1 files changed, 138 insertions, 0 deletions
diff --git a/src/events/app/events.rs b/src/events/app/events.rs
new file mode 100644
index 0000000..a8814c9
--- /dev/null
+++ b/src/events/app/events.rs
@@ -0,0 +1,138 @@
+use chrono::TimeDelta;
+use futures::{
+    future,
+    stream::{self, StreamExt as _},
+    Stream,
+};
+use sqlx::sqlite::SqlitePool;
+
+use super::Broadcaster;
+use crate::{
+    clock::DateTime,
+    events::repo::broadcast::{self, Provider as _},
+    repo::{
+        channel::{self, Provider as _},
+        error::NotFound as _,
+        login::Login,
+    },
+};
+
+pub struct Events<'a> {
+    db: &'a SqlitePool,
+    broadcaster: &'a Broadcaster,
+}
+
+impl<'a> Events<'a> {
+    pub const fn new(db: &'a SqlitePool, broadcaster: &'a Broadcaster) -> Self {
+        Self { db, broadcaster }
+    }
+
+    pub async fn send(
+        &self,
+        login: &Login,
+        channel: &channel::Id,
+        body: &str,
+        sent_at: &DateTime,
+    ) -> Result<broadcast::Message, EventsError> {
+        let mut tx = self.db.begin().await?;
+        let channel = tx
+            .channels()
+            .by_id(channel)
+            .await
+            .not_found(|| EventsError::ChannelNotFound(channel.clone()))?;
+        let message = tx
+            .broadcast()
+            .create(login, &channel, body, sent_at)
+            .await?;
+        tx.commit().await?;
+
+        self.broadcaster.broadcast(&channel.id, &message);
+        Ok(message)
+    }
+
+    pub async fn subscribe(
+        &self,
+        channel: &channel::Id,
+        subscribed_at: &DateTime,
+        resume_at: Option<broadcast::Sequence>,
+    ) -> Result<impl Stream<Item = broadcast::Message> + std::fmt::Debug, EventsError> {
+        // Somewhat arbitrarily, expire after 90 days.
+        let expire_at = subscribed_at.to_owned() - TimeDelta::days(90);
+
+        let mut tx = self.db.begin().await?;
+        let channel = tx
+            .channels()
+            .by_id(channel)
+            .await
+            .not_found(|| EventsError::ChannelNotFound(channel.clone()))?;
+
+        // Subscribe before retrieving, to catch messages broadcast while we're
+        // querying the DB. We'll prune out duplicates later.
+        let live_messages = self.broadcaster.subscribe(&channel.id);
+
+        tx.broadcast().expire(&expire_at).await?;
+        let stored_messages = tx.broadcast().replay(&channel, resume_at).await?;
+        tx.commit().await?;
+
+        let resume_broadcast_at = stored_messages
+            .last()
+            .map(|message| message.sequence)
+            .or(resume_at);
+
+        // This should always be the case, up to integer rollover, primarily
+        // because every message in stored_messages has a sequence not less
+        // than `resume_at`, or `resume_at` is None. We use the last message
+        // (if any) to decide when to resume the `live_messages` stream.
+        //
+        // It probably simplifies to assert!(resume_at <= resume_broadcast_at), but
+        // this form captures more of the reasoning.
+        assert!(
+            (resume_at.is_none() && resume_broadcast_at.is_none())
+                || (stored_messages.is_empty() && resume_at == resume_broadcast_at)
+                || resume_at < resume_broadcast_at
+        );
+
+        // no skip_expired or resume transforms for stored_messages, as it's
+        // constructed not to contain messages meeting either criterion.
+        //
+        // * skip_expired is redundant with the `tx.broadcasts().expire(…)` call;
+        // * resume is redundant with the resume_at argument to
+        //   `tx.broadcasts().replay(…)`.
+        let stored_messages = stream::iter(stored_messages);
+        let live_messages = live_messages
+            // Sure, it's temporally improbable that we'll ever skip a message
+            // that's 90 days old, but there's no reason not to be thorough.
+            .filter(Self::skip_expired(&expire_at))
+            // Filtering on the broadcast resume point filters out messages
+            // before resume_at, and filters out messages duplicated from
+            // stored_messages.
+            .filter(Self::resume(resume_broadcast_at));
+
+        Ok(stored_messages.chain(live_messages))
+    }
+
+    fn resume(
+        resume_at: Option<broadcast::Sequence>,
+    ) -> impl for<'m> FnMut(&'m broadcast::Message) -> future::Ready<bool> {
+        move |msg| {
+            future::ready(match resume_at {
+                None => true,
+                Some(resume_at) => msg.sequence > resume_at,
+            })
+        }
+    }
+    fn skip_expired(
+        expire_at: &DateTime,
+    ) -> impl for<'m> FnMut(&'m broadcast::Message) -> future::Ready<bool> {
+        let expire_at = expire_at.to_owned();
+        move |msg| future::ready(msg.sent_at > expire_at)
+    }
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum EventsError {
+    #[error("channel {0} not found")]
+    ChannelNotFound(channel::Id),
+    #[error(transparent)]
+    DatabaseError(#[from] sqlx::Error),
+}