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

namespace ConsoleApplication1
{
    class TestDateMethods
    {
        public TestDateMethods()
        {
            DateTime firstDay = DateHelpers.FirstDayOfYear();

            DateTime lastDay = DateHelpers.LastDayOfYear();

            DateTime tomorrow = DateHelpers.GetTomorrow();

            DateTime yesterday = DateHelpers.GetYesterday();
        }
    }


    /// <summary>
    /// A static class that stores our DateTime helper methods.
    /// </summary>
    static class DateHelpers
    {
        /// <summary>
        /// Example method to display the current day.
        /// </summary>
        static public void ShowToday()
        {
            // This is today.
            DateTime today = DateTime.Today;

            // Print out the result.
            Console.WriteLine("Today: " + today.ToShortDateString());
        }

        /// <summary>
        /// Method to find the previous day (yesterday) to the current day.
        /// </summary>
        /// <returns>The date for yesterday.</returns>
        static public DateTime GetYesterday()
        {
            // This is yesterday.
            DateTime yesterday = DateTime.Today.AddDays(-1);

            Console.WriteLine("Yesterday: " + yesterday.ToShortDateString());
            return yesterday;
        }

        /// <summary>
        /// Finds the next day (tomorrow) from the current day.
        /// </summary>
        /// <returns>The date corresponding to tomorrow.</returns>
        static public DateTime GetTomorrow()
        {
            // This is tomorrow.
            DateTime tomorrow = DateTime.Today.AddDays(1);

            Console.WriteLine("Tomorrow: " + tomorrow.ToShortDateString());
            return tomorrow;
        }

        /// <summary>
        /// Overloaded method to return the first day of the current year
        /// (from today).
        /// </summary>
        /// <returns>The first day of the current year.</returns>
        static public DateTime FirstDayOfYear()
        {
            return FirstDayOfYear(DateTime.Today);
        }

        /// <summary>
        /// Finds the first day of year in which the selected day
        /// falls (as in the first day of that year).
        /// </summary>
        /// <param name="selectedDay">The day of the year you want
        /// the first day of.</param>
        /// <returns>The first day of the year.</returns>
        static public DateTime FirstDayOfYear(DateTime selectedDay)
        {
            // First day of the current year.
            DateTime firstDay = DateTime.Parse(selectedDay.Year.ToString() + "-01-01");

            Console.WriteLine("First of this year: " + firstDay.ToShortDateString());
            return firstDay;
        }

        /// <summary>
        /// Finds the last day of the year for the current day (today).
        /// </summary>
        /// <returns>The last day of the current year.</returns>
        static public DateTime LastDayOfYear()
        {
            return LastDayOfYear(DateTime.Today);
        }

        /// <summary>
        /// Finds the last day of the year for the selected day's year.
        /// </summary>
        /// <param name="selectedDay">The day that falls in the year.</param>
        /// <returns>The last day of the year.</returns>
        static public DateTime LastDayOfYear(DateTime selectedDay)
        {
            // Find last day of the current year.
            // First, get the first day of the next year.
            DateTime firstNextYear = DateTime.Parse((selectedDay.Year + 1).ToString() + "-01-01");
            DateTime lastDay = firstNextYear.AddDays(-1);

            Console.WriteLine("Last of this year: " + lastDay.ToShortDateString());
            return lastDay;
        }

        // Leap years have 366 days, so we can't assume 365.

    }
}