WIP: Start on ActiveCall

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

crates/room/src/active_call.rs

@@ -0,0 +1,55 @@
+use crate::Room;
+use gpui::{Entity, ModelHandle, MutableAppContext};
+
+#[derive(Default)]
+pub struct ActiveCall {
+    room: Option<ModelHandle<Room>>,
+}
+
+impl Entity for ActiveCall {
+    type Event = ();
+}
+
+impl ActiveCall {
+    pub fn global(cx: &mut MutableAppContext) -> ModelHandle<Self> {
+        if cx.has_global::<ModelHandle<Self>>() {
+            let active_call = cx.add_model(|_| ActiveCall::default());
+            cx.set_global(active_call.clone());
+            active_call
+        } else {
+            cx.global::<ModelHandle<Self>>().clone()
+        }
+    }
+
+    pub fn observe<F>(cx: &mut MutableAppContext, mut callback: F) -> gpui::Subscription
+    where
+        F: 'static + FnMut(Option<ModelHandle<Room>>, &mut MutableAppContext),
+    {
+        cx.observe_default_global::<Option<ModelHandle<Room>>, _>(move |cx| {
+            let room = cx.global::<Option<ModelHandle<Room>>>().clone();
+            callback(room, cx);
+        })
+    }
+
+    pub fn get_or_create(
+        client: &Arc<Client>,
+        user_store: &ModelHandle<UserStore>,
+        cx: &mut MutableAppContext,
+    ) -> Task<Result<ModelHandle<Room>>> {
+        if let Some(room) = cx.global::<Option<ModelHandle<Room>>>() {
+            Task::ready(Ok(room.clone()))
+        } else {
+            let client = client.clone();
+            let user_store = user_store.clone();
+            cx.spawn(|mut cx| async move {
+                let room = cx.update(|cx| Room::create(client, user_store, cx)).await?;
+                cx.update(|cx| cx.set_global(Some(room.clone())));
+                Ok(room)
+            })
+        }
+    }
+
+    pub fn clear(cx: &mut MutableAppContext) {
+        cx.set_global::<Option<ModelHandle<Room>>>(None);
+    }
+}

crates/room/src/room.rs

@@ -1,3 +1,4 @@
+mod active_call;
 mod participant;
 
 use anyhow::{anyhow, Result};