Draft first version of event subscriptions 🎉

core/src/subscription.rs

@@ -0,0 +1,61 @@
+//! Generate events asynchronously for you application.
+
+/// An event subscription.
+pub struct Subscription<T> {
+    definitions: Vec<Box<dyn Definition<Message = T>>>,
+}
+
+impl<T> Subscription<T> {
+    pub fn none() -> Self {
+        Self {
+            definitions: Vec::new(),
+        }
+    }
+
+    pub fn batch(subscriptions: impl Iterator<Item = Subscription<T>>) -> Self {
+        Self {
+            definitions: subscriptions
+                .flat_map(|subscription| subscription.definitions)
+                .collect(),
+        }
+    }
+
+    pub fn definitions(self) -> Vec<Box<dyn Definition<Message = T>>> {
+        self.definitions
+    }
+}
+
+impl<T, A> From<A> for Subscription<T>
+where
+    A: Definition<Message = T> + 'static,
+{
+    fn from(definition: A) -> Self {
+        Self {
+            definitions: vec![Box::new(definition)],
+        }
+    }
+}
+
+/// The definition of an event subscription.
+pub trait Definition {
+    type Message;
+
+    fn id(&self) -> u64;
+
+    fn stream(
+        &self,
+    ) -> (
+        futures::stream::BoxStream<'static, Self::Message>,
+        Box<dyn Handle>,
+    );
+}
+
+pub trait Handle {
+    fn cancel(&mut self);
+}
+
+impl<T> std::fmt::Debug for Subscription<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("Command").finish()
+    }
+}