package elevator;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Random;

public class Elevator
{
    private static final int CAPACITY = 3;

    private static final int PERSONS_AT_START = 5;

    private static final int TOTAL_FLOORS = 5;

    private int direction;

    private int currentFloor = 1;

    private final List<Person> waitingPersons = new ArrayList<Person>();

    private final List<Person> personsIn = new ArrayList<Person>();

    private final Random random = new Random();

    public static void main(String[] args) {
        new Elevator().run();
    }

    public void run() {
        for (int i = 1; i <= PERSONS_AT_START; i++) {
            final Person person = new Person(this, i);
            waitingPersons.add(person);
        }
        while (!waitingPersons.isEmpty() || !personsIn.isEmpty()) {
            unloadPeople();
            loadPeople();
            moveToNextFloor();
        }
    }

    private void moveToNextFloor() {
        if (currentFloor == 1) {
            direction = 1;
        } else if (currentFloor == TOTAL_FLOORS) {
            direction = -1;
        }
        currentFloor += direction;
        System.out.format("Moving to floor %d%n", currentFloor);
    }

    private boolean hasCapacity() {
        return personsIn.size() < CAPACITY;
    }

    private void loadPeople() {
        if (hasCapacity()) {
            for (final Iterator<Person> iter = waitingPersons.iterator();
                    iter.hasNext();)
            {
                final Person person = iter.next();
                if (person.getStartFloor() == currentFloor) {
                    iter.remove();
                    personsIn.add(person);
                    System.out.format("Person %d entered at floor %d%n",
                            person.getId(), currentFloor);
                }
                if (!hasCapacity()) {
                    return;
                }
            }
        }
    }

    private void unloadPeople() {
        for (final Iterator<Person> iter = personsIn.iterator();
                iter.hasNext();)
        {
            final Person person = iter.next();
            if (person.getEndFloor() == currentFloor) {
                // person.delivered();
                iter.remove();
                System.out.format("Person %d exited at floor %d%n",
                        person.getId(), currentFloor);
            }
        }
    }

    public int getRandomFloor() {
        return random.nextInt(TOTAL_FLOORS) + 1;
    }
}

package elevator;

public class Person
{
    private final int id;

    private final int startFloor;

    private int endFloor;

    public Person(Elevator elevator, int id) {
        this.id = id;
        startFloor = elevator.getRandomFloor();
        while ((endFloor = elevator.getRandomFloor()) == startFloor) {
            // try again
        }
        System.out.format("Person %d want to ride from %d to %d%n",
                id, startFloor, endFloor);
    }

    public int getId() {
        return id;
    }

    public int getStartFloor() {
        return startFloor;
    }

    public int getEndFloor() {
        return endFloor;
    }

//  public void delivered() {
//  }
}