WP Settings API in OOP way

example.php

<?php

$settings = new WP_Settings('menu-page-slug');

// adding a section
$settings->add_section('Section Title', 'section_html_callback')
  ->add_field('settings-field-1', 'Settings Field 1', 'settings_field_1_html_callback')
  ->add_field('settings-field-2', 'Settings Field 2', 'settings_field_2_html_callback');

// adding another section (i used the same data only to show you how you can add another section)
$settings->add_section('Section Title', 'section_html_callback')
  ->add_field('settings-field-1', 'Settings Field 1', 'settings_field_1_html_callback')
  ->add_field('settings-field-2', 'Settings Field 2', 'settings_field_2_html_callback');

function section_html_callback() {}
function settings_field_1_html_callback() {}
function settings_field_2_html_callback() {}

// other code for creating menu page omitted except the one where Settings API would normally be used.
function menu_page_html_output() {
  ?>
  <div class="wrap">
    <form method="POST" action="options.php">
    <?php
      global $settings;
      $settings->do_sections();
      $settings->fields();

      submit_button();
     ?>
	  </form>
  </div>
  <?php
}

add_action('admin_init', array($settings, 'init'));

WP_Settings.php

<?php

class WP_Settings_Section {
  protected $id = '';
  protected $title = '';
  protected $output_callback = '';
  protected $fields = array();

  public function __construct($id, $title, $output_callback) {
    $this->id = $id;
    $this->title = $title;
    $this->output_callback = $output_callback;
  }

  public function add_field($id, $title, $output_callback) {
    $this->fields[$id] = array(
      'id'              => $id,
      'title'           => $title,
      'output_callback' => $output_callback
    );
    return $this;
  }

  public function get_id() {
    return $this->id;
  }

  public function get_title() {
    return $this->title;
  }

  public function get_output_callback() {
    return $this->output_callback;
  }

  public function get_fields() {
    return $this->fields;
  }
}

class WP_Settings {
  protected $page_id = '';
  protected $sections = array();
  protected $options_group = '';

  public function __construct($page_id) {
    $this->page_id = $page_id;
    $this->options_group = $page_id;
  }

  public function add_section($title = null, $output_callback = null) {
    $section_id = uniqid();
    $section = new WP_Settings_Section($section_id, $title, $output_callback);
    $this->sections[$section_id] = $section;
    return $section;
  }
  public function init() {
    foreach($this->sections as $section_id => $section) {
      add_settings_section(
        $section_id,
        $section->get_title(),
        $section->get_output_callback(),
        $this->page_id
      );
      foreach($section->get_fields() as $field_id => $field) {
        add_settings_field(
          $field_id,
          $field['title'],
          $field['output_callback'],
          $this->page_id,
          $section_id
        );
        register_setting($this->options_group, $field_id);
      }
    }
  }
  public function do_sections() {
    do_settings_sections($this->page_id);
  }
  public function fields() {
    settings_fields($this->options_group);
  }
}