import java.io.PrintStream;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.function.Supplier;

public final class Rendezvous {

	public static void main(String[] args) throws InterruptedException, ExecutionException {		
		List<String> motherGooseText = List.of( "Old Mother Goose,",
				  								"When she wanted to wander,",
				  								"Would ride through the air,",
				  								"On a very fine gander.",
				  								"Jack's mother came in,",
				  								"And caught the goose soon,",
				  								"And mounting its back,",
				  								"Flew up to the moon." );
		
		List<String> humptyDumptyText = List.of( "Humpty Dumpty sat on a wall.",
				     							 "Humpty Dumpty had a great fall.",
				     							 "All the king's horses and all the king's men,",
				     							 "Couldn't put Humpty together again." );
		
		Printer reserve = new Printer("Reserve", Optional.empty(), System.out);
		Printer main = new Printer("Main", Optional.of(reserve), System.out);
				
		Messenger motherGoose = new Messenger(motherGooseText, main);
		Messenger humptyDumpty = new Messenger(humptyDumptyText, main);
		
		while ( CompletableFuture.supplyAsync(motherGoose).get() |
				CompletableFuture.supplyAsync(humptyDumpty).get() ) { }
	}

}

final class Messenger implements Supplier<Boolean> {
	
    public Messenger(List<String> aMessage, Printer aPrinter) {
    	message = new ArrayList<String>(aMessage);
    	iterator = message.iterator();
        printer = aPrinter;
    }

    @Override
	public Boolean get() {
		if ( iterator.hasNext() ) {
			try {
				printer.display(iterator.next());
			} catch (OutOfInkException exception) {
				return false;
			}
			return true;
		}	
		return false;
	}

    private List<String> message;
	private Iterator<String> iterator;
    private Printer printer;

}

final class Printer {	
	
    public Printer(String aName, Optional<Printer> aReserve, PrintStream aPrintStream) {
        name = aName;
        reserve = aReserve;
        printStream = aPrintStream;
    }

    public void display(String message) throws OutOfInkException {
    	if ( inkLevelForClientUse > 0 ) {
    		printStream.println("(" + name + ") " + message);
    		inkLevelForClientUse -= 1;
    	} else {
    		if ( reserve.isPresent() ) {
    			reserve.get().display(message);
    		} else {
    			printStream.println("        Printer out of ink");	
    			throw new OutOfInkException();
    		}
    	}
    	
    }

    private String name;
    private Optional<Printer> reserve;
    private PrintStream printStream;
    private int inkLevelForClientUse = 5;

}

final class OutOfInkException extends Exception { }