FEATURE: Option to update category preferences of all users when site setting changed (#8180)

app/assets/javascripts/admin/components/site-setting.js.es6

@@ -1,10 +1,54 @@
 import BufferedContent from "discourse/mixins/buffered-content";
 import SiteSetting from "admin/models/site-setting";
 import SettingComponent from "admin/mixins/setting-component";
+import showModal from "discourse/lib/show-modal";
+import AboutRoute from "discourse/routes/about";
 
 export default Ember.Component.extend(BufferedContent, SettingComponent, {
-  _save() {
+  update(key, value, updateExistingUsers = false) {
+    if (updateExistingUsers) {
+      return SiteSetting.update(key, value, { updateExistingUsers: true });
+    } else {
+      return SiteSetting.update(key, value);
+    }
+  },
+
+  _save(callback) {
+    const defaultCategoriesSettings = [
+      "default_categories_watching",
+      "default_categories_tracking",
+      "default_categories_muted",
+      "default_categories_watching_first_post"
+    ];
     const setting = this.buffered;
-    return SiteSetting.update(setting.get("setting"), setting.get("value"));
+    const key = setting.get("setting");
+    const value = setting.get("value");
+
+    if (defaultCategoriesSettings.includes(key)) {
+      AboutRoute.create()
+        .model()
+        .then(result => {
+          const controller = showModal("site-setting-default-categories", {
+            model: {
+              count: result.stats.user_count,
+              key: key.replace(/_/g, " ")
+            },
+            admin: true
+          });
+
+          controller.setProperties({
+            onClose: () => {
+              const updateExistingUsers = controller.get("updateExistingUsers");
+              if (updateExistingUsers === true) {
+                callback(this.update(key, value, true));
+              } else if (updateExistingUsers === false) {
+                callback(this.update(key, value));
+              }
+            }
+          });
+        });
+    } else {
+      callback(this.update(key, value));
+    }
   }
 });