local thread subscriptions

This adds local nostrdb thread subscriptions. When navigating to a
thread, we first check to see if we have any active nostrdb
subscriptions for that thread. If not, we create a new subscription. If
we do, we re-use that subscription.

This works by storing thread state in the Threads struct in the Damus
application state.

When we pop a route, we check to see if its a thread route. If it is,
then we try to unsubscribe, but only if that is the last remaining
subscriber for that thread, as there could be more than one.

Signed-off-by: William Casarin <jb55@jb55.com>

src/note.rs

@@ -1,4 +1,5 @@
-use nostrdb::{NoteKey, QueryResult};
+use crate::Damus;
+use nostrdb::{NoteKey, QueryResult, Transaction};
 use std::cmp::Ordering;
 
 #[derive(Debug, Eq, PartialEq, Copy, Clone)]
@@ -35,3 +36,32 @@ impl PartialOrd for NoteRef {
         Some(self.cmp(other))
     }
 }
+
+pub fn root_note_id_from_selected_id<'a>(
+    app: &mut Damus,
+    txn: &'a Transaction,
+    selected_note_id: &'a [u8; 32],
+) -> &'a [u8; 32] {
+    let selected_note_key = if let Ok(key) = app
+        .ndb
+        .get_notekey_by_id(txn, selected_note_id)
+        .map(NoteKey::new)
+    {
+        key
+    } else {
+        return selected_note_id;
+    };
+
+    let note = if let Ok(note) = app.ndb.get_note_by_key(txn, selected_note_key) {
+        note
+    } else {
+        return selected_note_id;
+    };
+
+    app.note_cache_mut()
+        .cached_note_or_insert(selected_note_key, &note)
+        .reply
+        .borrow(note.tags())
+        .root()
+        .map_or_else(|| selected_note_id, |nr| nr.id)
+}