using System;

using System.Collections.Generic;

public class Program

{

    public void Main(string[] args)

    {

        DateTime scheduleStart = new DateTime(2021, 1, 7, 1, 0, 0, 0, DateTimeKind.Local);

        DateTime scheduleEnd = scheduleStart.AddDays(1).AddMinutes(-1);

        DateTime now = scheduleStart.AddMilliseconds(-33);

        long ticksPerInterval = TimeSpan.TicksPerMinute;

        int interval = 3;

        if (now > scheduleStart)

            scheduleStart = now;

        SortedList<DateTime, ScheduledTime> scheduledTimesList = new SortedList<DateTime, ScheduledTime>();

        // InitSortedDateList

        for (int i = 0; i <= 7; i++)

        {

            DateTime tmpTime = new DateTime(scheduleStart.Ticks);

            scheduledTimesList.Add(tmpTime.AddDays(i).Date, null);

        }

        // FillEverydayDates

        for (int i = 0; i <= 7; i++)

        {

            DateTime tmpTime = new DateTime(scheduleStart.Ticks);

            ScheduledTime tmpSched = new ScheduledTime();

            // AddScheduledTimeToTimesList

            int daysOffset = (int)(tmpTime.AddDays(i).Date - scheduleStart.Date).TotalDays;

            tmpSched.StartTime = scheduleStart.AddDays(daysOffset);

            tmpSched.EndTime = scheduleEnd.AddDays(daysOffset);

            scheduledTimesList[tmpTime.AddDays(i).Date] = tmpSched;

            Console.Out.WriteLine("FillEverydayDates: i = " + i.ToString() + ", start = " + tmpSched.StartTime.ToString() + ", end = " + tmpSched.EndTime.ToString());

        }

        bool useMinTime = false;

        ScheduledTime schedTime = null;

        foreach (KeyValuePair<DateTime,ScheduledTime> kvp in scheduledTimesList)

        {

            ScheduledTime tmpTime = new ScheduledTime(kvp.Value);

            Console.Out.WriteLine("ScheduleNext: kvp = " + kvp.Key.ToShortDateString() + " / " + kvp.Value.StartTime.ToString());

            if (tmpTime != null && kvp.Key.Date == scheduleStart.Date)

            {

                Console.Out.WriteLine("Same date");

                if (scheduleStart < tmpTime.EndTime || useMinTime)

                {

                    Console.Out.WriteLine(">> end time ok");

                    if (tmpTime.StartTime > scheduleStart || useMinTime)

                    {

                        Console.Out.WriteLine(">> start time ok");

                        schedTime = new ScheduledTime(tmpTime);

                        break;

                    }

                    else                        

                    {

                        Console.Out.WriteLine(">> start time NOT ok");

                        DateTime startTime = new DateTime(tmpTime.StartTime.Ticks);

                        DateTime endTime = new DateTime(tmpTime.EndTime.Ticks);

                        while (startTime < scheduleStart)

                        {

                            Console.Out.WriteLine(">> LOOP " + startTime.ToString() + " < " + scheduleStart.ToString());

                            startTime = startTime.AddTicks(ticksPerInterval * interval);

                            Console.Out.WriteLine(">> >> New start time = " + startTime.ToString());

                            if (startTime >= endTime)

                            {

                                Console.Out.WriteLine(">> >> Past end time; add one day");

                                scheduleStart = scheduleStart.AddDays(1);

                                useMinTime = true;

                                break;

                            }

                            if (startTime >= scheduleStart)

                            {

                                Console.Out.WriteLine(">> >> Past start time - interval looks good");

                                tmpTime.StartTime = startTime;

                                tmpTime.EndTime = tmpTime.StartTime.AddTicks(ticksPerInterval * interval);

                                schedTime = new ScheduledTime(tmpTime);

                                break;

                            }

                        }

                        if (schedTime != null)

                            break;

                    }

                }

                else

                {

                    Console.Out.WriteLine(">> end time NOT ok");

                    scheduleStart = scheduleStart.AddDays(1);

                    useMinTime = true;

                }

            }

            else

            {

                Console.Out.WriteLine("Different date: " + scheduleStart.Date.ToShortDateString());

                scheduleStart = scheduleStart.AddDays(1);

                useMinTime = true;

            }

        }

        if (schedTime != null)

        {

            Console.Out.WriteLine("Successfully scheduled for " + schedTime.StartTime.ToString() + " to " + schedTime.EndTime.ToString());

        }

        else

        {

            Console.Out.WriteLine("No scheduled time set for " + scheduleStart.DayOfWeek.ToString());

        }

    }

    private class ScheduledTime

    {

        public DateTime StartTime;

        public DateTime EndTime;

        public ScheduledTime() {}

        public ScheduledTime(ScheduledTime other)

        {

            StartTime = other.StartTime;

            EndTime = other.EndTime;

        }

    }

}