Add check for attribution button hiding and telemetry opt-out

include/mbgl/ios/MGLMapView.h

@@ -144,7 +144,9 @@ IB_DESIGNABLE
     [required](https://www.mapbox.com/help/metrics-opt-out-for-users/) to
     provide users with the option to disable anonymous usage and location
     sharing (telemetry). If this view is hidden, you must implement this
-    setting elsewhere in your app or via `Settings.bundle`.
+    setting elsewhere in your app or via `Settings.bundle`. See our
+    [website](https://www.mapbox.com/ios-sdk/#telemetry_opt_out)
+    for implementation help.
  */
 @property (nonatomic, readonly) UIButton *attributionButton;
 

platform/ios/src/MGLMapView.mm

@@ -334,6 +334,7 @@ - (void)commonInit
     _attributionButton.translatesAutoresizingMaskIntoConstraints = NO;
     [self addSubview:_attributionButton];
     _attributionButtonConstraints = [NSMutableArray array];
+    [_attributionButton addObserver:self forKeyPath:@"hidden" options:NSKeyValueObservingOptionNew context:NULL];
 
     // setup compass
     //
@@ -481,6 +482,7 @@ - (void)dealloc
 {
     [[NSNotificationCenter defaultCenter] removeObserver:self];
     [[MGLAccountManager sharedManager] removeObserver:self forKeyPath:@"accessToken"];
+    [_attributionButton removeObserver:self forKeyPath:@"hidden"];
 
     [self validateDisplayLink];
 
@@ -1486,7 +1488,8 @@ - (void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)
     }
     else if (buttonIndex == alertView.firstOtherButtonIndex)
     {
-        [[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"https://mapbox.com/telemetry/"]];
+        [[UIApplication sharedApplication] openURL:
+         [NSURL URLWithString:@"https://mapbox.com/telemetry/"]];
     }
     else if (buttonIndex == alertView.firstOtherButtonIndex + 1)
     {
@@ -1506,6 +1509,15 @@ - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(N
             _mbglFileSource->setAccessToken((std::string)[accessToken UTF8String]);
         }
     }
+    else if ([keyPath isEqualToString:@"hidden"] && object == _attributionButton)
+    {
+        NSNumber *hiddenNumber = change[NSKeyValueChangeNewKey];
+        BOOL attributionButtonWasHidden = [hiddenNumber boolValue];
+        if (attributionButtonWasHidden)
+        {
+            [MGLMapboxEvents ensureMetricsOptoutExists];
+        }
+    }
 }
 
 + (NS_SET_OF(NSString *) *)keyPathsForValuesAffectingZoomEnabled

platform/ios/src/MGLMapboxEvents.h

@@ -66,7 +66,10 @@ typedef NS_MUTABLE_DICTIONARY_OF(NSString *, id) MGLMutableMapboxEventAttributes
 + (void) flush;
 
 // Main thread only
-+ (void)validate;
++ (void) validate;
+
+// Main thread only
++ (void) ensureMetricsOptoutExists;
 
 @end
 

platform/ios/src/MGLMapboxEvents.m

@@ -740,6 +740,40 @@ + (BOOL) checkPushEnabled {
     return result;
 }
 
+// Main thread only
+//
++ (void) ensureMetricsOptoutExists {
+    NSNumber *shownInAppNumber = [[NSBundle mainBundle] objectForInfoDictionaryKey:@"MGLMapboxMetricsEnabledSettingShownInApp"];
+    BOOL hasMetricsEnabledSettingShownInAppFlag = [shownInAppNumber boolValue];
+
+    if ( ! hasMetricsEnabledSettingShownInAppFlag &&
+        [[NSUserDefaults standardUserDefaults] integerForKey:@"MGLMapboxAccountType"] == 0) {
+        // Opt-out is not configured in UI, so check for Settings.bundle
+        id defaultEnabledValue;
+        NSString *appSettingsBundle = [[NSBundle mainBundle] pathForResource:@"Settings" ofType:@"bundle"];
+
+        if (appSettingsBundle) {
+            // Dynamic Settings.bundle loading based on http://stackoverflow.com/a/510329/2094275
+            NSDictionary *settings = [NSDictionary dictionaryWithContentsOfFile:[appSettingsBundle stringByAppendingPathComponent:@"Root.plist"]];
+            NSArray *preferences = settings[@"PreferenceSpecifiers"];
+            for (NSDictionary *prefSpecification in preferences) {
+                if ([prefSpecification[@"Key"] isEqualToString:@"MGLMapboxMetricsEnabled"]) {
+                    defaultEnabledValue = prefSpecification[@"DefaultValue"];
+                }
+            }
+        }
+
+        if ( ! defaultEnabledValue) {
+            [NSException raise:@"Telemetry opt-out missing" format:
+             @"End users must be able to opt out of Mapbox Telemetry in your app, either inside Settings (via Settings.bundle) or inside this app. "
+             @"By default, this opt-out control is included as a menu item in the attribution action sheet. "
+             @"If you reimplement the opt-out control inside this app, disable this assertion by setting MGLMapboxMetricsEnabledSettingShownInApp to YES in Info.plist."
+             @"\r\n\r\nSee https://www.mapbox.com/ios-sdk/#telemetry_opt_out for more information."
+             @"\r\n\r\nAdditionally, by hiding this attribution control you agree to display the required attribution elsewhere in this app."];
+        }
+    }
+}
+
 #pragma mark CLLocationManagerDelegate
 - (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations {
     //  Iterate through locations to pass all data