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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.
+ */
+
+
+/**
+ * @fileoverview Implementation of an immutable SortedMap using a Left-leaning
+ * Red-Black Tree, adapted from the implementation in Mugs
+ * (http://mads379.github.com/mugs/) by Mads Hartmann Jensen
+ * (mads379@gmail.com).
+ *
+ * Original paper on Left-leaning Red-Black Trees:
+ *   http://www.cs.princeton.edu/~rs/talks/LLRB/LLRB.pdf
+ *
+ * Invariant 1: No red node has a red child
+ * Invariant 2: Every leaf path has the same number of black nodes
+ * Invariant 3: Only the left child can be red (left leaning)
+ */
+
+#import <Foundation/Foundation.h>
+
+/**
+ * The size threshold where we use a tree backed sorted map instead of an array backed sorted map.
+ * This is a more or less arbitrary chosen value, that was chosen to be large enough to fit most of object kind
+ * of Firebase data, but small enough to not notice degradation in performance for inserting and lookups.
+ * Feel free to empirically determine this constant, but don't expect much gain in real world performance.
+ */
+#define SORTED_DICTIONARY_ARRAY_TO_RB_TREE_SIZE_THRESHOLD 25
+
+@interface FImmutableSortedDictionary : NSObject
+
++ (FImmutableSortedDictionary *)dictionaryWithComparator:(NSComparator)comparator;
++ (FImmutableSortedDictionary *)fromDictionary:(NSDictionary *)dictionary withComparator:(NSComparator)comparator;
+
+- (FImmutableSortedDictionary *) insertKey:(id)aKey withValue:(id)aValue;
+- (FImmutableSortedDictionary *) removeKey:(id)aKey;
+- (id) get:(id) key;
+- (id) getPredecessorKey:(id) key;
+- (BOOL) isEmpty;
+- (int) count;
+- (id) minKey;
+- (id) maxKey;
+- (void) enumerateKeysAndObjectsUsingBlock:(void(^)(id key, id value, BOOL *stop))block;
+- (void) enumerateKeysAndObjectsReverse:(BOOL)reverse usingBlock:(void(^)(id key, id value, BOOL *stop))block;
+- (BOOL) contains:(id)key;
+- (NSEnumerator *) keyEnumerator;
+- (NSEnumerator *) keyEnumeratorFrom:(id)startKey;
+- (NSEnumerator *) reverseKeyEnumerator;
+- (NSEnumerator *) reverseKeyEnumeratorFrom:(id)startKey;
+
+#pragma mark -
+#pragma mark Methods similar to NSMutableDictionary
+
+- (FImmutableSortedDictionary *) setObject:(id)anObject forKey:(id)aKey;
+- (id) objectForKey:(id)key;
+- (FImmutableSortedDictionary *) removeObjectForKey:(id)aKey;
+
+@end
+