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/*
* 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>
#include "Firestore/core/src/firebase/firestore/auth/user.h"
@class FSTWriteGroup;
@protocol FSTMutationQueue;
@protocol FSTQueryCache;
@protocol FSTRemoteDocumentCache;
NS_ASSUME_NONNULL_BEGIN
/**
* FSTPersistence is the lowest-level shared interface to persistent storage in Firestore.
*
* FSTPersistence is used to create FSTMutationQueue and FSTRemoteDocumentCache instances backed
* by persistence (which might be in-memory or LevelDB).
*
* FSTPersistence also exposes an API to create and commit FSTWriteGroup instances.
* Implementations of FSTWriteGroup/FSTPersistence only need to guarantee that writes made
* against the FSTWriteGroup are not made to durable storage until commitGroup:action: is called
* here. Since memory-only storage components do not alter durable storage, they are free to ignore
* the group.
*
* This contract is enough to allow the FSTLocalStore be be written independently of whether or not
* the stored state actually is durably persisted. If persistent storage is enabled, writes are
* grouped together to avoid inconsistent state that could cause crashes.
*
* Concretely, when persistent storage is enabled, the persistent versions of FSTMutationQueue,
* FSTRemoteDocumentCache, and others (the mutators) will defer their writes into an FSTWriteGroup.
* Once the local store has completed one logical operation, it commits the write group using
* [FSTPersistence commitGroup:action:].
*
* When persistent storage is disabled, the non-persistent versions of the mutators ignore the
* FSTWriteGroup and [FSTPersistence commitGroup:action:] is a no-op. This short-cut is allowed
* because memory-only storage leaves no state so it cannot be inconsistent.
*
* This simplifies the implementations of the mutators and allows memory-only implementations to
* supplement the persistent ones without requiring any special dual-store implementation of
* FSTPersistence. The cost is that the FSTLocalStore needs to be slightly careful about the order
* of its reads and writes in order to avoid relying on being able to read back uncommitted writes.
*/
@protocol FSTPersistence <NSObject>
/**
* Starts persistent storage, opening the database or similar.
*
* @param error An error object that will be populated if startup fails.
* @return YES if persistent storage started successfully, NO otherwise.
*/
- (BOOL)start:(NSError **)error;
/** Releases any resources held during eager shutdown. */
- (void)shutdown;
/**
* Returns an FSTMutationQueue representing the persisted mutations for the given user.
*
* <p>Note: The implementation is free to return the same instance every time this is called for a
* given user. In particular, the memory-backed implementation does this to emulate the persisted
* implementation to the extent possible (e.g. in the case of uid switching from
* sally=>jack=>sally, sally's mutation queue will be preserved).
*/
- (id<FSTMutationQueue>)mutationQueueForUser:(const firebase::firestore::auth::User &)user;
/** Creates an FSTQueryCache representing the persisted cache of queries. */
- (id<FSTQueryCache>)queryCache;
/** Creates an FSTRemoteDocumentCache representing the persisted cache of remote documents. */
- (id<FSTRemoteDocumentCache>)remoteDocumentCache;
/**
* Creates an FSTWriteGroup with the specified action description.
*
* @param action A description of the action performed by this group, used for logging.
* @return The created group.
*/
- (FSTWriteGroup *)startGroupWithAction:(NSString *)action;
/**
* Commits all accumulated changes in the given group. If there are no changes this is a no-op.
*
* @param group The group of changes to write as a unit.
*/
- (void)commitGroup:(FSTWriteGroup *)group;
@end
NS_ASSUME_NONNULL_END
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