1 files changed, 114 insertions, 0 deletions
diff --git a/aero-proto/imap/flow.rs b/aero-proto/imap/flow.rs
new file mode 100644
index 0000000..86eb12e
--- /dev/null
+++ b/aero-proto/imap/flow.rs
@@ -0,0 +1,114 @@
+use std::error::Error as StdError;
+use std::fmt;
+use std::sync::Arc;
+
+use imap_codec::imap_types::core::Tag;
+use tokio::sync::Notify;
+
+use crate::imap::mailbox_view::MailboxView;
+use crate::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(Arc<User>),
+    Selected(Arc<User>, MailboxView, MailboxPerm),
+    Idle(
+        Arc<User>,
+        MailboxView,
+        MailboxPerm,
+        Tag<'static>,
+        Arc<Notify>,
+    ),
+    Logout,
+}
+impl State {
+    pub fn notify(&self) -> Option<Arc<Notify>> {
+        match self {
+            Self::Idle(_, _, _, _, anotif) => Some(anotif.clone()),
+            _ => None,
+        }
+    }
+}
+impl fmt::Display for State {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use State::*;
+        match self {
+            NotAuthenticated => write!(f, "NotAuthenticated"),
+            Authenticated(..) => write!(f, "Authenticated"),
+            Selected(..) => write!(f, "Selected"),
+            Idle(..) => write!(f, "Idle"),
+            Logout => write!(f, "Logout"),
+        }
+    }
+}
+
+#[derive(Clone)]
+pub enum MailboxPerm {
+    ReadOnly,
+    ReadWrite,
+}
+
+pub enum Transition {
+    None,
+    Authenticate(Arc<User>),
+    Select(MailboxView, MailboxPerm),
+    Idle(Tag<'static>, Notify),
+    UnIdle,
+    Unselect,
+    Logout,
+}
+impl fmt::Display for Transition {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use Transition::*;
+        match self {
+            None => write!(f, "None"),
+            Authenticate(..) => write!(f, "Authenticated"),
+            Select(..) => write!(f, "Selected"),
+            Idle(..) => write!(f, "Idle"),
+            UnIdle => write!(f, "UnIdle"),
+            Unselect => write!(f, "Unselect"),
+            Logout => write!(f, "Logout"),
+        }
+    }
+}
+
+// See RFC3501 section 3.
+// https://datatracker.ietf.org/doc/html/rfc3501#page-13
+impl State {
+    pub fn apply(&mut self, tr: Transition) -> Result<(), Error> {
+        tracing::debug!(state=%self, transition=%tr, "try change state");
+
+        let new_state = match (std::mem::replace(self, State::Logout), tr) {
+            (s, Transition::None) => s,
+            (State::NotAuthenticated, Transition::Authenticate(u)) => State::Authenticated(u),
+            (State::Authenticated(u) | State::Selected(u, _, _), Transition::Select(m, p)) => {
+                State::Selected(u, m, p)
+            }
+            (State::Selected(u, _, _), Transition::Unselect) => State::Authenticated(u.clone()),
+            (State::Selected(u, m, p), Transition::Idle(t, s)) => {
+                State::Idle(u, m, p, t, Arc::new(s))
+            }
+            (State::Idle(u, m, p, _, _), Transition::UnIdle) => State::Selected(u, m, p),
+            (_, Transition::Logout) => State::Logout,
+            (s, t) => {
+                tracing::error!(state=%s, transition=%t, "forbidden transition");
+                return Err(Error::ForbiddenTransition);
+            }
+        };
+        *self = new_state;
+        tracing::debug!(state=%self, "transition succeeded");
+
+        Ok(())
+    }
+}