/*
 * LineCounter.java: count non-empty lines in a file, where a line is empty
 *    if it consists of just spaces.
 *
 *    This illustrates using a file chooser dialog (with a frame)
 *    and reading data from a file.
 *
 * Warning: the design used here is pretty simplistic; a real application
 *    doing this sort of thing would likely have more classes.
 *
 * Author: Robert W. Hasker
 */

import javax.swing.*;
import javax.swing.filechooser.FileNameExtensionFilter;
import java.awt.FlowLayout;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class LineCounter extends JFrame {

   JLabel filenameLabel, countLabel;

   /**
    * Create the form. Warning: this is not terribly good design -
    * often the form creator is in a separate method.
    */
   public LineCounter() {
      setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
      setSize(200, 150);
      setTitle("Line Counter");

      filenameLabel = new JLabel("File:                     ");
      countLabel = new JLabel("Number of lines:          ");

      setLayout(new FlowLayout());
      add(filenameLabel);
      add(countLabel);
   }

   /**
    * Prompt user for file and return that file.
    * @return file to read
    */
   public File fileToRead() {
      JFileChooser chooser = new JFileChooser("c:/");
      chooser.setFileFilter(new FileNameExtensionFilter("Text Files", "txt"));
      int status = chooser.showOpenDialog(this);
      File targetFile = null;
      if (status == JFileChooser.APPROVE_OPTION)
         targetFile = chooser.getSelectedFile().getAbsoluteFile();
      return targetFile; // will be null if user clicked on cancel or file doesn't exist
   }

   /**
    * Check that the file actually exists and return a scanner to
    * use to read it.
    * @param target file to be processed
    * @return scanner to process target file
    */
   public Scanner fileStream(File target) {
      Scanner result = null;
      try {
         result = new Scanner(target);
      } catch (FileNotFoundException e) {
         JOptionPane.showMessageDialog(null, "That file does not exist\n" + e.getMessage());
      }

      return result; // will be null if user clicked on cancel or file doesn't exist
   }

   /**
    * Report number of lines in specified file.
    * @param filename name of file being processed
    * @param lines number of non-empty lines in specified file
    */
   public void setResult(String filename, int lines) {
      filenameLabel.setText("File: " + filename);
      countLabel.setText("Number of non-empty lines: " + lines);
   }

   /**
    * Reads lines from input, counting ones which aren't just whitespace
    * @param source input stream to process
    * @return number of nonempty files
    */
   public static int nonEmptyLinesInStream(Scanner source) {
      int count = 0;
      while (source.hasNextLine()) {
         String line = source.nextLine();
         line = line.trim();
         if (!line.isEmpty())
            ++count;
      }
      return count;
   }

   /**
    * main driver: creates form, prompts user, prints results
    * @param args ignored command line arguments
    */
   public static void main(String[] args) {
      LineCounter mainForm = new LineCounter();
      mainForm.setVisible(true);
      File target = mainForm.fileToRead();
      if ( target == null )
         mainForm.setResult("[none]", 0);
      else {
         Scanner input = mainForm.fileStream(target);
         int lines = nonEmptyLinesInStream(input);
         mainForm.setResult(target.getName(), lines);
      }
   }
}