1 files changed, 110 insertions, 0 deletions
diff --git a/src/swarm/document_file.rs b/src/swarm/document_file.rs
new file mode 100644
index 0000000..e9deca0
--- /dev/null
+++ b/src/swarm/document_file.rs
@@ -0,0 +1,110 @@
+//! The worker that keeps the document file (`document::file`) up to date: it looks at
+//! the node (ready, the document's epoch and heads, this node's actors), and the file
+//! says what is due. While a ready node rejoins, the file follows the document before
+//! the rejoin, which takes the node's writes meanwhile (`state::StaleView`): a restart
+//! then resumes on it, and rejoins again.
+
+use std::sync::Arc;
+
+use crate::document::Document;
+use crate::document::file::Due;
+use crate::document::replica::Epoch;
+use crate::locks::RwLockExt;
+use crate::state::AppState;
+
+/// Keeps the document file up to date. Runs for as long as the node does.
+pub(crate) async fn run(state: AppState) {
+    let Some(file) = state.document_file.clone() else {
+        return;
+    };
+    let mut tick = tokio::time::interval(file.append_every());
+    tick.set_missed_tick_behavior(tokio::time::MissedTickBehavior::Delay);
+    loop {
+        tick.tick().await;
+        flush(&state).await;
+    }
+}
+
+/// Writes what is due now (`DocumentFile::due`). Also called at shutdown.
+pub(crate) async fn flush(state: &AppState) {
+    let Some(file) = state.document_file.clone() else {
+        return;
+    };
+    if state.remake.is_rejoining() {
+        if let Some((epoch, stale)) = state.stale_document() {
+            flush_before_rejoin(&file, epoch, stale).await;
+        }
+        return;
+    }
+    if !state.is_ready().await {
+        return;
+    }
+    let own = state.remake.own_actors();
+    let (epoch, heads) = {
+        let replica = state.doc.read().await;
+        (replica.epoch, replica.heads().to_vec())
+    };
+    match file.due(epoch, own.len(), &heads) {
+        Due::Rewrite(reason) => {
+            let (epoch, copy) = {
+                let replica = state.doc.read().await;
+                (replica.epoch, replica.doc.clone())
+            };
+            file.rewrite(epoch, copy, own, reason).await;
+        }
+        Due::Append { epoch, since } => {
+            let (heads, increment) = {
+                let replica = state.doc.read().await;
+                // Switched since: the next flush rewrites the file instead.
+                if replica.epoch != epoch {
+                    return;
+                }
+                let heads = replica.heads().to_vec();
+                (heads, crate::document::save_since(&replica.doc, &since))
+            };
+            file.append(since, heads, increment).await;
+        }
+        Due::Nothing => {}
+    }
+}
+
+/// [`flush`] of the document before a rejoin (`epoch`'s), while it takes this node's
+/// writes. Only appends: a rewrite (another epoch, or the increments outgrew the full
+/// save) waits for the end of the rejoin, so the file keeps the actors it had.
+async fn flush_before_rejoin(
+    file: &Arc<crate::document::file::DocumentFile>,
+    epoch: Epoch,
+    stale: Arc<std::sync::RwLock<Document>>,
+) {
+    let heads = {
+        let stale = Arc::clone(&stale);
+        // Sorted, as the live document's (`Replica::heads`) the file compares with.
+        tokio::task::spawn_blocking(move || {
+            let mut heads = stale.read_or_recover().get_heads();
+            heads.sort_unstable();
+            heads
+        })
+        .await
+        .expect("document read task panicked")
+    };
+    let Some(actors) = file.actors() else {
+        return;
+    };
+    if let Due::Append {
+        epoch: written,
+        since,
+    } = file.due(epoch, actors, &heads)
+        && written == epoch
+    {
+        let since_then = since.clone();
+        let (heads, increment) = tokio::task::spawn_blocking(move || {
+            let doc = stale.read_or_recover();
+            let mut heads = doc.get_heads();
+            heads.sort_unstable();
+            (heads, crate::document::save_since(&doc, &since_then))
+        })
+        .await
+        .expect("document read task panicked");
+        file.append(since, heads, increment).await;
+    }
+}