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

import javax.swing.JFileChooser;
import javax.swing.JOptionPane;

/**
 * CompSci 100e NGram Lab
 * Name:
 * Collaborators:
 * Resources Used:
 */

public class NGram {
    private static final int RANDOM_SEED = 1234;
    // like a die, generates a series of random numbers
    private static final Random ourGenerator = new Random(RANDOM_SEED);
    
    // chooser allows users to select a file by navigating through
    // directories
    private static JFileChooser ourChooser = new JFileChooser(System.getProperties().getProperty("user.dir"));
    
    /**
     * Brings up chooser for user to select a file
     * 
     * @return Scanner for user selected file, null if file not found
     */
    public static Scanner getScanner() {
        
        int retval = ourChooser.showOpenDialog(null);
        
        if (retval == JFileChooser.APPROVE_OPTION) {
            File f = ourChooser.getSelectedFile();
            Scanner s;
            try {
                s = new Scanner(f);
            } catch (FileNotFoundException e) {
				return null;
            }
            return s;
        }
        return null;
    }
    
    /**
     * Read a file into a string.
     *
     * @return returns a string containing all of the text in the
     * file
     */
    public String readFile (Scanner input)
    {
        return input.useDelimiter("\\Z").next();
    }
    
    /**
     * Generates random text that is similar to the given reference text.
     *
     * @requires ngram > 0
     * @return returns string whose length is numLetters of randomly selected 
     *         characters based on picking representive characters that follow
     *         each ngram characters 
     */
    public String makeNGram (String referenceText, int ngram, int numLetters)
    {
        String predictor = getRandomSubstring(referenceText, ngram);
        String result = "";

        for (int k = 0; k < numLetters; k += 1)
        {
            // TODO: get all characters that immediately follow predictor
            // TODO: pick one character randomly and update predictor
        }

        return result;
    }

    /**
     * Choose a random substring of the given string.
     *
     * @requires subSize <= s.length()
     * @return random substring of s whose length is subSize
     */
    public String getRandomSubstring (String s, int subSize)
    {
        // TODO: choose random substring from s
        return s.substring(0, subSize);
    }

    /**
     * Find all characters that immediately follow toFind in the given string.
     *
     * @return a string containing each character that immediately
     *         follows toFind in s
     */
    public String getFollowingCharacters (String s, String toFind)
    {
        String result = "";
      
        // TODO: get each character following toFind in s and add to result

        return result;
    }


    
    /**
     * Main to be used for testing
     */
    public static void main(String[] args) {
        final int RANDOM_TEXT_LENGTH = 256;
        NGram model = new NGram();
        String input = JOptionPane.showInputDialog("Enter N:", "3");
        int n = Integer.parseInt(input);
        String referenceText = model.readFile(getScanner());
        // generate random text to varying degrees of accuracy
        System.out.println(n + "    -gram");
        for (int k = 0; k <= n; k++)	
        {
            System.out.println(model.makeNGram(referenceText, n, RANDOM_TEXT_LENGTH));
            System.out.println("--------");
        }
    }
}