From f93a0f0afe8aff4d0bbc8ee393918881cfdd9db8 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Fri, 21 Oct 2022 00:29:23 +0300
Subject: [PATCH] Emit events on entity and component creation and destruction

---
 source/game/events.h  | 36 ++++++++++++++++++++++++++++++++++++
 source/game/owned.h   | 19 +++++++++++++++++--
 source/game/stage.cpp |  1 +
 source/game/stage.h   |  8 ++++++++
 4 files changed, 62 insertions(+), 2 deletions(-)
 create mode 100644 source/game/events.h

diff --git a/source/game/events.h b/source/game/events.h
new file mode 100644
index 0000000..15988e5
--- /dev/null
+++ b/source/game/events.h
@@ -0,0 +1,36 @@
+#ifndef MSP_GAME_EVENTS_H_
+#define MSP_GAME_EVENTS_H_
+
+#include "handle.h"
+
+namespace Msp::Game {
+
+class Component;
+class Entity;
+
+namespace Events {
+
+struct EntityCreated
+{
+	Handle<Entity> entity;
+};
+
+struct EntityDestroyed
+{
+	Handle<Entity> entity;
+};
+
+struct ComponentCreated
+{
+	Handle<Component> component;
+};
+
+struct ComponentDestroyed
+{
+	Handle<Component> component;
+};
+
+} // namespace Events
+} // namespace Msp::Game
+
+#endif
diff --git a/source/game/owned.h b/source/game/owned.h
index e20ff77..620c6aa 100644
--- a/source/game/owned.h
+++ b/source/game/owned.h
@@ -2,6 +2,7 @@
 #define MSP_GAME_OWNED_H_
 
 #include <stdexcept>
+#include "events.h"
 #include "handle.h"
 #include "stage.h"
 
@@ -41,12 +42,19 @@ Owned<T>::Owned(Handle<P> parent, Args &&... args)
 	if(!parent)
 		throw std::invalid_argument("Owned::Owned");
 
-	Pool<T> &pool = get_stage(*parent).get_pools().template get_pool<T>();
+	Stage &stage = get_stage(*parent);
+	Pool<T> &pool = stage.get_pools().template get_pool<T>();
 	this->ptr = pool.create(parent, std::forward<Args>(args)...);
 	if constexpr(std::is_base_of_v<Component, T>)
+	{
 		parent->add_component(*this);
+		stage.get_event_source().emit<Events::ComponentCreated>(*this);
+	}
 	else
+	{
 		parent->add_child(*this);
+		stage.get_event_source().emit<Events::EntityCreated>(*this);
+	}
 }
 
 template<typename T>
@@ -77,13 +85,20 @@ void Owned<T>::destroy()
 	if(!obj)
 		return;
 
-	Pool<T> &pool = get_stage(*obj).get_pools().template get_pool<T>();
+	Stage &stage = get_stage(*obj);
 
 	if constexpr(std::is_base_of_v<Component, T>)
+	{
+		stage.get_event_source().emit<Events::ComponentDestroyed>(*this);
 		obj->get_entity()->remove_component(*this);
+	}
 	else if(auto parent = obj->get_parent().get())
+	{
+		stage.get_event_source().emit<Events::EntityDestroyed>(*this);
 		parent->remove_child(*this);
+	}
 
+	Pool<T> &pool = stage.get_pools().template get_pool<T>();
 	pool.destroy(this->ptr);
 }
 
diff --git a/source/game/stage.cpp b/source/game/stage.cpp
index a616d5a..73eb9a5 100644
--- a/source/game/stage.cpp
+++ b/source/game/stage.cpp
@@ -5,6 +5,7 @@
 namespace Msp::Game {
 
 Stage::Stage():
+	event_source(event_bus),
 	root(std::make_unique<Root>(*this))
 { }
 
diff --git a/source/game/stage.h b/source/game/stage.h
index dbffc99..80e7a4b 100644
--- a/source/game/stage.h
+++ b/source/game/stage.h
@@ -4,6 +4,8 @@
 #include <memory>
 #include <msp/time/timedelta.h>
 #include "eventbus.h"
+#include "events.h"
+#include "eventsource.h"
 #include "handle.h"
 
 namespace Msp::Game {
@@ -13,9 +15,14 @@ class System;
 
 class Stage
 {
+public:
+	using EventSource = Game::EventSource<Events::EntityCreated, Events::EntityDestroyed,
+		Events::ComponentCreated, Events::ComponentDestroyed>;
+
 private:
 	PoolPool pools;
 	EventBus event_bus;
+	EventSource event_source;
 	/* Use unique_ptr because there's only one root per stage so it's pointless
 	to put it in a pool. */
 	std::unique_ptr<Root> root;
@@ -27,6 +34,7 @@ public:
 
 	PoolPool &get_pools() { return pools; }
 	EventBus &get_event_bus() { return event_bus; }
+	EventSource &get_event_source() { return event_source; }
 	Handle<Root> get_root() { return Handle<Root>::from_object(root.get()); }
 
 	template<typename T, typename F>
-- 
2.43.0