use std::error::Error as StdError; use std::fmt; use crate::mail::mailbox::Mailbox; use crate::mail::user::User; #[derive(Debug)] pub enum Error { ForbiddenTransition, } impl fmt::Display for Error { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "Forbidden Transition") } } impl StdError for Error {} pub enum State { NotAuthenticated, Authenticated(User), Selected(User, Mailbox), Logout, } pub enum Transition { None, Authenticate(User), Select(Mailbox), Unselect, Logout, } // See RFC3501 section 3. // https://datatracker.ietf.org/doc/html/rfc3501#page-13 impl State { pub fn apply(self, tr: Transition) -> Result { match (self, tr) { (s, Transition::None) => Ok(s), (State::NotAuthenticated, Transition::Authenticate(u)) => Ok(State::Authenticated(u)), (State::Authenticated(u), Transition::Select(m)) => Ok(State::Selected(u, m)), (State::Selected(u, _), Transition::Unselect) => Ok(State::Authenticated(u)), (_, Transition::Logout) => Ok(State::Logout), _ => Err(Error::ForbiddenTransition), } } }