﻿namespace PrimusFlex.Infrastructure
{
    using System;
    using System.Globalization;

    public static class DateTimeHelper
    {
        // This presumes that weeks start with Monday.
        // Week 1 is the 1st week of the year with a Thursday in it.
        public static int GetIso8601WeekOfYear(DateTime time)
        {
            // Seriously cheat.  If its Monday, Tuesday or Wednesday, then it'll 
            // be the same week# as whatever Thursday, Friday or Saturday are,
            // and we always get those right
            DayOfWeek day = CultureInfo.InvariantCulture.Calendar.GetDayOfWeek(time);
            if (day >= DayOfWeek.Monday && day <= DayOfWeek.Wednesday)
            {
                time = time.AddDays(3);
            }

            // Return the week of our adjusted day
            return CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(time, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
        }
    }
}
