Given a path to a folder, replaces all occurrences of `snake_case` words (ignoring `ALL_CAPS` and `dispatch_foo` and `objc_foo`) with their `camelCase` equivalent.

snake_case_toCamelCase.m

#import <Foundation/Foundation.h>

#define kRegex @"(?<!\")\\b(?!dispatch)(?!objc)_?([A-Z]?[a-z]+_[A-Z]?[a-z]+)"

@interface NSString (Util)
- (NSArray *)matchesForRegex:(NSString *)pattern;
- (NSArray *)allCodeFilesInDirectory;
@end

@implementation NSString (Util)

- (NSArray *)allCodeFilesInDirectory {
    NSArray *allItems = [[NSFileManager defaultManager] contentsOfDirectoryAtPath:self error:nil];
    if (allItems.count) {
        NSMutableArray *files = [NSMutableArray array];
        
        for (NSString *file in allItems)
            if ([file hasSuffix:@".m"] || [file hasSuffix:@".h"])
                [files addObject:file];
        
        return files;
    }
    
    return @[];
}

- (NSArray *)matchesForRegex:(NSString *)pattern {
    NSError *error = nil;
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:pattern options:0 error:&error];
    if (error)
        return nil;
    NSArray *matches = [regex matchesInString:self options:0 range:NSMakeRange(0, self.length)];
    if (matches.count == 0)
        return nil;
    
    return matches;
}

@end

NSString *URStringByRemovingUnderscore(NSString *foo) {
    if (![foo containsString:@"_"]) return nil;
    if ([foo.uppercaseString isEqualToString:foo]) return nil;
    
    NSRange r = [foo rangeOfString:@"_"];
    foo = [foo stringByReplacingOccurrencesOfString:@"_" withString:@""];
    NSString *lowercase = [foo substringWithRange:r];
    foo = [foo stringByReplacingCharactersInRange:r withString:lowercase.uppercaseString];
    return foo;
}

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        
        NSString *folder = @"/Users/you/path/too/project/folder";
        NSArray *files = [folder allCodeFilesInDirectory];
        for (NSString *fileName in files) {
            NSData *data = [NSData dataWithContentsOfFile:[folder stringByAppendingString:fileName]];
            NSMutableString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding].mutableCopy;
            
            NSArray *matches = [string matchesForRegex:kRegex];
            while (matches.count) {
                
                NSString *replacement;
                for (NSTextCheckingResult *result in matches.reverseObjectEnumerator.allObjects) {
                    replacement = URStringByRemovingUnderscore([string substringWithRange:[result rangeAtIndex:1]]);
                    if (replacement)
                        [string replaceCharactersInRange:[result rangeAtIndex:1] withString:replacement];
                }
                
                matches = [string matchesForRegex:kRegex];
            }
            
            data = [string dataUsingEncoding:NSUTF8StringEncoding];
            [data writeToFile:[folder stringByAppendingString:fileName] atomically:YES];
        }
    }
    
    return 0;
}