Event broadcasting system (#692)

* broadcast system implemented but not everywhere

* unused types

* code review with keavon

* - optional signal mappings
- tool.rs simplification

* Cleanup

* reduced code duplication in `tool.rs`

* ran cargo fmt

* code review changes

* fix merge error

Co-authored-by: Keavon Chambers <keavon@keavon.com>

editor/src/communication/broadcast_message.rs

@@ -0,0 +1,26 @@
+use crate::message_prelude::*;
+
+use serde::{Deserialize, Serialize};
+
+#[impl_message(Message, Broadcast)]
+#[derive(PartialEq, Clone, Debug, Serialize, Deserialize)]
+pub enum BroadcastMessage {
+	SubscribeSignal {
+		on: BroadcastSignal,
+		send: Box<Message>,
+	},
+	UnsubscribeSignal {
+		on: BroadcastSignal,
+		message: Box<Message>,
+	},
+	#[child]
+	TriggerSignal(BroadcastSignal),
+}
+
+#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize, Hash)]
+#[impl_message(Message, BroadcastMessage, TriggerSignal)]
+pub enum BroadcastSignal {
+	DocumentIsDirty,
+	ToolAbort,
+	SelectionChanged,
+}

editor/src/communication/broadcast_message_handler.rs

@@ -0,0 +1,27 @@
+use crate::message_prelude::*;
+
+use std::collections::HashMap;
+
+#[derive(Debug, Clone, Default)]
+pub struct BroadcastMessageHandler {
+	listeners: HashMap<BroadcastSignal, Vec<Message>>,
+}
+
+impl MessageHandler<BroadcastMessage, ()> for BroadcastMessageHandler {
+	fn process_action(&mut self, action: BroadcastMessage, _data: (), responses: &mut VecDeque<Message>) {
+		use BroadcastMessage::*;
+		match action {
+			SubscribeSignal { on, send } => self.listeners.entry(on).or_default().push(*send),
+			UnsubscribeSignal { on, message } => self.listeners.entry(on).or_default().retain(|msg| *msg != *message),
+			TriggerSignal(signal) => {
+				for message in self.listeners.entry(signal).or_default() {
+					responses.push_front(message.clone())
+				}
+			}
+		}
+	}
+
+	fn actions(&self) -> ActionList {
+		vec![]
+	}
+}

editor/src/communication/dispatcher.rs

@@ -1,3 +1,4 @@
+use super::broadcast_message_handler::BroadcastMessageHandler;
 use crate::document::PortfolioMessageHandler;
 use crate::global::GlobalMessageHandler;
 use crate::input::{InputMapperMessageHandler, InputPreprocessorMessageHandler};
@@ -18,6 +19,7 @@ pub struct Dispatcher {
 #[remain::sorted]
 #[derive(Debug, Default)]
 struct DispatcherMessageHandlers {
+	broadcast_message_handler: BroadcastMessageHandler,
 	dialog_message_handler: DialogMessageHandler,
 	global_message_handler: GlobalMessageHandler,
 	input_mapper_message_handler: InputMapperMessageHandler,
@@ -43,7 +45,7 @@ const SIDE_EFFECT_FREE_MESSAGES: &[MessageDiscriminant] = &[
 	MessageDiscriminant::Frontend(FrontendMessageDiscriminant::UpdateActiveDocument),
 	MessageDiscriminant::Frontend(FrontendMessageDiscriminant::UpdateOpenDocumentsList),
 	MessageDiscriminant::Frontend(FrontendMessageDiscriminant::TriggerFontLoad),
-	MessageDiscriminant::Tool(ToolMessageDiscriminant::DocumentIsDirty),
+	MessageDiscriminant::Broadcast(BroadcastMessageDiscriminant::TriggerSignal(BroadcastSignalDiscriminant::DocumentIsDirty)),
 ];
 
 impl Dispatcher {
@@ -85,6 +87,7 @@ impl Dispatcher {
 			match message {
 				#[remain::unsorted]
 				NoOp => {}
+				Broadcast(message) => self.message_handlers.broadcast_message_handler.process_action(message, (), &mut queue),
 				Dialog(message) => {
 					self.message_handlers
 						.dialog_message_handler

editor/src/communication/message.rs

@@ -23,6 +23,8 @@ pub enum Message {
 	#[remain::unsorted]
 	NoOp,
 	#[child]
+	Broadcast(BroadcastMessage),
+	#[child]
 	Dialog(DialogMessage),
 	#[child]
 	Frontend(FrontendMessage),

editor/src/communication/mod.rs

@@ -1,3 +1,5 @@
+pub mod broadcast_message;
+pub mod broadcast_message_handler;
 pub mod dispatcher;
 pub mod message;
 pub mod message_handler;