Listen sequence numbers (#675)

* Generate and save sequence numbers for listens

* Add documentation

* Fix include path

* Fix unavailable comment

* Review feedback

1 files changed, 37 insertions, 0 deletions

diff --git a/Firestore/Source/Core/FSTListenSequence.h b/Firestore/Source/Core/FSTListenSequence.h
new file mode 100644
index 0000000..56d0e78
--- /dev/null
+++ b/Firestore/Source/Core/FSTListenSequence.h
@@ -0,0 +1,37 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#import <Foundation/Foundation.h>
+
+#import "FSTTypes.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ * FSTListenSequence is a monotonic sequence. It is initialized with a minimum value to
+ * exceed. All subsequent calls to next will return increasing values.
+ */
+@interface FSTListenSequence : NSObject
+
+- (instancetype)initStartingAfter:(FSTListenSequenceNumber)after NS_DESIGNATED_INITIALIZER;
+
+- (id)init NS_UNAVAILABLE;
+
+- (FSTListenSequenceNumber)next;
+
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file