session-ios/Signal/src/util/ObservableValue.h

#import <Foundation/Foundation.h>
#import "CollapsingFutures.h"
#import "Queue.h"

typedef void (^LatestValueCallback)(id latestValue);

/**
 *
 * An ObservableValue represents an asynchronous stream of values, such as 'latest state of toggle' or 'latest sensor
 * reading'.
 *
 */
@interface ObservableValue : NSObject {
   @protected
    NSMutableSet *callbacks;
   @private
    Queue *queuedActionsToRun;
   @private
    bool isRunningActions;
   @protected
    bool sealed;
}

@property (readonly, atomic) id currentValue;

- (void)watchLatestValueOnArbitraryThread:(LatestValueCallback)callback
                           untilCancelled:(TOCCancelToken *)untilCancelledToken;

- (void)watchLatestValue:(LatestValueCallback)callback
                onThread:(NSThread *)thread
          untilCancelled:(TOCCancelToken *)untilCancelledToken;

@end

@interface ObservableValueController : ObservableValue

+ (ObservableValueController *)observableValueControllerWithInitialValue:(id)value;
- (void)updateValue:(id)value;
- (void)adjustValue:(id (^)(id))adjustment;
- (void)sealValue;

@end