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from abc import abstractmethod
from typing import Any, Callable, Generic, Optional, TypeVar, Union
from reactivex import abc, typing
from reactivex.scheduler import ImmediateScheduler
from .observable import Observable
from .observer import Observer
_T = TypeVar("_T")
class Notification(Generic[_T]):
"""Represents a notification to an observer."""
def __init__(self) -> None:
"""Default constructor used by derived types."""
self.has_value = False
self.value: Optional[_T] = None
self.kind: str = ""
def accept(
self,
on_next: Union[typing.OnNext[_T], abc.ObserverBase[_T]],
on_error: Optional[typing.OnError] = None,
on_completed: Optional[typing.OnCompleted] = None,
) -> None:
"""Invokes the delegate corresponding to the notification or an
observer and returns the produced result.
Examples:
>>> notification.accept(observer)
>>> notification.accept(on_next, on_error, on_completed)
Args:
on_next: Delegate to invoke for an OnNext notification.
on_error: [Optional] Delegate to invoke for an OnError
notification.
on_completed: [Optional] Delegate to invoke for an
OnCompleted notification.
Returns:
Result produced by the observation."""
if isinstance(on_next, abc.ObserverBase):
return self._accept_observer(on_next)
return self._accept(on_next, on_error, on_completed)
@abstractmethod
def _accept(
self,
on_next: typing.OnNext[_T],
on_error: Optional[typing.OnError],
on_completed: Optional[typing.OnCompleted],
) -> None:
raise NotImplementedError
@abstractmethod
def _accept_observer(self, observer: abc.ObserverBase[_T]) -> None:
raise NotImplementedError
def to_observable(
self, scheduler: Optional[abc.SchedulerBase] = None
) -> abc.ObservableBase[_T]:
"""Returns an observable sequence with a single notification,
using the specified scheduler, else the immediate scheduler.
Args:
scheduler: [Optional] Scheduler to send out the
notification calls on.
Returns:
An observable sequence that surfaces the behavior of the
notification upon subscription.
"""
_scheduler = scheduler or ImmediateScheduler.singleton()
def subscribe(
observer: abc.ObserverBase[_T],
scheduler: Optional[abc.SchedulerBase] = None,
) -> abc.DisposableBase:
def action(scheduler: abc.SchedulerBase, state: Any) -> None:
self._accept_observer(observer)
if self.kind == "N":
observer.on_completed()
__scheduler = scheduler or _scheduler
return __scheduler.schedule(action)
return Observable(subscribe)
def equals(self, other: "Notification[_T]") -> bool:
"""Indicates whether this instance and a specified object are
equal."""
other_string = "" if not other else str(other)
return str(self) == other_string
def __eq__(self, other: Any) -> bool:
return self.equals(other)
class OnNext(Notification[_T]):
"""Represents an OnNext notification to an observer."""
def __init__(self, value: _T) -> None:
"""Constructs a notification of a new value."""
super(OnNext, self).__init__()
self.value: _T = value
self.has_value: bool = True
self.kind: str = "N"
def _accept(
self,
on_next: typing.OnNext[_T],
on_error: Optional[typing.OnError] = None,
on_completed: Optional[typing.OnCompleted] = None,
) -> None:
return on_next(self.value)
def _accept_observer(self, observer: abc.ObserverBase[_T]) -> None:
return observer.on_next(self.value)
def __str__(self) -> str:
val: Any = self.value
if isinstance(val, int):
val = float(val)
return "OnNext(%s)" % str(val)
class OnError(Notification[_T]):
"""Represents an OnError notification to an observer."""
def __init__(self, error: Union[Exception, str]) -> None:
"""Constructs a notification of an exception."""
super(OnError, self).__init__()
self.exception: Exception = (
error if isinstance(error, Exception) else Exception(error)
)
self.kind = "E"
def _accept(
self,
on_next: typing.OnNext[_T],
on_error: Optional[typing.OnError],
on_completed: Optional[typing.OnCompleted],
) -> None:
return on_error(self.exception) if on_error else None
def _accept_observer(self, observer: abc.ObserverBase[_T]) -> None:
return observer.on_error(self.exception)
def __str__(self) -> str:
return "OnError(%s)" % str(self.exception)
class OnCompleted(Notification[_T]):
"""Represents an OnCompleted notification to an observer."""
def __init__(self) -> None:
"""Constructs a notification of the end of a sequence."""
super(OnCompleted, self).__init__()
self.kind = "C"
def _accept(
self,
on_next: typing.OnNext[_T],
on_error: Optional[typing.OnError],
on_completed: Optional[typing.OnCompleted],
) -> None:
return on_completed() if on_completed else None
def _accept_observer(self, observer: abc.ObserverBase[_T]) -> None:
return observer.on_completed()
def __str__(self) -> str:
return "OnCompleted()"
def from_notifier(handler: Callable[[Notification[_T]], None]) -> Observer[_T]:
"""Creates an observer from a notification callback.
Args:
handler: Action that handles a notification.
Returns:
The observer object that invokes the specified handler using
a notification corresponding to each message it receives.
"""
def _on_next(value: _T) -> None:
return handler(OnNext(value))
def _on_error(error: Exception) -> None:
return handler(OnError(error))
def _on_completed() -> None:
return handler(OnCompleted())
return Observer(_on_next, _on_error, _on_completed)
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