python-gpiozero/gpiozero/mixins.py

from __future__ import (
    unicode_literals,
    print_function,
    absolute_import,
    division,
    )
nstr = str
str = type('')

import inspect
import weakref
from functools import wraps
from threading import Event
from collections import deque
try:
    from statistics import median, mean
except ImportError:
    from .compat import median, mean

from .threads import GPIOThread
from .exc import BadEventHandler, DeviceClosed


class ValuesMixin(object):
    """
    Adds a :attr:`values` property to the class which returns an infinite
    generator of readings from the :attr:`value` property.

    .. note::

        Use this mixin *first* in the parent class list.
    """

    @property
    def values(self):
        """
        An infinite iterator of values read from `value`.
        """
        while True:
            try:
                yield self.value
            except DeviceClosed:
                break


class SourceMixin(object):
    """
    Adds a :attr:`source` property to the class which, given an iterable,
    sets :attr:`value` to each member of that iterable until it is exhausted.

    .. note::

        Use this mixin *first* in the parent class list.
    """

    def __init__(self, *args, **kwargs):
        self._source = None
        self._source_thread = None
        self._source_delay = 0.01
        super(SourceMixin, self).__init__(*args, **kwargs)

    def close(self):
        try:
            super(SourceMixin, self).close()
        except AttributeError:
            pass
        self.source = None

    def _copy_values(self, source):
        for v in source:
            self.value = v
            if self._source_thread.stopping.wait(self._source_delay):
                break

    @property
    def source_delay(self):
        """
        The delay (measured in seconds) in the loop used to read values from
        :attr:`source`. Defaults to 0.01 seconds which is generally sufficient
        to keep CPU usage to a minimum while providing adequate responsiveness.
        """
        return self._source_delay

    @source_delay.setter
    def source_delay(self, value):
        if value < 0:
            raise GPIOBadSourceDelay('source_delay must be 0 or greater')
        self._source_delay = float(value)

    @property
    def source(self):
        """
        The iterable to use as a source of values for :attr:`value`.
        """
        return self._source

    @source.setter
    def source(self, value):
        if self._source_thread is not None:
            self._source_thread.stop()
            self._source_thread = None
        self._source = value
        if value is not None:
            self._source_thread = GPIOThread(target=self._copy_values, args=(value,))
            self._source_thread.start()


class SharedMixin(object):
    """
    This mixin marks a class as "shared". In this case, the meta-class
    (GPIOMeta) will use :meth:`_shared_key` to convert the constructor
    arguments to an immutable key, and will check whether any existing
    instances match that key. If they do, they will be returned by the
    constructor instead of a new instance. An internal reference counter is
    used to determine how many times an instance has been "constructed" in this
    way.

    When :meth:`close` is called, an internal reference counter will be
    decremented and the instance will only close when it reaches zero.
    """
    _INSTANCES = {}

    def __del__(self):
        self._refs = 0
        super(SharedMixin, self).__del__()

    @classmethod
    def _shared_key(cls, *args, **kwargs):
        """
        Given the constructor arguments, returns an immutable key representing
        the instance. The default simply assumes all positional arguments are
        immutable.
        """
        return args


class EventsMixin(object):
    """
    Adds edge-detected :meth:`when_activated` and :meth:`when_deactivated`
    events to a device based on changes to the :attr:`~Device.is_active`
    property common to all devices. Also adds :meth:`wait_for_active` and
    :meth:`wait_for_inactive` methods for level-waiting.

    .. note::

        Note that this mixin provides no means of actually firing its events;
        call :meth:`_fire_events` in sub-classes when device state changes to
        trigger the events. This should also be called once at the end of
        initialization to set initial states.
    """
    def __init__(self, *args, **kwargs):
        super(EventsMixin, self).__init__(*args, **kwargs)
        self._active_event = Event()
        self._inactive_event = Event()
        self._when_activated = None
        self._when_deactivated = None
        self._last_state = None

    def wait_for_active(self, timeout=None):
        """
        Pause the script until the device is activated, or the timeout is
        reached.

        :param float timeout:
            Number of seconds to wait before proceeding. If this is ``None``
            (the default), then wait indefinitely until the device is active.
        """
        return self._active_event.wait(timeout)

    def wait_for_inactive(self, timeout=None):
        """
        Pause the script until the device is deactivated, or the timeout is
        reached.

        :param float timeout:
            Number of seconds to wait before proceeding. If this is ``None``
            (the default), then wait indefinitely until the device is inactive.
        """
        return self._inactive_event.wait(timeout)

    @property
    def when_activated(self):
        """
        The function to run when the device changes state from inactive to
        active.

        This can be set to a function which accepts no (mandatory) parameters,
        or a Python function which accepts a single mandatory parameter (with
        as many optional parameters as you like). If the function accepts a
        single mandatory parameter, the device that activated will be passed
        as that parameter.

        Set this property to ``None`` (the default) to disable the event.
        """
        return self._when_activated

    @when_activated.setter
    def when_activated(self, value):
        self._when_activated = self._wrap_callback(value)

    @property
    def when_deactivated(self):
        """
        The function to run when the device changes state from active to
        inactive.

        This can be set to a function which accepts no (mandatory) parameters,
        or a Python function which accepts a single mandatory parameter (with
        as many optional parameters as you like). If the function accepts a
        single mandatory parameter, the device that deactivated will be
        passed as that parameter.

        Set this property to ``None`` (the default) to disable the event.
        """
        return self._when_deactivated

    @when_deactivated.setter
    def when_deactivated(self, value):
        self._when_deactivated = self._wrap_callback(value)

    def _wrap_callback(self, fn):
        if fn is None:
            return None
        elif not callable(fn):
            raise BadEventHandler('value must be None or a callable')
        elif inspect.isbuiltin(fn):
            # We can't introspect the prototype of builtins. In this case we
            # assume that the builtin has no (mandatory) parameters; this is
            # the most reasonable assumption on the basis that pre-existing
            # builtins have no knowledge of gpiozero, and the sole parameter
            # we would pass is a gpiozero object
            return fn
        else:
            # Try binding ourselves to the argspec of the provided callable.
            # If this works, assume the function is capable of accepting no
            # parameters
            try:
                inspect.getcallargs(fn)
                return fn
            except TypeError:
                try:
                    # If the above fails, try binding with a single parameter
                    # (ourselves). If this works, wrap the specified callback
                    inspect.getcallargs(fn, self)
                    @wraps(fn)
                    def wrapper():
                        return fn(self)
                    return wrapper
                except TypeError:
                    raise BadEventHandler(
                        'value must be a callable which accepts up to one '
                        'mandatory parameter')

    def _fire_events(self):
        old_state = self._last_state
        new_state = self._last_state = self.is_active
        if old_state is None:
            # Initial "indeterminate" state; set events but don't fire
            # callbacks as there's not necessarily an edge
            if new_state:
                self._active_event.set()
            else:
                self._inactive_event.set()
        else:
            if not old_state and new_state:
                self._inactive_event.clear()
                self._active_event.set()
                if self.when_activated:
                    self.when_activated()
            elif old_state and not new_state:
                self._active_event.clear()
                self._inactive_event.set()
                if self.when_deactivated:
                    self.when_deactivated()


class GPIOQueue(GPIOThread):
    """
    Extends :class:`GPIOThread`. Provides a background thread that monitors a
    device's values and provides a running *average* (defaults to median) of
    those values. If the *parent* device includes the :class:`EventsMixin` in
    its ancestry, the thread automatically calls
    :meth:`~EventsMixin._fire_events`.
    """
    def __init__(
            self, parent, queue_len=5, sample_wait=0.0, partial=False,
            average=median):
        assert callable(average)
        super(GPIOQueue, self).__init__(target=self.fill)
        if queue_len < 1:
            raise GPIOBadQueueLen('queue_len must be at least one')
        if sample_wait < 0:
            raise GPIOBadSampleWait('sample_wait must be 0 or greater')
        self.queue = deque(maxlen=queue_len)
        self.partial = partial
        self.sample_wait = sample_wait
        self.full = Event()
        self.parent = weakref.proxy(parent)
        self.average = average

    @property
    def value(self):
        if not self.partial:
            self.full.wait()
        try:
            return self.average(self.queue)
        except ZeroDivisionError:
            # No data == inactive value
            return 0.0

    def fill(self):
        try:
            while (not self.stopping.wait(self.sample_wait) and
                    len(self.queue) < self.queue.maxlen):
                self.queue.append(self.parent._read())
                if self.partial and isinstance(self.parent, EventsMixin):
                    self.parent._fire_events()
            self.full.set()
            while not self.stopping.wait(self.sample_wait):
                self.queue.append(self.parent._read())
                if isinstance(self.parent, EventsMixin):
                    self.parent._fire_events()
        except ReferenceError:
            # Parent is dead; time to die!
            pass