Refactor legacy database watcher system.

Signed-off-by: Jason Volk <jason@zemos.net>

src/database/map/watch.rs

@@ -0,0 +1,69 @@
+use std::{
+	collections::{BTreeMap, btree_map::Entry},
+	future::Future,
+	ops::RangeToInclusive,
+	sync::Mutex,
+};
+
+use futures::pin_mut;
+use tokio::sync::watch::{Sender, channel};
+use tuwunel_core::implement;
+
+use crate::keyval::KeyBuf;
+
+type Watchers = Mutex<BTreeMap<KeyBuf, Sender<()>>>;
+
+#[derive(Default)]
+pub(super) struct Watch {
+	watchers: Watchers,
+}
+
+#[implement(super::Map)]
+pub fn watch_raw_prefix<K>(&self, prefix: &K) -> impl Future<Output = ()> + Send + use<K>
+where
+	K: AsRef<[u8]> + ?Sized,
+{
+	let rx = match self
+		.watch
+		.watchers
+		.lock()
+		.expect("locked")
+		.entry(prefix.as_ref().into())
+	{
+		| Entry::Occupied(node) => node.get().subscribe(),
+		| Entry::Vacant(node) => {
+			let (tx, rx) = channel(());
+			node.insert(tx);
+			rx
+		},
+	};
+
+	async move {
+		pin_mut!(rx);
+		rx.changed()
+			.await
+			.expect("watcher sender dropped");
+	}
+}
+
+#[implement(super::Map)]
+pub(crate) fn notify<K>(&self, key: &K)
+where
+	K: AsRef<[u8]> + Ord + ?Sized,
+{
+	let range = RangeToInclusive::<KeyBuf> { end: key.as_ref().into() };
+
+	let mut watchers = self.watch.watchers.lock().expect("locked");
+
+	watchers
+		.range(range)
+		.rev()
+		.take_while(|(k, _)| key.as_ref().starts_with(k))
+		.filter_map(|(k, tx)| tx.send(()).is_err().then_some(k))
+		.cloned()
+		.collect::<Vec<_>>()
+		.into_iter()
+		.for_each(|k| {
+			watchers.remove(&k);
+		});
+}