Signal+Extensions.swift

//
//  Signal+Extensions.swift
//  Khan Academy
//
//  Created by Nacho Soto on 10/1/15.
//  Copyright © 2015 Khan Academy. All rights reserved.
//

import ReactiveCocoa

extension SignalProducerType {
	public final func takeUntilObjectDeallocates(object: NSObject) -> SignalProducer<Self.Value, Self.Error> {
		return self.lift { $0.takeUntilObjectDeallocates(object) }
	}

	#if os(iOS)
	public final func takeUntilViewControllerDisappears(viewController: UIViewController) -> SignalProducer<Self.Value, Self.Error> {
		return self.lift { $0.takeUntilViewControllerDisappears(viewController) }
	}
	#endif

	/// Converts values into `Optional.Some`.
	public func wrapValuesInOptional() -> SignalProducer<Optional<Self.Value>, Self.Error> {
		return self.lift { $0.wrapValuesInOptional() }
	}

	/// Ignores errors emitted by this producer after logging them.
	///
	/// IMPORTANT: this operators should not be used lightly.
	/// Consider using `flatMapError` to implement better error handling.
	public func logAndIgnoreErrors(errorMessage: String) -> SignalProducer<Self.Value, NoError> {
		return self.lift { $0.logAndIgnoreErrors(errorMessage) }
	}

	/// Returns a `SignalProducer` that will emit `value`, followed by this producer.
	public func startingWith(value: Self.Value) -> SignalProducer<Self.Value, Self.Error> {
		return SignalProducer<Value, Error>(value: value).concat(self.producer)
	}

	public func toBoxedRACSignal() -> RACSignal {
		return toRACSignal(self.map(Box.init))
	}

	/// Assumes that the signal will never emit errors by asserting at runtime
	/// if it emits one.
	/// Note: this is not the preferred way of handling errors, consider using
	/// `flatMapError` instead. This is only recommended for signals bridged
	/// from `RACSignal` that you know will never emit errors.
	public func assumeNoErrors() -> SignalProducer<Self.Value, NoError> {
		return self.lift { $0.assumeNoErrors() }
	}
}

extension SignalType {
	public final func takeUntilObjectDeallocates(object: NSObject) -> Signal<Self.Value, Self.Error> {
		return self.takeUntil(object.willDeallocSignal())
	}

	#if os(iOS)
	public final func takeUntilViewControllerDisappears(viewController: UIViewController) -> Signal<Self.Value, Self.Error> {
		return self
			.takeUntil(viewController.viewDidDisappearSignal())
			.takeUntilObjectDeallocates(viewController)
	}
	#endif
	
	/// Converts values into `Optional.Some`.
	public func wrapValuesInOptional() -> Signal<Optional<Self.Value>, Self.Error> {
		return self.map { .Some($0) }
	}

	/// Ignores errors emitted by this producer after logging them.
	///
	/// IMPORTANT: this operators should not be used lightly.
	/// Consider using `flatMapError` to implement better error handling.
	public func logAndIgnoreErrors(errorMessage: String) -> Signal<Self.Value, NoError> {
		return self.flatMapError { error in
			print("\(errorMessage): \(error)")

			return .empty
		}
	}
	
	public func toBoxedRACSignal() -> RACSignal {
		return toRACSignal(self.map(Box.init))
	}

	/// Assumes that the signal will never emit errors by asserting at runtime
	/// if it emits one.
	/// Note: this is not the preferred way of handling errors, consider using
	/// `flatMapError` instead. This is only recommended for signals bridged
	/// from `RACSignal` that you know will never emit errors.
	public func assumeNoErrors() -> Signal<Self.Value, NoError> {
		return signal.mapError { error in
			fatalError("Unexpected error found in signal that shouldn't error: \(error)")
			()
		}
	}
}

// Note(nacho): there is no way to write these as extensions
// because it's impossible to constrain SignalProducer.T to (),
// since `Void` is not a type.
public func toRACSignal(producer: SignalProducer<(), NoError>) -> RACSignal {
	return producer.toBoxedRACSignal()
}

public func toRACSignal(signal: Signal<(), NoError>) -> RACSignal {
	return signal.toBoxedRACSignal()
}

extension NSObject {
	private final func willDeallocSignal() -> Signal<(), NoError> {
		return self
			.rac_willDeallocSignal()
			.toTriggerSignal()
	}
}

#if os(iOS)
extension UIViewController {
	private final func viewDidDisappearSignal() -> Signal<(), NoError> {
		return self
			.rac_signalForSelector("viewDidDisappear:")
			.toTriggerSignal()
	}
}
#endif

extension RACSignal {
	/// RAC 4 does not provide a method to create a `Signal` from a `RACSignal`
	/// because it can't know whether these underlying `RACSignal`s are hot or cold.
	/// For certain things, like event streams (see `UIControl.signalForControlEvents`)
	/// we use this method to be able to expose these inherently hot streams
	/// as `Signal`s.
	public func toSignalAssumingHot() -> Signal<AnyObject?, NSError> {
		return Signal { observer in
			return self.toSignalProducer().start(observer)
		}
	}

	/// Converts this signal into a `SignalProducer` that can be used
	/// with the `takeUntil` operator, or as an "activation" signal,
	/// for a button, for example.
	public final func toTriggerSignal() -> SignalProducer<(), NoError> {
		return self
			.toSignalProducer()
			.map { _ in () }
			.assumeNoErrors()
	}

	private final func toTriggerSignal() -> Signal<(), NoError> {
		return self
			.toSignalAssumingHot()
			.map { _ in () }
			.assumeNoErrors()
	}

	/// Converts a `RACSignal<Box<T>>` into a `SignalProducer<T, NoError>`
	public final func producerFromBoxedValues<T>(type: T.Type) -> SignalProducer<T, NoError> {
		return self
			.toSignalProducer()
			.map { ($0 as! Box<T>).value }
			.assumeNoErrors()
	}
}

#if os(iOS)

extension UIControl {
	public final func signalForControlEvents(events: UIControlEvents) -> Signal<(), NoError> {
		return self
			.rac_signalForControlEvents(events)
			.toTriggerSignal()
	}
}

extension UICollectionReusableView {
	public final func prepareForReuseSignal() -> Signal<(), NoError> {
		return self
			.rac_prepareForReuseSignal
			.toTriggerSignal()
	}
}

extension UITableViewCell {
	public final func prepareForReuseSignal() -> Signal<(), NoError> {
		return self
			.rac_prepareForReuseSignal
			.toTriggerSignal()
	}
}

extension UIGestureRecognizer {
	public final func gestureSignal() -> Signal<UIGestureRecognizerState, NoError> {
		return self
			.rac_gestureSignal()
			.toSignalAssumingHot()
			.assumeNoErrors()
			.map { $0 as! UIGestureRecognizer }
			.map { $0.state }
	}
}

#endif

extension MutablePropertyType {
	/// Returns a "view" of this property that can only be modified.
	public var immutableView: AnyProperty<Value> {
		return AnyProperty(self)
	}
}