# © 2014 Mark Harviston <mark.harviston@gmail.com>
# © 2014 Arve Knudsen <arve.knudsen@gmail.com>
# BSD License

"""UNIX specific Quamash functionality."""

import asyncio
import selectors
try:
	from collections import Mapping
except ImportError:
	from collections.abc import Mapping

from . import QtCore, with_logger


EVENT_READ = (1 << 0)
EVENT_WRITE = (1 << 1)


def _fileobj_to_fd(fileobj):
	"""
	Return a file descriptor from a file object.

	Parameters:
	fileobj -- file object or file descriptor

	Returns:
	corresponding file descriptor

	Raises:
	ValueError if the object is invalid

	"""
	if isinstance(fileobj, int):
		fd = fileobj
	else:
		try:
			fd = int(fileobj.fileno())
		except (AttributeError, TypeError, ValueError) as ex:
			raise ValueError("Invalid file object: {!r}".format(fileobj)) from ex
	if fd < 0:
		raise ValueError("Invalid file descriptor: {}".format(fd))
	return fd


class _SelectorMapping(Mapping):

	"""Mapping of file objects to selector keys."""

	def __init__(self, selector):
		self._selector = selector

	def __len__(self):
		return len(self._selector._fd_to_key)

	def __getitem__(self, fileobj):
		try:
			fd = self._selector._fileobj_lookup(fileobj)
			return self._selector._fd_to_key[fd]
		except KeyError:
			raise KeyError("{!r} is not registered".format(fileobj)) from None

	def __iter__(self):
		return iter(self._selector._fd_to_key)


@with_logger
class _Selector(selectors.BaseSelector):
	def __init__(self, parent):
		# this maps file descriptors to keys
		self._fd_to_key = {}
		# read-only mapping returned by get_map()
		self.__map = _SelectorMapping(self)
		self.__read_notifiers = {}
		self.__write_notifiers = {}
		self.__parent = parent

	def select(self, *args, **kwargs):
		"""Implement abstract method even though we don't need it."""
		raise NotImplementedError

	def _fileobj_lookup(self, fileobj):
		"""Return a file descriptor from a file object.

		This wraps _fileobj_to_fd() to do an exhaustive search in case
		the object is invalid but we still have it in our map.  This
		is used by unregister() so we can unregister an object that
		was previously registered even if it is closed.  It is also
		used by _SelectorMapping.
		"""
		try:
			return _fileobj_to_fd(fileobj)
		except ValueError:
			# Do an exhaustive search.
			for key in self._fd_to_key.values():
				if key.fileobj is fileobj:
					return key.fd
			# Raise ValueError after all.
			raise

	def register(self, fileobj, events, data=None):
		if (not events) or (events & ~(EVENT_READ | EVENT_WRITE)):
			raise ValueError("Invalid events: {!r}".format(events))

		key = selectors.SelectorKey(fileobj, self._fileobj_lookup(fileobj), events, data)

		if key.fd in self._fd_to_key:
			raise KeyError("{!r} (FD {}) is already registered".format(fileobj, key.fd))

		self._fd_to_key[key.fd] = key

		if events & EVENT_READ:
			notifier = QtCore.QSocketNotifier(key.fd, QtCore.QSocketNotifier.Read)
			notifier.activated.connect(self.__on_read_activated)
			self.__read_notifiers[key.fd] = notifier
		if events & EVENT_WRITE:
			notifier = QtCore.QSocketNotifier(key.fd, QtCore.QSocketNotifier.Write)
			notifier.activated.connect(self.__on_write_activated)
			self.__write_notifiers[key.fd] = notifier

		return key

	def __on_read_activated(self, fd):
		self._logger.debug('File {} ready to read'.format(fd))
		key = self._key_from_fd(fd)
		if key:
			self.__parent._process_event(key, EVENT_READ & key.events)

	def __on_write_activated(self, fd):
		self._logger.debug('File {} ready to write'.format(fd))
		key = self._key_from_fd(fd)
		if key:
			self.__parent._process_event(key, EVENT_WRITE & key.events)

	def unregister(self, fileobj):
		def drop_notifier(notifiers):
			try:
				notifier = notifiers.pop(key.fd)
			except KeyError:
				pass
			else:
				notifier.activated.disconnect()

		try:
			key = self._fd_to_key.pop(self._fileobj_lookup(fileobj))
		except KeyError:
			raise KeyError("{!r} is not registered".format(fileobj)) from None

		drop_notifier(self.__read_notifiers)
		drop_notifier(self.__write_notifiers)

		return key

	def modify(self, fileobj, events, data=None):
		try:
			key = self._fd_to_key[self._fileobj_lookup(fileobj)]
		except KeyError:
			raise KeyError("{!r} is not registered".format(fileobj)) from None
		if events != key.events:
			self.unregister(fileobj)
			key = self.register(fileobj, events, data)
		elif data != key.data:
			# Use a shortcut to update the data.
			key = key._replace(data=data)
			self._fd_to_key[key.fd] = key
		return key

	def close(self):
		self._logger.debug('Closing')
		self._fd_to_key.clear()
		self.__read_notifiers.clear()
		self.__write_notifiers.clear()

	def get_map(self):
		return self.__map

	def _key_from_fd(self, fd):
		"""
		Return the key associated to a given file descriptor.

		Parameters:
		fd -- file descriptor

		Returns:
		corresponding key, or None if not found

		"""
		try:
			return self._fd_to_key[fd]
		except KeyError:
			return None


class _SelectorEventLoop(asyncio.SelectorEventLoop):
	def __init__(self):
		self._signal_safe_callbacks = []

		selector = _Selector(self)
		asyncio.SelectorEventLoop.__init__(self, selector)

	def _before_run_forever(self):
		pass

	def _after_run_forever(self):
		pass

	def _process_event(self, key, mask):
		"""Selector has delivered us an event."""
		self._logger.debug('Processing event with key {} and mask {}'.format(key, mask))
		fileobj, (reader, writer) = key.fileobj, key.data
		if mask & selectors.EVENT_READ and reader is not None:
			if reader._cancelled:
				self.remove_reader(fileobj)
			else:
				self._logger.debug('Invoking reader callback: {}'.format(reader))
				reader._run()
		if mask & selectors.EVENT_WRITE and writer is not None:
			if writer._cancelled:
				self.remove_writer(fileobj)
			else:
				self._logger.debug('Invoking writer callback: {}'.format(writer))
				writer._run()