A plugin to perform theme customizations, including functions.php, JS and CSS.

wp-theme-plugin.php

<?php
/**
 * Plugin Name: WP Theme Plugin
 * Description: Theme customizations (including functions.php, JS and CSS) are added to this plugin.
 * Plugin URI: https://gist.github.com/earth3300/545db2db83486fbd731b3c9ec401076a
 * Version: 1.0.1
 * Author: earth3300
 * Author URI: http://github.com/earth3300/
 * Requires at least: 4.9.1
 * Tested up to: 5.2.1
 *
 * @package WPThemePlugin
 *
 * Notes: Placing theme customizations in a plugin allows them to be moved
 * easily and prevents them from being overwritten by theme customizations.
 * (Also works with WooCommerce). The functions.php file in this plugin is
 * intended to replace the theme functions.php file.
 *
 * This plugin contains a chained series of checks to ensure that
 * it operates in the correct environment and that it is authorized to do so.
 * Also, a global ON/OFF switch has been set internally, so that it can
 * be completely disabled if need be. That switch is further down in the code.
 *
 * In terms of optimization, although these checks may *look* bulky, they can
 * be performed very quickly, as PHP caches file based functions such as
 * `file_exists`†. These functions are separated out to improve readability
 * and so that the logic applied can be traced more easily.
 *
 * The net result is the loading of the files in the private `load` function
 * and the running of the private `run` function. It is expected that a class
 * is instantiated and then initialized in the `run` function.
 *
 * †{@link https://www.php.net/manual/en/function.clearstatcache.php}
 *
 * File: plugin.php
 * Created: 2019-04-30
 * Updated: 2019-11-02
 * Time: 15:43 EDT
 */

/*
Credits: WooCommerce.

Note: This plugin has been HEAVILY modified from the original
provided by WooCommerce. However the idea is gratefully ackowledged
as a relevant way to perform theme customizations.
*/

// No direct access.
defined('ABSPATH') || exit;

/**
 * WP Theme Plugin
 *
 * Allows for the customization of a theme, including JS, CSS
 * and PHP functions.
 *
 * @version	1.0.0
 * @since 1.0.0
 * @package	WPThemePlugin
 */
class WPThemePlugin
{
  /**
   * Construct
   */
  public function __construct()
  {
  }

  /**
   * Initialize
   *
   * This function performs a chained series of checks.
   * If they all pass, the sript runs.
   *
   * @return void
   */
  public function init()
  {
    // Server Check
    if( $this->server() )
    {
      // Platform Check
      if ( $env = $this->platform() )
      {
        // Authorization Check
        if( $this->authorize( $env ) )
        {
          // Is online and allowed, or run local.
          if( $this->isOnline() && $this->allowOnline() || $this->isLocal() )
          {
            // Load the required files.
            if ( $this->load() )
            {
              // Run the script...
              $this->run();
            }
            else
            {
              exit( 'Required file(s) could not be loaded: WP Theme Plugin' );
            }
          }
          else
          {
            exit( 'Online authorization has been revoked: WP Theme Plugin' );
          }
        }
        else
        {
          exit( 'Authorization has been revoked: WP Theme Plugin' );
        }
      }
      else
      {
        exit( 'Platform not supported: WP Theme Plugin' );
      }
    }
    else
    {
      exit( 'Server Not Supported: (WP Theme Plugin). Unknown environment?');
    }
  }

  /**
   * Verify the Server
   *
   * Verify the environment with a function check.
   *
   * @return bool
   */
  private function server()
  {
    if ( 'Apache' == substr( $_SERVER['SERVER_SOFTWARE'], 0, 6 ) )
    {
      return true;
    }
    else
    {
      exit( 'This script does not work with this server (WP Theme Plugin). Apache Required.' );
    }
  }

  /**
   * Verify the Platform
   *
   * Verify the platform with a function check.
   *
   * @return bool
   */
  private function platform()
  {
    $env['platform'] = null;

    if ( function_exists( 'wp_title' ) )
    {
      $env['platform'] = 'wp';
    }
    else
    {
      $env['platform'] = false;
    }

    return $env;
  }

  /**
   * Authorize
   *
   * Authorize the execution of the scripts contained herein.
   *
   * @return bool
   */
  private function authorize( $env )
  {
    // 0 to turn OFF (1 to turn ON).
    if( 'wp' == $env['platform'] )
    {
      return true;
    }
    else
    {
      return false;
    }
  }

  /**
   * Is Online
   *
   * Returns true if the script is in an online environment.
   *
   * @return bool
   */
  private function isOnline()
  {
    if( '127.0.0.1' !== $_SERVER['SERVER_ADDR'] )
    {
      return true;
    }
    else
    {
      return false;
    }
  }

  /**
   * Is Local
   *
   * Returns true if the script is in a local environment.
   *
   * @return bool
   */
  private function isLocal()
  {
    if( '127.0.0.1' == $_SERVER['SERVER_ADDR'] )
    {
      return true;
    }
    else
    {
      return false;
    }
  }

  /**
   * Load the required files.
   *
   * Returns null if all files are turned OFF.
   * Returns false if at least one file is not available.
   *
   * @return bool
   */
  private function load()
  {
    $loaded = null;

    $load['files'] = [
      [ 'name' => 'functions.php', 'load' => 1 ],
      [ 'name' => 'setup.php', 'load' => 1 ],
    ];

    foreach( $load['files'] as $file )
    {
      if( $file['load'] )
      {
        if ( file_exists( __DIR__ . '/' . $file['name'] ) )
        {
          $loaded = true;

          require_once( __DIR__ . '/' . $file['name'] );
        }
        else
        {
          $loaded = false;
        }
      }
    }

    return $loaded;
  }

  /**
   * Run the class.
   */
  private function run()
  {
    if( class_exists( 'WPThemePluginSetup' ) )
    {
      $class = new WPThemePluginSetup;

      $class->init();
    }
  }
} // End Class

/**
 * WP Theme Plugin Global Function
 *
 * Instantiate the class and intialize it.
 *
 * @return void
 */
function wp_theme_plugin()
{
  $class = new WPThemePlugin();

  $class->init();
}

/**
 * Initialise the plugin with the init action (always loads).
 *
 * Check to ensure the correct environment exists.
 */
if( function_exists( 'add_action' ) )
{
  add_action( 'init', 'wp_theme_plugin' );
}
else
{
  exit( 'File is not in the correct environment: WordPress (WP Theme Plugin).' );
}