Recursive function based on 2 conditions - recursion

Question

I want to write a recursive function which exits on 2 conditions.
Let's say I want to make a directory and ask the user for input. He may enter something like this:
Valid: /existing-dir1/existing-DIR2/non-existence-dir1/non-existence-dir2
Invalid: /existing-dir1/existing-FILE1/non-existence-dir1/non-existence-dir2
To loop through the filename, I have the function dirname() which take /foo/bar and returns /foo. I also have function exist() to check if a filename exist and isdir() to see if it is a file or directory.
Basically, I need to loop recursively from the end of the filename, ignore non-existence nodes, and check if any node is a file - which is invalid. The recursion ends when one of the 2 conditions happens, whichever comes first:
A file is found
dirname() returns /
I am not familiar with recursion, and 2 conditions is a bit too much for me. I am using POSIX script but code samples in C++ / Java / C# are all good.
Edit: I know I can do a mkdir -p and get its status code, but it will create the directory. Nontheless, I want to do that in recursion for the purpose of learning.

Answer 1

In JS, you might write the recursion like this:
const isValid = (path) =>
path === '/'
? 'valid'
: exist(path) && !isdir(path)
? 'invalid'
: isValid(dirname(path))
You might be able to skip the exist check depending upon how your isdir function works.
This should show the logic, but I'm not sure how to write this in your Posix script environment.

Answer 2

I solved it myself. Written in POSIX script, but it is quite easy to read and port to other languages:
RecursivelyCheckFilename ()
{
if [ -e "$1" ] # if exists
then
if [ -d "$1" ] # if is directory
then
if [ "$1" = "/" ]
then
return 0;
else
RecursivelyCheckFilename "$(dirname -- "$1")";
return $?; # returns the value returned by previous function
fi
else
return 1;
fi
else
RecursivelyCheckFilename "$(dirname -- "$1")";
return $?;
fi
}
There are still a few issues with filename ending with a trailing slash, which I must find a way to deal with. But the code above is how I want it to work.