NSURL Relativize

NSString * relativize(NSURL * to, NSURL * from, BOOL fromIsDir) {
    NSString * toString = [[to absoluteString] stringByStandardizingPath];
    NSMutableArray * toPieces = [NSMutableArray arrayWithArray:[toString pathComponents]];

    NSString * fromString = [[from absoluteString] stringByStandardizingPath];
    NSMutableArray * fromPieces = [NSMutableArray arrayWithArray:[fromString pathComponents]];

    NSMutableString * relPath = [NSMutableString string];

    NSString * toTrimmed = toString;
    NSString * toPiece = NULL;
    NSString * fromTrimmed = fromString;
    NSString * fromPiece = NULL;

    NSMutableArray * parents = [NSMutableArray array];
    NSMutableArray * pieces = [NSMutableArray array];

    if(toPieces.count >= fromPieces.count) {
        NSUInteger toCount = toPieces.count;
        while(toCount > fromPieces.count) {
            toPiece = [toTrimmed lastPathComponent];
            toTrimmed = [toTrimmed stringByDeletingLastPathComponent];
            [pieces insertObject:toPiece atIndex:0];
            toCount--;
        }

        while(![fromTrimmed isEqualToString:toTrimmed]) {
            toPiece = [toTrimmed lastPathComponent];
            toTrimmed = [toTrimmed stringByDeletingLastPathComponent];
            fromPiece = [fromTrimmed lastPathComponent];
            fromTrimmed = [fromTrimmed stringByDeletingLastPathComponent];
            if(![toPiece isEqualToString:fromPiece]) {
                if(![fromPiece isEqualToString:[fromPiece lastPathComponent]] || fromIsDir) {
                    [parents addObject:@".."];
                }
                [pieces insertObject:toPiece atIndex:0];
            }
        }

    } else {
        NSUInteger fromCount = fromPieces.count;

        while(fromCount > toPieces.count) {
            fromPiece = [fromTrimmed lastPathComponent];
            fromTrimmed = [fromTrimmed stringByDeletingLastPathComponent];
            if(![fromPiece isEqualToString:[fromString lastPathComponent]] || fromIsDir) {
                [parents addObject:@".."];
            }
            fromCount--;
        }

        while(![toTrimmed isEqualToString:fromTrimmed]) {
            toPiece = [toTrimmed lastPathComponent];
            toTrimmed = [toTrimmed stringByDeletingLastPathComponent];
            fromPiece = [fromTrimmed lastPathComponent];
            fromTrimmed = [fromTrimmed stringByDeletingLastPathComponent];
            [parents addObject:@".."];
            [pieces insertObject:toPiece atIndex:0];
        }

    }

    [relPath appendString:[parents componentsJoinedByString:@"/"]];
    if(parents.count > 0) [relPath appendString:@"/"];
    else [relPath appendString:@"./"];
    [relPath appendString:[pieces componentsJoinedByString:@"/"]];

    NSLog(@"%@",relPath);

    return relPath;
}