Get text box data after pressing button in plugin

Dev
1

I’m working on my first plugin, and I want to be able to get the text content of a text box in the admin panel (part of the plugin) after pressing a button. Then, I want to do some stuff with the content in Ruby. Is there a way for the Ember frontend to send data back to the Ruby backend?
My plugin.rb:

# name: Discourse Sample Plugin
# about: A simple plugin to play around with
# version: 1.0.0
# authors: NateDhaliwal 
# url: https://google.com

enabled_site_setting :plugin_enabled

add_admin_route 'sample_page.title', 'sample-page'

Discourse::Application.routes.append do
  get '/admin/plugins/sample-page' => 'admin/plugins#index', constraints: StaffConstraint.new
end

My assets/javascripts/discourse/templates/admin/plugin-sample-plugin.hbs:

<div class="textbox">
  <input id="textbox-data" type="text" />
</div>

<div class="buttons">
  <DButton
    @label="sample_page.send"
    @action={{action "sendTextboxData"}}
    @icon"arrow-right"
    @id="send-textbox-data"
  />
</div>

Not sure what by sendTextboxData should do.
My assets/javascripts/discourse/sample-page-route-map.js:

export default {
  resource: 'admin.adminPlugins',
  path: '/plugins',
  map() {
    this.route('sample-page');
  }
};

My assets/javascripts/discourse/controllers/admin-plugins-sample-plugin.js.es6:

import Controller from "@ember/controller";
import { action } from "@ember/object";

export default class AdminPluginsSamplePlugin extends Controller {

  @action
  sendTextboxData() {
    // How do I send the data?
  }
}

If I do manage to get the data to the Ruby backend, where do I put the logic for dealing with the data? In plugin.rb? Or some other file?