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.

1 files changed, 88 insertions, 0 deletions

diff --git a/src/message/app.rs b/src/message/app.rs
new file mode 100644
index 0000000..51f772e
--- /dev/null
+++ b/src/message/app.rs
@@ -0,0 +1,88 @@
+use chrono::TimeDelta;
+use itertools::Itertools;
+use sqlx::sqlite::SqlitePool;
+
+use super::{repo::Provider as _, Message};
+use crate::{
+    channel::{self, repo::Provider as _},
+    clock::DateTime,
+    db::NotFound as _,
+    event::{broadcaster::Broadcaster, repo::Provider as _, Sequence},
+    login::Login,
+};
+
+pub struct Messages<'a> {
+    db: &'a SqlitePool,
+    events: &'a Broadcaster,
+}
+
+impl<'a> Messages<'a> {
+    pub const fn new(db: &'a SqlitePool, events: &'a Broadcaster) -> Self {
+        Self { db, events }
+    }
+
+    pub async fn send(
+        &self,
+        channel: &channel::Id,
+        sender: &Login,
+        sent_at: &DateTime,
+        body: &str,
+    ) -> Result<Message, Error> {
+        let mut tx = self.db.begin().await?;
+        let channel = tx
+            .channels()
+            .by_id(channel)
+            .await
+            .not_found(|| Error::ChannelNotFound(channel.clone()))?;
+        let sent = tx.sequence().next(sent_at).await?;
+        let message = tx
+            .messages()
+            .create(&channel.snapshot(), sender, &sent, body)
+            .await?;
+        tx.commit().await?;
+
+        for event in message.events() {
+            self.events.broadcast(event);
+        }
+
+        Ok(message.snapshot())
+    }
+
+    pub async fn expire(&self, relative_to: &DateTime) -> Result<(), sqlx::Error> {
+        // Somewhat arbitrarily, expire after 90 days.
+        let expire_at = relative_to.to_owned() - TimeDelta::days(90);
+
+        let mut tx = self.db.begin().await?;
+        let expired = tx.messages().expired(&expire_at).await?;
+
+        let mut events = Vec::with_capacity(expired.len());
+        for (channel, message) in expired {
+            let deleted = tx.sequence().next(relative_to).await?;
+            let message = tx.messages().delete(&channel, &message, &deleted).await?;
+            events.push(
+                message
+                    .events()
+                    .filter(Sequence::start_from(deleted.sequence)),
+            );
+        }
+
+        tx.commit().await?;
+
+        for event in events
+            .into_iter()
+            .kmerge_by(|a, b| a.instant.sequence < b.instant.sequence)
+        {
+            self.events.broadcast(event);
+        }
+
+        Ok(())
+    }
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    #[error("channel {0} not found")]
+    ChannelNotFound(channel::Id),
+    #[error(transparent)]
+    DatabaseError(#[from] sqlx::Error),
+}