1 files changed, 50 insertions, 0 deletions
diff --git a/src/imap/flow.rs b/src/imap/flow.rs
new file mode 100644
index 0000000..8ba75bc
--- /dev/null
+++ b/src/imap/flow.rs
@@ -0,0 +1,50 @@
+use crate::mailbox::Mailbox;
+
+pub struct User {
+    pub name: String,
+    pub creds: Credentials,
+}
+
+pub enum State {
+    NotAuthenticated,
+    Authenticated(User),
+    Selected(User, Mailbox),
+    Logout
+}
+pub enum Error {
+    ForbiddenTransition,
+}
+
+// See RFC3501 section 3.
+// https://datatracker.ietf.org/doc/html/rfc3501#page-13
+impl State {
+    pub fn authenticate(&mut self, user: User) -> Result<(), Error> {
+        self = match state {
+            State::NotAuthenticated => State::Authenticated(user),
+            _ => return Err(ForbiddenTransition),
+        };
+        Ok(())
+    }
+
+    pub fn logout(&mut self) -> Self {
+        self = State::Logout;
+        Ok(())
+    }
+
+    pub fn select(&mut self, mailbox: Mailbox) -> Result<(), Error> {
+        self = match state {
+            State::Authenticated(user) => State::Selected(user, mailbox),
+            _ => return Err(ForbiddenTransition),
+        };
+        Ok(())
+    }
+
+    pub fn unselect(state: State) -> Result<(), Error> {
+        self = match state {
+            State::Selected(user, _) => State::Authenticated(user),
+            _ => return Err(ForbiddenTransition),
+        };
+        Ok(())
+    }
+}
+