package visitor;

import java.util.List;

/**
 * Visitor Design Pattern — Runnable Demo
 * Run: javac visitor/*.java -d out/visitor && java -cp out/visitor visitor.Main
 * Article: https://ankurm.com/visitor-design-pattern-java/
 */
public class Main {
    public static void main(String[] args) {
        System.out.println("=== Visitor Design Pattern Demo ===\n");

        List<Shape> shapes = List.of(
            new Circle(5),
            new Rectangle(4, 6),
            new Triangle(3, 8)
        );

        System.out.println("-- Area Calculator Visitor --");
        ShapeVisitor areaCalc = new AreaCalculator();
        for (Shape shape : shapes) {
            shape.accept(areaCalc);
        }

        System.out.println("\n-- Perimeter Calculator Visitor --");
        ShapeVisitor perimCalc = new PerimeterCalculator();
        for (Shape shape : shapes) {
            shape.accept(perimCalc);
        }

        System.out.println("\n-- Key insight --");
        System.out.println("Added PerimeterCalculator without touching Shape, Circle, Rectangle, Triangle.");
        System.out.println("To add another operation: write one new Visitor class.");

        System.out.println("\n=== Demo complete ===");
    }
}