OOP plugin

auto-add.php

/*
Plugin Name:       Auto Add Read Posts
Description:       A plugin that adds read posts to the user's read list - requires the Unread Posts plugin
Version:           1.0.0
Author:            Daniel Pataki
Author URI:        http://danielpataki.com/
License:           GPLv2 or later
*/

add_action( 'wp', 'auto_add_post_to_read_list' );

function auto_add_post_to_read_list() {
	global $up_unread_posts;
        if( is_singular() ) {
            global $post;
            $up_unread_posts->set_posts_as_read( $post->ID );
        }
}

class-implements.php

class UP_Unread_Posts_Handler_DB implements UP_Unread_Posts_Handler_Interface {
	
}

class-up-unread-posts-handler-interface.php

interface UP_Unread_Posts_Handler_Interface {

    /**
     * Set posts as read
     *
     * @param array|int $posts post/posts to set as read
     * @author Daniel Pataki
     * @since 1.0.0
     *
     */
    public function set_posts_as_read( $posts );

    /**
     * Sets posts as unread
     *
     * @param array|int $posts post/posts to set as unread
     * @author Daniel Pataki
     * @since 1.0.0
     *
     */
    public function set_posts_as_unread( $posts );

    /**
     * Get read posts
     *
     * @author Daniel Pataki
     * @since 1.0.0
     *
     */
    public function get_read_posts();

    /**
     * Get unread posts
     *
     * @author Daniel Pataki
     * @since 1.0.0
     *
     */
    public function get_unread_posts();

    /**
     * Delete read posts
     *
     * @author Daniel Pataki
     * @since 1.0.0
     *
     */
    public function delete_read_posts();
}

cookie_handler_1.php

class UP_Unread_Posts_Handler_Cookie extends UP_Unread_Posts_Handler implements UP_Unread_Posts_Handler_Interface {

    var $cookie_name;
    protected $read_posts;

    function __construct() {
        parent::__construct();
        $this->set_cookie_name();
        $this->set_read_posts();
    }

    function set_cookie_name() {
        $cookie_name = sanitize_title_with_dashes( get_bloginfo('title') . '-up_read_posts' );
        $cookie_name = apply_filters( 'up/cookie_name', $cookie_name );
        $this->cookie_name = $cookie_name;
    }

    function set_read_posts() {
        if( !empty( $_COOKIE[$this->cookie_name] ) ) {
            $this->read_posts = explode( ', ', gzuncompress( $_COOKIE[$this->cookie_name] ) );
        }
        else {
            $this->read_posts = array();
        }
    }

}

cookie_handler_2.php

function set_posts_as_read( $posts ) {
	if( is_numeric( $posts ) ) {
  		$posts = array( $posts );
	}
	
	if( array_intersect( $this->read_posts, $posts ) == $posts ) {
    		return ;
	}

	$this->read_posts = array_unique( array_merge( $this->read_posts, $posts ) );
	$cookie_value = gzcompress( implode( ',', $this->read_posts ) );

	setcookie( $this->cookie_name, $cookie_value, time() + 3600 * 24 * 365 * 10 , COOKIEPATH, COOKIE_DOMAIN, false );
}

function set_posts_as_unread( $posts ) {
	if( is_numeric( $posts ) ) {
    		$posts = array( $posts );
	}

	$this->read_posts = array_diff( $this->read_posts, $posts );
	$cookie_value = gzcompress( implode( ',', $this->read_posts ) );

	setcookie( $this->cookie_name, $cookie_value, time() + 3600 * 24 * 365 * 10 , COOKIEPATH, COOKIE_DOMAIN, false );

}

function delete_read_posts() {
	if( isset( $_COOKIE[$this->cookie_name] ) ) {
    		unset( $_COOKIE[$this->cookie_name] );
    		setcookie( $this->cookie_name, null, -1, '/' );
	}
}

db-set_posts_as_read.php

function set_posts_as_read( $posts ) {
	if( is_numeric( $posts ) ) {
    		$posts = array( $posts );
	}

	if( array_intersect( $this->read_posts, $posts ) == $posts ) {
    		return ;
	}

	$this->read_posts = array_unique( array_merge( $this->read_posts, $posts ) );

	update_user_meta( $this->user_id, $this->meta_field, $this->read_posts );

}

db_handler_1.php

class UP_Unread_Posts_Handler_DB extends UP_Unread_Posts_Handler implements UP_Unread_Posts_Handler_Interface {

    public $meta_field;
    public $user_id;
    protected $read_posts;
    
    function __construct() {
        $this->set_meta_field();
        $this->set_user_id();
        $this->set_read_posts();
    }

    protected function set_meta_field() {
        $this->meta_field = apply_filters( 'up/meta_field', 'up_read_posts' );
    }

     protected function set_user_id() {
        $current_user = wp_get_current_user();
        $this->user_id = $current_user->ID;
    }

     protected function set_read_posts() {
        $read_posts = get_user_meta( $this->user_id, $this->meta_field, true );
        $read_posts = ( empty( $read_posts ) ) ? array() : $read_posts;
        $this->read_posts = $read_posts;
    }

}

db_handler_2.php

function set_posts_as_unread( $posts ) {
	if( is_numeric( $posts ) ) {
    		$posts = array( $posts );
	}

	$this->read_posts = array_diff( $this->read_posts, $posts );

	update_user_meta( $this->user_id, $this->meta_field, $this->read_posts );
	
}

function delete_read_posts() {
	delete_user_meta( $this->user_id, $this->meta_field );
}

dynamic-calls.php

$type = 'cookie';
if( is_user_logged_in() $$ function_exists( 'some_api_plugins_function' ) ) {
	$type = 'someapi';
}
elseif( is_user_logged_in() ) {
	$type = 'db';
}

call_user_func( 'delete_read_posts_' . $type );

get_read_posts.php

function get_read_posts() {
	return $this->read_posts;
}

get_unread_posts.php

    function get_unread_posts( $args = array() ) {
        $defaults = array(
            'post_type' => 'post',
            'post_status' => 'publish',
            'post__not_in' => $this->get_read_posts(),
            'fields' => 'ids',
            'posts_per_page' => -1,
            'orderby' => 'DESC'
        );

        $args = wp_parse_args( $args, $defaults );
        $args = apply_filters( 'up/unread_query_args', $args );

        $unread = new WP_Query( $args );

        if( $unread->found_posts == 0 ) {
            return array();
        }

        else {
            return $unread;
        }

    }

inheritance.php

class UP_Unread_Posts_Handler {

    function get_unread_posts( $args = array() ) {}

    function get_read_posts() {}
}

class UP_Unread_Posts_Handler_DB extends UP_Unread_Posts_Handler implements UP_Unread_Posts_Handler_Interface {

    function set_posts_as_read( $posts ) {}

    function set_posts_as_unread( $posts ) {}
    
    function delete_read_posts() {}
    
}

class UP_Unread_Posts_Handler_Cookie extends UP_Unread_Posts_Handler implements UP_Unread_Posts_Handler_Interface {

    function set_posts_as_read( $posts ) {}

    function set_posts_as_unread( $posts ) {}
    
    function delete_read_posts() {}
    
}

instantiate-1.php

if( is_user_logged_in() ) {
	$read_posts = UP_Unread_Posts_Handler_DB;
}
else {
	$read_posts = UP_Unread_Posts_Handler_Cookie;
}
$read_posts->set_posts_as_read(12);

instantiation.php

add_action( 'plugins_loaded', 'up_initialize_plugin' );
function up_initialize_plugin() {
    global $up_unread_posts;
    $up_unread_posts_handler = ( is_user_logged_in() ) ? "UP_Unread_Posts_Handler_DB" : "UP_Unread_Posts_Handler_Cookie";

    add_filter( 'up/handler', $up_unread_posts_handler );

    $up_unread = new UP_Unread_Posts( new $up_unread_posts_handler );
    $up_unread_posts = $up_unread->handler;
}

main-class-1.php

class UP_Unread_Posts {

    public $handler;


    function __construct( UP_Unread_Posts_Handler_Interface $handler = null ) {
        $this->handler = $handler ?: new UP_Unread_Posts_Handler_Cookie;
    }
    
}

spaghetti-functions.php

function get_read_posts() {
	if( is_user_logged_in() ) {
		// Get from DB
	}
	else {
		// Get from Cookie
	}
}

function delete_read_posts() {
	if( is_user_logged_in() ) {
		// Delete from DB
	}
	else {
		// Delete the Cookie
	}
}

widget.php

/*
Plugin Name:       Unread Posts Widget
Description:       A plugin displays a list of unread posts
Version:           1.0.0
Author:            Daniel Pataki
Author URI:        http://danielpataki.com/
License:           GPLv2 or later
*/

add_action( 'widgets_init', 'unread_posts_widget_init' )
function unread_posts_widget_init() {
	register_widget( 'UP_Unread_Posts_Widget' );
}

class UP_Unread_Posts_Widget extends WP_Widget {

    public function __construct() {
        $widget_details = array(
            'classname' => 'up-unread-posts-widget',
            'description' => __( 'A customizable widget that displays unread posts', 'unread-posts' )
        );

        parent::__construct( 'up-unread-posts', __( 'Unread Posts', 'unread-posts' ), $widget_details );

    }

    public function form( $instance ) {
        $title = ( !empty( $instance['title'] ) ) ? $instance['title'] : '';

        ?>

        <div class='unread-posts'>
            <p>
                <label for="<?php echo $this->get_field_name( 'title' ); ?>"><?php _e( 'Title:', 'unread-posts' ) ?> </label>
                <input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo esc_attr( $title ); ?>" />
            </p>

        </div>
        <?php
    }

     public function widget( $args, $instance ) {

         global $up_unread_posts;

         $query_args = array(
             'posts_per_page' => 5,
             'fields' => 'all'
         );

         $unread = $up_unread_posts->get_unread_posts( $query_args );

         if( $unread->found_posts == 0 ) {
             return;
         }

         echo $args['before_widget'];

         if( !empty( $instance['title'] ) ) {
             echo $args['before_title'] . apply_filters( 'widget_title', $instance['title'], $instance, $this->id_base ) . $args['after_title'];
         }

         $output = '<ul>';
         while( $unread->have_posts() ) {
             $unread->the_post();
             $output .= '<li><a href="' . get_permalink( get_the_ID() ) . '">' . the_title( '','', false) . '</a></li>';
         }
         $output .= '</ul>';

         echo $args['after_widget'];

     }

}