using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    // Desired start time for a given Weekly Search

    // 09:00 hours - In the tenant-specific timezone, regardless of UTC offset

    private static readonly TimeSpan StartTimeHour = TimeSpan.Parse("16:00:00");

    private static readonly List<int> TenantTimeZoneIds = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8 };

    public static void Main()

    {

        Console.WriteLine("Desired run time: " + StartTimeHour);

        // Should be set at the top level of each cron Lambda's execution as the current 'run' time

        var utcNow = DateTime.UtcNow;

        var timeZoneIdsToSend = GetTimeZoneIdsToSend(utcNow);

​

        Console.WriteLine("Utc: " + DateTime.UtcNow + Environment.NewLine);

        Console.WriteLine("Sending Tenant TimeZoneIds: " + string.Join(',', timeZoneIdsToSend));

    }

    private static IEnumerable<int> GetTimeZoneIdsToSend(DateTime currentUtcDateTime)

    {       

        return TenantTimeZoneIds.Where(id => ShouldSendTimeZoneId(currentUtcDateTime, id));

    }

    private static bool ShouldSendTimeZoneId(DateTime currentUtcDateTime, int newTimeZoneId)

    {

        var convertedTimeZoneId = newTimeZoneId;

        var utcDateTimeOffset = ((DateTimeOffset) DateTime.SpecifyKind(currentUtcDateTime, DateTimeKind.Utc));

        // Necessary to convert to Eastern to determine DST, as UTC times will 

        // always return false

        var isDaylightSavingsTime = utcDateTimeOffset.ToEasternTime().IsDaylightSavingTime();

​

        // Special case for Arizona

        if (newTimeZoneId == 5)

        {

            if (isDaylightSavingsTime)

                convertedTimeZoneId = 4;

            else

                convertedTimeZoneId = 3;

        }

​

        // Case for Alaska

        if (newTimeZoneId == 6)

            convertedTimeZoneId = 5;

​

        // Case for Hawaii

        if (newTimeZoneId == 7 && !isDaylightSavingsTime)

            convertedTimeZoneId = 6;

​

        // Special case for Saskatchewan

        // They observe Central Standard time year round

        if (newTimeZoneId == 8)

        {

            if (DateTime.Now.IsDaylightSavingTime())

                convertedTimeZoneId = 3;

            else

                convertedTimeZoneId = 2;

        }

​

        // Determine Eastern-based UTC offset for the desired TimeZoneID

        // This is necessary, as all dbo.Tenant.TimeZoneIDs were originally

        // created with an Eastern basis. (1 is EST, 2 is CST, etc.)

        var newOffset = -1 * (convertedTimeZoneId - 1);

        var easternTime = utcDateTimeOffset.ToEasternTime();

        var easternTimeOffset = easternTime.AddHours(newOffset);

        Console.WriteLine(newTimeZoneId + " -- " + easternTimeOffset.TimeOfDay + " > " + StartTimeHour + " -- " + (easternTimeOffset.TimeOfDay > StartTimeHour));

​

        return easternTimeOffset.TimeOfDay > StartTimeHour;

    }

}

​

public static class DateTimeOffsetExtensions

{

    public static DateTime ToEasternTime(this DateTimeOffset dateTime)

    {

        // https://github.com/dotnet/corefx/issues/2538 - details why this exists

        TimeZoneInfo estInfo;

​

        try

        {

            // This application runs in a unix docker container, so this is the common use case

            // Timezones in *nix are stored in /usr/share/zoneinfo/

            estInfo = TimeZoneInfo.FindSystemTimeZoneById("America/New_York");

        }

        catch (TimeZoneNotFoundException)

        {

            // Windows named their timezones differently

            // Timezones in Windows are stored HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Time Zones

            estInfo = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");

        }

​

        return TimeZoneInfo.ConvertTime(dateTime, estInfo).DateTime;

    }

}