/* 
  * program featuring an array to store and interactively manipulate a list of numbers. 
  */

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

 public class NumberList {

       // variables local to the class and thus global to the method
       private static final int LIMIT = 1000;
       private static int[] numbers = new int [LIMIT];
       private static int numberOfNumbers = 0;
       private static Scanner commandReader = new Scanner(System.in);

       public static void main(String[] args) {
           try {

               // establish the array of numbers
               readNumbers();

               // check the data
               System.out.println("The original list of numbers ...");
               displayNumbers();

               // enter the interpreter
               interpreter();
           } catch (FileNotFoundException ex) {
               System.out.println("The file was not found. Please think again.");
               System.exit(-1);
           }
       }

       // assuming that the data file will be found in public_html/data
       // subdirectory of the user's home directory.
       private static Scanner establishScanner(String fn) throws FileNotFoundException {
           String separator = File.separator;
           String homeDirectory = System.getProperty("user.home");
           String path = homeDirectory + separator + "public_html" + separator + "data" + separator;
           String fullFileName = path + fn;
           return new Scanner(new File(fullFileName));
       }

       private static void readNumbers() throws FileNotFoundException {
           Scanner scanner = establishScanner("NumberSet.text");
           while (scanner.hasNext()) {
               numbers[numberOfNumbers] = scanner.nextInt();
               numberOfNumbers = numberOfNumbers + 1;
           }
       }

       private static void displayNumbers() {
           for (int x = 0; x < numberOfNumbers; x = x + 1) {
               System.out.println(numbers[x]);
           }
       }

       private static void interpreter() {
           System.out.print(">>>");
           String command = commandReader.next();
           if (command.equalsIgnoreCase("DISPLAY")) {
               interpreterDisplayCommand();
           } else if (command.equalsIgnoreCase("PRINT")) {
               interpretPrintCommand();
           } else if (command.equalsIgnoreCase("SWAP")) {
               interpretSwapCommand();
           } else if (command.equalsIgnoreCase("ADD")) {
               interpretAddCommand();
           } else if (command.equalsIgnoreCase("HELP")) {
               interpretHelpCommand();
           } else if (command.equalsIgnoreCase("EXIT")) {
               System.exit(0);
           } else {
               System.out.println("### Unrecognizable command: " + command);
           }
           interpreter();
       }

       private static void interpreterDisplayCommand() {
           displayNumbers();
       }

       private static void interpretPrintCommand() {
           String operand = commandReader.next();
           if (operand.equalsIgnoreCase("FIRST")) {
               System.out.println(numbers[0]);
           } else if (operand.equalsIgnoreCase("LAST")) {
               System.out.println(numbers[numberOfNumbers-1]);
           } else {
               int index = Integer.valueOf(operand);
               System.out.println(numbers[index-1]);
           }
       }

       private static void interpretHelpCommand() {
           System.out.println("HELP - display a menu of commands");
           System.out.println("DISPLAY - display the list of numbers");
           System.out.println("PRINT - print a number (FIRST;LAST,nth)");
           System.out.println("SWAP - exchange two elements (nth;mth)");
           System.out.println("ADD - add a number to the list (FIRST;LAST)");
           System.out.println("EXIT - terminate execution of the program");
       }

       private static void interpretSwapCommand() {
           int position1 = commandReader.nextInt();
           int position2 = commandReader.nextInt();
           int temp = numbers[position1 -1];
           numbers[position1 - 1] = numbers[position2 - 1];
           numbers[position2-1] = temp;
       }

       private static void interpretAddCommand() {
           String position = commandReader.next();
           if (position.equalsIgnoreCase("LAST")) {
               addLast();
           } else if (position.equalsIgnoreCase("FIRST")) {
               addFirst();
           } else {
               System.out.println("### invalid operand for add command");
           }
           numberOfNumbers = numberOfNumbers + 1;
       }

       private static void addLast() {
           numbers[numberOfNumbers] = commandReader.nextInt();
       }

       private static void addFirst() {
           for (int x = numberOfNumbers; x > 0; x = x-1) {
               numbers[x] = numbers[x -1];
           }
           numbers[0] = commandReader.nextInt();
       }
  }