text: /*
   * Copyright 2017 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 "FIRMessaging.h"
  #import "FIRMessagingTopicsCommon.h"
  
  NS_ASSUME_NONNULL_BEGIN
  
  /**
   *  Represents a single batch of topics, with the same action.
   *
   *  Topic operations which have the same action (subscribe or unsubscribe) can be executed
   *  simultaneously, as the order of operations do not matter with the same action. The set of
   *  topics is unique, as it doesn't make sense to apply the same action to the same topic
   *  repeatedly; the result would be the same as the first time.
   */
  @interface FIRMessagingTopicBatch : NSObject <NSCoding>
  
  @property(nonatomic, readonly, assign) FIRMessagingTopicAction action;
  @property(nonatomic, readonly, copy) NSMutableSet <NSString *> *topics;
  
  - (instancetype)init NS_UNAVAILABLE;
  - (instancetype)initWithAction:(FIRMessagingTopicAction)action NS_DESIGNATED_INITIALIZER;
  
  @end
  
  @class FIRMessagingPendingTopicsList;
  /**
   *  This delegate must be supplied to the instance of FIRMessagingPendingTopicsList, via the
   *  @cdelegate property. It lets the
   *  pending topics list know whether or not it can begin making requests via
   *  @c-pendingTopicsListCanRequestTopicUpdates:, and handles the request to actually
   *  perform the topic operation. The delegate also handles when the pending topics list is updated,
   *  so that it can be archived or persisted.
   *
   *  @see FIRMessagingPendingTopicsList
   */
  @protocol FIRMessagingPendingTopicsListDelegate <NSObject>
  
  - (void)pendingTopicsList:(FIRMessagingPendingTopicsList *)list
    requestedUpdateForTopic:(NSString *)topic
                     action:(FIRMessagingTopicAction)action
                 completion:(FIRMessagingTopicOperationCompletion)completion;
  - (void)pendingTopicsListDidUpdate:(FIRMessagingPendingTopicsList *)list;
  - (BOOL)pendingTopicsListCanRequestTopicUpdates:(FIRMessagingPendingTopicsList *)list;
  
  @end
  
  /**
   *  FIRMessagingPendingTopicsList manages a list of topic subscription updates, batched by the same
   *  action (subscribe or unsubscribe). The list roughly maintains the order of the topic operations,
   *  batched together whenever the topic action (subscribe or unsubscribe) changes.
   *
   *  Topics operations are batched by action because it is safe to perform the same topic action
   *  (subscribe or unsubscribe) on many topics simultaneously. After each batch is successfully
   *  completed, the next batch operations can begin.
   *
   *  When asked to resume its operations, FIRMessagingPendingTopicsList will begin performing updates
   *  of its current batch of topics. For example, it may begin subscription operations for topics
   *  [A, B, C] simultaneously.
   *
   *  When the current batch is completed, the next batch of operations will be started. For example
   *  the list may begin unsubscribe operations for [D, A, E]. Note that because A is in both batches,
   *  A will be correctly subscribed in the first batch, then unsubscribed as part of the second batch
   *  of operations. Without batching, it would be ambiguous whether A's subscription operation or the
   *  unsubscription operation would be completed first.
   *
   *  An app can subscribe and unsubscribe from many topics, and this class helps persist the pending
   *  topics and perform the operation safely and correctly.
   *
   *  When a topic fails to subscribe or unsubscribe due to a network error, it is considered a
   *  recoverable error, and so it remains in the current batch until it is succesfully completed.
   *  Topic updates are completed when they either (a) succeed, (b) are cancelled, or (c) result in an
   *  unrecoverable error. Any error outside of `NSURLErrorDomain` is considered an unrecoverable
   *  error.
   *
   *  In addition to maintaining the list of pending topic updates, FIRMessagingPendingTopicsList also
   *  can track completion handlers for topic operations.
   *
   *  @discussion Completion handlers for topic updates are not maintained if it was restored from a
   *  keyed archive. They are only called if the topic operation finished within the same app session.
   *
   *  You must supply an object conforming to FIRMessagingPendingTopicsListDelegate in order for the
   *  topic operations to execute.
   *
   *  @see FIRMessagingPendingTopicsListDelegate
   */
  @interface FIRMessagingPendingTopicsList : NSObject <NSCoding>
  
  @property(nonatomic, weak) NSObject <FIRMessagingPendingTopicsListDelegate> *delegate;
  
  @property(nonatomic, readonly, strong, nullable) NSDate *archiveDate;
  @property(nonatomic, readonly) NSUInteger numberOfBatches;
  
  
  - (instancetype)init NS_DESIGNATED_INITIALIZER;
  - (void)addOperationForTopic:(NSString *)topic
                    withAction:(FIRMessagingTopicAction)action
                    completion:(nullable FIRMessagingTopicOperationCompletion)completion;
  - (void)resumeOperationsIfNeeded;
  
  @end
  
  NS_ASSUME_NONNULL_END
  