Reactive Location Service

MPXLocationService.h

//
// Created by Rob Pearson on 28/08/13.
// Copyright (c) 2013 Maple Pixel Pty. Ltd. All rights reserved.
//
// To change the template use AppCode | Preferences | File Templates.
//


#import <Foundation/Foundation.h>
#import <CoreLocation/CoreLocation.h>

@class RACSignal;

@interface MPXLocationService : NSObject <CLLocationManagerDelegate>

+ (MPXLocationService *)sharedInstance;

- (BOOL)locationServicesEnabled;

- (CLAuthorizationStatus)authorizationStatus;

- (RACSignal *)requestAuthorizationSignal;

- (RACSignal *)locationSignal;

@end

MPXLocationService.m

//
// Created by Rob Pearson on 28/08/13.
// Copyright (c) 2013 Maple Pixel Pty. Ltd. All rights reserved.
//
// To change the template use AppCode | Preferences | File Templates.
//

#import "MPXLocationService.h"
#import "ReactiveCocoa.h"

NSString * const MPXLocationServiceErrorDomain = @"MPXLocationServiceErrorDomain";
NSString * const MPXLocationNotAuthorisedErrorKey = @"MPXLocationNotAuthorisedErrorKey";

@interface MPXLocationService ()

@property(nonatomic, strong) CLLocationManager *locationManager;

@end

@implementation MPXLocationService

+ (MPXLocationService *)sharedInstance {

    static MPXLocationService *sharedLocationService;
    static dispatch_once_t pred;

    dispatch_once(&pred, ^{
        sharedLocationService = [[MPXLocationService alloc] init];
    });

    return sharedLocationService;
}

- (id)init {
    self = [super init];
    if (self) {
        self.locationManager = [CLLocationManager new];
        self.locationManager.delegate = self;
        self.locationManager.desiredAccuracy = kCLLocationAccuracyHundredMeters;
        self.locationManager.distanceFilter = 100; // 100m accuracy
    }

    return self;
}

- (BOOL)locationServicesEnabled {

    // TODO: Expose as signal as well
    BOOL enabled = CLLocationManager.locationServicesEnabled;
    return enabled;

}

- (CLAuthorizationStatus)authorizationStatus {

    // TODO: Expose as signal as well
    CLAuthorizationStatus status = [CLLocationManager authorizationStatus];
    return status;

}

- (RACSignal *)requestAuthorizationSignal {

    RACSignal *authorizationSignal = [RACSignal createSignal:^RACDisposable *(id <RACSubscriber> subscriber) {

        [[self rac_signalForSelector:@selector(locationManager:didChangeAuthorizationStatus:) fromProtocol:@protocol(CLLocationManagerDelegate)] subscribeNext:^(RACTuple *value) {

            NSNumber *status = (NSNumber *) value[1]; // Ignore the location manager
            [subscriber sendNext:status];
            [subscriber sendCompleted];

        }];

        CLAuthorizationStatus authorizationStatus = self.authorizationStatus;
        if (authorizationStatus == kCLAuthorizationStatusNotDetermined) {
            [self.locationManager requestWhenInUseAuthorization];
        }
        else if (authorizationStatus == kCLAuthorizationStatusDenied || authorizationStatus == kCLAuthorizationStatusRestricted) {
            NSError *error = [NSError errorWithDomain:MPXLocationServiceErrorDomain code:MPXLocationNotAuthorisedErrorKey userInfo:nil];
            [subscriber sendError:error];
        }
        else {
            [subscriber sendCompleted]; // All Good.  Do Nothing
        }

        return nil;

    }];

    return authorizationSignal;
}

- (RACSignal *)locationSignal {

    // TODO: Review previous service code to add checks on last object to ensure that it's up-to-date and of the correct accuracy.
    // TODO: Review how to restart the timer. I'm currently using take: 1 so it's not needed immediately.

    RACSignal *locationSignal = [[self requestAuthorizationSignal]
            then:^RACSignal * {

                RACSignal *tmpSignal;

                if (self.authorizationStatus == kCLAuthorizationStatusAuthorizedWhenInUse) {
                    tmpSignal = [RACSignal
                            createSignal:^RACDisposable *(id <RACSubscriber> subscriber) {

                                [[self rac_signalForSelector:@selector(locationManager:didUpdateLocations:) fromProtocol:@protocol(CLLocationManagerDelegate)] subscribeNext:^(RACTuple *value) {

                                    NSArray *locations = value[1]; // Ignore the location manager
                                    [subscriber sendNext:locations.lastObject];

                                }];

                                [[self rac_signalForSelector:@selector(locationManager:didFailWithError:) fromProtocol:@protocol(CLLocationManagerDelegate)] subscribeNext:^(RACTuple *value) {

                                    NSError *error = value[1]; // Ignore the location manager
                                    if (error.domain == kCLErrorDomain && error.code == kCLErrorLocationUnknown) {
                                        return;
                                    }
                                    [subscriber sendError:error];

                                }];

                                [self start];

                                return [RACDisposable disposableWithBlock:^{
                                    [self stop];
                                }];
                            }
                    ];

                } else {
                    tmpSignal = [RACSignal empty];
                }

                return tmpSignal;
            }];


    return locationSignal;

}

- (void)start {

    [self.locationManager startUpdatingLocation];

}

- (void)stop {

    [self.locationManager stopUpdatingLocation];

}

@end

If two or more subscriptions are created to locationSignal, and then one gets disposed, it will cause the other signals to stop. This could be avoided using a count of subscriptions. When the count goes to zero, stopUpdatingLocation can be called.