function acf_load_select_country( $field ) {
  // Reset choices
  $field['choices'] = array();

  // Get field from options page
  $countries_and_areas = get_field('countries_and_areas', 'options');

  // Get only countries in array
  foreach ($countries_and_areas as $key => $value) {
    $countries[] = $value['country'];
  }

  // Sort countries alphabetically
  natsort( $countries );

  // Populate choices
  foreach( $countries as $choice ) {
    $field['choices'][ $choice ] = $choice;
  }

  // Return choices
  return $field;

}


// Populate select field using filter
add_filter('acf/load_field/name=field_5c7f1915175b2', 'acf_load_select_country');




function acf_admin_enqueue( $hook ) {

  $type = get_post_type(); // Check current post type
  $types = array( 'post' ); // Allowed post types

  if( !in_array( $type, $types ) )
      return; // Only applies to post types in array

  wp_enqueue_script( 'populate-area', get_stylesheet_directory_uri() . '/assets/js/autopopulate.js' );

  wp_localize_script( 'populate-area', 'pa_vars', array(
        'pa_nonce' => wp_create_nonce( 'pa_nonce' ), // Create nonce which we later will use to verify AJAX request
      )
  );
}

add_action( 'admin_enqueue_scripts', 'acf_admin_enqueue' );






// Return areas by country
function area_by_country( $selected_country ) {

  // Verify nonce
  if( !isset( $_POST['pa_nonce'] ) || !wp_verify_nonce( $_POST['pa_nonce'], 'pa_nonce' ) )
    die('Permission denied');

  // Get country var
  $selected_country = $_POST['country'];

  // Get field from options page
  $countries_and_areas = get_field('countries_and_areas', 'options');

  // Simplify array to look like: country => areas
  foreach ($countries_and_areas as $key => $value) {
    $countries[$value['country']] = $value['area'];
  }

  // Returns Area by Country selected if selected country exists in array
  if (array_key_exists( $selected_country, $countries)) {

    // Convert areas to array
    $arr_data = explode( ', ', $countries[$selected_country] );
    return wp_send_json($arr_data);

  } else {

    $arr_data = array();
    return wp_send_json($arr_data);
  }

  die();
}

add_action('wp_ajax_pa_add_areas', 'area_by_country');
add_action('wp_ajax_nopriv_pa_add_areas', 'area_by_country');