Breeding.java

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

/**
 * Breeding control and gene mutation.
 * 
 * @author Kexin Wang
 * @time 2025.02.21
 * @version 1.0
 */

public class Breeding {
    private static final Random rand = new Random();
    
    /** avoiding reduplicationclear */
    private static List<Animal> alreadyBred = new ArrayList<>();

    /** 
     * clear breeding list before each step
     */
    public static void clearBreedingList() {
        alreadyBred.clear();
    }

    /**
     * Check whether or not this predator is to give birth at this step.
     * New births will be made into free adjacent locations.
     * @param newPredators A list to return newly born predators.
     */
    public static void giveBirth(Animal animal, List<Animal> newAnimals) {
        // New preys are born into adjacent locations.
        // Get a list of adjacent free locations.
        Field field = animal.getField();
        List<Location> free = field.getFreeAdjacentLocations(animal.getLocation());

        if (canBreed(animal, newAnimals) && free.size() > 0) {
            canBreed(animal, newAnimals);
        }
    }

    /**
     * A animal can breed if it has reached the breeding age and find a valid mate.
     * @return true if the animal can breed, false otherwise.
     */
    private static boolean canBreed(Animal animal, List<Animal> newAnimals) {
        if (animal.getAge() < animal.getBreedingAge() || alreadyBred.contains(animal)) {
            return false;
        }

        List<Animal> candidates = new ArrayList<>();
        List<Location> adjacent = animal.getField().adjacentLocations(animal.getLocation());
        // find valid mates in adjacent locations
        for (Location loc : adjacent) {
            Animal neighbor = animal.getField().getObjectAt(loc);
            if (neighbor != null 
                && neighbor.getType() == animal.getType()
                && neighbor.getGender() != animal.getGender()
                && neighbor.getAge() >= neighbor.getBreedingAge()
                && !alreadyBred.contains(neighbor)) {
                candidates.add(neighbor);
            }
        }
        // try to breed until success once or fail all
        for (Animal mate : candidates) {
            if (rand.nextDouble() <= animal.getBreedingProbability()) {
                mateWith(animal, mate, newAnimals);
                alreadyBred.add(animal);
                alreadyBred.add(mate);
                return true;
            }
        }
        return false;
    }

    private static void mateWith(Animal animal1, Animal animal2, List<Animal> newAnimals) {
        int litterSize = rand.nextInt(animal1.getLitterSize()) + 1;
        for (int i = 0; i < litterSize; i++) {
            Location loc = animal1.getField().getFreeAdjacentLocation(animal1.getLocation());
            if (loc == null) return;

            String childGene = combineGenes(animal1.getGene(), animal2.getGene()); // generate child gene

            Animal young;
            if (animal1 instanceof Predator) {
                young = new Predator(animal1.getField(), loc, animal1.getColor(), animal1.getType(), false);
            } else {
                young = new Prey(animal1.getField(), loc, animal1.getColor(), animal1.getType(), false);
            }

            young.setGene(childGene); // give child gene
            newAnimals.add(young);
            
            // print new borned animal and their genes
            // System.out.println("New " + animal1.getType() + " born! Gene: " + childGene);
        }
    }

    private static String combineGenes(String gene1, String gene2) {
        if (gene1.length() != 14 || gene2.length() != 14) {
            throw new IllegalArgumentException("Invalid parent genes: " + gene1 + ", " + gene2);
        }
        String newGene = gene1.substring(0, 7) + gene2.substring(7, 14);
        if (newGene.length() != 14) {
            throw new IllegalStateException("Generated invalid gene: " + newGene);
        }
        if (rand.nextDouble() < 0.2)
        {
            char[] geneArray = newGene.toCharArray();
            int mutateIndex = rand.nextInt(14); // mutate random one digit
            int oldValue = Character.getNumericValue(geneArray[mutateIndex]);

            // 50% +1; 50% -1
            int newValue = (rand.nextBoolean()) ? (oldValue + 1) % 10 : (oldValue + 9) % 10;
            // ensure mutate value is valid
            while (!isValidGene(mutateIndex, newGene.substring(0, mutateIndex) 
                                   + newValue 
                                   + newGene.substring(mutateIndex + 1, 14)))  {
                newValue = (rand.nextBoolean()) ? (newValue + 1) % 10 : (newValue + 9) % 10;
            }
            
            geneArray[mutateIndex] = Character.forDigit(newValue, 10);
            newGene = new String(geneArray);
        }

        return newGene;
    }

    private static boolean isValidGene(int index, String gene) {
        if (gene.length() != 14) {
            throw new IllegalArgumentException("Invalid gene length in validation: " + gene);
        }
        int value;
        
        if (index < 2) // breeding age (12-90) inclusive
        {   value = Integer.parseInt(gene.substring(0, 2));
            return value >= 12 && value <= 90;
        } else if (index < 5) // max age (10-120) inclusive
        {   value = Integer.parseInt(gene.substring(2, 5));
            return value >= 10 && value <= 120;
        } else if (index < 7) // breeding probability (0.00-0.50)
        {   value = Integer.parseInt(gene.substring(5, 7));
            return value > 0 && value < 50;
        } else if (index < 9) // litter size (1-12) inclusive
        {   value = Integer.parseInt(gene.substring(7, 9));
            return value >= 1 && value <= 12;
        } else if (index < 11) // diseable probability (0.00-0.50)
        {   value = Integer.parseInt(gene.substring(9, 11));
            return value > 0 && value < 50;
        } else // metabolism (0.25-1.00) inclusive
        {   value = value = Integer.parseInt(gene.substring(11, 14));
            return value >= 25 && value <= 100; 
        }    
    }
}