"""Abstract Transport class."""

__all__ = (
 'BaseTransport', 'ReadTransport', 'WriteTransport',
 'Transport', 'DatagramTransport', 'SubprocessTransport',
)


class BaseTransport:
 """Base class 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 is_closing(self):
 """Return True if the transport is closing or closed."""
 raise NotImplementedError

 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

 def set_protocol(self, protocol):
 """Set a new protocol."""
 raise NotImplementedError

 def get_protocol(self):
 """Return the current protocol."""
 raise NotImplementedError


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

 def is_reading(self):
 """Return True if the transport is receiving."""
 raise NotImplementedError

 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):
 """Interface 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 an
 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 concatenates the arguments and
 calls write() on the result.
 """
 data = b''.join(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):
 """Interface 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):
 """Interface 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


class _FlowControlMixin(Transport):
 """All the logic for (write) flow control in a mix-in base class.

 The subclass must implement get_write_buffer_size(). It must call
 _maybe_pause_protocol() whenever the write buffer size increases,
 and _maybe_resume_protocol() whenever it decreases. It may also
 override set_write_buffer_limits() (e.g. to specify different
 defaults).

 The subclass constructor must call super().__init__(extra). This
 will call set_write_buffer_limits().

 The user may call set_write_buffer_limits() and
 get_write_buffer_size(), and their protocol's pause_writing() and
 resume_writing() may be called.
 """

 def __init__(self, extra=None, loop=None):
 super().__init__(extra)
 assert loop is not None
 self._loop = loop
 self._protocol_paused = False
 self._set_write_buffer_limits()

 def _maybe_pause_protocol(self):
 size = self.get_write_buffer_size()
 if size <= self._high_water:
 return
 if not self._protocol_paused:
 self._protocol_paused = True
 try:
 self._protocol.pause_writing()
 except Exception as exc:
 self._loop.call_exception_handler({
 'message': 'protocol.pause_writing() failed',
 'exception': exc,
 'transport': self,
 'protocol': self._protocol,
 })

 def _maybe_resume_protocol(self):
 if (self._protocol_paused and
 self.get_write_buffer_size() <= self._low_water):
 self._protocol_paused = False
 try:
 self._protocol.resume_writing()
 except Exception as exc:
 self._loop.call_exception_handler({
 'message': 'protocol.resume_writing() failed',
 'exception': exc,
 'transport': self,
 'protocol': self._protocol,
 })

 def get_write_buffer_limits(self):
 return (self._low_water, self._high_water)

 def _set_write_buffer_limits(self, high=None, low=None):
 if high is None:
 if low is None:
 high = 64 * 1024
 else:
 high = 4 * low
 if low is None:
 low = high // 4

 if not high >= low >= 0:
 raise ValueError(
 f'high ({high!r}) must be >= low ({low!r}) must be >= 0')

 self._high_water = high
 self._low_water = low

 def set_write_buffer_limits(self, high=None, low=None):
 self._set_write_buffer_limits(high=high, low=low)
 self._maybe_pause_protocol()

 def get_write_buffer_size(self):
 raise NotImplementedError