namespace Extensions;

public enum Days
{
  Monday, Tuesday, Wednesday,
  Thursday, Friday, Saturday, Sunday
}

class Program
{    
  static void Main(string[] args)
  {
    var dict = new Dictionary<Days, List<Activity>>();
    Activity a = new Activity
    {
      Person = "John",
      Hours = 3,
      Period = DayPeriod.Morning
    };
    dict.GetOrCreate(Days.Monday).Add(a);

    a = new Activity
    {
      Person = "Mary",
      Hours = 12,
      Period = DayPeriod.Evening | DayPeriod.Night
    };
    dict.GetOrCreate(Days.Monday).Add(a);

    a = new Activity
    {
      Person = "Peter",
      Hours = 8,
      Period = DayPeriod.Night
    };
    dict.GetOrCreate(Days.Tuesday).Add(a);

    a = new Activity
    {
      Person = "Lisa",
      Hours = 5,
      Period = DayPeriod.Night | DayPeriod.Morning
    };
    dict.GetOrCreate(Days.Monday).Add(a);

    int sum = SumNightActivity(dict);
    Console.WriteLine(sum);

  }

  private static int SumNightActivity(Dictionary<Days, List<Activity>> dict)
  {
    int sum = 0;
    foreach(var list in dict.Values)
    {
      sum += list.Where(a => (a.Period & DayPeriod.Night) == DayPeriod.Night)
                 .Sum(a => a.Hours);                   
    }
    return sum;  
  }
}