firebase-ios-sdk/Firebase/Database/Core/FWriteTreeRef.m

/*
 * 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 "FWriteTreeRef.h"
#import "FPath.h"
#import "FNode.h"
#import "FWriteTree.h"
#import "FChildrenNode.h"
#import "FNamedNode.h"
#import "FWriteRecord.h"
#import "FIndex.h"
#import "FCacheNode.h"

@interface FWriteTreeRef ()
/**
* The path to this particular FWriteTreeRef. Used for calling methods on writeTree while exposing a simpler interface
* to callers.
*/
@property (nonatomic, strong) FPath *path;
/**
* A reference to the actual tree of the write data. All methods are pass-through to the tree, but with the appropriate
* path prefixed.
*
* This lets us make cheap references to points in the tree for sync points without having to copy and maintain all of
* the data.
*/
@property (nonatomic, strong) FWriteTree *writeTree;
@end

/**
* A FWriteTreeRef wraps a FWriteTree and a FPath, for convenient access to a particular subtree. All the methods just
* proxy to the underlying FWriteTree.
*/
@implementation FWriteTreeRef
- (id) initWithPath:(FPath *)aPath writeTree:(FWriteTree *)tree {
    self = [super init];
    if (self) {
        self.path = aPath;
        self.writeTree = tree;
    }
    return self;
}

/**
* @return If possible, returns a complete event cache, using the underlying server data if possible. In addition, can
* be used to get a cache that includes hidden writes, and excludes arbitrary writes. Note that customizing the returned
* node can lead to a more expensive calculation.
*/
- (id <FNode>) calculateCompleteEventCacheWithCompleteServerCache:(id<FNode>)completeServerCache {
    return [self.writeTree calculateCompleteEventCacheAtPath:self.path completeServerCache:completeServerCache excludeWriteIds:nil includeHiddenWrites:NO];
}

/**
* @return If possible, returns a children node containing all of the complete children we have data for. The returned
* data is a mix of the given server data and write data.
*/
- (FChildrenNode *) calculateCompleteEventChildrenWithCompleteServerChildren:(id<FNode>)completeServerChildren {
    return [self.writeTree calculateCompleteEventChildrenAtPath:self.path completeServerChildren:completeServerChildren];
}

/**
* Given that either the underlying server data has updated or the outstanding writes have been updating, determine what,
* if anything, needs to be applied to the event cache.
*
* Possibilities:
*
* 1. No writes are shadowing. Events should be raised, the snap to be applied comes from the server data.
*
* 2. Some writes are completly shadowing. No events to be raised.
*
* 3. Is partially shadowed. Events should be raised.
*
* Either existingEventSnap or existingServerSnap must exist, this is validated via an assert.
*/
- (id<FNode>) calculateEventCacheAfterServerOverwriteWithChildPath:(FPath *)childPath existingEventSnap:(id <FNode>)existingEventSnap existingServerSnap:(id <FNode>)existingServerSnap {
    return [self.writeTree calculateEventCacheAfterServerOverwriteAtPath:self.path childPath:childPath existingEventSnap:existingEventSnap existingServerSnap:existingServerSnap];
}

/**
* Returns a node if there is a complete overwrite for this path. More specifically, if there is a write at a higher
* path, this will return the child of that write relative to the write and this path.
* Returns nil if there is no write at this path.
*/
- (id<FNode>) shadowingWriteAtPath:(FPath *)path {
    return [self.writeTree shadowingWriteAtPath:[self.path child:path]];
}

/**
* This method is used when processing child remove events on a query. If we can, we pull in children that are outside
* the window, but may now be in the window.
*/
- (FNamedNode *)calculateNextNodeAfterPost:(FNamedNode *)post
                        completeServerData:(id<FNode>)completeServerData
                                   reverse:(BOOL)reverse
                                     index:(id<FIndex>)index
{
    return [self.writeTree calculateNextNodeAfterPost:post
                                               atPath:self.path
                                   completeServerData:completeServerData
                                              reverse:reverse
                                                index:index];
}

/**
* Returns a complete child for a given server snap after applying all user writes or nil if there is no complete child
* for this child key.
*/
- (id<FNode>) calculateCompleteChild:(NSString *)childKey cache:(FCacheNode *)existingServerCache {
    return [self.writeTree calculateCompleteChildAtPath:self.path childKey:childKey cache:existingServerCache];
}

/**
* @return a WriteTreeref for a child.
*/
- (FWriteTreeRef *) childWriteTreeRef:(NSString *)childKey {
    return [[FWriteTreeRef alloc] initWithPath:[self.path childFromString:childKey] writeTree:self.writeTree];
}


@end