Dynamically set taxonomy term and show admin notice on post save

Question

I have a taxonomy of "date" listing all months of the year. And I have a custom field of "start_date". I would like to update the 'date' taxonomy dynamically so the user doesnt need to click both when setting up a post. So far my efforts have not shown results. What am I doing wrong?

/**
 * Check value of date, set date taxonomy on post save, then show admin notice
 * @param  string $id post id
 * @return void
 */
function trip_location_post_published_notification( $ID, $post ) {

    // get acf value of start date
    $date = get_field( 'start_date', $ID );

    // get the month off the beginning of the string (ex. 11/01/2017), 11 is month
    $moNum = explode('/',$date);
    $moNum = $moNum[0];
    $moList = array("January","February","March","April","May","June","July","August","September","October","November","December");
    $monthName = $moList[$moNum];

    // set taxonomy to this post ID
    wp_set_object_terms($ID,$monthName,'date');

    // setup notice message via WP_Error class?
    if ( $date ) {
        $notice = new WP_Error('date_notice','This trip location start date month is set to '.$monthName);
    } else {
        $notice = new WP_Error('date_notice','You did not set a trip start date.');
    }

    add_filter('redirect_post_location', function( $location ) use ( $notice) {
        return add_query_arg( 'date_notice', $notice->get_error_code(), $location );
    });

    // now add an admin notice
    add_action( 'admin_notices', 'tax_date_set_notice' );
    function tax_date_set_notice(){
        if ( array_key_exists( 'date_notice', $_GET) ) { 
            $notice = $_GET['date_notice'];
        ?>
        <div class="update-nag notice is-dismissable">
            <p><?php _e( $notice, 'mydomain' ); ?></p>
        </div>
        <?php
        }
    }
}
add_action( 'save_post_trip-location', 'trip_location_post_published_notification', 12, 2 );

Answer 1

Okay, so just in case anyone needs help on the same thing I did... here is my solution. Instead of a php/wordpress solution, I used javascript. Id love to see the php/wordpress solution if someone wants to post it.

<?php
// Admin Custom JS
add_action('admin_head', 'admin_custom_js');
function admin_custom_js() {
?>
<script>

    // update date (month) taxonomy term on change of start date acf field
    jQuery(function($){

        var $startDateInput = $('div[data-name="start_date"] input');
        if ($startDateInput.length) {
            $startDateInput.on('change',function(){

                var val = $(this).val();
                var moList = ["January","February","March","April","May","June","July","August","September","October","November","December"];

                if (val === ''){

                } else {
                    var moNum = val.substr(0,2);
                        moNum = moNum.replace('0','');
                        moNum = Number(moNum) - 1;
                    var moName = moList[moNum];

                    var termVal = $('#datechecklist').find('label:contains("'+moName+'")').find('input').val();
                    var msg = 'Start date month set to '+moName;

                    $('#datechecklist input').prop('checked',false);
                    $('input[value="'+termVal+'"]').prop('checked',true);
                    $('div[data-name="start_date"] .acf-label p').remove();
                    $('div[data-name="start_date"] label').after('<p class="description" style="font-weight:bold;color: #0a81d2">'+msg+'</p>');

                }

            });

        }

    });
</script>
<?php
}