using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Church.Net.Utility
{
    public static class DateTimeHelper
    {

        private static TimeZoneInfo pacificZone = TimeZoneInfo.FindSystemTimeZoneById("Pacific Standard Time");
        public static DateTime GetNextWeekday(DateTime start, DayOfWeek day)
        {
            // The (... + 7) % 7 ensures we end up with a value in the range [0, 6]
            int daysToAdd = ((int)day - (int)start.DayOfWeek + 7) % 7;
            return start.AddDays(daysToAdd);
        }
        public static DateTime Now(string timeZoneCode=null)
        {
            TimeZoneInfo timeZone;
            if (null== timeZoneCode)
            {
                timeZone = pacificZone;
            }
            else
            {
                timeZone = TimeZoneInfo.FindSystemTimeZoneById(timeZoneCode);
            }
            return TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, pacificZone);
        }
        public static DateTime Today(string timeZoneCode = null)
        {
            return Now(timeZoneCode).Date;
        }
        public static DateTime ToUtc(this DateTime time,string timeZoneCode)
        {
            TimeZoneInfo timeZone = TimeZoneInfo.FindSystemTimeZoneById(timeZoneCode);
            return TimeZoneInfo.ConvertTimeToUtc(time, timeZone);
        }
        public static DateTime ToLocal(this DateTime time, string timeZoneCode)
        {
            TimeZoneInfo timeZone = TimeZoneInfo.FindSystemTimeZoneById(timeZoneCode);
            return TimeZoneInfo.ConvertTimeFromUtc(time, timeZone);
        }
    }
}