Add TopicEvent.

src/room/topic.rs

@@ -1 +1,51 @@
 //! Types for the *m.room.topic* event.
+
+use core::{Event, EventType, RoomEvent, StateEvent};
+
+/// A topic is a short message detailing what is currently being discussed in the room.
+pub struct TopicEvent<'a, 'b> {
+    content: TopicEventContent<'a>,
+    event_id: &'a str,
+    prev_content: Option<TopicEventContent<'b>>,
+    room_id: &'a str,
+    user_id: &'a str,
+}
+
+impl<'a, 'b> Event<'a, TopicEventContent<'a>> for TopicEvent<'a, 'b> {
+    fn content(&'a self) -> &'a TopicEventContent<'a> {
+        &self.content
+    }
+
+    fn event_type(&self) -> EventType {
+        EventType::RoomTopic
+    }
+}
+
+impl<'a, 'b> RoomEvent<'a, TopicEventContent<'a>> for TopicEvent<'a, 'b> {
+    fn event_id(&'a self) -> &'a str {
+        &self.event_id
+    }
+
+    fn room_id(&'a self) -> &'a str {
+        &self.room_id
+    }
+
+    fn user_id(&'a self) -> &'a str {
+        &self.user_id
+    }
+}
+
+impl<'a, 'b> StateEvent<'a, 'b, TopicEventContent<'a>> for TopicEvent<'a, 'b> {
+    fn prev_content(&'a self) -> Option<&'b TopicEventContent> {
+        match self.prev_content {
+            Some(ref prev_content) => Some(prev_content),
+            None => None,
+        }
+    }
+}
+
+/// The payload of a `TopicEvent`.
+pub struct TopicEventContent<'a> {
+    /// The topic text.
+    topic: &'a str,
+}