reorganize database crate.

split database Cork into unit.

split database migrations from mod.rs

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

src/database/watchers.rs

@@ -0,0 +1,55 @@
+use std::{
+	collections::{hash_map, HashMap},
+	future::Future,
+	pin::Pin,
+	sync::RwLock,
+};
+
+use tokio::sync::watch;
+
+type Watcher = RwLock<HashMap<Vec<u8>, (watch::Sender<()>, watch::Receiver<()>)>>;
+
+#[derive(Default)]
+pub(super) struct Watchers {
+	watchers: Watcher,
+}
+
+impl Watchers {
+	pub(super) fn watch<'a>(&'a self, prefix: &[u8]) -> Pin<Box<dyn Future<Output = ()> + Send + 'a>> {
+		let mut rx = match self.watchers.write().unwrap().entry(prefix.to_vec()) {
+			hash_map::Entry::Occupied(o) => o.get().1.clone(),
+			hash_map::Entry::Vacant(v) => {
+				let (tx, rx) = watch::channel(());
+				v.insert((tx, rx.clone()));
+				rx
+			},
+		};
+
+		Box::pin(async move {
+			// Tx is never destroyed
+			rx.changed().await.unwrap();
+		})
+	}
+
+	pub(super) fn wake(&self, key: &[u8]) {
+		let watchers = self.watchers.read().unwrap();
+		let mut triggered = Vec::new();
+
+		for length in 0..=key.len() {
+			if watchers.contains_key(&key[..length]) {
+				triggered.push(&key[..length]);
+			}
+		}
+
+		drop(watchers);
+
+		if !triggered.is_empty() {
+			let mut watchers = self.watchers.write().unwrap();
+			for prefix in triggered {
+				if let Some(tx) = watchers.remove(prefix) {
+					_ = tx.0.send(());
+				}
+			}
+		};
+	}
+}