// This program computes the trajectory of a projectile.  It's modified
// to prompt the user for the parameters, and further modified to do this
// a given number of times.

import java.awt.*;
import java.util.*;

public class Projectile3 {
    // constant for Earth's gravity acceleration in meters/second^2
    public static final double ACCELERATION = -9.81;

    public static void main(String[] args) {
        Scanner console = new Scanner(System.in);
        System.out.println("Projectile calculator here!");
        System.out.print("Please enter the total number of projectiles: ");
        int count = console.nextInt();
        DrawingPanel panel = new DrawingPanel(420, 220);
        Graphics g = panel.getGraphics();
        for (int i=1; i<=count; i++) {
            oneProjectile(g, console);
        }
        System.out.println("Projectile calculator is finished ... please close the drawing panel to exit");
    }

    public static void oneProjectile(Graphics g, Scanner console) {
        System.out.print("Please enter the initial velocity: ");
        double v0 = console.nextDouble();
        System.out.print("Please enter the initial angle in degrees: ");
        double angle = console.nextDouble();
        System.out.print("Please enter the number of steps: ");
        int steps = console.nextInt();
        table(g, v0, angle, steps);
    }

    // prints a table showing the trajectory of an object given
    // its initial velocity v and angle and number of steps
    public static void table(Graphics g, double v0, double angle, int steps) {
        double radians = Math.toRadians(angle);
        double v0x = v0 * Math.cos(radians);
        double v0y = v0 * Math.sin(radians);
        double totalTime = -2.0 * v0y / ACCELERATION;
        double dt = totalTime / steps;

        System.out.println("    step       x       y    time");
        for (int i = 0; i <= steps; i++) {
            double time = i * dt;
            double x = displacement(v0x, time, 0.0);
            double y = displacement(v0y, time, ACCELERATION);
            System.out.printf("%8d%8.2f%8.2f%8.2f\n", i, x, y, time);
            g.fillOval((int) x, (int) (220 - y), 5, 5);
        }
    }

    // returns the horizontal displacement for a body
    public static double displacement(double v, double t, double a) {
        return v * t + 0.5 * a * t * t;
    }
}