InviteManager.h

#import <Foundation/Foundation.h>

@interface InviteManager : NSObject

- (void)inviteClients;

@end

InviteManager.m

#import "InviteManager.h"
#import <UIKit/UIKit.h>
#import <math.h>

const CGFloat officeLatitude = 53.3381985 * M_PI / 180.0;
const CGFloat officeLongitude = -6.2592576;

const CGFloat EARTH_RADIUS_KM = 6371.0;
const CGFloat ACCEPTED_RADIUS_KM = 100.0;

@implementation InviteManager

- (void)inviteClients
{
    NSString *requestUrl = @"https://gist.githubusercontent.com/brianw/19896c50afa89ad4dec3/raw/6c11047887a03483c50017c1d451667fd62a53ca/gistfile1.txt";
    
    NSURL *url = [NSURL URLWithString:requestUrl];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];
    
    __weak typeof (self)weakSelf = self;
    [[session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        
        NSString *clientsString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        clientsString = [clientsString stringByReplacingOccurrencesOfString:@"\n" withString:@","];
        clientsString = [NSString stringWithFormat:@"[%@]", clientsString];
        
        NSData *clientsData = [clientsString dataUsingEncoding:NSUTF8StringEncoding];
        NSError *e = nil;
        
        NSArray *clients = [NSJSONSerialization JSONObjectWithData:clientsData options:0 error:&e];
        
        typeof(weakSelf)strongSelf = weakSelf;
        [strongSelf filterClientsWithinAcceptedDistance:clients];
        
    }] resume];
}

- (void)filterClientsWithinAcceptedDistance:(NSArray *)clients
{
    NSMutableArray *invitedClients = [NSMutableArray new];
    for (NSDictionary *client in clients)
    {
        if ([self isWithinAcceptedRadius:client])
            [invitedClients addObject:client];
    }
    
    NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:@"user_id" ascending:YES];
    [invitedClients sortUsingDescriptors:@[descriptor]];
    
    for (NSDictionary *client in invitedClients)
        NSLog(@"\nName: %@, user id : %@ \n", client[@"name"], client[@"user_id"]);
}

- (BOOL)isWithinAcceptedRadius:(NSDictionary *)client
{
    CGFloat latitude = [client[@"latitude"] floatValue];
    CGFloat latitudeRad = latitude * M_PI / 180.0;
    CGFloat longitude = [client[@"longitude"] floatValue];
    CGFloat longitudeDiff = fabs(officeLongitude - longitude) * M_PI / 180.0;
    
    CGFloat centralAngle = acos(sinf(latitudeRad) * sinf(officeLatitude) + cosf(latitudeRad) * cosf(officeLatitude) * cosf(longitudeDiff));
    CGFloat distance = centralAngle * EARTH_RADIUS_KM;
    NSLog(@"Distance: %f", distance);
    return distance <= ACCEPTED_RADIUS_KM;
}

@end