import java.util.Scanner;

/**
 * Aid user keyboard input with prompts and error catching.
 *  
 * @version 2017.09.24
 */
public class UI 
{
   private static Scanner in = new Scanner(System.in);

   /**
    *  Encourage ONLY ONE keyboard Scanner.
    *  @return the Scanner reading the keyboard.
    */
   public static Scanner getKeyboardScanner()
   {
      return in;
   }


   /** Prompt the user for a line and return the line entered.
    *  @param prompt
    *      The prompt for the user to enter the input line.
    *  @return
    *      The line entered by the user.
    */
   public static String promptLine(String prompt) {
      System.out.print(prompt);
      return in.nextLine();
   }


   /** Prompt for a character.
    *  @param prompt
    *      The prompt for the user to enter a character
    *  @return
    *     The first character of the line entered or a blank if the line
    *     is empty.
    */
   public static char promptChar(String prompt)
   {
      String line = promptLine(prompt);
      if (line.length() == 0)
         return ' ';
      return line.charAt(0);
   }

   /** Print a question and return a response.
    *  Repeat until a valid answer is given.
    * @param question
    *    The yes/no question for the user to answer.
    * @return
    *    True if the answer is yes, or False if it is no.
    */
   public static boolean agree(String question)
   {
      String yesStr = "yYtT", noStr = "nNfF", 
             legalStr = yesStr + noStr;

      char ans = promptChar(question);
      while (legalStr.indexOf(ans) == -1)
      {
         System.out.println("Respond 'y or 'n':");
         ans = promptChar(question);

      }
      return yesStr.indexOf(ans) >= 0;
   }

   /** Prompt and read an int.
    * Repeat until there is a legal value to return.
    * Read through the end of the line
    *  @param prompt
    *      The prompt for the user to enter a value.
    *  @return
    *      The value entered by the user.
    */
   public static int promptInt(String prompt)
   {
      System.out.print(prompt);
      while (! in.hasNextInt())
      {
         in.next();  // dump the bad token
         in.nextLine(); // dump through the newline
         System.out.println("!! Bad int format!!");
         System.out.print(prompt);
      }
      int val = in.nextInt();
      String rest = in.nextLine().trim(); //clear line
      if (rest.length() > 0)
          System.out.println("Skipping rest of input line.");
      return val;
   }

   /** Prompt and read a double.
    * Repeat until there is a legal value to return.
    *  @param prompt
    *      The prompt for the user to enter a value.
    *  @return
    *      The value entered by the user.
    */
   public static double promptDouble(String prompt)
   {
      System.out.print(prompt);
      while (! in.hasNextDouble())
      {
         in.next();  // dump the bad token
         in.nextLine(); // dump through the newline
         System.out.println("!! Bad double format!!");
         System.out.print(prompt);
      }
      double val = in.nextDouble();
      String rest = in.nextLine().trim(); //clear line
      if (rest.length() > 0)
          System.out.println("Skipping rest of input line.");
      return val;
   }

   /** Prompt and read a line of integers.
    * Repeat until there is a legal line to process.
    *  @param prompt
    *      The prompt for the user to enter data.
    *  @return
    *      The int values entered by the user.
    */
   public static int[] promptIntArray(String prompt)
   {
      while (true) { // exit via return statement
         String line = promptLine(prompt);
         String[] tokens = line.trim().split("\\s+");
         int n = tokens.length;
         int[] nums = new int[n];
         Scanner lineScan = new Scanner(line);
         int i = 0;
         while (i < n && lineScan.hasNextInt() )
         {
            nums[i] = lineScan.nextInt();
            i++;
         }
         if (i == n)
            return nums;
         System.out.format(
           "Bad input %s. Start your line over.\n", tokens[i]);
      }
   }

   /** Prompt and read a line of numbers.
    * Repeat until there is a legal line to process.
    *  @param prompt
    *      The prompt for the user to enter data.
    *  @return
    *      The double values entered by the user.
    */
   public static double[] promptDoubleArray(String prompt)
   {
      while (true) { // exit via return statement
         String line = promptLine(prompt);
         String[] tokens = line.trim().split("\\s+");
         int n = tokens.length;
         double[] nums = new double[n];
         Scanner lineScan = new Scanner(line);
         int i = 0;
         while (i < n && lineScan.hasNextDouble() )
         {
            nums[i] = lineScan.nextDouble();
            i++;
         }
         if (i == n)
            return nums;
         System.out.format(
           "Bad input %s. Start the line over.\n", tokens[i]);
      }
   }
}