using System;
using System.Collections.ObjectModel;

public class AnimalFarm: Collection<Animal>{

  // Auto insert animal of opposite sex
  protected override void InsertItem(int i, Animal a){
    if(a.Sex == Sex.Male){
      base.InsertItem(i,a);
      base.InsertItem(i, new Animal(a.Name, a.Group, Sex.Female));
    } else {
      base.InsertItem(i,a);
      base.InsertItem(i,new Animal(a.Name, a.Group, Sex.Male));
    }   
  }

  // Prevent removal
  protected override void RemoveItem(int i){
    Console.WriteLine("[Removal denied]");
  }

  // Prevent clearing
  protected override void ClearItems(){
    Console.WriteLine("[Clearing denied]");
  }

  // Return all male animals in a given group
  public AnimalFarm GetGroup(AnimalGroup g){
    AnimalFarm res = new AnimalFarm();
    foreach(Animal a in this)
      if (a.Group == g && a.Sex == Sex.Male) res.Add(a);
    return res;
  }

}