Implement storage of synchronized entities in terms of events, not state.

Conversations, users, messages, and all other "synchronized" entities now have an in-memory implementation of their lifecycle, rather than a database-backed one. These operations take a history, apply one lifecycle change to that history, and emit a new history. Storage is then implemented by applying the events in this new history to the database.

The storage methods in repo types, which process these events by emitting SQL statements, make necessary assumptions that the events being passed to them are coherent with the data already in storage. For example, the code to handle a conversation's delete event is allowed to assume that the database already contains a row for that conversation, inserted in response to a prior conversation creation event.

Data retrieval is not modified in this commit, and probably never will be without a more thorough storage rewrite. The whole intention of the data modelling approach I've been using is that a single row per entity represents its entire history, in turn so that the data in the database should be legible to people approaching it using normal SQL tools.

Developed as an aesthetic response to increasing unease with the lack of an ORM versus the boring-ness of our actual queries.

Merges event-based-storage into main.

1 files changed, 51 insertions, 36 deletions

diff --git a/src/conversation/app.rs b/src/conversation/app.rs
index 81ccdcf..26886af 100644
--- a/src/conversation/app.rs
+++ b/src/conversation/app.rs
@@ -3,15 +3,15 @@ use itertools::Itertools;
 use sqlx::sqlite::SqlitePool;
 
 use super::{
-    Conversation, Id,
+    Conversation, History, Id, history,
     repo::{LoadError, Provider as _},
     validate,
 };
 use crate::{
     clock::DateTime,
     db::{Duplicate as _, NotFound as _},
-    event::{Broadcaster, Event, Sequence, repo::Provider as _},
-    message::{self, repo::Provider as _},
+    event::{Broadcaster, Sequence, repo::Provider as _},
+    message::repo::Provider as _,
     name::{self, Name},
 };
 
@@ -36,15 +36,20 @@ impl<'a> Conversations<'a> {
 
         let mut tx = self.db.begin().await?;
         let created = tx.sequence().next(created_at).await?;
-        let conversation = tx
-            .conversations()
-            .create(name, &created)
+        let conversation = History::begin(name, created);
+
+        // This filter technically includes every event in the history, but it's easier to follow if
+        // the various event-manipulating app methods are consistent, and it's harmless to have an
+        // always-satisfied filter.
+        let events = conversation.events().filter(Sequence::start_from(created));
+        tx.conversations()
+            .record_events(events.clone())
             .await
             .duplicate(|| CreateError::DuplicateName(name.clone()))?;
+
         tx.commit().await?;
 
-        self.events
-            .broadcast(conversation.events().map(Event::from).collect::<Vec<_>>());
+        self.events.broadcast_from(events);
 
         Ok(conversation.as_created())
     }
@@ -78,33 +83,28 @@ impl<'a> Conversations<'a> {
             .by_id(conversation)
             .await
             .not_found(|| DeleteError::NotFound(conversation.clone()))?;
-        conversation
-            .as_snapshot()
-            .ok_or_else(|| DeleteError::Deleted(conversation.id().clone()))?;
-
-        let mut events = Vec::new();
 
         let messages = tx.messages().live(&conversation).await?;
+        let deleted_at = tx.sequence().next(deleted_at).await?;
+
         let has_messages = messages
             .iter()
-            .map(message::History::as_snapshot)
+            .map(|message| message.as_of(deleted_at))
             .any(|message| message.is_some());
         if has_messages {
             return Err(DeleteError::NotEmpty(conversation.id().clone()));
         }
 
-        let deleted = tx.sequence().next(deleted_at).await?;
-        let conversation = tx.conversations().delete(&conversation, &deleted).await?;
-        events.extend(
-            conversation
-                .events()
-                .filter(Sequence::start_from(deleted.sequence))
-                .map(Event::from),
-        );
+        let conversation = conversation.delete(deleted_at)?;
+
+        let events = conversation
+            .events()
+            .filter(Sequence::start_from(deleted_at));
+        tx.conversations().record_events(events.clone()).await?;
 
         tx.commit().await?;
 
-        self.events.broadcast(events);
+        self.events.broadcast_from(events);
 
         Ok(())
     }
@@ -120,23 +120,20 @@ impl<'a> Conversations<'a> {
         let mut events = Vec::with_capacity(expired.len());
         for conversation in expired {
             let deleted = tx.sequence().next(relative_to).await?;
-            let conversation = tx.conversations().delete(&conversation, &deleted).await?;
-            events.push(
-                conversation
-                    .events()
-                    .filter(Sequence::start_from(deleted.sequence)),
-            );
+            let conversation = conversation.delete(deleted)?;
+
+            let conversation_events = conversation.events().filter(Sequence::start_from(deleted));
+            tx.conversations()
+                .record_events(conversation_events.clone())
+                .await?;
+
+            events.push(conversation_events);
         }
 
         tx.commit().await?;
 
-        self.events.broadcast(
-            events
-                .into_iter()
-                .kmerge_by(Sequence::merge)
-                .map(Event::from)
-                .collect::<Vec<_>>(),
-        );
+        self.events
+            .broadcast_from(events.into_iter().kmerge_by(Sequence::merge));
 
         Ok(())
     }
@@ -218,8 +215,18 @@ impl From<LoadError> for DeleteError {
     }
 }
 
+impl From<history::DeleteError> for DeleteError {
+    fn from(error: history::DeleteError) -> Self {
+        match error {
+            history::DeleteError::Deleted(conversation) => Self::Deleted(conversation.id().clone()),
+        }
+    }
+}
+
 #[derive(Debug, thiserror::Error)]
 pub enum ExpireError {
+    #[error("tried to expire already-deleted conversation: {0}")]
+    Deleted(Id),
     #[error(transparent)]
     Database(#[from] sqlx::Error),
     #[error(transparent)]
@@ -234,3 +241,11 @@ impl From<LoadError> for ExpireError {
         }
     }
 }
+
+impl From<history::DeleteError> for ExpireError {
+    fn from(error: history::DeleteError) -> Self {
+        match error {
+            history::DeleteError::Deleted(conversation) => Self::Deleted(conversation.id().clone()),
+        }
+    }
+}