import java.util.Scanner;
import java.io.PrintStream;

/**
 * A user interface for our Quadratic Solver
 * 
 * @author P. Conrad 
 * @version for CS10, lab04, UCSB, Spring 2009
 */
public class QuadraticSolver
{
    /** A main method for a user interface for a program to solve 
     * Quadratic equations---even for complex roots
     * 
     * @param args  Not used for this program
     */
    public static void main(String [] args)
    {
        
        Scanner in = new Scanner(System.in);
        
        boolean userWantsToContinue = true;
        while (userWantsToContinue)
        {
            QuadraticEqn q = getQuadraticEqnFromUser(in, System.out);   
            
            
            if (q.hasDegenerateRoot())
              System.out.println("One degenerate root: " + q.degenerateRoot());
            else if (q.getA() == 0.0)
            {
              assert(q.getB()==0.0);
              System.out.println("Can't calcuate any roots: a is 0, and b is 0");
            } 
            else 
            {
              switch (q.numRealRoots())
              {
                case 0: System.out.println("Complex roots: " + q.complexRoot1() + " and " + q.complexRoot2() );    
                        break;
                case 1: System.out.println("One real root: " + q.realRoot1());
                        break;
                case 2: System.out.println("Two real roots: " + q.realRoot1() + " and " + q.realRoot2());
                        break;
               } // end switch          
            } // end else
                
            System.out.println("Do you want to calculate another equation? Y/N");
            
            userWantsToContinue = getYesOrNoAsBoolean(in);
            
        } // end while loop
        
        System.out.println("Goodbye!");
    }  // end main
    
    /** Get a quadratic equation object by asking the user for 
     *  values for a, b, and c.   Note: You should NOT do something like this directly in a constructor!
     *  Instead, separate the user interface from the actual object construction, as done here.
     *  
     *  @param in   A scanner object used to get the input from
     *  @param out  A PrintStream used to print out the messages on
     *  @return A Quadratic Equation object, constructed based on the user input for a, b, c
     */
    
    private static QuadraticEqn getQuadraticEqnFromUser(Scanner in, PrintStream out)
    {
        
        out.println("Please enter values for a quadratic equation below.\n\n");
        
        double a = getDouble("a", in, out);
        double b = getDouble("b", in, out);
        double c = getDouble("c", in, out);
        
        return new QuadraticEqn(a,b,c);
    }
    
     /** Get a double value.  This function abstracts away the whole "keep asking until you get it right",
      *   and is also reslient to recovering from bad input---we say it is "robust".
      * 
     *  @param name  The name of the value we will ask the user for
     *  @param in   A scanner object used to get the input from
     *  @param out  A PrintStream used to print out the messages on
     *  @return a double value
     */
    
    private static double getDouble(String name, Scanner in, PrintStream out)
    {
        double returnValue = 0;

        while (true) // infinite loop---we exit via "return"
        {
            
            out.print("Please enter a value for " + name + ":");   
            String theInput = in.nextLine();
            try {
                returnValue = Double.parseDouble(theInput);   
                return returnValue; // here is where we exit the loop
            } catch (Exception e) {
                out.println("Sorry, an error occurred: " + e);
            }
            out.println("Please try again!\n");
        }
    }
    
    /**  Ask a yes/no question, and return answer as a boolean
     * @param in  a Scanner object to ask the question on
     * @return true if the first letter of the response is y or Y
     */
    private static boolean getYesOrNoAsBoolean(Scanner in)
    {
        String response = in.nextLine().toLowerCase();
        return response.startsWith("y");
    }
}