how to upload posts in code

Hello,
I have a question regarding uploading new posts to wordpress.

Our website publishes newsletter-posts on a daily basis. At the moment the newsletters are manually added as new posts each day (image + text related to the image). We are however considering automizing this process.

So what I would like to do is internally generate the whole post as a php file and then upload this file to wordpress directly, instead of going through the wordpress UI. So in this php file I would have the text plus the image reference and I would specify all the parameters I need such as the post category, the tags… Of course I would still have to upload the media contained in the post to wordpress, but I have seen some solutions online to do this ‘programatically’.

Is it possible to upload such a php file directly to wp as a post? How would I go about doing this?
thank you,
Dario