Settings API + Tabs. Not bad. More complicated than it needs to be?

settings-api-tabs.php

<?php
/**
 * Plugin Name: Settings API + Tabs
 * Plugin URI: http://christopherdavis.me
 * Description: Turn settings sections into tabs on an options page. A simple example.
 * Version: 0.1
 * Text Domain: settings-tabs
 * Author: Christopher Davis
 * Author URI: http://christopherdavis.me
 * License: MIT
 *
 * Copyright (c) 2012 Christopher Davis <http://christopherdavis.me>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 *
 * @category    WordPress
 * @author      Christopher Davis <http://christopherdavis.me>
 * @copyright   2012 Christopher Davis
 * @license     http://opensource.org/licenses/MIT MIT
 */

!defined('ABSPATH') && exit;

Settings_Tabs_Tut::init();

class Settings_Tabs_Tut
{
    /**
     * The settings we'll use.
     *
     * @since   0.1
     */
    const PAGE = 'settings_tabs_tut';

    /**
     * container for the instance of this class.
     *
     * @since   0.1
     * @access  private
     * @var     Settings_Tab_Tut
     * @static
     */
    private static $ins = null;

    /**
     * Get the instance of this class.
     *
     * @since   0.1
     * @access  public
     * @return  void
     * @static
     */
    public static function instance()
    {
        is_null(self::$ins) && self::$ins = new self;
        return self::$ins;
    }

    /**
     * Kick everything off.  At the `_setup` method to the `plugins_loaded`
     * hook.
     *
     * @since   0.1
     * @access  public
     * @uses    add_action
     * @return  void
     * @static
     */
    public static function init()
    {
        add_action('plugins_loaded', array(self::instance(), '_setup'));
    }

    /**
     * Adds and actions and such.
     *
     * @since   0.1
     * @access  public
     * @uses    add_action
     * @uses    add_filter
     * @return  void
     */
    public function _setup()
    {
        add_action('admin_menu', array($this, 'page'));
        add_filter('whitelist_options', array($this, 'change_whitelist'), 11);
        add_action('admin_init', array($this, 'register'));
    }

    /**
     * Adds a new admin page.
     *
     * @since   0.1
     * @access  public
     * @uses    add_options_page
     * @return  void
     */
    public function page()
    {
        $p = add_options_page(
            __('Settings Tabs', 'settings-tabs'),
            __('Settings Tabs', 'settings-tabs'),
            'manage_options',
            'settings-tabs-tut',
            array($this, 'page_cb')
        );
    }

    /**
     * Alter the whitelist options on the `options.php` admin page so we
     * don't loose changes to settings due to the fields not beeing there.
     *
     * @since   0.1
     * @access  public
     * @param   array $opts A multi-dimensional array of options.
     * @return  void
     */
    public function change_whitelist($opts)
    {
        if(empty($_POST) || $_POST['action'] != 'update')
            return $opts;

        // since WP tries to update ALL settings assigned to a particular page.
        // We want to make sure that we unset the other settings that aren't 
        // on the current request so they don't get overwritten.
        // this is going to have to be on a case by case basis -- 
        // sections aren't added with a knowledge of the setting to which
        // they belong. One section per setting makes it easy!
        $sect = isset($_POST['current_section']) ? $_POST['current_section'] : 'default';

        $s = 'default' == $sect ? 'settings_tab_test_two' : 'settings_tab_test';

        if(($pos = array_search($s, $opts[self::PAGE])) !== false) 
        {
            unset($opts[self::PAGE][$pos]);
        }

        return $opts;
    }

    /**
     * Registers settings, sections and fields.
     *
     * @since   0.1
     * @access  public
     * @uses    register_setting
     * @uses    add_settings_section
     * @uses    add_settings_field
     * @return  void
     */
    public function register()
    {
        // so we can sections and they'll show up as tabs.
        register_setting(
            self::PAGE,
            'settings_tab_test'
        );

        add_settings_section(
            'default',
            __('Settings Tut', 'settings-tabs'),
            '__return_false',
            self::PAGE
        );

        add_settings_field(
            'some-field',
            __('Some Field', 'settings-tabs'),
            array($this, 'field_cb'),
            self::PAGE,
            'default',
            array('setting' => 'settings_tab_test')
        );

        // another one just for fun.
        register_setting(
            self::PAGE,
            'settings_tab_test_two'
        );

        add_settings_section(
            'again',
            __('Another Tab', 'settings-tabs'),
            '__return_false',
            self::PAGE
        );

        add_settings_field(
            'another-field',
            __('Another Field', 'settings-tabs'),
            array($this, 'field_cb'),
            self::PAGE,
            'again',
            array('setting' => 'settings_tab_test_two')
        );
    }

    /**
     * Callback for the page.
     *
     * @since   0.1
     * @access  public
     * @return  void
     */
    public function page_cb()
    {
        global $wp_settings_sections;

        // current section.
        $sect = isset($_GET['tab']) ? $_GET['tab'] : 'default';

        // sections on this page.
        $sections = $this->get_sections();

        // url of this page.
        $url = add_query_arg(
            'page', 'settings-tabs-tut', admin_url('options-general.php'));

        ?>
        <div class="wrap">
            <?php screen_icon(); ?>
            <?php if($sections): ?>
                <h2 class="nav-tab-wrapper">
                    <?php foreach($sections as $id => $data): ?>
                        <a class="nav-tab <?php echo ($sect == $id ? 'nav-tab-active' : ''); ?>" 
                           href="<?php echo add_query_arg('tab', $id, $url); ?>"><?php echo esc_html($data['title']); ?></a>
                    <?php endforeach; ?>
                </h2>
            <?php else: ?>
                <h2><?php esc_html_e('Settings Tab Tut', 'settings-tabs'); ?></h2>
            <?php endif; ?>

            <?php settings_errors(self::PAGE); ?>

            <?php 
            if(isset($sections[$sect]['callback']))
            {
                call_user_func($sections[$sect]['callback']);
            }
            ?>

            <form method="post" action="<?php echo admin_url('options.php'); ?>">

                <input type="hidden" name="current_section" value="<?php echo esc_attr($sect); ?>" />

                <table class="form-table">
                    <?php
                    settings_fields(self::PAGE);
                    do_settings_fields(self::PAGE, $sect);
                    ?>
                </table>

                <p><?php submit_button(__('Save Settings', 'settings-tabs')); ?></p>
            </form>
        </div>
        <?php
    }

    /**
     * callback for our example fields.
     *
     * @since   0.1
     * @access  public
     * @return  void
     */
    public function field_cb($args)
    {
        $opt = get_option($args['setting']);
        printf(
            '<input type="text" name="%1$s" id="%1$s" value="%2$s" class="widefat" />',
            esc_attr($args['setting']),
            esc_attr($opt)
        );
    }

    /**
     * Get all the sections for the page.
     *
     * @since   0.1
     * @access  private
     * @return  array
     */
    private function get_sections()
    {
        global $wp_settings_sections;

        return isset($wp_settings_sections[self::PAGE]) ?
                $wp_settings_sections[self::PAGE] : array();
    }
}