From ec804134c33aedb001c426c5f42f43f53c47848f Mon Sep 17 00:00:00 2001
From: Owen Jacobson <owen@grimoire.ca>
Date: Wed, 2 Oct 2024 12:25:36 -0400
Subject: Represent channels and messages using a split "History" and
 "Snapshot" model.

This separates the code that figures out what happened to an entity from the code that represents it to a user, and makes it easier to compute a snapshot at a point in time (for things like bootstrap). It also makes the internal logic a bit easier to follow, since it's easier to tell whether you're working with a point in time or with the whole recorded history.

This hefty.
---
 src/channel/snapshot.rs | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 src/channel/snapshot.rs

(limited to 'src/channel/snapshot.rs')

diff --git a/src/channel/snapshot.rs b/src/channel/snapshot.rs
new file mode 100644
index 0000000..6462f25
--- /dev/null
+++ b/src/channel/snapshot.rs
@@ -0,0 +1,38 @@
+use super::{
+    event::{Created, Event, Kind},
+    Id,
+};
+
+#[derive(Clone, Debug, Eq, PartialEq, serde::Serialize)]
+pub struct Channel {
+    pub id: Id,
+    pub name: String,
+}
+
+impl Channel {
+    fn apply(state: Option<Self>, event: Event) -> Option<Self> {
+        match (state, event.kind) {
+            (None, Kind::Created(event)) => Some(event.into()),
+            (Some(channel), Kind::Deleted(event)) if channel.id == event.channel => None,
+            (state, event) => panic!("invalid channel event {event:#?} for state {state:#?}"),
+        }
+    }
+}
+
+impl FromIterator<Event> for Option<Channel> {
+    fn from_iter<I: IntoIterator<Item = Event>>(events: I) -> Self {
+        events.into_iter().fold(None, Channel::apply)
+    }
+}
+
+impl From<&Created> for Channel {
+    fn from(event: &Created) -> Self {
+        event.channel.clone()
+    }
+}
+
+impl From<Created> for Channel {
+    fn from(event: Created) -> Self {
+        event.channel
+    }
+}
-- 
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