Babel: tangling questions

[Jarmo Hurri <jarmo.hurri@iki.fi>]

Greetings.

I am trying to tangle code to a specific directory.

1. I want to tangle to the default filename (derived from name of org
   file and programming language). However, the :tangle header argument
   only takes either "yes" or "filename." If the value is "yes", then
   the filename is deduced automatically. How can I specify a tangling
   directory and still have the default filename?

   There was a related question on stack exchange, but it did not use
   the default filename:
   https://emacs.stackexchange.com/questions/41806/org-babel-set-root-dir-for-tangled-files

2. The question above implies a feature request: third possible value
   for :tangle, a directory. In this case code would be tangled into the
   specified directory into a file with default filename. Any support?

3. Is it possible to tangle automatically on (every) export? I always
   export, but I might forget to tangle, in which case export and tangle
   would be out of sync.

   Someone asked about this a while ago on stack exchange, but maybe
   things have changed:
   https://emacs.stackexchange.com/questions/24645/exporting-and-tangling-simultaneously-in-org-mode

Thanks a bunch in advance.

Jarmo