Chapter 11 - Chat App/ChatAppFinished/Pods/FirebaseDatabase/Firebase/Database/FKeyIndex.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 "FKeyIndex.h"
#import "FNamedNode.h"
#import "FSnapshotUtilities.h"
#import "FUtilities.h"
#import "FEmptyNode.h"

@interface FKeyIndex ()

@property (nonatomic, strong) FNamedNode *maxPost;

@end

@implementation FKeyIndex

- (id)init {
    self = [super init];
    if (self) {
        self.maxPost = [[FNamedNode alloc] initWithName:[FUtilities maxName] andNode:[FEmptyNode emptyNode]];
    }
    return self;

}

- (NSComparisonResult) compareKey:(NSString *)key1
                          andNode:(id<FNode>)node1
                       toOtherKey:(NSString *)key2
                          andNode:(id<FNode>)node2
{
    return [FUtilities compareKey:key1 toKey:key2];
}

- (NSComparisonResult) compareKey:(NSString *)key1
                          andNode:(id<FNode>)node1
                       toOtherKey:(NSString *)key2
                          andNode:(id<FNode>)node2
                          reverse:(BOOL)reverse
{
    if (reverse) {
        return [self compareKey:key2 andNode:node2 toOtherKey:key1 andNode:node1];
    } else {
        return [self compareKey:key1 andNode:node1 toOtherKey:key2 andNode:node2];
    }
}

- (NSComparisonResult) compareNamedNode:(FNamedNode *)namedNode1 toNamedNode:(FNamedNode *)namedNode2
{
    return [self compareKey:namedNode1.name andNode:namedNode1.node toOtherKey:namedNode2.name andNode:namedNode2.node];
}

- (BOOL)isDefinedOn:(id <FNode>)node {
    return YES;
}

- (BOOL)indexedValueChangedBetween:(id <FNode>)oldNode and:(id <FNode>)newNode {
    return NO;  // The key for a node never changes.
}

- (FNamedNode *)minPost {
    return [FNamedNode min];
}

- (FNamedNode *)makePost:(id<FNode>)indexValue name:(NSString*)name {
    NSString *key = indexValue.val;
    NSAssert([key isKindOfClass:[NSString class]], @"KeyIndex indexValue must always be a string.");
    // We just use empty node, but it'll never be compared, since our comparator only looks at name.
    return [[FNamedNode alloc] initWithName:key andNode:[FEmptyNode emptyNode]];
}

- (NSString *) queryDefinition {
    return @".key";
}

- (NSString *) description {
    return @"FKeyIndex";
}

- (id)copyWithZone:(NSZone *)zone {
    return self;
}

- (BOOL) isEqual:(id)other {
    // since we're a singleton.
    return (other == self);
}

- (NSUInteger) hash {
    return [@".key" hash];
}


+ (id<FIndex>) keyIndex {
    static id<FIndex> keyIndex;
    static dispatch_once_t once;
    dispatch_once(&once, ^{
       keyIndex = [[FKeyIndex alloc] init];
    });
    return keyIndex;
}
@end
