Display notice in EDD if email already exists and not logged in

gistfile1.txt

/**
 * Redirect the user to the appropriate page upon login.
 */
add_filter( 'login_redirect', function( $url, $query, $user ) {
  if ( is_wp_error( $user ) ) {
    return $url;
  }

  if ( current_user_can('administrator') ) {
    return $url;
  }

  if ( EDD()->cart()->is_empty() ) {
    return home_url( "/account" );
  } else {
    return edd_get_checkout_uri();
  }
}, 10, 3 );


/**
 * Check if an email exists during checkout and encourage the user to login
 * @return {[type]} [description]
 */
add_action('wp_ajax_nopriv_edd_check_if_customer_email_exists', function() {
  if ( is_user_logged_in() ) {
    return;
  }

  check_ajax_referer( 'edd_check_if_customer_email_exists' );

  if ( empty( $_REQUEST['email'] ) ) {
    return;
  }

  $email = sanitize_email( $_REQUEST['email'] );

  if ( username_exists($email) || email_exists( $email ) ) {
    echo "1";
    die;
  }

  echo "0";
  die;
});

function edd_check_if_email_exists_during_checkout() {
  if ( is_user_logged_in() ) {
    return;
  }

  ob_start();?>
    <script>
      var $emailInput = jQuery('#edd-email');
      var emailFound = false;

      $emailInput.blur(function(e) {
        var value = e.target.value;

        jQuery.ajax({
          url: "/wp/wp-admin/admin-ajax.php",
          type: "POST",
          data: {
            "action": "edd_check_if_customer_email_exists",
            "_wpnonce": "<?php echo wp_create_nonce( 'edd_check_if_customer_email_exists' ); ?>",
            "email": value
          },
          success: function(exists) {
            if (exists == "1" && emailFound == false) {
              jQuery("#edd-purchase-button").prop("disabled", true);

              var emailTemplate = '<div style="margin: 15px 0 0;color: #fafafa;background: #12af95;padding: 15px;border-radius: 2px;box-shadow: 0 2px 2px rgba(0, 0, 0, 0.15);"><h2 style="margin: 0;">Welcome back!</h2><p style="color: #fafafa;">Before you purchase, <a href="/account" style="color: #292d33; font-weight: bold;">please sign in to your account.</a></p></div>';
              $emailInput.after(emailTemplate);
              emailFound = true;
            }
          },
          error: function(error) {
            console.error(error);
          }
        })
      });
    </script>

  <?php
  echo ob_get_clean();
}

add_action('edd_purchase_form_after_user_info', 'edd_check_if_email_exists_during_checkout', 11);