Query String with Hash (Objective-C + ARC)

NSArray+flatten.h

@interface NSArray (flatten)
- (NSArray *)flatten;
@end

NSArray+flatten.m

@implementation NSArray (flatten)
- (NSArray *)flatten
{
    __block NSMutableArray *copiedArray = [NSMutableArray array];
    __block void (^f)(NSArray *array) = ^(NSArray *array) {
        for (id obj in array) {
            if ([obj isKindOfClass:[NSArray class]]) {
                f(obj);
            } else {
                [copiedArray addObject:obj];
            }
        }
    };
    f(self);
    return [copiedArray copy];
}
@end

NSURL+queryStrings.h

@interface NSURL (queryStrings)

- (NSURL *)URLByAppendingQueryParameters:(NSDictionary *)parameters;
+ (NSString *)queryStringWithParameters:(NSDictionary *)parameters;

@end

NSURL+queryStrings.m

@implementation NSURL (queryStrings)

- (NSURL *)URLByAppendingQueryParameters:(NSDictionary *)parameters
{
    if (parameters == nil) {
        return self;
    }
    
    NSString *string = self.absoluteString;
    NSString *queryString = [self.class queryStringWithParameters:parameters];
    NSString *delimiter = nil;
    
    if ([string rangeOfString:@"?"].length == 0) {
        delimiter = @"?";
    } else {
        delimiter = @"&";
    }
    
    NSString *URLString = [NSString stringWithFormat:@"%@%@%@", self.absoluteString, delimiter, queryString];
    return [NSURL URLWithString:URLString];
}

+ (NSArray *)queryStringsWithKey:(NSString *)key value:(id)value
{
    __block NSMutableArray *queries = [NSMutableArray array];
    if ([value isKindOfClass:[NSArray class]]) {
        [(NSArray *)value enumerateObjectsUsingBlock:^(id innerValue, NSUInteger idx, BOOL *stop) {
            id query = [self queryStringsWithKey:[NSString stringWithFormat:@"%@[]", key]
                                           value:innerValue];
            [queries addObject:query];
        }];
    } else if([value isKindOfClass:[NSDictionary class]]) {
        [(NSDictionary *)value enumerateKeysAndObjectsUsingBlock:^(id innerKey, id innerValue, BOOL *stop) {
            id query = [self queryStringsWithKey:[NSString stringWithFormat:@"%@[%@]", key, innerKey]
                                           value:innerValue];
            [queries addObject:query];
        }];
    } else {
        [queries addObject:[NSString stringWithFormat:@"%@=%@", key, value]];
    }
    
    return [queries flatten];
}

+ (NSString *)queryStringWithParameters:(NSDictionary *)parameters
{
    NSMutableArray *queryStrings = [NSMutableArray array];
    
    for (NSString *key in parameters.allKeys) {
        id value = [parameters objectForKey:key];
        [queryStrings addObject:[self queryStringsWithKey:key value:value]];
    }
    
    return [[queryStrings flatten] componentsJoinedByString:@"&"];
}

@end