chore:extracted the group monitor to a different monitoring type (#4395)

server/monitor-types/group.js

@@ -0,0 +1,49 @@
+const { UP, PENDING, DOWN } = require("../../src/util");
+const { MonitorType } = require("./monitor-type");
+const Monitor = require("../model/monitor");
+
+class GroupMonitorType extends MonitorType {
+    name = "group";
+
+    /**
+     * @inheritdoc
+     */
+    async check(monitor, heartbeat, _server) {
+        const children = await Monitor.getChildren(monitor.id);
+
+        if (children.length > 0) {
+            heartbeat.status = UP;
+            heartbeat.msg = "All children up and running";
+            for (const child of children) {
+                if (!child.active) {
+                    // Ignore inactive childs
+                    continue;
+                }
+                const lastBeat = await Monitor.getPreviousHeartbeat(child.id);
+
+                // Only change state if the monitor is in worse conditions then the ones before
+                // lastBeat.status could be null
+                if (!lastBeat) {
+                    heartbeat.status = PENDING;
+                } else if (heartbeat.status === UP && (lastBeat.status === PENDING || lastBeat.status === DOWN)) {
+                    heartbeat.status = lastBeat.status;
+                } else if (heartbeat.status === PENDING && lastBeat.status === DOWN) {
+                    heartbeat.status = lastBeat.status;
+                }
+            }
+
+            if (heartbeat.status !== UP) {
+                heartbeat.msg = "Child inaccessible";
+            }
+        } else {
+            // Set status pending if group is empty
+            heartbeat.status = PENDING;
+            heartbeat.msg = "Group empty";
+        }
+    }
+}
+
+module.exports = {
+    GroupMonitorType,
+};
+