/**
 * Plugin Name: Home Page CPT
 **/

class WP_Homepage_CPT {

    function __construct() {

        // add the default homepage on plugin activation
        register_activation_hook( __FILE__, array( &$this, 'add_home_page_post' ) );

        // register the homepage post type
        add_action( 'init', array( &$this, 'register_homepage_cpt' ) );

        // add the menu link
        add_action( 'admin_menu', array( &$this, 'edit_homepage_link' ) );
    }

    function edit_homepage_link() {
        global $submenu, $pagenow;

        // query the homepage posts
        $homepage = new WP_Query( 'post_type=homepage' );

        // if its new post page and we have homepage
        if ( $pagenow == 'post-new.php' && $homepage->have_posts() ) {
            wp_die('You cant add more then one homepage');
        }

        // if we have homepage post, show the edit link else the add homepage link
        if ( $homepage->have_posts() ) {
            $homepage->the_post();
            $link = get_edit_post_link( get_the_ID(), 'return' );
            $title = 'Edit Home Page';
        } else {
            // in case if the user has deleted the default post
            $link = get_bloginfo( 'url' ). '/wp-admin/post-new.php?post_type=homepage';
            $title = 'Add Home Page';
        }
        $submenu['edit.php'] = array( array( $title, 'manage_options', $link ) ) + $submenu['edit.php'];
    }

    function register_homepage_cpt() {
        $args = array(
            'label' => 'homepage',
            'description' => 'Home Page post type',
            'public' => true,
            'show_in_menu' => false
        );
        register_post_type( 'homepage', $args );
    }

    function add_home_page_post() {
        // on activation first regsiter the post type
        $this->register_homepage_cpt();

        // add the first and only post
        $post_data = array(
            'post_title' => 'Home Page',
            'post_type' => 'homepage',
            'post_statue' => 'publish',
            'post_author' => 1
        );
        wp_insert_post( $post_data );
    }

}

$GLOBALS['wp_homepage_cpt'] = new WP_Homepage_CPT;