#include <iostream>
#include <list>
using namespace std;

class Iobserver
{
   public:
   virtual void notify(string msg) = 0;
};

class observer1 : public Iobserver
{
   public:
   void notify(string msg)
   {
      cout<<"Observer1 : "<<msg<<endl;
   }   
};

class observer2 : public Iobserver
{
   public:
   void notify(string msg)
   {
      cout<<"Observer2 : "<<msg<<endl;
   }   
};

class observer3 : public Iobserver
{
   public:
   void notify(string msg)
   {
      cout<<"Observer3 : "<<msg<<endl;
   }   
};


class observermanager
{
   list<Iobserver*>users;

   public:
     void register_user(Iobserver* usr)
     {
         users.push_back(usr);
     }

     void deregister_user(Iobserver* usr)
     {
         users.remove(usr);
     }

     void send_notification(string msg)
     {
           for(auto *itr:users)
               {
                   itr->notify(msg);
               }
     }
};



int main() {

    // observer1 user1;
    // observer2 user2;
    // observer3 user3; 

    Iobserver *user1 = new observer1();
    Iobserver *user2 = new observer2();
    Iobserver *user3 = new observer3();
    
    observermanager *obsmgr = new observermanager();
    obsmgr->register_user(user1);
    obsmgr->register_user(user2);
    obsmgr->register_user(user3);

    obsmgr->send_notification("this is a messsage");

    obsmgr->deregister_user(user2);
    obsmgr->send_notification("new messsage");
    
    return 0;
}