data-model: have more structs use a state machine

crates/data-model/src/oauth2/mod.rs

@@ -1,4 +1,4 @@
-// Copyright 2021, 2022 The Matrix.org Foundation C.I.C.
+// Copyright 2021-2023 The Matrix.org Foundation C.I.C.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -19,5 +19,5 @@ pub(self) mod session;
 pub use self::{
     authorization_grant::{AuthorizationCode, AuthorizationGrant, AuthorizationGrantStage, Pkce},
     client::{Client, InvalidRedirectUriError, JwksOrJwksUri},
-    session::Session,
+    session::{Session, SessionState},
 };

crates/data-model/src/oauth2/session.rs

@@ -1,4 +1,4 @@
-// Copyright 2021 The Matrix.org Foundation C.I.C.
+// Copyright 2021-2023 The Matrix.org Foundation C.I.C.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -19,22 +19,69 @@ use ulid::Ulid;
 
 use crate::InvalidTransitionError;
 
+trait T {
+    type State;
+}
+
+impl T for Session {
+    type State = SessionState;
+}
+
+#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize)]
+pub enum SessionState {
+    #[default]
+    Valid,
+    Finished {
+        finished_at: DateTime<Utc>,
+    },
+}
+
+impl SessionState {
+    /// Returns `true` if the session state is [`Valid`].
+    ///
+    /// [`Valid`]: SessionState::Valid
+    #[must_use]
+    pub fn is_valid(&self) -> bool {
+        matches!(self, Self::Valid)
+    }
+
+    /// Returns `true` if the session state is [`Finished`].
+    ///
+    /// [`Finished`]: SessionState::Finished
+    #[must_use]
+    pub fn is_finished(&self) -> bool {
+        matches!(self, Self::Finished { .. })
+    }
+
+    pub fn finish(self, finished_at: DateTime<Utc>) -> Result<Self, InvalidTransitionError> {
+        match self {
+            Self::Valid => Ok(Self::Finished { finished_at }),
+            Self::Finished { .. } => Err(InvalidTransitionError),
+        }
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq, Serialize)]
 pub struct Session {
     pub id: Ulid,
+    pub state: SessionState,
+    pub created_at: DateTime<Utc>,
     pub user_session_id: Ulid,
     pub client_id: Ulid,
     pub scope: Scope,
-    pub finished_at: Option<DateTime<Utc>>,
+}
+
+impl std::ops::Deref for Session {
+    type Target = SessionState;
+
+    fn deref(&self) -> &Self::Target {
+        &self.state
+    }
 }
 
 impl Session {
     pub fn finish(mut self, finished_at: DateTime<Utc>) -> Result<Self, InvalidTransitionError> {
-        if self.finished_at.is_some() {
-            return Err(InvalidTransitionError);
-        }
-
-        self.finished_at = Some(finished_at);
+        self.state = self.state.finish(finished_at)?;
         Ok(self)
     }
 }