using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var employeeVacationOne = new EmployeeVacationDetails("Vince", new DateTime(2021, 5, 25), new DateTime(2021, 6, 20));

        var employeeVacationTwo = new EmployeeVacationDetails("Jennifer", new DateTime(2021, 2, 1), new DateTime(2021, 2, 14));

        var employeeVacationThree = new EmployeeVacationDetails("Vince", new DateTime(2021, 10, 5), new DateTime(2021, 10, 15));

        var employeeVacationFour = new EmployeeVacationDetails("Sam", new DateTime(2021, 1, 11), new DateTime(2021, 1, 15));

        var employeeVacationFive = new EmployeeVacationDetails("John", new DateTime(2021, 1, 11), new DateTime(2021, 1, 30));

        var orgVacation = new OrganizationVacationsManagement();

        orgVacation.addVacation(employeeVacationOne);

        orgVacation.addVacation(employeeVacationTwo);

        orgVacation.addVacation(employeeVacationThree);

        orgVacation.addVacation(employeeVacationFour);

        orgVacation.addVacation(employeeVacationFive);

        //double result = orgVacation.GetAverageVacationLengthOfOrganization();

        //Console.WriteLine(result);

        /*foreach(var employee in orgVacation.GetAverageVacationLengthOfEachEmployee())

        {

            Console.WriteLine($"{employee.Item1}: {employee.Item2}");

        }

        foreach(var month in orgVacation.GetNumberOfEmployeesOnVacationByEachMonth())

        {

            Console.WriteLine($"Number of the month of the year: {month.Item1}, " +

            $"number of employees on vacation this month: {month.Item2}");

        }

        */

        Console.WriteLine("List of days when no employee is having vacation:");

        foreach(var day in orgVacation.GetDatesWhenNoEmployeesAreOnVacation())

        {

            Console.WriteLine(day.Date);

        }

    }

}

​

public record EmployeeVacationDetails

{

    public string EmployeeName { get; }

    public DateTime DateOfFirstVacationDay { get; }

    public DateTime DateOfLastVacationDay { get; }

    public EmployeeVacationDetails(string employeeName, DateTime dateOfFirstVacationDay, DateTime dateOfLastVacationDay)

    {

        if (dateOfFirstVacationDay.Year == 2021 && dateOfLastVacationDay.Year == 2021)

        {

            EmployeeName = employeeName;

            DateOfFirstVacationDay = dateOfFirstVacationDay;

            DateOfLastVacationDay = dateOfLastVacationDay;

        }

        else

        {

            throw new ArgumentException($"You can only add vacation records of year 2021");

        }

    }

    public double GetEmployeeVacationLength()

    {

        return (DateOfLastVacationDay - DateOfFirstVacationDay).Days + 1;

    }

    public IEnumerable<DateTime> GetAllEmployeeVacationDates()

    {

        return  Enumerable.Range(0, DateOfLastVacationDay.Subtract(DateOfFirstVacationDay).Days + 1)

          .Select(day => DateOfFirstVacationDay.AddDays(day)); 

    }

}

​

public class OrganizationVacationsManagement

{

    private List<EmployeeVacationDetails> _employeeVacations;

    public OrganizationVacationsManagement()

    {

        _employeeVacations = new List<EmployeeVacationDetails>();

    }

    public void addVacation(EmployeeVacationDetails vacation)

    {

        _employeeVacations.Add(vacation);

    }

    public double GetAverageVacationLengthOfOrganization()

    {

        return _employeeVacations.Average(employee => employee.GetEmployeeVacationLength());

    }

    public IEnumerable<(string, double)> GetAverageVacationLengthOfEachEmployee()

    {

        var employeeVacationAverage = _employeeVacations.GroupBy(employee => employee.EmployeeName,

            employeeVacation => employeeVacation.GetEmployeeVacationLength())

            .Select(employeVacationAvg => new 

                    {

                        employeeName = employeVacationAvg.Key,

                        avgVacationVacationLength = employeVacationAvg.Average() 

                    });

        foreach(var employee in employeeVacationAverage)    

        {    

            yield return (employee.employeeName, employee.avgVacationVacationLength);

        }    

    }

    public IEnumerable<(int, int)> GetNumberOfEmployeesOnVacationByEachMonth()

    {

        var months = Enumerable.Range(1,12).ToList();

        foreach(var month in months)

        {

            yield return (month, _employeeVacations.Count(vacation => vacation.DateOfFirstVacationDay.Month == month

            || vacation.DateOfLastVacationDay.Month == month));

        }

    }

    public IEnumerable<DateTime> GetDatesWhenNoEmployeesAreOnVacation()

    {

        var startOfYearDate = new DateTime(2021, 01, 01);

        var endOfYearDate = new DateTime(2021, 12, 31);

        var allDatesOfYear = Enumerable.Range(0, endOfYearDate.Subtract(startOfYearDate).Days + 1)

            .Select(day => startOfYearDate.AddDays(day)); 

        return allDatesOfYear.Except(_employeeVacations.SelectMany(employee => employee.GetAllEmployeeVacationDates()

            .Distinct()));

    }

    public bool DoDatesOfEmployeeVacationIntersect()

    {

        var test = _employeeVacations.GroupBy(employee => employee.EmployeeName, vacationDates => (vacationDates.DateOfFirstVacationDay, vacationDates.DateOfLastVacationDay));

        return true;

    }

}

​

​