import java.util.Scanner;

public class GeometryCalculator {
	public static void main(String[] args) {
		int userResponse;
		double [] sides;
		
		System.out.println("Welcome to the Geometry Calculator");
		displayMenu();
		
		userResponse = getUserInput();
		
		switch(userResponse) {
			case 1:
				 sides = getSideLengths(3);
				 System.out.println("The area of your Triangle is " + computeTriangleArea(sides));
				 break;
			case 2:
				sides = getSideLengths(2);
				System.out.println("The area of your Rectangle is " + computeRectangleArea(sides));
				break;
			case 3:
				sides = getSideLengths(1);
				System.out.println("The area of your Pentagon is " + computePentagonArea(sides));
				break;
			default:
				System.out.println("Your response was invalid!");
		}
		
	}


	public static void displayMenu() {
		
		System.out.println("*************************************");
		System.out.println("1 - Triangle Area (3 Sides)");
		System.out.println("2 - Rectangle Area (Length and Width)");
		System.out.println("3 - Regular Pentagon Area (1 Side)");
		System.out.println("*************************************");
	}
	
	public static int getUserInput() {
		String userInput;
		
		Scanner keyboard = new Scanner(System.in);
		
		userInput = keyboard.nextLine();
		
		if(userInput.equals("1")) {
			return 1;
		}
		else if(userInput.equals("2")) {
			return 2;
		}
		else if(userInput.equals("3")) {
			return 3;
		}
		else {
			return -1;
		}
	}
	
	private static double[] getSideLengths(int numSides) {
		double[] sideLengths = new double[numSides];
		
		Scanner keyboard = new Scanner(System.in);
		
		for(int i = 0; i < numSides; i++) {
			System.out.print("Enter side " + (i+1)+ ": ");
			sideLengths[i] = keyboard.nextDouble();
		}
		
		return sideLengths;
	}
	private static double computeTriangleArea(double[] sideLengths) {
		double s = (sideLengths[0] + sideLengths[1] + sideLengths[2])/2;
		return Math.sqrt(s * (s - sideLengths[0]) * (s - sideLengths[1]) * (s - sideLengths[2]));
	}

	private static double computeRectangleArea(double[] sideLengths) {
		return sideLengths[0] * sideLengths[1];
	}

	private static double computePentagonArea(double[] sideLengths) {
		double apothem = sideLengths[0]/(2*Math.tan(Math.PI/5));
		return ((sideLengths[0]/4)*apothem)*10;
	}
}