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/event/repo.rs | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 src/event/repo.rs

(limited to 'src/event/repo.rs')

diff --git a/src/event/repo.rs b/src/event/repo.rs
new file mode 100644
index 0000000..40d6a53
--- /dev/null
+++ b/src/event/repo.rs
@@ -0,0 +1,50 @@
+use sqlx::{sqlite::Sqlite, SqliteConnection, Transaction};
+
+use crate::{
+    clock::DateTime,
+    event::{Instant, Sequence},
+};
+
+pub trait Provider {
+    fn sequence(&mut self) -> Sequences;
+}
+
+impl<'c> Provider for Transaction<'c, Sqlite> {
+    fn sequence(&mut self) -> Sequences {
+        Sequences(self)
+    }
+}
+
+pub struct Sequences<'t>(&'t mut SqliteConnection);
+
+impl<'c> Sequences<'c> {
+    pub async fn next(&mut self, at: &DateTime) -> Result<Instant, sqlx::Error> {
+        let next = sqlx::query_scalar!(
+            r#"
+                update event_sequence
+                set last_value = last_value + 1
+                returning last_value as "next_value: Sequence"
+            "#,
+        )
+        .fetch_one(&mut *self.0)
+        .await?;
+
+        Ok(Instant {
+            at: *at,
+            sequence: next,
+        })
+    }
+
+    pub async fn current(&mut self) -> Result<Sequence, sqlx::Error> {
+        let next = sqlx::query_scalar!(
+            r#"
+                select last_value as "last_value: Sequence"
+                from event_sequence
+            "#,
+        )
+        .fetch_one(&mut *self.0)
+        .await?;
+
+        Ok(next)
+    }
+}
-- 
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