From 6b97387630cedb2ef098659d65e77b1c790d62a0 Mon Sep 17 00:00:00 2001
From: Ruben Beltran del Rio <git@r.bdr.sh>
Date: Wed, 8 May 2024 13:50:45 +0200
Subject: Make node components event emitters

---
 lib/serpentity/node_collection.js |  4 +++-
 lib/serpentity/observable.js      | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 lib/serpentity/observable.js

(limited to 'lib')

diff --git a/lib/serpentity/node_collection.js b/lib/serpentity/node_collection.js
index d2aa599..cb2f932 100644
--- a/lib/serpentity/node_collection.js
+++ b/lib/serpentity/node_collection.js
@@ -1,3 +1,5 @@
+import { makeObservable } from './observable.js';
+
 /*
  * Node Collections contain nodes, in order to keep the lists of nodes
  * that belong to each type.
@@ -35,7 +37,7 @@ export class NodeCollection extends EventTarget {
       node.entity = entity;
 
       for (const typeName of typeNames) {
-        node[typeName] = entity.getComponent(types[typeName]);
+        node[typeName] = makeObservable(entity.getComponent(types[typeName]));
       }
 
       this.nodes.push(node);
diff --git a/lib/serpentity/observable.js b/lib/serpentity/observable.js
new file mode 100644
index 0000000..a75377d
--- /dev/null
+++ b/lib/serpentity/observable.js
@@ -0,0 +1,38 @@
+/*
+ * Observable wrapper. Wraps objects so any property modifications emit
+ * a change event. Used internally for node collections, which make the
+ * components observable.
+ */
+class ObserverHandler extends EventTarget {
+  #emitChangeEvent({property, to, from}) {
+    const event = new Event('change');
+    event.property = property;
+    event.to = to;
+    event.from = from;
+    this.dispatchEvent(event);
+  }
+
+  get(target, property) {
+    if (property in this && typeof this[property] === 'function') {
+      return this[property].bind(this);
+    }
+
+    return target[property]
+  }
+
+  set(target, property, value) {
+    const oldValue = target[property];
+    target[property] = value;
+    this.#emitChangeEvent({property, to: value, from: oldValue});
+    return true;
+  }
+}
+
+/**
+  * @param {Object} object the object to observe
+  * @return {tObserverProxy} the proxied object
+  */
+export function makeObservable(object) {
+
+  return new Proxy(object, new ObserverHandler());
+};
-- 
cgit