feat(sync): add typed presence projection

req: sync/001

req: sync/005

examples/kanban/src/main.rs

@@ -15,7 +15,7 @@ use hemx_axum::{
 use hemx_kanban_example::ui::board::{self as board};
 use hemx_kanban_example::ui::board_card as card_board;
 use hemx_kanban_example::ui::{self, board as board_ui};
-use hemx_sync::{Channel, SyncEffect};
+use hemx_sync::{Channel, PresenceScope, PresenceTracker, PresenceUpdate};
 use serde::{Deserialize, Serialize};
 use std::collections::BTreeMap;
 use std::convert::Infallible;
@@ -46,6 +46,7 @@ struct AppState {
     sync_store: Option<SyncStore>,
     sync_sessions: SyncSessionTokens,
     acknowledgement_heartbeat_interval: Duration,
+    presence: Mutex<PresenceTracker<String>>,
 }
 
 #[derive(Default)]
@@ -494,6 +495,7 @@ async fn main() {
             .filter(|milliseconds| *milliseconds > 0)
             .map(Duration::from_millis)
             .unwrap_or(ACKNOWLEDGEMENT_HEARTBEAT_INTERVAL),
+        presence: Mutex::new(PresenceTracker::default()),
     });
 
     let ordinary_routes = Router::new()
@@ -581,7 +583,28 @@ async fn interact(
 }
 
 // req: push/001 req: push/003 req: examples/001
-async fn sync_broadcast(Query(params): Query<BTreeMap<String, String>>) -> Response {
+struct PresenceSignal {
+    channel: Channel,
+    count: usize,
+}
+
+impl PresenceScope for PresenceSignal {
+    fn presence_channel(&self) -> Channel {
+        self.channel.clone()
+    }
+}
+
+#[hemx_sync::presence]
+fn presence_changed(signal: PresenceSignal) -> impl hemx::IntoEffect {
+    board::presence.put(&Presence {
+        count: u64::try_from(signal.count).expect("presence count fits u64"),
+    })
+}
+
+async fn sync_broadcast(
+    State(state): State<Arc<AppState>>,
+    Query(params): Query<BTreeMap<String, String>>,
+) -> Response {
     let Some(channel) = params
         .get("channel")
         .and_then(|channel| Channel::new(channel).ok())
@@ -591,10 +614,21 @@ async fn sync_broadcast(Query(params): Query<BTreeMap<String, String>>) -> Respo
     if channel.as_str() != "board" {
         return StatusCode::NOT_FOUND.into_response();
     }
-    let batch = board::presence
-        .put(&Presence { count: 7 })
-        .into_batch(ui::BUILD_FINGERPRINT);
-    let broadcast = SyncEffect::broadcast(channel, batch);
+    let member = params.get("member").cloned();
+    let count = {
+        let mut presence = state.presence.lock().unwrap();
+        match (params.get("action").map(String::as_str), member.as_ref()) {
+            (Some("join"), Some(member)) => presence.join(channel.clone(), member.clone()).count,
+            (Some("leave"), Some(member)) => presence.leave(&channel, member).count,
+            (None | Some("snapshot"), None) => presence.count(&channel),
+            _ => {
+                return (StatusCode::BAD_REQUEST, "invalid presence action or member")
+                    .into_response();
+            }
+        }
+    };
+    let broadcast =
+        presence_changed(PresenceSignal { channel, count }).into_broadcast(ui::BUILD_FINGERPRINT);
     let (_channel, effect_batch) = broadcast.into_parts();
     sse(stream::iter([Ok::<_, Infallible>(effect_batch)]).boxed()).into_response()
 }