Adds new tile on the admin home page with system data. (#301)

* Adds new tile on the admin home page with system data. Also fixes the active users bug in the pie chart

* Fixes missing parentheses

* Updates user stats cache when signing in

* Reads active number of users from session provider

* Removes unused variable

* Small improvements

* Removes acl properties from system data websocket and performs initial push of data

* fix: remove acl fetch

---------

Co-authored-by: DecDuck <declanahofmeyr@gmail.com>

server/internal/system-data/index.ts

@@ -0,0 +1,58 @@
+import os from "os";
+
+export type SystemData = {
+  totalRam: number;
+  freeRam: number;
+  cpuLoad: number;
+  cpuCores: number;
+};
+
+class SystemManager {
+  // userId to acl to listenerId
+  private listeners = new Map<
+    string,
+    Map<string, { callback: (systemData: SystemData) => void }>
+  >();
+
+  listen(
+    userId: string,
+    id: string,
+    callback: (systemData: SystemData) => void,
+  ) {
+    if (!this.listeners.has(userId)) this.listeners.set(userId, new Map());
+    // eslint-disable-next-line @typescript-eslint/no-extra-non-null-assertion
+    this.listeners.get(userId)!!.set(id, { callback });
+    this.pushUpdate(userId, id);
+    setInterval(() => this.pushUpdate(userId, id), 3000);
+  }
+
+  unlisten(userId: string, id: string) {
+    this.listeners.get(userId)?.delete(id);
+  }
+
+  private async pushUpdate(userId: string, id: string) {
+    const listener = this.listeners.get(userId)?.get(id);
+    if (!listener) {
+      throw new Error("Failed to catch-up listener: callback does not exist");
+    }
+    listener.callback(this.getSystemData());
+  }
+
+  getSystemData(): SystemData {
+    return {
+      cpuLoad: this.cpuLoad(),
+      totalRam: os.totalmem(),
+      freeRam: os.freemem(),
+      cpuCores: os.cpus().length,
+    };
+  }
+
+  private cpuLoad() {
+    const [oneMinLoad, _fiveMinLoad, _fiftenMinLoad] = os.loadavg();
+    const numberCpus = os.cpus().length;
+    return 100 - ((numberCpus - oneMinLoad) / numberCpus) * 100;
+  }
+}
+
+export const systemManager = new SystemManager();
+export default systemManager;