[Core] Support watchOS lifecycle notifications (#10112)

* [Core] Support watchOS lifecycle notifications

* Rework for so version is checked in runtime

Author: ncooke3

FirebaseCore/Sources/FIRApp.m

@@ -22,6 +22,10 @@
 #import <AppKit/AppKit.h>
 #endif
 
+#if __has_include(<WatchKit/WatchKit.h>)
+#import <WatchKit/WatchKit.h>
+#endif
+
 #import "FirebaseCore/Sources/Public/FirebaseCore/FIRApp.h"
 
 #import "FirebaseCore/Sources/FIRAnalyticsConfiguration.h"
@@ -871,14 +875,23 @@ - (void)subscribeForAppDidBecomeActiveNotifications {
   NSNotificationName notificationName = UIApplicationDidBecomeActiveNotification;
 #elif TARGET_OS_OSX
   NSNotificationName notificationName = NSApplicationDidBecomeActiveNotification;
+#elif TARGET_OS_WATCH
+  // TODO(ncooke3): Remove when minimum supported watchOS version is watchOS 7.0.
+  // On watchOS 7.0+, heartbeats are logged when the watch app becomes active.
+  // On watchOS 6.0, heartbeats are logged when the Firebase app is configuring.
+  // While it does not cover all use cases, logging when the Firebase app is
+  // configuring is done because watchOS lifecycle notifications are a
+  // watchOS 7.0+ feature.
+  NSNotificationName notificationName = kFIRAppReadyToConfigureSDKNotification;
+  if (@available(watchOS 7.0, *)) {
+    notificationName = WKApplicationDidBecomeActiveNotification;
+  }
 #endif
 
-#if !TARGET_OS_WATCH
   [[NSNotificationCenter defaultCenter] addObserver:self
                                            selector:@selector(appDidBecomeActive:)
                                                name:notificationName
                                              object:nil];
-#endif
 }
 
 - (void)appDidBecomeActive:(NSNotification *)notification {

FirebaseCore/Tests/Unit/FIRAppTest.m

@@ -12,6 +12,18 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#if __has_include(<UIKit/UIKit.h>)
+#import <UIKit/UIKit.h>
+#endif
+
+#if __has_include(<AppKit/AppKit.h>)
+#import <AppKit/AppKit.h>
+#endif
+
+#if __has_include(<WatchKit/WatchKit.h>)
+#import <WatchKit/WatchKit.h>
+#endif
+
 #import "FirebaseCore/Tests/Unit/FIRTestCase.h"
 #import "FirebaseCore/Tests/Unit/FIRTestComponents.h"
 
@@ -827,7 +839,6 @@ - (void)testIsDefaultAppConfigured {
 
 #pragma mark - Core Telemetry
 
-#if !TARGET_OS_WATCH
 - (void)testCoreDiagnosticsLoggedWhenAppDidBecomeActive {
   FIRApp *app = [self createConfiguredAppWithName:NSStringFromSelector(_cmd)];
   [self expectCoreDiagnosticsDataLogWithOptions:app.options];
@@ -845,7 +856,6 @@ - (void)testHeartbeatLogIsAttemptedWhenAppDidBecomeActive {
                                          object:nil];
   OCMVerifyAll(self.mockHeartbeatLogger);
 }
-#endif  // TARGET_OS_WATCH
 
 #pragma mark - private
 
@@ -890,10 +900,15 @@ - (void)expectCoreDiagnosticsDataLogWithOptions:(nullable FIROptions *)expectedO
 - (NSNotificationName)appDidBecomeActiveNotificationName {
 #if TARGET_OS_IOS || TARGET_OS_TV
   return UIApplicationDidBecomeActiveNotification;
-#endif
-
-#if TARGET_OS_OSX
+#elif TARGET_OS_OSX
   return NSApplicationDidBecomeActiveNotification;
+#elif TARGET_OS_WATCH
+  // See comment in `- [FIRApp subscribeForAppDidBecomeActiveNotifications]`.
+  if (@available(watchOS 7.0, *)) {
+    return WKApplicationDidBecomeActiveNotification;
+  } else {
+    return kFIRAppReadyToConfigureSDKNotification;
+  }
 #endif
 }