OfflineUpdater.m

// An object that will run a piece of code every <<interval>> seconds while the application has connectivity to the network, 
// automatically pauses the loop when isNetworkReachable is false.

#import <ReactiveCocoa/ReactiveCocoa.h>
#import <ReactiveCocoa/NSNotificationCenter+RACSupport.h>

@interface PWOfflineUpdater : NSObject

-(id)initWithUpdateInterval:(NSTimeInterval)interval targetOperationQueue:(NSOperationQueue *)queue;

-(void)start;
-(void)stop;


+(NSNotificationCenter *)notificationCenter;
@end


@implementation PWOfflineUpdater{
    NSOperationQueue *__weak queue;
    NSTimeInterval update_interval;
    RACDisposable *workSubscription;
}

-(id)initWithUpdateInterval:(NSTimeInterval)interval targetOperationQueue:(NSOperationQueue *)targetQueue{
    if (self = [super init]){
        update_interval = interval;
        queue = targetQueue;
    }
    return self;
}

//subscribe to the do work signal.
-(void)start{
    workSubscription = [self.doWorkSignal subscribeNext:^(NSDate *date){
        NSLog(@"BACON -> should be fetching some things.");
    }];
}

//unsubscribe to the do work signal.
-(void)stop{
    [workSubscription dispose];
    workSubscription = nil;
}

-(void)dealloc{
    [self stop];
}

//Signal that immediately returns the current reachability state.
-(RACSignal *)currentReachabilitySignal{
    return [RACSignal return:@(self.class.reachabilityHandler.isNetworkReachable)];
}

//signal that maps reachability notifications into true/false values and only sendsNext on a change.
-(RACSignal *)booleanReachabilityNotificationSignal{
    return [[[self.class.notificationCenter rac_addObserverForName:PWReachabilityChangedNotification object:nil]
            map:^NSNumber *(NSNotification *notification){
                PWReachabilityHandler *handler = (PWReachabilityHandler *)notification.object;
                return @(handler.isNetworkReachable);
            }]
            distinctUntilChanged];
}

//signal that concatenates the notification signal onto the end of the current reachability signal.
-(RACSignal *)reachabilitySignalWithStart{
    return [[self currentReachabilitySignal] concat:[self booleanReachabilityNotificationSignal]];
}


// signal that posts a date every <<interval>> seconds while the network reachability signal has 
// a value of true and sends nothing while the reachability signal has a value of false.
-(RACSignal *)doWorkSignal{
    RACSignal *reachable = [self reachabilitySignalWithStart];
    RACSignal *update = [RACSignal interval:update_interval];
    RACSignal *nothing = [RACSignal empty];
    
    return [RACSignal if:reachable then:update else:nothing];
}


//Testing Swizzle Points.
+(NSNotificationCenter *)notificationCenter{
    return [NSNotificationCenter defaultCenter];
}

+(PWReachabilityHandler *)reachabilityHandler{
    return [PWReachabilityHandler sharedHandler];
}

@end