Handle the "share file" / "open with" intent for appropriate filetypes

[thw0rted]

I'm trying to find a good way of getting books onto the phone, especially for my family, who have little patience for complex solutions. The best I've come up with is to run a simple web server where they can download individual books as a single M4A / M4B file, after which they have to move the file into the Audiobooks folder (under its own subfolder, due to #809) using their file-manager app. It's OK, but it's not great -- I usually have to do the latter half of the process for them myself.

It occurred to me that I can use a "cloud drive" application like Google Drive, OneDrive, DropBox, etc, to save all my books, then share the folder of books using those platforms' built-in sharing mechanisms. This would let them download the book from those platforms, then use the Android "share" verb (called "open with" in Google drive, "send files" in OneDrive, not sure about others) to choose a player.

On my phone right now, this gives me an option for VLC (which doesn't work), Pocket Casts (which considers "open a local file" to be a premium/paid feature?), Bluetooth transfer, email, WhatsApp, etc etc. I'm not sure exactly which intent is used or how you'd have to handle it, but I would love to enable a workflow that lets me "send" a book to Voice and have it be available in the library.

This would also require some design work. Could opening a "shared" file add a single-book entry in the "Audiobook folders" list, pointing to wherever the cloud-drive app actually stores it? Would it be necessary to save a copy of the file instead? (Maybe require at least one multi-book folder be defined?)