[ios] Optimize event uploading (#6737)

Upload any events collected when the app was in use for apps that only
have "when in use" location permissions. Also, for all apps, avoid
posting event data if there is only a single event.

1 files changed, 22 insertions, 5 deletions

diff --git a/platform/ios/src/MGLMapboxEvents.m b/platform/ios/src/MGLMapboxEvents.m
index 15b78b65ae..d86114d016 100644
--- a/platform/ios/src/MGLMapboxEvents.m
+++ b/platform/ios/src/MGLMapboxEvents.m
@@ -129,6 +129,7 @@ const NSTimeInterval MGLFlushInterval = 180;
 
 @implementation MGLMapboxEvents {
     NSString *_instanceID;
+    UIBackgroundTaskIdentifier _backgroundTaskIdentifier;
 }
 
 + (void)initialize {
@@ -257,9 +258,20 @@ const NSTimeInterval MGLFlushInterval = 180;
 }
 
 - (void)pauseOrResumeMetricsCollectionIfRequired {
+    UIApplication *application = [UIApplication sharedApplication];
+    
     // Prevent blue status bar when host app has `when in use` permission only and it is not in foreground
     if ([CLLocationManager authorizationStatus] == kCLAuthorizationStatusAuthorizedWhenInUse &&
-        [UIApplication sharedApplication].applicationState == UIApplicationStateBackground) {
+        application.applicationState == UIApplicationStateBackground) {
+        
+        if (_backgroundTaskIdentifier == UIBackgroundTaskInvalid) {
+            _backgroundTaskIdentifier = [application beginBackgroundTaskWithExpirationHandler:^{
+                [application endBackgroundTask:_backgroundTaskIdentifier];
+                _backgroundTaskIdentifier = UIBackgroundTaskInvalid;
+            }];
+            [self flush];
+        }
+        
         [self pauseMetricsCollection];
         return;
     }
@@ -307,7 +319,10 @@ const NSTimeInterval MGLFlushInterval = 180;
         return;
     }
     
-    if ([self.eventQueue count] == 0) {
+    if ([self.eventQueue count] <= 1) {
+        [self.eventQueue removeAllObjects];
+        [[UIApplication sharedApplication] endBackgroundTask:_backgroundTaskIdentifier];
+        _backgroundTaskIdentifier = UIBackgroundTaskInvalid;
         return;
     }
     
@@ -485,10 +500,12 @@ const NSTimeInterval MGLFlushInterval = 180;
             if (error) {
                 [strongSelf pushDebugEvent:MGLEventTypeLocalDebug withAttributes:@{MGLEventKeyLocalDebugDescription: @"Network error",
                                                                                         @"error": error}];
-                return;
+            } else {
+                [strongSelf pushDebugEvent:MGLEventTypeLocalDebug withAttributes:@{MGLEventKeyLocalDebugDescription: @"post",
+                                                                                   @"debug.eventsCount": @(events.count)}];
             }
-            [strongSelf pushDebugEvent:MGLEventTypeLocalDebug withAttributes:@{MGLEventKeyLocalDebugDescription: @"post",
-                                                                                    @"debug.eventsCount": @(events.count)}];
+            [[UIApplication sharedApplication] endBackgroundTask:_backgroundTaskIdentifier];
+            _backgroundTaskIdentifier = UIBackgroundTaskInvalid;
         }];
     });
 }