Validation Fields Custom Form Plugin

<?php
/**
 * Contact form functionality
 * Used within the loop
 * @link https://developer.wordpress.org/reference/functions/wp_nonce_field/
 * @link https://codex.wordpress.org/Class_Reference/WP_Error
 * @link https://developer.wordpress.org/reference/functions/wp_is_mobile/
 * @link https://developer.wordpress.org/reference/functions/wp_kses_data/
 * @link https://developer.wordpress.org/reference/functions/wp_remote_retrieve_response_code/
 * @link https://developer.wordpress.org/reference/functions/wp_get_referer/
 */


defined( 'ABSPATH' ) or die( 'No script kiddies please!' );

 get_header();

class Gymclub_contact_form {


    private $reg_errors = array();

    public function __construct() {
              // add form template
              add_action( 'init', array( $this, 'load_form' ) );

            }


    public function load_form($obj) {

     ob_start();

     get_template_part( 'templates/contac_form');

        //include_once plugin_dir_url(__FILE__) . '/templates/contact_form.php';


     return ob_get_clean();

     }

    public function validate_form( $name, $email, $phone, $message, $response ) {

              $not_human  = "Human verification incorrect.";
              $failed_connect = "An error has occurred while validating the recaptcha";
              $email_invalid   = "Email Address Invalid.";
              $name_error   = "Name should be at least 4 characters";
              $missing_content = "Please supply all information.";


              $response = wp_safe_remote_post( "https://www.google.com/recaptcha/api/siteverify", array(
                'method' => 'POST',
                'timeout' => 45,
                'redirection' => 5,
                'httpversion' => '1.0',
                'blocking' => true,
                'headers' => array(),
                'body' => array(
                  'secret' => "6Ld61NkUAAAAAI0JuA0dp_RL5_T9EucRdgLX2nVj",
                  'response' => esc_attr($_POST['g-recaptcha-response'])),
                'cookies' => array()
                )
              );


          // If any field is left empty, add the error message to the error array
            if ( empty($name) || empty($email) || empty($phone) || empty($message) || empty($response) ) {
                $this->reg_errors->add( esc_html__( $missing_content, 'gymclub') );
            }

            // if the name field isn't alphabetic, add the error message
            if ( strlen($name) < 4 ) {
                $this->reg_errors->add( esc_html__( $name_error, 'gymclub') );
            }

            // Check if the email is valid
            if ( !is_email($email) ) {
                $this->reg_errors->add( esc_html__( $email_invalid, 'gymclub') );
            }

            //Check if we have some kind of error in the connection with google
            if (is_wp_error( $response )) {
                $this->reg_errors->add( esc_html__( $failed_connect, 'gymclub' ));
            } else{
              //If we have successfully connected to google, we check if the answer is true or false
               $response = json_decode($response['body']);
            }if ($response->success == false) {
                $this->reg_errors->add( esc_html__( $not_human, 'gymclub' ));
            }
    }

    public function send_email( $name, $email, $phone, $message, $response ) {

            $message_sent    = "Thanks! Your message has been sent.";


         if (count( $this->reg_errors )  < 1 ) {


                  $name = isset ($_POST['message_name'])? esc_sql(sanitize_text_field($_POST['message_name'])):"";
                  $email = isset($_POST['message_email'])? esc_sql(sanitize_text_field(sanitize_email($_POST['message_email']))):"";
                  $phone = isset($_POST['message_phone'])? esc_sql(sanitize_text_field($_POST['message_phone'])):"";
                  $message = isset($_POST['message_text'])? esc_sql(sanitize_text_field($_POST['message_text'])):"";

                  $to = get_option('gym_contact_admin_email');

                  $headers[] = 'From: '. $name . ' <' . $email . '>';

                  if ( wp_mail($to, $subject, $message, $headers)) { ?>
                      <div class="row margin-button-small">
                          <div class="col-md-12 alert alert-success">
                              <button type="button" class="close" data-dismiss="alert" aria-label="close">
                                  <span aria-hidden="true">&times;</span>
                              </button>
                              <p class="message"><?php echo __( $message_sent, 'gymclub'); ?></p>
                          </div>
                     </div> <!-- end row -->
                  <?php}


              }

    }

  public function process_functions() {

       if (isset($_POST['submit']) && isset($_POST['gymclub_nonce_field'])) {

              return;

           } //end isset

       if (wp_verify_nonce( $_POST['gymclub_nonce_field'], 'custom_action_nonce')) {

              return;

           }// end verify nonce

         $url = wp_get_referer();

         $this->validate_form($_POST['message_name'], $_POST['message_email'], $_POST[''], $_POST['message_phone'], $_POST['message_text']), ($_POST['g-recaptcha-response']);

          if (is_wp_error( $this->reg_errors) && count( $this->reg_errors->get_error_messages() ) > 0 ) {
                   foreach ( $this->reg_errors->get_error_messages() as $error ) {?>
                       <div class="row margin-button-small">
                          <div class="col-md-12 alert alert-success">
                              <button type="button" class="close" data-dismiss="alert" aria-label="close">
                                  <span aria-hidden="true">&times;</span>
                              </button>
                              <p class="message"><?php echo __( $error, 'gymclub'); ?></p>
                          </div>
                       </div> <!-- end row -->
                  <?php }  //end reg_errors

            } // end is_wp_error

            wp_safe_redirect( $url );
            exit();

        } //end public function



}


// WordPress Ajax
add_action( 'wp_ajax_gym_contact_create_entry', 'gym_contact_create_entry' );
add_action( 'wp_ajax_nopriv_my_contact', 'gym_contact_create_entry' );


// Ajax insert data contact entry
function gym_contact_create_entry($name, $email, $phone, $message ) {
  global $wpdb;
  $table_name = $wpdb->prefix . 'contact';

  $wpdb->insert(
        $table_name,
        array(
            'name' => $name,
            'email' => $email,
            'phone' => $phone,
            'message' => $message,
            'time' => current_time( 'mysql' )
        )
    );
}


 ?>

<?php get_footer(); ?>