Delete app from Database when deleted in Core. (#194)

* Delete an app from Database when deleted in Core.

When a FIRApp is deleted in Core, it should also be deleted from
the instances array in Database.

See #160 for more details.

* Add tests for deleting databases.

* Add call to clean up deleted FIRDatabase instance.

Author: ryanwilson

Example/Database/Tests/Integration/FIRDatabaseTests.m

@@ -53,6 +53,56 @@ - (void) testDatabaseForAppWithInvalidURLs {
     XCTAssertThrows([self databaseForURL:@"http://x.example.com/paths/are/bad"]);
 }
 
+- (void) testDeleteDatabase {
+    FIRDatabase *defaultDatabase = [FIRDatabase database];
+    FIRApp *defaultApp = [FIRApp defaultApp];
+    XCTAssertEqualObjects(defaultDatabase.app, defaultApp);
+
+    // Set up expectation for the default app to be deleted.
+    XCTestExpectation *defaultAppDeletedExpectation =
+        [self expectationWithDescription:@"Deleting the default app should invalidate the default "
+                                         @"database."];
+    [defaultApp deleteApp:^(BOOL success) {
+        // Deleting the default app should make the default database unavailable.
+        XCTAssertThrows([FIRDatabase database]);
+
+        [defaultAppDeletedExpectation fulfill];
+    }];
+
+    // Wait for the default app to be deleted.
+    [self waitForExpectations:@[defaultAppDeletedExpectation] timeout:2];
+
+    // Set up a custom FIRApp with a custom database based on it.
+    FIROptions *options = [[FIROptions alloc] initWithGoogleAppID:@"1:123:ios:123abc"
+                                                      GCMSenderID:@"gcm_sender_id"];
+    options.databaseURL = self.databaseURL;
+    NSString *customAppName = @"MyCustomApp";
+    [FIRApp configureWithName:customAppName options:options];
+    FIRApp *customApp = [FIRApp appNamed:customAppName];
+    FIRDatabase *customDatabase = [FIRDatabase databaseForApp:customApp];
+    XCTAssertNotNil(customDatabase);
+
+    // Delete the custom app and wait for it to be done.
+    XCTestExpectation *customAppDeletedExpectation =
+        [self expectationWithDescription:@"Deleting the custom app should be successful."];
+    [customApp deleteApp:^(BOOL success) {
+        // The app shouldn't exist anymore, ensure that the databaseForApp throws.
+        XCTAssertThrows([FIRDatabase databaseForApp:[FIRApp appNamed:customAppName]]);
+
+        [customAppDeletedExpectation fulfill];
+    }];
+
+    // Wait for the custom app to be deleted.
+    [self waitForExpectations:@[customAppDeletedExpectation] timeout:2];
+
+    // Configure the app again, then grab a reference to the database. Assert it's different.
+    [FIRApp configureWithName:customAppName options:options];
+    FIRApp *secondCustomApp = [FIRApp appNamed:customAppName];
+    FIRDatabase *secondCustomDatabase = [FIRDatabase databaseForApp:secondCustomApp];
+    XCTAssertNotNil(secondCustomDatabase);
+    XCTAssertNotEqualObjects(customDatabase, secondCustomDatabase);
+}
+
 - (void) testReferenceWithPath {
     FIRDatabase *db = [self defaultDatabase];
     NSString *expectedURL = [NSString stringWithFormat:@"%@/foo", self.databaseURL];

Firebase/Database/Api/FIRDatabase.m

@@ -42,6 +42,26 @@ @implementation FIRDatabase
 #define STR_EXPAND(x) #x
 static const char *FIREBASE_SEMVER = (const char *)STR(FIRDatabase_VERSION);
 
++ (void)load {
+  NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
+  [center addObserverForName:kFIRAppDeleteNotification
+                      object:nil
+                       queue:nil
+                  usingBlock:^(NSNotification * _Nonnull note) {
+      NSString *appName = note.userInfo[kFIRAppNameKey];
+      if (appName == nil) { return; }
+
+      NSMutableDictionary *instances = [self instances];
+      @synchronized (instances) {
+          FIRDatabase *deletedApp = instances[appName];
+          // Clean up the deleted instance in an effort to remove any resources still in use.
+          // Note: Any leftover instances of this exact database will be invalid.
+          [FRepoManager disposeRepos:deletedApp.config];
+          [instances removeObjectForKey:appName];
+      }
+  }];
+}
+
 /**
  * A static NSMutableDictionary of FirebaseApp names to FirebaseDatabase instance. To ensure thread-
  * safety, it should only be accessed in databaseForApp, which is synchronized.