Google and Yahoo Calendar MVC HTML Helpers

CalendarHelpers.cs

public static class CalendarHelpers
{
    //Google Calender

    public static string GoogleCalendar(this HtmlHelper helper, string linkText, string what, DateTime start, DateTime? end, string description, string location, string websiteName, string websiteAddress, string attributes)
    {
        //parse dates
        var dates = start.ToString("yyyyMMddTHHmmssZ");
        if (end.HasValue && end > start)
        {
            dates += "/" + end.Value.ToString("yyyyMMddTHHmmssZ");
        }
        else
        {
            dates += "/" + start.ToString("yyyyMMddTHHmmssZ");
        }

        var path = string.Format("http://www.google.com/calendar/event?action=TEMPLATE&text={0}&dates={1}&details={2}&location={3}&trp=false&sprop={4}&sprop=name:{5}",
                                        what,
                                        dates,
                                        description,
                                        location,
                                        websiteName,
                                        websiteAddress);

        var calendar = string.Format("<a href='{0}' target='_blank' {1}>{2}</a>",
                                        HttpUtility.UrlPathEncode(path),
                                        helper.AttributeEncode(attributes),
                                        linkText);

        return calendar;
    }

    public static string GoogleCalendar(this HtmlHelper helper, string linkText, string what, DateTime start, DateTime? end, string description, string location, string websiteName, string websiteAddress)
    {
        return GoogleCalendar(helper, linkText, what, start, end, description, location, websiteName, websiteAddress, "");
    }

    public static string GoogleCalendar(this HtmlHelper helper, string linkText, string what, DateTime start, string description)
    {
        return GoogleCalendar(helper, linkText, what, start, null, description, "", "", "", "");
    }

    //Yahoo Calendar

    public static string YahooCalendar(this HtmlHelper helper, string linkText, string what, DateTime start, DateTime? end, string description, string venue, string street, string city, string attributes)
    {
        //parse duration
        var duration = "";
        if(end.HasValue && end > start)
        {
            var span = (TimeSpan)(end - start);
            duration = "&dur=" + span.ToString("HHMM");
        }

        var path = string.Format("http://calendar.yahoo.com/?v=60&view=d&type=10&title={0}&st={1}{2}&desc={3}&in_loc={4}&in_st={5}&in_csz={6}'",
                            what,
                            start.ToString("yyyyMMddTHHmmssZ"),
                            duration,
                            description,
                            venue,
                            street,
                            city);

        var calendar = string.Format("<a href='{0}' target='_blank' {1}>{2}</a>",
                                        HttpUtility.UrlPathEncode(path),
                                        helper.AttributeEncode(attributes),
                                        linkText);

        return calendar;
    }

    public static string YahooCalendar(this HtmlHelper helper, string linkText, string what, DateTime start, DateTime? end, string description, string venue, string street, string city)
    {
        return YahooCalendar(helper, linkText, what, start, end, description, venue, street, city, "");
    }

    public static string YahooCalendar(this HtmlHelper helper, string linkText, string what, DateTime start, string description)
    {
        return YahooCalendar(helper, linkText, what, start, null, description, "", "", "");
    }
}