AirLocate/APLCalibrationCalculator.m

/*
     File: APLCalibrationCalculator.m
 Abstract: Illustrates how to calibrate the measured power of a beacon.
 
  Version: 1.1
 
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 */
 
#import "APLCalibrationCalculator.h"
#import "APLDefaults.h"
 
@import CoreLocation;
 
 
static const NSTimeInterval ALCalibrationDwell = 20.0f;
 
NSString *AppErrorDomain = @"com.example.apple-samplecode.AirLocate";
 
 
 
@interface APLCalibrationCalculator()
 
@property CLLocationManager *locationManager;
@property CLBeaconRegion *region;
@property (getter=isCalibrating) BOOL calibrating;
@property NSMutableArray *rangedBeacons;
@property NSTimer *timer;
 
@property (strong) APLCalibrationProgressHandler progressHandler;
@property (strong) APLCalibrationCompletionHandler completionHandler;
 
@property float percentComplete;
 
@end
 
 
 
@implementation APLCalibrationCalculator
 
 
- (id)initWithRegion:(CLBeaconRegion *)region completionHandler:(APLCalibrationCompletionHandler)handler
{
    self = [super init];
    if(self)
    {
        // This location manager will be used to collect RSSI samples from the targeted beacon.
        _locationManager = [[CLLocationManager alloc] init];
        _locationManager.delegate = self;
        
        _region = region;
        _completionHandler = [handler copy];
        _rangedBeacons = [[NSMutableArray alloc] init];
    }
    
    return self;
}
 
- (void)locationManager:(CLLocationManager *)manager didRangeBeacons:(NSArray *)beacons inRegion:(CLBeaconRegion *)region
{
    // CoreLocation will call this delegate method at 1 Hz with updated range information.
    @synchronized(self)
    {
        [_rangedBeacons addObject:beacons];
        
        if(_progressHandler)
        {
            dispatch_async(dispatch_get_main_queue(), ^{
                // Bump the progress callback back to the UI thread as we'll be updating the UI.
                _percentComplete += 1.0f / ALCalibrationDwell;
                _progressHandler(_percentComplete);
            });
        }
    }
}
 
- (void)performCalibrationWithProgressHandler:(APLCalibrationProgressHandler)handler
{
    @synchronized(self)
    {
        if(!self.calibrating)
        {
            // Calibration consists of collecting RSSI samples for 20 seconds.
            // Once we have all the samples we will average the mid-80th percentile in timerElapsed:.
            self.calibrating = YES;
            [self.rangedBeacons removeAllObjects];
            
            self.percentComplete = 0.0f;
            self.progressHandler = [handler copy];
            
            [self.locationManager startRangingBeaconsInRegion:self.region];
            
            self.timer = [[NSTimer alloc] initWithFireDate:[NSDate dateWithTimeIntervalSinceNow:ALCalibrationDwell] interval:0 target:self selector:@selector(timerElapsed:) userInfo:nil repeats:NO];
            [[NSRunLoop currentRunLoop] addTimer:self.timer  forMode:NSDefaultRunLoopMode];
        }
        else
        {
            // Send back an error if calibration is already in progress.
            NSString *localizedErrorString = NSLocalizedString(@"Calibration is already in progress", @"Error string");
            NSDictionary *userInfo = @{ NSLocalizedDescriptionKey : localizedErrorString };
            NSError *error = [NSError errorWithDomain:AppErrorDomain code:4 userInfo:userInfo];
            dispatch_async(dispatch_get_main_queue(), ^{
                _completionHandler(0, error);
            });
        }
    }
}
 
- (void)cancelCalibration
{
    @synchronized(self)
    {
        // Fire the timer early if calibration is being cancelled.
        // timerElapsed: will handle reporting the cancellation.
        if(self.calibrating)
        {
            self.calibrating = NO;
            [self.timer fire];
        }
    }
}
 
- (void)timerElapsed:(id)sender
{
    @synchronized(self)
    {
        // We can stop ranging at this point as we've either been cancelled or
        // collected all of the RSSI samples we need.
        [_locationManager stopRangingBeaconsInRegion:_region];
        
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            @synchronized(self) {                
                __block NSError *error = nil;
                NSMutableArray *allBeacons = [[NSMutableArray alloc] init];
                NSInteger measuredPower = 0;
                if(!self.calibrating)
                {
                    NSString *localizedErrorString = NSLocalizedString(@"Calibration was cancelled", @"Error string");
                    NSDictionary *userInfo = @{ NSLocalizedDescriptionKey : localizedErrorString };
                    error = [NSError errorWithDomain:AppErrorDomain code:2 userInfo:userInfo];
                }
                else
                {
                    [self.rangedBeacons enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
                        NSArray *beacons = (NSArray *)obj;
                        if(beacons.count > 1)
                        {
                            NSString *localizedErrorString = NSLocalizedString(@"More than one beacon of the specified type was found", @"Error string");
                            NSDictionary *userInfo = @{ NSLocalizedDescriptionKey : localizedErrorString };
                            error = [NSError errorWithDomain:AppErrorDomain code:1 userInfo:userInfo];
                            *stop = YES;
                        }
                        else
                        {
                            [allBeacons addObjectsFromArray:beacons];
                        }
                    }];
                    
                    if(allBeacons.count <= 0)
                    {
                        NSString *localizedErrorString = NSLocalizedString(@"No beacon of the specified type was found", @"Error string");
                        NSDictionary *userInfo = @{ NSLocalizedDescriptionKey : localizedErrorString };
                        error = [NSError errorWithDomain:AppErrorDomain code:3 userInfo:userInfo];
                    }
                    else
                    {
                        // Measured power is an average of the mid-80th percentile of RSSI samples.
                        NSUInteger outlierPadding = allBeacons.count * 0.1f;                    
                        [allBeacons sortUsingDescriptors:@[[NSSortDescriptor sortDescriptorWithKey:@"rssi" ascending:YES]]];
                        NSArray *sample = [allBeacons subarrayWithRange:NSMakeRange(outlierPadding, allBeacons.count - (outlierPadding * 2))];
                        measuredPower = [[sample valueForKeyPath:@"@avg.rssi"] integerValue];
                    }
                }
                
                // Bump the completion callback to the UI thread as we'll be updating the UI.
                dispatch_async(dispatch_get_main_queue(), ^{
                    _completionHandler(measuredPower, error);
                });
                
                self.calibrating = NO;
                [self.rangedBeacons removeAllObjects];
                
                self.progressHandler = nil;
            }
        });
    }
}
 
@end