size of the write buffer."""
        raise NotImplementedError

    def write(self, data):
        """Write some data bytes to the transport.

        This does not block; it buffers the data and arranges for it
        to be sent out asynchronously.
        """
        raise NotImplementedError

    def writelines(self, list_of_data):
        """Write a list (or any iterable) of data bytes to the transport.

        The default implementation just calls write() for each item in
        the list/iterable.
        """
        for data in list_of_data:
            self.write(data)

    def write_eof(self):
        """Close the write end after flushing buffered data.

        (This is like typing ^D into a UNIX program reading from stdin.)

        Data may still be received.
        """
        raise NotImplementedError

    def can_write_eof(self):
        """Return True if this transport supports write_eof(), False if not."""
        raise NotImplementedError

    def abort(self):
        """Close the transport immediately.

        Buffered data will be lost.  No more data will be received.
        The protocol's connection_lost() method will (eventually) be
        called with None as its argument.
        """
        raise NotImplementedError


class Transport(ReadTransport, WriteTransport):
    """ABC representing a bidirectional transport.

    There may be several implementations, but typically, the user does
    not implement new transports; rather, the platform provides some
    useful transports that are implemented using the platform's best
    practices.

    The user never instantiates a transport directly; they call a
    utility function, passing it a protocol factory and other
    information necessary to create the transport and protocol.  (E.g.
    EventLoop.create_connection() or EventLoop.create_server().)

    The utility function will asynchronously create a transport and a
    protocol and hook them up by calling the protocol's
    connection_made() method, passing it the transport.

    The implementation here raises NotImplemented for every method
    except writelines(), which calls write() in a loop.
    """


class DatagramTransport(BaseTransport):
    """ABC for datagram (UDP) transports."""

    def sendto(self, data, addr=None):
        """Send data to the transport.

        This does not block; it buffers the data and arranges for it
        to be sent out asynchronously.
        addr is target socket address.
        If addr is None use target address pointed on transport creation.
        """
        raise NotImplementedError

    def abort(self):
        """Close the transport immediately.

        Buffered data will be lost.  No more data will be received.
        The protocol's connection_lost() method will (eventually) be
        called with None as its argument.
        """
        raise NotImplementedError


class SubprocessTransport(BaseTransport):

    def get_pid(self):
        """Get subprocess id."""
        raise NotImplementedError

    def get_returncode(self):
        """Get subprocess returncode.

        See also
        http://docs.python.org/3/library/subprocess#subprocess.Popen.returncode
        """
        raise NotImplementedError

    def get_pipe_transport(self, fd):
        """Get transport for pipe with number fd."""
        raise NotImplementedError

    def send_signal(self, signal):
        """Send signal to subprocess.

        See also:
        docs.python.org/3/library/subprocess#subprocess.Popen.send_signal
        """
        raise NotImplementedError

    def terminate(self):
        """Stop the subprocess.

        Alias for close() method.

        On Posix OSs the method sends SIGTERM to the subprocess.
        On Windows the Win32 API function TerminateProcess()
         is called to stop the subprocess.

        See also:
        http://docs.python.org/3/library/subprocess#subprocess.Popen.terminate
        """
        raise NotImplementedError

    def kill(self):
        """Kill the subprocess.

        On Posix OSs the function sends SIGKILL to the subprocess.
        On Windows kill() is an alias for terminate().

        See also:
        http://docs.python.org/3/library/subprocess#subprocess.Popen.kill
        """
        raise NotImplementedError
