using System;

using System.Linq;

using System.Collections;

using System.Collections.Generic;

using System.Globalization;

​

public static class Program

{

    public static void Main()

    {

        int anio = 2018;

        for(int i=1 ; i<=12; i++){

           var month = new DateTime(anio,i,1).financialWeeklyRange().ToList();

           month.ForEach(x=>{

               Console.WriteLine(x);

           });

           Console.WriteLine("----------------------------------");

        } 

​

    }

    public static IEnumerable<DateTime> financialWeekly(this DateTime date)

    {

        DateTime firstDateOfMonth = new DateTime(date.Year,date.Month,1);

        var lastDayOfMonth = DateTime.DaysInMonth(date.Year, date.Month);

        DateTime lastDateOfMonth = new DateTime(date.Year,date.Month,lastDayOfMonth);

        IEnumerable<DateTime> dayOfMonth = firstDateOfMonth.RangeDate(lastDateOfMonth);

        List<DateTime> month = new List<DateTime>();

        List<Week> weeks = new List<Week>();

        var DaysOfMonth =  dayOfMonth.ToList().Where(x=>x.DayOfWeek == DayOfWeek.Thursday || x.DayOfWeek == DayOfWeek.Friday);

        if(!DaysOfMonth.Contains(firstDateOfMonth)){

          month.Add(firstDateOfMonth);

        }

        if(!DaysOfMonth.Contains(lastDateOfMonth)){

          month.Add(lastDateOfMonth);

        }

        month.AddRange(DaysOfMonth);

        if(firstDateOfMonth.DayOfWeek == DayOfWeek.Thursday){

        month.Remove(firstDateOfMonth);

        }

        if(lastDateOfMonth.DayOfWeek == DayOfWeek.Friday){

        month.Remove(lastDateOfMonth);

        }

        return month.ToList().OrderBy(x=>x).ToList();

​

    }

    public static IEnumerable<Week> financialWeeklyRange(this DateTime date)

    {

​

        List<DateTime> month = date.financialWeekly().ToList();

        List<Week> weeks = new List<Week>();

        var range = month;

        int count =0;

        int size = month.Count;

        range.ForEach(x=>{

​

              if(count<size){

              var m=  month.Skip(count).Take(2);

              weeks.Add(new Week(){ startWeek= m.FirstOrDefault(), endWeek = m.LastOrDefault() });

              count=count+2;

              }

         });

        return weeks;

​

    }

    public static IEnumerable<DateTime> RangeDate(this DateTime startDate, DateTime endDate)

    {

        return Enumerable.Range(0, (endDate - startDate).Days + 1).Select(d => startDate.AddDays(d));

    }

}

​

public class Week

{

    public DateTime startWeek{get; set;}

    public DateTime endWeek{get; set;}

    public override string ToString()

    {

        return startWeek.ToString("yyyy/MM/dd")+"-"+endWeek.ToString("yyyy/MM/dd");

    }

}