Track event sequences globally, not per channel.

Per-channel event sequences were a cute idea, but it made reasoning about event resumption much, much harder (case in point: recovering the order of events in a partially-ordered collection is quadratic, since it's basically graph sort). The minor overhead of a global sequence number is likely tolerable, and this simplifies both the API and the internals.

1 files changed, 45 insertions, 0 deletions

diff --git a/src/repo/sequence.rs b/src/repo/sequence.rs
new file mode 100644
index 0000000..8fe9dab
--- /dev/null
+++ b/src/repo/sequence.rs
@@ -0,0 +1,45 @@
+use sqlx::{sqlite::Sqlite, SqliteConnection, Transaction};
+
+pub trait Provider {
+    fn sequence(&mut self) -> Sequences;
+}
+
+impl<'c> Provider for Transaction<'c, Sqlite> {
+    fn sequence(&mut self) -> Sequences {
+        Sequences(self)
+    }
+}
+
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    Eq,
+    Ord,
+    PartialEq,
+    PartialOrd,
+    serde::Deserialize,
+    serde::Serialize,
+    sqlx::Type,
+)]
+#[serde(transparent)]
+#[sqlx(transparent)]
+pub struct Sequence(i64);
+
+pub struct Sequences<'t>(&'t mut SqliteConnection);
+
+impl<'c> Sequences<'c> {
+    pub async fn next(&mut self) -> Result<Sequence, 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(next)
+    }
+}