From 13ed4f6c4748019787d24c2b686d417b71604242 Mon Sep 17 00:00:00 2001
From: Pascal Kuthe
Date: Fri, 1 Dec 2023 00:03:26 +0100
Subject: Add hook/event system

---
 helix-event/src/registry.rs | 131 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 131 insertions(+)
 create mode 100644 helix-event/src/registry.rs

(limited to 'helix-event/src/registry.rs')

diff --git a/helix-event/src/registry.rs b/helix-event/src/registry.rs
new file mode 100644
index 00000000..d43c48ac
--- /dev/null
+++ b/helix-event/src/registry.rs
@@ -0,0 +1,131 @@
+//! A global registry where events are registered and can be
+//! subscribed to by registering hooks. The registry identifies event
+//! types using their type name so multiple event with the same type name
+//! may not be registered (will cause a panic to ensure soundness)
+
+use std::any::TypeId;
+
+use anyhow::{bail, Result};
+use hashbrown::hash_map::Entry;
+use hashbrown::HashMap;
+use parking_lot::RwLock;
+
+use crate::hook::ErasedHook;
+use crate::runtime_local;
+
+pub struct Registry {
+    events: HashMap<&'static str, TypeId, ahash::RandomState>,
+    handlers: HashMap<&'static str, Vec<ErasedHook>, ahash::RandomState>,
+}
+
+impl Registry {
+    pub fn register_event<E: Event + 'static>(&mut self) {
+        let ty = TypeId::of::<E>();
+        assert_eq!(ty, TypeId::of::<E::Static>());
+        match self.events.entry(E::ID) {
+            Entry::Occupied(entry) => {
+                if entry.get() == &ty {
+                    // don't warn during tests to avoid log spam
+                    #[cfg(not(feature = "integration_test"))]
+                    panic!("Event {} was registered multiple times", E::ID);
+                } else {
+                    panic!("Multiple events with ID {} were registered", E::ID);
+                }
+            }
+            Entry::Vacant(ent) => {
+                ent.insert(ty);
+                self.handlers.insert(E::ID, Vec::new());
+            }
+        }
+    }
+
+    /// # Safety
+    ///
+    /// `hook` must be totally generic over all lifetime parameters of `E`. For
+    /// example if `E` was a known type `Foo<'a, 'b> then the correct trait bound
+    /// would be `F: for<'a, 'b, 'c> Fn(&'a mut Foo<'b, 'c>)` but there is no way to
+    /// express that kind of constraint for a generic type with the rust type system
+    /// right now.
+    pub unsafe fn register_hook<E: Event>(
+        &mut self,
+        hook: impl Fn(&mut E) -> Result<()> + 'static + Send + Sync,
+    ) {
+        // ensure event type ids match so we can rely on them always matching
+        let id = E::ID;
+        let Some(&event_id) = self.events.get(id) else {
+            panic!("Tried to register handler for unknown event {id}");
+        };
+        assert!(
+            TypeId::of::<E::Static>() == event_id,
+            "Tried to register invalid hook for event {id}"
+        );
+        let hook = ErasedHook::new(hook);
+        self.handlers.get_mut(id).unwrap().push(hook);
+    }
+
+    pub fn register_dynamic_hook(
+        &mut self,
+        hook: impl Fn() -> Result<()> + 'static + Send + Sync,
+        id: &str,
+    ) -> Result<()> {
+        // ensure event type ids match so we can rely on them always matching
+        if self.events.get(id).is_none() {
+            bail!("Tried to register handler for unknown event {id}");
+        };
+        let hook = ErasedHook::new_dynamic(hook);
+        self.handlers.get_mut(id).unwrap().push(hook);
+        Ok(())
+    }
+
+    pub fn dispatch<E: Event>(&self, mut event: E) {
+        let Some(hooks) = self.handlers.get(E::ID) else {
+            log::error!("Dispatched unknown event {}", E::ID);
+            return;
+        };
+        let event_id = self.events[E::ID];
+
+        assert_eq!(
+            TypeId::of::<E::Static>(),
+            event_id,
+            "Tried to dispatch invalid event {}",
+            E::ID
+        );
+
+        for hook in hooks {
+            // safety: event type is the same
+            if let Err(err) = unsafe { hook.call(&mut event) } {
+                log::error!("{} hook failed: {err:#?}", E::ID);
+                crate::status::report_blocking(err);
+            }
+        }
+    }
+}
+
+runtime_local! {
+    static REGISTRY: RwLock<Registry> = RwLock::new(Registry {
+        // hardcoded random number is good enough here we don't care about DOS resistance
+        // and avoids the additional complexity of `Option<Registry>`
+        events: HashMap::with_hasher(ahash::RandomState::with_seeds(423, 9978, 38322, 3280080)),
+        handlers: HashMap::with_hasher(ahash::RandomState::with_seeds(423, 99078, 382322, 3282938)),
+    });
+}
+
+pub(crate) fn with<T>(f: impl FnOnce(&Registry) -> T) -> T {
+    f(&REGISTRY.read())
+}
+
+pub(crate) fn with_mut<T>(f: impl FnOnce(&mut Registry) -> T) -> T {
+    f(&mut REGISTRY.write())
+}
+
+/// # Safety
+/// The number of specified lifetimes and the static type *must* be correct.
+/// This is ensured automatically by the [`events`](crate::events)
+/// macro.
+pub unsafe trait Event: Sized {
+    /// Globally unique (case sensitive)  string that identifies this type.
+    /// A good candidate is the events type name
+    const ID: &'static str;
+    const LIFETIMES: usize;
+    type Static: Event + 'static;
+}
-- 
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