1 files changed, 69 insertions, 0 deletions
diff --git a/src/conversation/history.rs b/src/conversation/history.rs
new file mode 100644
index 0000000..601614c
--- /dev/null
+++ b/src/conversation/history.rs
@@ -0,0 +1,69 @@
+use itertools::Itertools as _;
+
+use super::{
+    Conversation, Id,
+    event::{Created, Deleted, Event},
+};
+use crate::event::{Instant, Sequence};
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct History {
+    pub conversation: Conversation,
+    pub deleted: Option<Instant>,
+}
+
+// State interface
+impl History {
+    pub fn id(&self) -> &Id {
+        &self.conversation.id
+    }
+
+    // Snapshot of this conversation as it was when created. (Note to the future:
+    // it's okay if this returns a redacted or modified version of the conversation.
+    // If we implement renames by redacting the original name, then this should
+    // return the renamed conversation, not the original, even if that's not how
+    // it was "as created.")
+    pub fn as_created(&self) -> Conversation {
+        self.conversation.clone()
+    }
+
+    pub fn as_of<S>(&self, sequence: S) -> Option<Conversation>
+    where
+        S: Into<Sequence>,
+    {
+        self.events()
+            .filter(Sequence::up_to(sequence.into()))
+            .collect()
+    }
+
+    // Snapshot of this conversation as of all events recorded in this history.
+    pub fn as_snapshot(&self) -> Option<Conversation> {
+        self.events().collect()
+    }
+}
+
+// Event factories
+impl History {
+    pub fn events(&self) -> impl Iterator<Item = Event> + use<> {
+        [self.created()]
+            .into_iter()
+            .merge_by(self.deleted(), Sequence::merge)
+    }
+
+    fn created(&self) -> Event {
+        Created {
+            conversation: self.conversation.clone(),
+        }
+        .into()
+    }
+
+    fn deleted(&self) -> Option<Event> {
+        self.deleted.map(|instant| {
+            Deleted {
+                instant,
+                id: self.conversation.id.clone(),
+            }
+            .into()
+        })
+    }
+}