<?php
defined( 'ABSPATH' ) or exit;

add_action( 'plugins_loaded', array( 'PoorMansNameSpaceAJAX', 'getInstance' ) );
class PoorMansNameSpaceAJAX
{
	public static $instance = null;

	public $nonce = '';

	public $name = 'ajaxexample';

	public static function getInstance()
	{
		null === self::$instance AND self::$instance = new self;
		return self::$instance;
	}

	public function __construct()
	{
		add_action( 'wp_loaded', array( $this, 'scriptsRegister' ) );
		# Could as well be: wp_enqueue_scripts or login_enqueue_scripts
		add_action( 'admin_enqueue_scripts', array( $this, 'scriptsEnqueue' ) );

		# Logged in users:
		# add_action( "wp_ajax_{$this->name}_action", array( $this, 'ajaxCb' ) );
		# Guests:
		add_action( "wp_ajax_nopriv_{$this->name}_action", array( $this, 'ajaxCb' ) );

		add_action( 'admin_enqueue_scripts', array( $this, 'scriptsLocalize' ) );
	}

	public function scriptsRegister( $page )
	{
		$file = 'YourAJAXHandlingFile.js';
		wp_register_script(
			$this->name,
			plugins_url( "assets/scripts/{$file}", __FILE__ ),
			array(
				'jquery',
			),
			filemtime( plugin_dir_path( __FILE__ )."assets/scripts/{$file}" ),
			true
		);
	}

	public function scriptsEnqueue( $page )
	{
		wp_enqueue_script( $this->name );
	}

	public function scriptsLocalize( $page )
	{
		$this->nonce = wp_create_nonce( "{$this->name}_action" );
		wp_localize_script( $this->name, "{$this->name}Object", array(
			'ajaxurl'          => admin_url( 'admin-ajax.php' ),
			'_ajax_nonce'      => $this->nonce,
			'action'           => "{$this->name}_action",
			'post_type'        => get_current_screen()->post_type,
			# etc.
		) );
	}

	public function renderForm()
	{
		wp_nonce_field( "{$this->name}_action", $this->name );
		# @TODO Build form
		# @TODO Hook somewhere
	}

	public function ajaxCb( $data )
	{
		$data = array_map( 'esc_attr', $_GET );

		check_ajax_referer( $data['action'] );

		# @TODO Handle processing of data in here
		# @TODO Validate data with absint(), esc_*(), etc.

		# @TODO Check if we got an error and if so, send it
		# @example #1)
		! wp_verify_nonce( $this->nonce, "{$this->name}_action" )
			AND wp_send_json_error();

		# @example #2)
		if ( ! $data['foo'] )
			wp_send_json_error();

		wp_send_json_success( array(
			#'foo' => 'bar',
		) );
	}
}