import java.util.Scanner;
import java.io.File;
import java.io.FileNotFoundException;

/* Java application having as its purpose to test the methods in the 
** CSV_Utility class.
** Author: R. McCloskey
*/
public class CSV_Utility_Tester {

   private static Scanner input;
   private static boolean echo;
   private static boolean keepGoing;
   private static String s;
   
   public static void main(String[] args) {
      establishInputSource(args);

      s = getString("Enter a CSV string: ");

      keepGoing = true;
      while (keepGoing) {
         try {
            performCommand();
         }
         catch (Exception e) {
            e.printStackTrace();
         }
      } 
      System.out.println("\nGoodbye."); 

   }


   private static void performCommand() {
      String COMMAND_CODES = "QHP#GSRIN";

      // Prompt for a command and read it.
      String command = getString("\nEnter command (H for help): ").trim();
    
      // Parse the command.
      char operation = Character.toUpperCase(command.charAt(0));

      if (COMMAND_CODES.indexOf(operation) == -1)
         { System.out.println("ERROR: Invalid command"); }
      else if (operation == 'Q') 
         { keepGoing = false; }
      else if (operation == 'H')
         { displayHelp(); }
      else if (operation == 'P')  // print the current string
         { System.out.println(s); }
      else if (operation == '#') 
         { System.out.println(CSV_Utility.numberOfFieldsIn(s)); }
      else if (operation == 'N')  // establish new current CSV-string
         { s = command.substring(2); }
      else {
         String rest = command.substring(1);
         // Each of remaining operations requires that an integer appears
         // after the command code.
         Scanner commandScanner = new Scanner(rest);
         int k = commandScanner.nextInt();

         if (operation == 'G') { 
            System.out.println(CSV_Utility.getIthField(s,k));
         }
         else if (operation == 'R') { 
            s = CSV_Utility.removeIthField(s,k);
            System.out.println(s);
         }
         else {
            // Each of two remaining operations requires that a field value
            // appears next.
            String field = commandScanner.nextLine().trim();
            if (field.indexOf(',') != -1) {
               System.out.println("**ERROR; a field cannot include a comma");
            }
            else {
               // The remaining possibilities are 'S' and 'I' 
               if (operation == 'S')
                  { s = CSV_Utility.setIthField(s,k,field); }
               else if (operation == 'I') 
                  { s = CSV_Utility.insertIthField(s,k,field); }
               else 
                  { System.out.println("This is impossible!"); }
            }
            System.out.println(s);
         }  
      }
   } 


   private static void displayHelp() {
      System.out.println("Examples of commands:");
      System.out.println("  H   (display this!)");
      System.out.println("  Q   (quit)");
      System.out.println("  P   (print current string)");
      System.out.println("  #   (ascertain # fields)");
      System.out.println("  G 5 (print field #5 in current string)");
      System.out.println("  R 3 (remove field #3 from current string)");
      System.out.println("  S 2 glork  (set field #2 to \"glork\")");
      System.out.println("  I 4 glork  (insert \"glork\" as field #4)");
      System.out.println("  N don't,look,now   (establish a new CSV-string)");
   }

  
   /* Displays the given prompt and returns the response to it, as read
   ** using the 'input' Scanner.  (If 'echo' is true, indicating that the
   ** input is being read from a file --as opposed to the keyboard-- the
   ** response is printed.)
   */
   private static String getString(String prompt) {
      System.out.print(prompt);
      String response = input.nextLine();
      if (echo) { System.out.println(response); }
      return response;
   }

   /* Attaches the 'input' Scanner to either the keyboard or to
   ** the file named by args[0], the latter if args.length != 0.
   ** Also assigns value to 'echo'.
   */
   private static void establishInputSource(String[] args) {
      if (args.length == 0) {   // read input from keyboard
         input = new Scanner(System.in);
         echo = false;
      }
      else {    // read input from file named args[0]
         try {
            input = new Scanner(new File(args[0]));
            echo = true;
         }
         catch (FileNotFoundException e) {
            System.out.printf("No file named %s exists; program aborting.\n",
                              args[0]);
            System.exit(0);
         }
      }

   }

}