doi-helper.php

<?php
/*
 * Plugin Name: Double Opt-In Helper
 * Plugin URI: https://contactform7.com/doi-helper/
 * Description: A WordPress plugin that helps developers implement the double opt-in process in their plugins.
 * Author: Takayuki Miyoshi
 * Author URI: https://ideasilo.wordpress.com/
 * License: GPL v2 or later
 * License URI: https://www.gnu.org/licenses/gpl-2.0.html
 * Version: 1.0
 * Requires at least: 6.4
 * Requires PHP: 7.4
 */

define( 'DOIHELPER_VERSION', '1.0' );

define( 'DOIHELPER_PLUGIN', __FILE__ );


/**
 * Wrapper function for DOIHELPER_Manager::register_agent().
 */
function doihelper_register_agent( $agent_name, $args = '' ) {
	$manager = DOIHELPER_Manager::get_instance();
	return $manager->register_agent( $agent_name, $args );
}


/**
 * Wrapper function for DOIHELPER_Manager::start_session().
 */
function doihelper_start_session( $agent_name, $args = array() ) {
	$manager = DOIHELPER_Manager::get_instance();
	return $manager->start_session( $agent_name, $args );
}


add_action( 'init',
	static function () {
		doihelper_register_post_types();

		do_action( 'doihelper_init' );

		if ( isset( $_REQUEST['doitoken'] ) ) {
			$token = wp_unslash( $_REQUEST['doitoken'] );
			$token_sanitized = sanitize_text_field( $token );

			if ( $token === $token_sanitized ) {
				$manager = DOIHELPER_Manager::get_instance();
				$manager->verify_token( $token );
			}
		}
	},
	10, 0
);


add_action( 'wp_after_insert_post',
	static function ( $post_id ) {
		$post_type = get_post_type( $post_id );
		$post_status = get_post_status( $post_id );

		if ( 'doihelper_entry' === $post_type and 'future' !== $post_status ) {
			wp_delete_post( $post_id, true );
		}
	},
	10, 1
);


/**
 * Registers the post types and post metas for this plugin.
 */
function doihelper_register_post_types() {
	register_post_type(
		'doihelper_entry',
		array(
			'labels' => array(
				'name' => __( 'DOI Entries', 'doi-helper' ),
				'singular_name' => __( 'DOI Entry', 'doi-helper' ),
			),
			'public' => false,
			'rewrite' => false,
			'query_var' => false,
		)
	);

	register_post_meta(
		'doihelper_entry',
		'_agent',
		array(
			'type' => 'string',
			'single' => true,
			'sanitize_callback' => 'sanitize_key',
		)
	);

	register_post_meta(
		'doihelper_entry',
		'_properties',
		array(
			'type' => 'array',
			'single' => true,
		)
	);

	register_post_meta(
		'doihelper_entry',
		'_token',
		array(
			'type' => 'string',
			'single' => true,
		)
	);
}


class DOIHELPER_Manager {

	private static $instance;

	private $agents = array();

	private function __construct() {}


	/**
	 * Retrieves the singleton instance of DOI manager.
	 *
	 * @param DOIHELPER_Manager The manager object.
	 */
	public static function get_instance() {
		if ( empty( self::$instance ) ) {
			self::$instance = new self;
		}

		return self::$instance;
	}


	/**
	 * Registers an agent.
	 *
	 * @param string $agent_name Agent name.
	 * @param string|array $args Optional. Arguments for the agent.
	 */
	public function register_agent( $agent_name, $args = '' ) {
		$agent_name = sanitize_key( $agent_name );

		$args = wp_parse_args( $args, array(
			'acceptance_period' => 24 * HOUR_IN_SECONDS,
			'optin_callback' => null,
			'email_callback' => null,
		) );

		$this->agents[$agent_name] = $args;
	}


	/**
	 * Calls an agent.
	 *
	 * @param string $agent_name Agent name.
	 * @return array|null The array of arguments for the agent
	 *                    if the agent exists, null otherwise.
	 */
	public function call_agent( $agent_name ) {
		$agent_name = sanitize_key( $agent_name );

		if ( ! empty( $this->agents[$agent_name] ) ) {
			return $this->agents[$agent_name];
		}

		return null;
	}


	/**
	 * Starts a double opt-in session.
	 *
	 * @param string $agent_name Agent name.
	 * @param string|array $args Optional. Arguments for the session.
	 * @return string|bool The token on success, false on failure.
	 */
	public function start_session( $agent_name, $args = '' ) {
		$args = wp_parse_args( $args, array(
			'properties' => array(),
		) );

		$agent_name = sanitize_key( $agent_name );
		$agent = $this->call_agent( $agent_name );

		if ( ! $agent ) {
			return false;
		}

		$expires_at = date_create(
			sprintf( '@%d', time() + (int) $agent['acceptance_period'] )
		);

		$expires_at->setTimezone( wp_timezone() );

		$properties = (array) $args['properties'];

		$token = wp_generate_password( 24, false );

		$post_id = wp_insert_post( array(
			'post_type' => 'doihelper_entry',
			'post_status' => 'future',
			'post_date' => $expires_at->format( 'Y-m-d H:i:s' ),
			'post_title' => __( 'DOI Entry', 'doi-helper' ),
			'post_content' => '',
		) );

		if ( $post_id ) {
			add_post_meta( $post_id, '_agent', $agent_name, true );
			add_post_meta( $post_id, '_properties', $properties, true );
			add_post_meta( $post_id, '_token', $token, true );

			$args = array_merge( $args, array(
				'token' => $token,
				'expires_at' => $expires_at,
			) );

			$this->send_email( $agent_name, $args );

			return $token;
		}

		return false;
	}


	/**
	 * Sends a confirmation email.
	 *
	 * @param string $agent_name Agent name.
	 * @param string|array $args Optional. Arguments for the email.
	 * @return bool True if email has been sent successfully. False otherwise.
	 */
	public function send_email( $agent_name, $args = '' ) {
		$args = wp_parse_args( $args, array(
			'email_to' => null,
		) );

		if ( empty( $args['email_to'] ) or ! is_email( $args['email_to'] ) ) {
			return false;
		}

		$agent_name = sanitize_key( $agent_name );
		$agent = $this->call_agent( $agent_name );

		if ( ! $agent ) {
			return false;
		}

		if ( is_callable( $agent['email_callback'] ) ) {
			return call_user_func( $agent['email_callback'], $args );
		} else {
			$site_title = wp_specialchars_decode(
				get_bloginfo( 'name' ),
				ENT_QUOTES
			);

			$link = add_query_arg(
				array( 'doitoken' => $args['token'] ),
				home_url()
			);

			$to = $args['email_to'];

			$subject = sprintf(
				/* translators: %s: blog name */
				__( 'Opt-in confirmation from %s', 'doi-helper' ),
				$site_title
			);

			$message = sprintf(
				/* translators: 1: blog name, 2: confirmation link */
				__( 'Hello,

This is a confirmation email sent from %1$s.

We have received your submission to our site, according to which you have allowed us to add you to our contact list. But, the process has not yet been completed. To complete it, please click the following link.

%2$s

If it was not your intention, or if you have no idea why you received this message, please do not click on the link, and ignore this message.

Sincerely,
%1$s', 'doi-helper' ),
				$site_title,
				$link
			);

			wp_mail( $to, $subject, $message );
		}
	}


	/**
	 * Verifies the given token.
	 *
	 * @param string $token The token.
	 * @return bool True if the token is valid, false otherwise.
	 */
	public function verify_token( $token ) {
		$q = new WP_Query();

		$posts = $q->query( array(
			'post_type' => 'doihelper_entry',
			'post_status' => 'future',
			'posts_per_page' => 1,
			'offset' => 0,
			'orderby' => 'ID',
			'order' => 'ASC',
			'meta_key' => '_token',
			'meta_value' => $token,
		) );

		if ( ! isset( $posts[0] ) ) {
			return false;
		}

		$post = get_post( $posts[0] );

		if ( $post ) {

			if ( get_post_timestamp( $post ) < time() ) {
				wp_delete_post( $post->ID, true );
				return false;
			}

			$agent_name = get_post_meta( $post->ID, '_agent', true );
			$agent = $this->call_agent( $agent_name );

			if ( ! $agent ) {
				return false;
			}

			if ( is_callable( $agent['optin_callback'] ) ) {
				$properties = (array) get_post_meta( $post->ID, '_properties', true );
				call_user_func( $agent['optin_callback'], $properties );
			}

			wp_delete_post( $post->ID, true );
			return true;
		}

		return false;
	}

}