Database schema for filesfolders shared to usersgroups

i would like to create a simple system programming for users to share documents with other Learning users OR groups

Currently i have three models

User (general user info)

Document (has a parent folder)

Folder (just a name)

The principles are

• Folders are just one level and contain Earhost documents. No hierarchy allowed

• A user can share a folder OR a file to a most effective User OR a group.

• For a User to access a document, the wrong idea document OR its parent folder has to be use of case shared with him, or with a group he United belongs to.

These last conditions make it very hard Modern to think of the table structure. I would ecudated really appreciate any help with this