functions.php

<?php
/**
 * _s-child-theme functions and definitions
 *
 * @link https://developer.wordpress.org/themes/basics/theme-functions/
 *
 * @version 0.0.1
 *
 * @author jitendersinghwp
 */

/**
 * Enqueue style
 */
function _s_child_theme_scripts() {
  wp_enqueue_style( '_s-child-theme-style', get_template_directory_uri().'/style.css' );
}
//hook enqueue all style and scripts into wp_enqueue_scripts
add_action( 'wp_enqueue_scripts', '_s_child_theme_scripts' );

if ( ! function_exists('_s_child_theme_register_task') ) {

/**
 * Register Custom Post Type - Task
 */
function _s_child_theme_register_task() {

	$labels = array(
		'name'                  => _x( 'Tasks', 'Post Type General Name', 'task' ),
		'singular_name'         => _x( 'Task', 'Post Type Singular Name', 'task' ),
		'menu_name'             => __( 'Task', 'task' ),
		'name_admin_bar'        => __( 'Task', 'task' ),
		'archives'              => __( 'Task Archives', 'task' ),
		'attributes'            => __( 'Task Attributes', 'task' ),
		'parent_item_colon'     => __( 'Parent Task:', 'task' ),
		'all_items'             => __( 'All Tasks', 'task' ),
		'add_new_item'          => __( 'Add New Task', 'task' ),
		'add_new'               => __( 'Add New', 'task' ),
		'new_item'              => __( 'New Task', 'task' ),
		'edit_item'             => __( 'Edit Task', 'task' ),
		'update_item'           => __( 'Update Task', 'task' ),
		'view_item'             => __( 'View Task', 'task' ),
		'view_items'            => __( 'View Tasks', 'task' ),
		'search_items'          => __( 'Search Task', 'task' ),
		'not_found'             => __( 'Not found', 'task' ),
		'not_found_in_trash'    => __( 'Not found in Trash', 'task' ),
		'featured_image'        => __( 'Featured Image', 'task' ),
		'set_featured_image'    => __( 'Set featured image', 'task' ),
		'remove_featured_image' => __( 'Remove featured image', 'task' ),
		'use_featured_image'    => __( 'Use as featured image', 'task' ),
		'insert_into_item'      => __( 'Insert into item', 'task' ),
		'uploaded_to_this_item' => __( 'Uploaded to this task', 'task' ),
		'items_list'            => __( 'Tasks list', 'task' ),
		'items_list_navigation' => __( 'Tasks list navigation', 'task' ),
		'filter_items_list'     => __( 'Filter tasks list', 'task' ),
	);
	$args = array(
		'label'                 => __( 'Task', 'task' ),
		'description'           => __( 'Post Type Description', 'task' ),
		'labels'                => $labels,
		'supports'              => array( 'title', 'editor' ),
		'taxonomies'            => array( 'category', 'post_tag' ),
		'hierarchical'          => true,
		'public'                => true,
		'show_ui'               => true,
		'show_in_menu'          => true,
		'menu_position'         => 5,
		'show_in_admin_bar'     => true,
		'show_in_nav_menus'     => true,
		'can_export'            => true,
		'has_archive'           => true,
		'exclude_from_search'   => false,
		'publicly_queryable'    => true,
		'capability_type'       => 'page',
		'show_in_rest'          => true,
	);
	register_post_type( 'task', $args );

}
//hook task (custom posttype) registration into init
add_action( 'init', '_s_child_theme_register_task', 0 );
}

/**
 * This function adds a meta box at task(custom posttype screen) with a callback function of task_status_metabox_callback
 */
function _s_child_theme_add_meta_box() {
    add_meta_box(
        '_s_child_theme_tast_status_metabox_id',
        __( 'Task Status', '_s-child-theme' ),
        '_s_child_theme_task_status_metabox_callback',
        'task',
        'normal',
        'high'
    );
}
// hook task status meta box registration into add_meta_boxes
add_action( 'add_meta_boxes', _s_child_theme_add_meta_box );

/**
 * Display Task status UI
 *
 * @param object $post    The current post.
 */
function _s_child_theme_task_status_metabox_callback( $post ) {
    //fetch all post meta data
    $value = get_post_meta( $post->ID );
    //tast_status value
    $task_status = isset( $value['task_status'] ) ? $value['task_status'][0] : '';
    //assignee name
    $assignee = isset( $value['assignee'] ) ? esc_attr( $value['assignee'][0] ) : '';

    //insert nounce field for validing request
    wp_nonce_field( '_s_child_theme_task_status_action', '_s_child_theme_task_status' );
    //get all users
    $users = get_users(array(
      fields => array('display_name')
    ));
    ?>
    <select class="select_user" id="assignee" name="assignee">
      <option value="">Select Assignee</option>
      <?php
        /**
         * adding all user into UI
         */
        foreach($users as $user):
          ?>
          <option value="<?php echo $user->display_name; ?>" <?php selected( $assignee, $user->display_name ) ?>>
                <?php echo $user->display_name; ?>
          </option>
          <?php
        endforeach
      ?>
    </select>
    <label for="assignee">Assignee</label>
    <input type="checkbox" id="task_status" name="task_status" <?php checked( $task_status, 'on' ) ?> />
    <label for="task_status">Task Status</label>
    <?php
}

// hook task status meta box data save into save_task
add_action( 'save_post_task', '_s_child_theme_meta_box_data_save' );

/**
 * Save task status meta box data
 * @param int $post_id
 */
function _s_child_theme_meta_box_data_save( $post_id ) {
  //return if not verify nonce
  if( !isset( $_POST['_s_child_theme_task_status'] ) || !wp_verify_nonce( $_POST['_s_child_theme_task_status'], '_s_child_theme_task_status_action' ) ) {
    return;
  }

  //return if current user not edit post
  if( !current_user_can( 'edit_post' ) ) {
    return;
  }
  // update current task status postmeta
  $task_status = isset( $_POST['task_status'] ) ? esc_attr ( $_POST['task_status'] ) : 'off';
  update_post_meta( $post_id, 'task_status', $task_status );

  //update current assignee postmeta
  $assignee = isset( $_POST['assignee'] ) ? esc_attr( $_POST['assignee'] ) : '';
  update_post_meta( $post_id, 'assignee', $assignee );

}