public class Audience {
  private Ticket ticket = Ticket.EMPTY;
  private Invitation invitation = Invitation.EMPTY;
  private Long amount;
  public Audience(Long amount){this.amount = amount;}
  public void buyTicket(TicketSeller seller){
    ticket = seller.getTicket(this);
  }
  public boolean hasAmount(Long amount){
    return this.amount >= amount;
  }
  public boolean minusAmount(Long amount){
    if(amount > this.amount) return false;
    this.amount -= amount;
    return true;
  }
  public Invitation getInvitation(){return invitation;}
  public void removeInvitation(){
    invitation = Invitation.EMPTY;
  }
  public Ticket getTicket(){return ticket;}
  public void setInvitation(Invitation invitation){
    this.invitation = invitation;
  }
}

public class Invitation {
  final static public Invitation EMPTY = new Invitation(null);
  final private Theater theater;
  public Invitation(Theater theater){
    this.theater = theater;
  }
}

public class Main {
  public static void main(String[] args) {
    Theater theater = new Theater(100L);
    Audience audience1 = new Audience(0L);
    Audience audience2 = new Audience(50L);
    TicketOffice ticketOffice = new TicketOffice(0L);
    TicketSeller seller = new TicketSeller();

    theater.setTicketOffices(ticketOffice);
    theater.setTicket(10L);
    theater.setInvitation(audience1);

    seller.setTicketOffice(ticketOffice);

    audience1.buyTicket(seller);
    audience2.buyTicket(seller);

    boolean isOk1 = theater.enter(audience1);
    boolean isOk2 = theater.enter(audience2);

    System.out.println(isOk1);//true
    System.out.println(isOk2);//false

  }
}

public class Theater{
  private TicketOffice ticketOffice = TicketOffice.EMPTY ;
  final private Long fee;
  public Theater( Long fee){
    this.fee = fee;
  }
  Long getFee(){
    return this.fee;
  }

  public void setTicketOffices(TicketOffice ticketOffice ) {
    this.ticketOffice = ticketOffice;
  }
  public void setTicket(Long num){
    if(this.ticketOffice == TicketOffice.EMPTY) return;
    while(num-- > 0) {
      this.ticketOffice.addTicket(new Ticket(this));
    }
  }
  public void setInvitation(Audience audience){
    audience.setInvitation(new Invitation(this));
  }
  public boolean enter(Audience audience){
    Ticket ticket = audience.getTicket();
    return ticket.isValid(this);
  }
}

public class Ticket {
  final static public Ticket EMPTY = new Ticket(null);
  final private Theater theater;
  private boolean isEntered = false;
  public Ticket(Theater theater){
    this.theater = theater;
  }
  public boolean isValid(Theater theater){
    if(isEntered || theater != this.theater || this == EMPTY){
      return false;
    }else{
      isEntered = true;
      return true;
    }
  }
  public Long getFee(){
    return theater.getFee();
  }
}

import java.util.ArrayList;
import java.util.List;

public class TicketOffice {
  final static public TicketOffice EMPTY = new TicketOffice(null);
  private Long amount;
  private List<Ticket> tickets = new ArrayList<>();
  public TicketOffice(Long amount){this.amount = amount;}
  public void addTicket(Ticket ticket){
    this.tickets.add(ticket);
  }
  public Ticket getTicketWithFee(){
    if(tickets.size() == 0) return Ticket.EMPTY;
    else{
      Ticket ticket = tickets.remove(0);
      amount += ticket.getFee();
      return ticket;
    }
  }
  public Ticket getTicketWithNoFee(){
    if(tickets.size() == 0) return Ticket.EMPTY;
    else return tickets.remove(0);
  }
  public Long getTicketPrice(){
    if(tickets.size() == 0) return 0L;
    else return tickets.get(0).getFee();
  }
}


public class TicketSeller {
  private TicketOffice ticketOffice;
  public void setTicketOffice(TicketOffice ticketOffice){
    this.ticketOffice = ticketOffice;
  }
  public Ticket getTicket(Audience audience){
    Ticket ticket = Ticket.EMPTY;
    if(audience.getInvitation() != Invitation.EMPTY){
      ticket = ticketOffice.getTicketWithNoFee();
      if(ticket != Ticket.EMPTY) audience.removeInvitation();
    }else{
      Long price = ticketOffice.getTicketPrice();
      if(price > 0 && audience.hasAmount(price)){
        ticket = ticketOffice.getTicketWithFee();
        if(ticket != Ticket.EMPTY) audience.minusAmount(price);
      }
    }
    return ticket;
  }
}