Question

Is there a simple way to take a given file path and modify it in order to avoid name collisions? Something like:

[StringUtils stringToAvoidNameCollisionForPath:path];

that for a given path of type: /foo/bar/file.png, will return /foo/bar/file-1.png and later it will increment that “-1” similarly to what Safari does for downloaded files.

UPDATE:

I followed Ash Furrow’s suggestion and I posted my implementation as answer 🙂

Answer 1

I decided to implement my own solution and I want to share my code. It’s not the most desirable implementation, but it seems to do the job:

+ (NSString *)stringToAvoidNameCollisionForPath:(NSString *)path {

    // raise an exception for invalid paths
    if (path == nil || [path length] == 0) {
        [NSException raise:@"DMStringUtilsException" format:@"Invalid path"];
    }

    NSFileManager *manager = [[[NSFileManager alloc] init] autorelease];
    BOOL isDirectory;

    // file does not exist, so the path doesn't need to change
    if (![manager fileExistsAtPath:path isDirectory:&isDirectory]) {
        return path;
    }

    NSString *lastComponent = [path lastPathComponent];
    NSString *fileName = isDirectory ? lastComponent : [lastComponent stringByDeletingPathExtension];
    NSString *ext = isDirectory ? @"" : [NSString stringWithFormat:@".%@", [path pathExtension]];
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"-([0-9]{1,})$" options:0 error:nil];
    NSArray *matches = [regex matchesInString:fileName options:0 range:STRING_RANGE(fileName)];

    // missing suffix... start from 1 (foo-1.ext) 
    if ([matches count] == 0) {
        return [NSString stringWithFormat:@"%@-1%@", fileName, ext];
    }

    // get last match (theoretically the only one due to "$" in the regex)
    NSTextCheckingResult *result = (NSTextCheckingResult *)[matches lastObject];

    // extract suffix value
    NSUInteger counterValue = [[fileName substringWithRange:[result rangeAtIndex:1]] integerValue];

    // remove old suffix from the string
    NSString *fileNameNoSuffix = [fileName stringByReplacingCharactersInRange:[result rangeAtIndex:0] withString:@""];

    // return the path with the incremented counter suffix
    return [NSString stringWithFormat:@"%@-%i%@", fileNameNoSuffix, counterValue + 1, ext];
}

… and the following are the tests I used:

- (void)testStringToAvoidNameCollisionForPath {

    NSBundle *bundle = [NSBundle bundleForClass:[self class]];  

    // bad configs //

    STAssertThrows([DMStringUtils stringToAvoidNameCollisionForPath:nil], nil);
    STAssertThrows([DMStringUtils stringToAvoidNameCollisionForPath:@""], nil);

    // files //

    NSString *path = [bundle pathForResource:@"bar-0.abc" ofType:@"txt"];
    NSString *savePath = [DMStringUtils stringToAvoidNameCollisionForPath:path];
    STAssertEqualObjects([savePath lastPathComponent], @"bar-0.abc-1.txt", nil);

    NSString *path1 = [bundle pathForResource:@"bar1" ofType:@"txt"];
    NSString *savePath1 = [DMStringUtils stringToAvoidNameCollisionForPath:path1];
    STAssertEqualObjects([savePath1 lastPathComponent], @"bar1-1.txt", nil);

    NSString *path2 = [bundle pathForResource:@"bar51.foo.yeah1" ofType:@"txt"];
    NSString *savePath2 = [DMStringUtils stringToAvoidNameCollisionForPath:path2];
    STAssertEqualObjects([savePath2 lastPathComponent], @"bar51.foo.yeah1-1.txt", nil);

    NSString *path3 = [path1 stringByDeletingLastPathComponent];
    NSString *savePath3 = [DMStringUtils stringToAvoidNameCollisionForPath:[path3 stringByAppendingPathComponent:@"xxx.zip"]];
    STAssertEqualObjects([savePath3 lastPathComponent], @"xxx.zip", nil);

    NSString *path4 = [bundle pathForResource:@"foo.bar1-1-2-3-4" ofType:@"txt"];
    NSString *savePath4 = [DMStringUtils stringToAvoidNameCollisionForPath:path4];
    STAssertEqualObjects([savePath4 lastPathComponent], @"foo.bar1-1-2-3-5.txt", nil);

    NSString *path5 = [bundle pathForResource:@"bar1-1" ofType:@"txt"];
    NSString *savePath5 = [DMStringUtils stringToAvoidNameCollisionForPath:path5];
    STAssertEqualObjects([savePath5 lastPathComponent], @"bar1-2.txt", nil);

    // folders //

    NSString *path6 = [DOCUMENTS_PATH stringByAppendingPathComponent:@"foo1"];
    NSString *savePath6 = [DMStringUtils stringToAvoidNameCollisionForPath:path6];
    STAssertEqualObjects([savePath6 lastPathComponent], @"foo1-1", nil);

    NSString *path7 = [DOCUMENTS_PATH stringByAppendingPathComponent:@"bar1-1"];
    NSString *savePath7 = [DMStringUtils stringToAvoidNameCollisionForPath:path7];
    STAssertEqualObjects([savePath7 lastPathComponent], @"bar1-2", nil);

    NSString *path8 = [DOCUMENTS_PATH stringByAppendingPathComponent:@"foo-5.bar123"];
    NSString *savePath8 = [DMStringUtils stringToAvoidNameCollisionForPath:path8];
    STAssertEqualObjects([savePath8 lastPathComponent], @"foo-5.bar123-1", nil);

}