Create Duplicate Posts and Pages

// NAV: Create Duplicate Posts and Pages
// Add the duplicate link to action list for post_row_actions
// for "post" and custom post types
add_filter( 'post_row_actions', 'wpcoder_duplicate_post_link', 10, 2 );
// for "page" post type
add_filter( 'page_row_actions', 'wpcoder_duplicate_post_link', 10, 2 );
function wpcoder_duplicate_post_link( $actions, $post ) {
if( ! current_user_can( 'edit_posts' ) ) {
    return $actions;
}

$url = wp_nonce_url(
    add_query_arg(
        array(
            'action' => 'wpcoder_duplicate_post_as_draft',
            'post' => $post->ID,
        ),
        'admin.php'
    ),
    basename(__FILE__),
    'duplicate_nonce'
);

$actions[ 'duplicate' ] = '<a href="' . esc_url($url) . '" title="Duplicate this item" rel="permalink">Duplicate</a>';

return $actions;
}
/*

Function creates post duplicate as a draft and redirects then to the edit post screen
*/
add_action( 'admin_action_wpcoder_duplicate_post_as_draft', 'wpcoder_duplicate_post_as_draft' );

function wpcoder_duplicate_post_as_draft(){
// check if post ID has been provided and action
if ( empty( $_GET[ 'post' ] ) ) {
    wp_die( 'No post to duplicate has been provided!' );
}

// Nonce verification
if ( ! isset( $_GET[ 'duplicate_nonce' ] ) || ! wp_verify_nonce( $_GET[ 'duplicate_nonce' ], basename( __FILE__ ) ) ) {
    return;
}

// Get the original post id
$post_id = absint( $_GET[ 'post' ] );

// And all the original post data then
$post = get_post( $post_id );

/*
 * if you don't want current user to be the new post author,
 * then change next couple of lines to this: $new_post_author = $post->post_author;
 */
$current_user = wp_get_current_user();
$new_post_author = $current_user->ID;

// if post data exists (I am sure it is, but just in a case), create the post duplicate
if ( $post ) {

    // new post data array
    $args = array(
        'comment_status' => $post->comment_status,
        'ping_status'    => $post->ping_status,
        'post_author'    => $new_post_author,
        'post_content'   => $post->post_content,
        'post_excerpt'   => $post->post_excerpt,
        'post_name'      => $post->post_name,
        'post_parent'    => $post->post_parent,
        'post_password'  => $post->post_password,
        'post_status'    => 'draft',
        'post_title'     => $post->post_title,
        'post_type'      => $post->post_type,
        'to_ping'        => $post->to_ping,
        'menu_order'     => $post->menu_order
    );

    // insert the post by wp_insert_post() function
    $new_post_id = wp_insert_post( $args );

    /*
     * get all current post terms ad set them to the new post draft
     */
    $taxonomies = get_object_taxonomies( get_post_type( $post ) ); // returns array of taxonomy names for post type, ex array("category", "post_tag");
    if( $taxonomies ) {
        foreach ( $taxonomies as $taxonomy ) {
            $post_terms = wp_get_object_terms( $post_id, $taxonomy, array( 'fields' => 'slugs' ) );
            wp_set_object_terms( $new_post_id, $post_terms, $taxonomy, false );
        }
    }

    // duplicate all post meta
    $post_meta = get_post_meta( $post_id );
    if( $post_meta ) {

        foreach ( $post_meta as $meta_key => $meta_values ) {

            if( '_wp_old_slug' == $meta_key ) { // do nothing for this meta key
                continue;
            }

            foreach ( $meta_values as $meta_value ) {
                add_post_meta( $new_post_id, $meta_key, $meta_value );
            }
        }
    }

    // finally, redirect to the edit post screen for the new draft
    wp_safe_redirect(
        add_query_arg(
            array(
                'action' => 'edit',
                'post' => $new_post_id
            ),
            admin_url( 'post.php' )
        )
    );
    exit;
    // or we can redirect to all posts with a message
//      wp_safe_redirect(
//          add_query_arg(
//              array(
//                  'post_type' => ( 'post' !== get_post_type( $post ) ? get_post_type( $post ) : false ),
//                  'saved' => 'post_duplication_created' // just a custom slug here
//              ),
//              admin_url( 'edit.php' )
//          )
//      );
//      exit;
} else {
    wp_die( 'Post creation failed, could not find original post.' );
}
}
/*

In case we decided to add admin notices
*/
add_action( 'admin_notices', 'wpcoder_duplication_admin_notice' );

function wpcoder_duplication_admin_notice() {
// Get the current screen
$screen = get_current_screen();

if ( 'edit' !== $screen->base ) {
    return;
}

//Checks if settings updated
if ( isset( $_GET[ 'saved' ] ) && 'post_duplication_created' == $_GET[ 'saved' ] ) {

     echo '<div class="notice notice-success is-dismissible"><p>Post copy created.</p></div>';

}
}