"""Selectors module.

This module allows high-level and efficient I/O multiplexing, built upon the
`select` module primitives.
"""


from abc import ABCMeta, abstractmethod
from collections import namedtuple
from collections.abc import Mapping
import math
import select
import sys


# generic events, that must be mapped to implementation-specific ones
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):
 raise ValueError("Invalid file object: "
 "{!r}".format(fileobj)) from None
 if fd < 0:
 raise ValueError("Invalid file descriptor: {}".format(fd))
 return fd


SelectorKey = namedtuple('SelectorKey', ['fileobj', 'fd', 'events', 'data'])

SelectorKey.__doc__ = """SelectorKey(fileobj, fd, events, data)

 Object used to associate a file object to its backing
 file descriptor, selected event mask, and attached data.
"""
if sys.version_info >= (3, 5):
 SelectorKey.fileobj.__doc__ = 'File object registered.'
 SelectorKey.fd.__doc__ = 'Underlying file descriptor.'
 SelectorKey.events.__doc__ = 'Events that must be waited for on this file object.'
 SelectorKey.data.__doc__ = ('''Optional opaque data associated to this file object.
 For example, this could be used to store a per-client session ID.''')

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)


class BaseSelector(metaclass=ABCMeta):
 """Selector abstract base class.

 A selector supports registering file objects to be monitored for specific
 I/O events.

 A file object is a file descriptor or any object with a `fileno()` method.
 An arbitrary object can be attached to the file object, which can be used
 for example to store context information, a callback, etc.

 A selector can use various implementations (select(), poll(), epoll()...)
 depending on the platform. The default `Selector` class uses the most
 efficient implementation on the current platform.
 """

 @abstractmethod
 def register(self, fileobj, events, data=None):
 """Register a file object.

 Parameters:
 fileobj -- file object or file descriptor
 events -- events to monitor (bitwise mask of EVENT_READ|EVENT_WRITE)
 data -- attached data

 Returns:
 SelectorKey instance

 Raises:
 ValueError if events is invalid
 KeyError if fileobj is already registered
 OSError if fileobj is closed or otherwise is unacceptable to
 the underlying system call (if a system call is made)

 Note:
 OSError may or may not be raised
 """
 raise NotImplementedError

 @abstractmethod
 def unregister(self, fileobj):
 """Unregister a file object.

 Parameters:
 fileobj -- file object or file descriptor

 Returns:
 SelectorKey instance

 Raises:
 KeyError if fileobj is not registered

 Note:
 If fileobj is registered but has since been closed this does
 *not* raise OSError (even if the wrapped syscall does)
 """
 raise NotImplementedError

 def modify(self, fileobj, events, data=None):
 """Change a registered file object monitored events or attached data.

 Parameters:
 fileobj -- file object or file descriptor
 events -- events to monitor (bitwise mask of EVENT_READ|EVENT_WRITE)
 data -- attached data

 Returns:
 SelectorKey instance

 Raises:
 Anything that unregister() or register() raises
 """
 self.unregister(fileobj)
 return self.register(fileobj, events, data)

 @abstractmethod
 def select(self, timeout=None):
 """Perform the actual selection, until some monitored file objects are
 ready or a timeout expires.

 Parameters:
 timeout -- if timeout > 0, this specifies the maximum wait time, in
 seconds
 if timeout <= 0, the select() call won't block, and will
 report the currently ready file objects
 if timeout is None, select() will block until a monitored
 file object becomes ready

 Returns:
 list of (key, events) for ready file objects
 `events` is a bitwise mask of EVENT_READ|EVENT_WRITE
 """
 raise NotImplementedError

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

 This must be called to make sure that any underlying resource is freed.
 """
 pass

 def get_key(self, fileobj):
 """Return the key associated to a registered file object.

 Returns:
 SelectorKey for this file object
 """
 mapping = self.get_map()
 if mapping is None:
 raise RuntimeError('Selector is closed')
 try:
 return mapping[fileobj]
 except KeyError:
 raise KeyError("{!r} is not registered".format(fileobj)) from None

 @abstractmethod
 def get_map(self):
 """Return a mapping of file objects to selector keys."""
 raise NotImplementedError

 def __enter__(self):
 return self

 def __exit__(self, *args):
 self.close()


class _BaseSelectorImpl(BaseSelector):
 """Base selector implementation."""

 def __init__(self):
 # this maps file descriptors to keys
 self._fd_to_key = {}
 # read-only mapping returned by get_map()
 self._map = _SelectorMapping(self)

 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 = 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
 return key

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

 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 SelectSelector(_BaseSelectorImpl):
 """Select-based selector."""

 def __init__(self):
 super().__init__()
 self._readers = set()
 self._writers = set()

 def register(self, fileobj, events, data=None):
 key = super().register(fileobj, events, data)
 if events & EVENT_READ:
 self._readers.add(key.fd)
 if events & EVENT_WRITE:
 self._writers.add(key.fd)
 return key

 def unregister(self, fileobj):
 key = super().unregister(fileobj)
 self._readers.discard(key.fd)
 self._writers.discard(key.fd)
 return key

 if sys.platform == 'win32':
 def _select(self, r, w, _, timeout=None):
 r, w, x = select.select(r, w, w, timeout)
 return r, w + x, []
 else:
 _select = select.select

 def select(self, timeout=None):
 timeout = None if timeout is None else max(timeout, 0)
 ready = []
 try:
 r, w, _ = self._select(self._readers, self._writers, [], timeout)
 except InterruptedError:
 return ready
 r = set(r)
 w = set(w)
 for fd in r | w:
 events = 0
 if fd in r:
 events |= EVENT_READ
 if fd in w:
 events |= EVENT_WRITE

 key = self._key_from_fd(fd)
 if key:
 ready.append((key, events & key.events))
 return ready


class _PollLikeSelector(_BaseSelectorImpl):
 """Base class shared between poll, epoll and devpoll selectors."""
 _selector_cls = None
 _EVENT_READ = None
 _EVENT_WRITE = None

 def __init__(self):
 super().__init__()
 self._selector = self._selector_cls()

 def register(self, fileobj, events, data=None):
 key = super().register(fileobj, events, data)
 poller_events = 0
 if events & EVENT_READ:
 poller_events |= self._EVENT_READ
 if events & EVENT_WRITE:
 poller_events |= self._EVENT_WRITE
 try:
 self._selector.register(key.fd, poller_events)
 except:
 super().unregister(fileobj)
 raise
 return key

 def unregister(self, fileobj):
 key = super().unregister(fileobj)
 try:
 self._selector.unregister(key.fd)
 except OSError:
 # This can happen if the FD was closed since it
 # was registered.
 pass
 return key

 def modify(self, fileobj, events, data=None):
 try:
 key = self._fd_to_key[self._fileobj_lookup(fileobj)]
 except KeyError:
 raise KeyError(f"{fileobj!r} is not registered") from None

 changed = False
 if events != key.events:
 selector_events = 0
 if events & EVENT_READ:
 selector_events |= self._EVENT_READ
 if events & EVENT_WRITE:
 selector_events |= self._EVENT_WRITE
 try:
 self._selector.modify(key.fd, selector_events)
 except:
 super().unregister(fileobj)
 raise
 changed = True
 if data != key.data:
 changed = True

 if changed:
 key = key._replace(events=events, data=data)
 self._fd_to_key[key.fd] = key
 return key

 def select(self, timeout=None):
 # This is shared between poll() and epoll().
 # epoll() has a different signature and handling of timeout parameter.
 if timeout is None:
 timeout = None
 elif timeout <= 0:
 timeout = 0
 else:
 # poll() has a resolution of 1 millisecond, round away from
 # zero to wait *at least* timeout seconds.
 timeout = math.ceil(timeout * 1e3)
 ready = []
 try:
 fd_event_list = self._selector.poll(timeout)
 except InterruptedError:
 return ready
 for fd, event in fd_event_list:
 events = 0
 if event & ~self._EVENT_READ:
 events |= EVENT_WRITE
 if event & ~self._EVENT_WRITE:
 events |= EVENT_READ

 key = self._key_from_fd(fd)
 if key:
 ready.append((key, events & key.events))
 return ready


if hasattr(select, 'poll'):

 class PollSelector(_PollLikeSelector):
 """Poll-based selector."""
 _selector_cls = select.poll
 _EVENT_READ = select.POLLIN
 _EVENT_WRITE = select.POLLOUT


if hasattr(select, 'epoll'):

 class EpollSelector(_PollLikeSelector):
 """Epoll-based selector."""
 _selector_cls = select.epoll
 _EVENT_READ = select.EPOLLIN
 _EVENT_WRITE = select.EPOLLOUT

 def fileno(self):
 return self._selector.fileno()

 def select(self, timeout=None):
 if timeout is None:
 timeout = -1
 elif timeout <= 0:
 timeout = 0
 else:
 # epoll_wait() has a resolution of 1 millisecond, round away
 # from zero to wait *at least* timeout seconds.
 timeout = math.ceil(timeout * 1e3) * 1e-3

 # epoll_wait() expects `maxevents` to be greater than zero;
 # we want to make sure that `select()` can be called when no
 # FD is registered.
 max_ev = max(len(self._fd_to_key), 1)

 ready = []
 try:
 fd_event_list = self._selector.poll(timeout, max_ev)
 except InterruptedError:
 return ready
 for fd, event in fd_event_list:
 events = 0
 if event & ~select.EPOLLIN:
 events |= EVENT_WRITE
 if event & ~select.EPOLLOUT:
 events |= EVENT_READ

 key = self._key_from_fd(fd)
 if key:
 ready.append((key, events & key.events))
 return ready

 def close(self):
 self._selector.close()
 super().close()


if hasattr(select, 'devpoll'):

 class DevpollSelector(_PollLikeSelector):
 """Solaris /dev/poll selector."""
 _selector_cls = select.devpoll
 _EVENT_READ = select.POLLIN
 _EVENT_WRITE = select.POLLOUT

 def fileno(self):
 return self._selector.fileno()

 def close(self):
 self._selector.close()
 super().close()


if hasattr(select, 'kqueue'):

 class KqueueSelector(_BaseSelectorImpl):
 """Kqueue-based selector."""

 def __init__(self):
 super().__init__()
 self._selector = select.kqueue()

 def fileno(self):
 return self._selector.fileno()

 def register(self, fileobj, events, data=None):
 key = super().register(fileobj, events, data)
 try:
 if events & EVENT_READ:
 kev = select.kevent(key.fd, select.KQ_FILTER_READ,
 select.KQ_EV_ADD)
 self._selector.control([kev], 0, 0)
 if events & EVENT_WRITE:
 kev = select.kevent(key.fd, select.KQ_FILTER_WRITE,
 select.KQ_EV_ADD)
 self._selector.control([kev], 0, 0)
 except:
 super().unregister(fileobj)
 raise
 return key

 def unregister(self, fileobj):
 key = super().unregister(fileobj)
 if key.events & EVENT_READ:
 kev = select.kevent(key.fd, select.KQ_FILTER_READ,
 select.KQ_EV_DELETE)
 try:
 self._selector.control([kev], 0, 0)
 except OSError:
 # This can happen if the FD was closed since it
 # was registered.
 pass
 if key.events & EVENT_WRITE:
 kev = select.kevent(key.fd, select.KQ_FILTER_WRITE,
 select.KQ_EV_DELETE)
 try:
 self._selector.control([kev], 0, 0)
 except OSError:
 # See comment above.
 pass
 return key

 def select(self, timeout=None):
 timeout = None if timeout is None else max(timeout, 0)
 max_ev = len(self._fd_to_key)
 ready = []
 try:
 kev_list = self._selector.control(None, max_ev, timeout)
 except InterruptedError:
 return ready
 for kev in kev_list:
 fd = kev.ident
 flag = kev.filter
 events = 0
 if flag == select.KQ_FILTER_READ:
 events |= EVENT_READ
 if flag == select.KQ_FILTER_WRITE:
 events |= EVENT_WRITE

 key = self._key_from_fd(fd)
 if key:
 ready.append((key, events & key.events))
 return ready

 def close(self):
 self._selector.close()
 super().close()


# Choose the best implementation, roughly:
# epoll|kqueue|devpoll > poll > select.
# select() also can't accept a FD > FD_SETSIZE (usually around 1024)
if 'KqueueSelector' in globals():
 DefaultSelector = KqueueSelector
elif 'EpollSelector' in globals():
 DefaultSelector = EpollSelector
elif 'DevpollSelector' in globals():
 DefaultSelector = DevpollSelector
elif 'PollSelector' in globals():
 DefaultSelector = PollSelector
else:
 DefaultSelector = SelectSelector