Chapter 11 - Chat App/ChatAppFinished/Pods/FirebaseDatabase/Firebase/Database/Core/Utilities/FImmutableTree.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 "FImmutableTree.h"
#import "FImmutableSortedDictionary.h"
#import "FPath.h"
#import "FUtilities.h"

@interface FImmutableTree ()
@property (nonatomic, strong, readwrite) id value;
/**
* Maps NSString -> FImmutableTree<T>, where <T> is type of value.
*/
@property (nonatomic, strong, readwrite) FImmutableSortedDictionary *children;
@end

@implementation FImmutableTree
@synthesize value;
@synthesize children;

- (id) initWithValue:(id)aValue {
    self = [super init];
    if (self) {
        self.value = aValue;
        self.children = [FImmutableTree emptyChildren];
    }
    return self;
}

- (id) initWithValue:(id)aValue children:(FImmutableSortedDictionary *)childrenMap {
    self = [super init];
    if (self) {
        self.value = aValue;
        self.children = childrenMap;
    }
    return self;
}

+ (FImmutableSortedDictionary *) emptyChildren {
    static dispatch_once_t emptyChildrenToken;
    static FImmutableSortedDictionary *emptyChildren;
    dispatch_once(&emptyChildrenToken, ^{
        emptyChildren = [FImmutableSortedDictionary dictionaryWithComparator:[FUtilities stringComparator]];
    });
    return emptyChildren;
}

+ (FImmutableTree *) empty {
    static dispatch_once_t emptyImmutableTreeToken;
    static FImmutableTree *emptyTree = nil;
    dispatch_once(&emptyImmutableTreeToken, ^{
        emptyTree = [[FImmutableTree alloc] initWithValue:nil];
    });
    return emptyTree;
}

- (BOOL) isEmpty {
    return self.value == nil && [self.children isEmpty];
}

/**
* Given a path and a predicate, return the first node and the path to that node where the predicate returns true
* // TODO Do a perf test. If we're creating a bunch of FTuplePathValue objects on the way back out, it may be better to pass down a pathSoFar FPath
*/
- (FTuplePathValue *) findRootMostMatchingPath:(FPath *)relativePath predicate:(BOOL (^)(id value))predicate {
    if (self.value != nil && predicate(self.value)) {
        return [[FTuplePathValue alloc] initWithPath:[FPath empty] value:self.value];
    } else {
        if ([relativePath isEmpty]) {
            return nil;
        } else {
            NSString *front = [relativePath getFront];
            FImmutableTree *child = [self.children get:front];
            if (child != nil) {
                FTuplePathValue *childExistingPathAndValue = [child findRootMostMatchingPath:[relativePath popFront] predicate:predicate];
                if (childExistingPathAndValue != nil) {
                    FPath *fullPath = [[[FPath alloc] initWith:front] child:childExistingPathAndValue.path];
                    return [[FTuplePathValue alloc] initWithPath:fullPath value:childExistingPathAndValue.value];
                } else {
                    return nil;
                }
            } else {
                // No child matching path
                return nil;
            }
        }
    }
}

/**
* Find, if it exists, the shortest subpath of the given path that points a defined value in the tree
*/
- (FTuplePathValue *) findRootMostValueAndPath:(FPath *)relativePath {
    return [self findRootMostMatchingPath:relativePath predicate:^BOOL(__unsafe_unretained id value){
        return YES;
    }];
}

- (id) rootMostValueOnPath:(FPath *)path {
    return [self rootMostValueOnPath:path matching:^BOOL(id value) {
        return YES;
    }];
}

- (id) rootMostValueOnPath:(FPath *)path matching:(BOOL (^)(id))predicate {
    if (self.value != nil && predicate(self.value)) {
        return self.value;
    } else if (path.isEmpty) {
        return nil;
    } else {
        return [[self.children get:path.getFront] rootMostValueOnPath:[path popFront] matching:predicate];
    }
}

- (id) leafMostValueOnPath:(FPath *)path {
    return [self leafMostValueOnPath:path matching:^BOOL(id value) {
        return YES;
    }];
}

- (id) leafMostValueOnPath:(FPath *)relativePath matching:(BOOL (^)(id))predicate {
    __block id currentValue = self.value;
    __block FImmutableTree *currentTree = self;
    [relativePath enumerateComponentsUsingBlock:^(NSString *key, BOOL *stop) {
        currentTree = [currentTree.children get:key];
        if (currentTree == nil) {
            *stop = YES;
        } else {
            id treeValue = currentTree.value;
            if (treeValue != nil && predicate(treeValue)) {
                currentValue = treeValue;
            }
        }
    }];
    return currentValue;
}

- (BOOL) containsValueMatching:(BOOL (^)(id))predicate {
    if (self.value != nil && predicate(self.value)) {
        return YES;
    } else {
        __block BOOL found = NO;
        [self.children enumerateKeysAndObjectsUsingBlock:^(NSString *key, FImmutableTree *subtree, BOOL *stop) {
            found = [subtree containsValueMatching:predicate];
            if (found) *stop = YES;
        }];
        return found;
    }
}

- (FImmutableTree *) subtreeAtPath:(FPath *)relativePath {
    if ([relativePath isEmpty]) {
        return self;
    } else {
        NSString *front = [relativePath getFront];
        FImmutableTree *childTree = [self.children get:front];
        if (childTree != nil) {
            return [childTree subtreeAtPath:[relativePath popFront]];
        } else {
            return [FImmutableTree empty];
        }
    }
}

/**
* Sets a value at the specified path
*/
- (FImmutableTree *) setValue:(id)newValue atPath:(FPath *)relativePath {
    if ([relativePath isEmpty]) {
        return [[FImmutableTree alloc] initWithValue:newValue children:self.children];
    } else {
        NSString *front = [relativePath getFront];
        FImmutableTree *child = [self.children get:front];
        if (child == nil) {
            child = [FImmutableTree empty];
        }
        FImmutableTree *newChild = [child setValue:newValue atPath:[relativePath popFront]];
        FImmutableSortedDictionary *newChildren = [self.children insertKey:front withValue:newChild];
        return [[FImmutableTree alloc] initWithValue:self.value children:newChildren];
    }
}

/**
* Remove the value at the specified path
*/
- (FImmutableTree *) removeValueAtPath:(FPath *)relativePath {
    if ([relativePath isEmpty]) {
        if ([self.children isEmpty]) {
            return [FImmutableTree empty];
        } else {
            return [[FImmutableTree alloc] initWithValue:nil children:self.children];
        }
    } else {
        NSString *front = [relativePath getFront];
        FImmutableTree *child = [self.children get:front];
        if (child) {
            FImmutableTree *newChild = [child removeValueAtPath:[relativePath popFront]];
            FImmutableSortedDictionary *newChildren;
            if ([newChild isEmpty]) {
                newChildren = [self.children removeKey:front];
            } else {
                newChildren = [self.children insertKey:front withValue:newChild];
            }
            if (self.value == nil && [newChildren isEmpty]) {
                return [FImmutableTree empty];
            } else {
                return [[FImmutableTree alloc] initWithValue:self.value children:newChildren];
            }
        } else {
            return self;
        }
    }
}

/**
* Gets a value from the tree
*/
- (id) valueAtPath:(FPath *)relativePath {
    if ([relativePath isEmpty]) {
        return self.value;
    } else {
        NSString *front = [relativePath getFront];
        FImmutableTree *child = [self.children get:front];
        if (child) {
            return [child valueAtPath:[relativePath popFront]];
        } else {
            return nil;
        }
    }
}

/**
* Replaces the subtree at the specified path with the given new tree
*/
- (FImmutableTree *) setTree:(FImmutableTree *)newTree atPath:(FPath *)relativePath {
    if ([relativePath isEmpty]) {
        return newTree;
    } else {
        NSString *front = [relativePath getFront];
        FImmutableTree *child = [self.children get:front];
        if (child == nil) {
            child = [FImmutableTree empty];
        }
        FImmutableTree *newChild = [child setTree:newTree atPath:[relativePath popFront]];
        FImmutableSortedDictionary *newChildren;
        if ([newChild isEmpty]) {
            newChildren = [self.children removeKey:front];
        } else {
            newChildren = [self.children insertKey:front withValue:newChild];
        }
        return [[FImmutableTree alloc] initWithValue:self.value children:newChildren];
    }
}

/**
* Performs a depth first fold on this tree. Transforms a tree into a single value, given a function that operates on
* the path to a node, an optional current value, and a map of the child names to folded subtrees
*/
- (id) foldWithBlock:(id (^)(FPath *path, id value, NSDictionary *foldedChildren))block {
    return [self foldWithPathSoFar:[FPath empty] withBlock:block];
}

/**
* Recursive helper for public facing foldWithBlock: method
*/
- (id) foldWithPathSoFar:(FPath *)pathSoFar withBlock:(id (^)(FPath *path, id value, NSDictionary *foldedChildren))block {
    __block NSMutableDictionary *accum = [[NSMutableDictionary alloc] init];
    [self.children enumerateKeysAndObjectsUsingBlock:^(NSString *childKey, FImmutableTree *childTree, BOOL *stop) {
        accum[childKey] = [childTree foldWithPathSoFar:[pathSoFar childFromString:childKey] withBlock:block];
    }];
    return block(pathSoFar, self.value, accum);
}

/**
* Find the first matching value on the given path. Return the result of applying block to it.
*/
- (id) findOnPath:(FPath *)path andApplyBlock:(id (^)(FPath *path, id value))block {
    return [self findOnPath:path pathSoFar:[FPath empty] andApplyBlock:block];
}

- (id) findOnPath:(FPath *)pathToFollow pathSoFar:(FPath *)pathSoFar andApplyBlock:(id (^)(FPath *path, id value))block {
    id result = self.value ? block(pathSoFar, self.value) : nil;
    if (result != nil) {
        return result;
    } else {
        if ([pathToFollow isEmpty]) {
            return nil;
        } else {
            NSString *front = [pathToFollow getFront];
            FImmutableTree *nextChild = [self.children get:front];
            if (nextChild != nil) {
                return [nextChild findOnPath:[pathToFollow popFront] pathSoFar:[pathSoFar childFromString:front] andApplyBlock:block];
            } else {
                return nil;
            }
        }
    }
}
/**
* Call the block on each value along the path for as long as that function returns true
* @return The path to the deepest location inspected
*/
- (FPath *) forEachOnPath:(FPath *)path whileBlock:(BOOL (^)(FPath *, id))block {
    return [self forEachOnPath:path pathSoFar:[FPath empty] whileBlock:block];
}

- (FPath *) forEachOnPath:(FPath *)pathToFollow pathSoFar:(FPath *)pathSoFar whileBlock:(BOOL (^)(FPath *, id))block {
    if ([pathToFollow isEmpty]) {
        if (self.value) {
            block(pathSoFar, self.value);
        }
        return pathSoFar;
    } else {
        BOOL shouldContinue = YES;
        if (self.value) {
            shouldContinue = block(pathSoFar, self.value);
        }
        if (shouldContinue) {
            NSString *front = [pathToFollow getFront];
            FImmutableTree *nextChild = [self.children get:front];
            if (nextChild) {
                return [nextChild forEachOnPath:[pathToFollow popFront] pathSoFar:[pathSoFar childFromString:front] whileBlock:block];
            } else {
                return pathSoFar;
            }
        } else {
            return pathSoFar;
        }
    }
}

- (FImmutableTree *) forEachOnPath:(FPath *)path performBlock:(void (^)(FPath *path, id value))block {
    return [self forEachOnPath:path pathSoFar:[FPath empty] performBlock:block];
}

- (FImmutableTree *) forEachOnPath:(FPath *)pathToFollow pathSoFar:(FPath *)pathSoFar performBlock:(void (^)(FPath *path, id value))block {
    if ([pathToFollow isEmpty]) {
        return self;
    } else {
        if (self.value) {
            block(pathSoFar, self.value);
        }
        NSString *front = [pathToFollow getFront];
        FImmutableTree *nextChild = [self.children get:front];
        if (nextChild) {
            return [nextChild forEachOnPath:[pathToFollow popFront] pathSoFar:[pathSoFar childFromString:front] performBlock:block];
        } else {
            return [FImmutableTree empty];
        }
    }
}
/**
* Calls the given block for each node in the tree that has a value. Called in depth-first order
*/
- (void) forEach:(void (^)(FPath *path, id value))block {
    [self forEachPathSoFar:[FPath empty] withBlock:block];
}

- (void) forEachPathSoFar:(FPath *)pathSoFar withBlock:(void (^)(FPath *path, id value))block {
    [self.children enumerateKeysAndObjectsUsingBlock:^(NSString *childKey, FImmutableTree *childTree, BOOL *stop) {
        [childTree forEachPathSoFar:[pathSoFar childFromString:childKey] withBlock:block];
    }];
    if (self.value) {
        block(pathSoFar, self.value);
    }
}

- (void) forEachChild:(void (^)(NSString *childKey, id childValue))block {
    [self.children enumerateKeysAndObjectsUsingBlock:^(NSString *childKey, FImmutableTree *childTree, BOOL *stop) {
        if (childTree.value) {
            block(childKey, childTree.value);
        }
    }];
}

- (BOOL)isEqual:(id)object {
    if (![object isKindOfClass:[FImmutableTree class]]) {
        return NO;
    }
    FImmutableTree *other = (FImmutableTree *)object;
    return (self.value == other.value || [self.value isEqual:other.value]) && [self.children isEqual:other.children];
}

- (NSUInteger)hash {
    return self.children.hash * 31 + [self.value hash];
}

- (NSString *) description {
    NSMutableString *string = [[NSMutableString alloc] init];
    [string appendString:@"FImmutableTree { value="];
    [string appendString:(self.value ? [self.value description] : @"<nil>")];
    [string appendString:@", children={"];
    [self.children enumerateKeysAndObjectsUsingBlock:^(NSString *childKey, FImmutableTree *childTree, BOOL *stop) {
        [string appendString:@" "];
        [string appendString:childKey];
        [string appendString:@"="];
        [string appendString:[childTree.value description]];
    }];
    [string appendString:@" } }"];
    return [NSString stringWithString:string];
}

- (NSString *) debugDescription {
    return [self description];
}


@end
