import java.util.List;
 import java.util.Iterator;
 import java.util.Random;
 /**
  * A simple model of a fox.
  * Foxes age, move, eat rabbits, and die.
  *
  * @author Gede
  * @version (22/11/2018)
  */
 public class Fox
 {
   // Characteristics shared by all foxes (static fields).
   // The age at which a fox can start to breed.
   private static final int BREEDING_AGE = 10;
   // The age to which a fox can live.
   private static final int MAX_AGE = 150;
   // The likelihood of a fox breeding.
   private static final double BREEDING_PROBABILITY = 0.35;
   // The maximum number of births.
   private static final int MAX_LITTER_SIZE = 5;
   // The food value of a single rabbit. In effect, this is the
   // number of steps a fox can go before it has to eat again.
   private static final int RABBIT_FOOD_VALUE = 7;
   // A shared random number generator to control breeding.
   private static final Random rand = Randomizer.getRandom();
   // Individual characteristics (instance fields).
   // The fox's age.
   private int age;
   // Whether the fox is alive or not.
   private boolean alive;
   // The fox's position.
   private Location location;
   // The field occupied.
   private Field field;
   // The fox's food level, which is increased by eating rabbits.
   private int foodLevel;
   /**
    * Create a fox. A fox can be created as a new born (age zero
    * and not hungry) or with a random age and food level.
    *
    * @param randomAge If true, the fox will have random age and hunger level.
    * @param field The field currently occupied.
    * @param location The location within the field.
    */
   public Fox(boolean randomAge, Field field, Location location)
   {
     age = 0;
     alive = true;
     this.field = field;
     setLocation(location);
     if(randomAge) {
       age = rand.nextInt(MAX_AGE);
       foodLevel = rand.nextInt(RABBIT_FOOD_VALUE);
     }
     else {
       // leave age at 0
       foodLevel = RABBIT_FOOD_VALUE;
     }
   }
   /**
    * This is what the fox does most of the time: it hunts for
    * rabbits. In the process, it might breed, die of hunger,
    * or die of old age.
    * @param field The field currently occupied.
    * @param newFoxes A list to add newly born foxes to.
    */
   public void hunt(List<Fox> newFoxes)
   {
     incrementAge();
     incrementHunger();
     if(alive) {
       giveBirth(newFoxes);
       // Move towards a source of food if found.
       Location newLocation = findFood(location);
       if(newLocation == null) {
         // No food found - try to move to a free location.
         newLocation = field.freeAdjacentLocation(location);
       }
       // See if it was possible to move.
       if(newLocation != null) {
         setLocation(newLocation);
       }
       else {
         // Overcrowding.
         setDead();
       }
     }
   }
   /**
    * Check whether the fox is alive or not.
    * @return True if the fox is still alive.
    */
   public boolean isAlive()
   {
     return alive;
   }
   /**
    * Return the fox's location.
    * @return The fox's location.
    */
   public Location getLocation()
   {
     return location;
   }
   /**
    * Place the fox at the new location in the given field.
    * @param newLocation The fox's new location.
    */
   private void setLocation(Location newLocation)
   {
     if(location != null) {
       field.clear(location);
     }
     location = newLocation;
     field.place(this, newLocation);
   }
   /**
    * Increase the age. This could result in the fox's death.
    */
   private void incrementAge()
   {
     age++;
     if(age > MAX_AGE) {
       setDead();
     }
   }
   /**
    * Make this fox more hungry. This could result in the fox's death.
    */
   private void incrementHunger()
   {
     foodLevel--;
     if(foodLevel <= 0) {
       setDead();
     }
   }
   /**
    * Tell the fox to look for rabbits adjacent to its current location.
    * Only the first live rabbit is eaten.
    * @param location Where in the field it is located.
    * @return Where food was found, or null if it wasn't.
    */
   private Location findFood(Location location)
   {
     List<Location> adjacent = field.adjacentLocations(location);
     Iterator<Location> it = adjacent.iterator();
     while(it.hasNext()) {
       Location where = it.next();
       Object animal = field.getObjectAt(where);
       if(animal instanceof Rabbit) {
         Rabbit rabbit = (Rabbit) animal;
         if(rabbit.isAlive()) {
           rabbit.setDead();
           foodLevel = RABBIT_FOOD_VALUE;
           // Remove the dead rabbit from the field.
           return where;
         }
       }
     }
     return null;
   }
   /**
    * Check whether or not this fox is to give birth at this step.
    * New births will be made into free adjacent locations.
    * @param newFoxes A list to add newly born foxes to.
    */
   private void giveBirth(List<Fox> newFoxes)
   {
     // New foxes are born into adjacent locations.
     // Get a list of adjacent free locations.
     List<Location> free = field.getFreeAdjacentLocations(location);
     int births = breed();
     for(int b = 0; b < births && free.size() > 0; b++) {
       Location loc = free.remove(0);
       Fox young = new Fox(false, field, loc);
       newFoxes.add(young);
     }
   }
   /**
    * Generate a number representing the number of births,
    * if it can breed.
    * @return The number of births (may be zero).
    */
   private int breed()
   {
     int births = 0;
     if(canBreed() && rand.nextDouble() <= BREEDING_PROBABILITY) {
       births = rand.nextInt(MAX_LITTER_SIZE) + 1;
     }
     return births;
   }
   /**
    * A fox can breed if it has reached the breeding age.
    */
   private boolean canBreed()
   {
     return age >= BREEDING_AGE;
   }
   /**
    * Indicate that the fox is no longer alive.
    * It is removed from the field.
    */
   private void setDead()
   {
     alive = false;
     if(location != null) {
       field.clear(location);
       location = null;
       field = null;
     }
   }
 }