#include<stdio.h>
#include<iostream>
#include<memory>
#include<list>

using namespace std;

class IObserver {
 public:
  IObserver() {}	 
  virtual ~IObserver();
  virtual void Update(const std::string &message_from_subject) = 0;
  virtual int GetObjectId() = 0;
};

class ISubject {
 public:
  ISubject() {}	 
  virtual ~ISubject();
  virtual void Attach(shared_ptr<IObserver> pObserver) = 0; 
  virtual void Detach(shared_ptr<IObserver> pObserver) = 0; 
  virtual void Notify() = 0;
};

class Subject : public ISubject {
  public:
  Subject() { cout<<"Subject constructor"<<endl; }	  
    ~Subject() {
    std::cout << "Subject Destructor.\n";
  }
 
  void Attach(shared_ptr<IObserver> pObserver); 
  void Detach(shared_ptr<IObserver> pObserver);
  void Notify(); 
  void CreateMessage(std::string message);

  private:
  typedef shared_ptr<IObserver> PtrObserver;
  std::list<PtrObserver> plist_observer;
  std::string message;
};

class Observer : public IObserver {
 public:
  Observer(shared_ptr<Subject> pSubject);
    ~Observer() {
    std::cout << "Observer Destructor Id " <<objId<<endl; 
  }

  void Update(const std::string &message_from_subject);
  void DeleteFromList();
  int GetObjectId();

 private:
  std::string message_from_subject_;
  shared_ptr<Subject> ptrSubject;
  int objId;
  static int objCount;
 };

#include "ObserverPattern.hpp"

int Observer::objCount = 0;

IObserver::~IObserver() {
 cout<<"Done with IObserver"<<endl;
}


ISubject::~ISubject() {
 cout<<"Done with ISubject"<<endl;
 	
}	

/* Subject::Attach
 * Description : Attach/subscribe the interested obersever
 * param : pObserver 
 */ 
void Subject::Attach(shared_ptr<IObserver> pObserver) {
 cout<<"Subject::Attach attaching Object"<<pObserver->GetObjectId()<<endl;	 
 plist_observer.push_back(pObserver);
}

/* Subject::Attach
 * Description : Detach/unsubscribe  the interested obersever
 * param : pObserver
 * */

void Subject::Detach(shared_ptr<IObserver> pObserver) {
 cout<<"Subject::Detach detaching Object"<<pObserver->GetObjectId()<<endl;	
 plist_observer.remove(pObserver);
}

/* Subject::Notify
 * Description : Notify the subscribed observers about the message
 * */
void Subject::Notify() {
    cout<<"Subject::Notify"<<endl;	
    std::list<PtrObserver>::iterator iterator = plist_observer.begin();
    
    while (iterator != plist_observer.end()) {
      (*iterator)->Update(message);
      ++iterator;
    }
}

/* Subject::CreateMessage
 * Description : Create a message and notify the same for all the interested observers
 * */
void Subject::CreateMessage(std::string message) { 
 cout<<"######### Subject::CreateMessage ########## "<<message<<endl;
 this->message = message;
 Notify();
}

Observer::Observer(shared_ptr<Subject> pSubject) : ptrSubject(pSubject) {
 objCount++;
 objId = objCount;
 cout<<" Constructing Object "<<objId<<endl;
 ptrSubject->Attach(make_shared<Observer>(*this));
}


/* Observer::GetObjectId
 * Description : Return the object Id associated with the object.
 */
int Observer::GetObjectId() {
  return objId;
}

/* Observer::Update
 * Description : Receives the updates from the subject
 */ 
void Observer::Update(const std::string &message_from_subject) {
    message_from_subject_ = message_from_subject;
    cout<<"Object Id "<<objId<<" Received "<<message_from_subject_<<" message"<<endl;
  }

/* Observer::DeleteFromList
 * Description : 
 * */
void Observer::DeleteFromList() {
  shared_ptr<IObserver> observer(this);	
  ptrSubject->Detach((observer));
}


int main() {

 shared_ptr<Subject> subject = make_shared<Subject>();
 
 shared_ptr<Observer> observer1(make_shared<Observer>(subject));
 shared_ptr<Observer> observer2(make_shared<Observer>(subject));
 shared_ptr<Observer> observer3(make_shared<Observer>(subject));


 subject->CreateMessage("Hi Hello");
 
 //observer2->DeleteFromList(); // Double free or corruption error
 subject->Detach(observer2); // does not detach observer2
 
 shared_ptr<Observer> observer4(make_shared<Observer>(subject));

 subject->CreateMessage("Welcome");


 return 0;
}

Subject constructor
 Constructing Object 1
Subject::Attach attaching Object1
 Constructing Object 2
Subject::Attach attaching Object2
 Constructing Object 3
Subject::Attach attaching Object3
######### Subject::CreateMessage ########## Hi Hello
Subject::Notify
Object Id 1 Received Hi Hello message
Object Id 2 Received Hi Hello message
Object Id 3 Received Hi Hello message
Subject::Detach detaching Object2
 Constructing Object 4
Subject::Attach attaching Object4
######### Subject::CreateMessage ########## Welcome
Subject::Notify
Object Id 1 Received Welcome message
Object Id 2 Received Welcome message
Object Id 3 Received Welcome message
Object Id 4 Received Welcome message
Observer Destructor Id 4
Done with IObserver
Observer Destructor Id 3
Done with IObserver
Observer Destructor Id 2
Done with IObserver
Observer Destructor Id 1
Done with IObserver