Why is my JTAppleCalendar 1 day ahead?

Question

I'm using JTAppleCalendar and each months date is 1 day ahead than it should be. This is my code for the configuration:

func configureCalendar(_ calendar: JTAppleCalendarView) -> ConfigurationParameters {

    formatter.dateFormat = "yyyy MM dd"
    formatter.timeZone = Calendar.current.timeZone
    formatter.locale = Calendar.current.locale

    let currentYear = Calendar.current.component(.year, from: Date())
    let stringCurrentYear = String(currentYear)
    let nextYear = currentYear + 1
    let stringNextYear = String(nextYear)
    let currentMonth = Calendar.current.component(.month, from: Date())
    let stringCurrentMonth = String(currentMonth)

    let startDate = formatter.date(from: "\(stringCurrentYear) \(stringCurrentMonth) 01")!
    let endDate = formatter.date(from: "\(stringNextYear) 12 31")!

    let parameters = ConfigurationParameters(startDate: startDate, endDate: endDate)

    return parameters

}

This is the current output:

The 1st of January 2018 should be a Monday however is appearing as a Tuesday.

Answer 1

Found my own answer. I used the following code to fix it:

    let parameters = ConfigurationParameters(
        startDate: startDate,
        endDate: endDate,
        numberOfRows: 6,
        calendar: calendar,
        generateOutDates: .tillEndOfRow,
        firstDayOfWeek: .monday
    )

    return parameters

I think the issue was that by default the first day of the week was by default Sunday. So setting it to Monday resolved the problem.