Code added as an onBeforeAdd to the business calendar year ItemType, which gathers a list of holidays for the given year/country and creates exceptions

labs_getCalendar.cs

/*
 * There is a publicly available API that can be used to get a list of holidays for a given country
 * in a given year. The goal of this method is to help automate the process of creating a business calendar
 * by creating the Business Calendar Exceptions for an admin.
 *
 * Documentation for this API can be found at https://date.nager.at/Api
 */
Innovator inn = this.getInnovator();
// The URL we will be pinging to get the list of public holidays for our country
string dateApiUrl = "https://date.nager.at/api/v2";
// Validate that we have the data needed to request the holidays
string year = this.getProperty("year", "");
if (string.IsNullOrEmpty(year)) return inn.newError("Cannot run without 'year' property");
string countryCode = this.getProperty("country_code", "");
if (string.IsNullOrEmpty(year)) return inn.newError("Cannot run without 'country_code' property");
// Make our request to the publicly available API
string fullApiRequestUrl = String.Format("{0}/publicholidays/{1}/{2}", dateApiUrl, year, countryCode);
using (WebClient wc = new WebClient())
{
    string responseString = wc.DownloadString(fullApiRequestUrl);
    // Since the response is a JSON object, we'll turn it into an array so it's easier to work with
    Newtonsoft.Json.Linq.JArray responseArray = Newtonsoft.Json.Linq.JArray.Parse(responseString);
    
    
    // Loop through the list of holidays returned by the API and create an Exception to represent each one
    foreach (var dateObject in responseArray)
    {
        var newCalendarException = this.createRelationship("Business Calendar Exception", "add");
        newCalendarException.setProperty("day_date", inn.getI18NSessionContext().ConvertToNeutral((string)dateObject["date"], "string", ""));
        newCalendarException.setProperty("description", (string)dateObject["name"]);
        newCalendarException.setProperty("day_off", "1");
    }
    // Since this is an OnBeforeAdd event, we will return the context item without applying. Relationships will be saved during the “add” action.
    return this;
}