add_action('wp_ajax_jctgbtg_get_cell_groups', 'jctgbtg_get_cell_groups_ajax');
add_action('wp_ajax_nopriv_jctgbtg_get_cell_groups', 'jctgbtg_get_cell_groups_ajax');

function jctgbtg_get_cell_groups_ajax() {
    $district = isset($_POST['district'])
        ? sanitize_text_field(wp_unslash($_POST['district']))
        : '';

    if ($district === '') {
        wp_send_json_success([]);
    }

    $groups = [];

    $rows = function_exists('get_field') ? get_field('cell_groups', 'option') : [];

    if (is_array($rows)) {
        foreach ($rows as $row) {
            $row_district = isset($row['district']) ? trim((string) $row['district']) : '';
            $cell_group   = isset($row['cell_group']) ? trim((string) $row['cell_group']) : '';

            if ($row_district !== '' && $cell_group !== '' && strcasecmp($row_district, $district) === 0) {
                $groups[] = $cell_group;
            }
        }
    }

    $groups = array_values(array_unique($groups));
    sort($groups);

    wp_send_json_success($groups);
}