import java.io.*;

import java.util.*;
import java.net.*;
import javax.swing.*;

/** Demo IO */
public class DemoIO {

    public static String courseLinksPage=
        "http://www.cs.cornell.edu/courses/CS2110/2014sp/links.html";

    /** Demo IO stuff */
    public static void main(String[] pars) throws IOException {
        fileDec();   // Demo 1: File declaration and use.
        fileDirectory(); // Demo getting files in a directory

        int n= getSize(new File("res/map1.xml"));
        System.out.println("number of lines in map1.xml: " + n);

        URLlines(40, new URL(courseLinksPage));

        System.out.println("Finished writing URL lines: \n\n");


        BufferedReader d= getReader(null);
        if (d != null ) {
            System.out.println("Ready to read from File" +
                               d);
        }
    }

    /** Show a File declaration, print length of file, and absolute path */
    public static void fileDec() {
        File f= new File("res/map1.xml");
        System.out.println("length of File f is " + f.length());
        System.out.println("Absolute path is " + f.getAbsolutePath());
    }

    /** Demo the use of a file that is a directory */
    public static void fileDirectory() {
        File f= new File("res");
        if (f.isDirectory()) {
            File[] l= f.listFiles();
            System.out.println("files in res are: " + Arrays.toString(l));
        }
    }

    /** Return the number of lines in file f */
    public static int getSize(File f) throws IOException {
        FileReader fr= new FileReader(f);
        BufferedReader br= new BufferedReader(fr);
        int n= 0;  // number of lines read so far
        String line= br.readLine();
        // invariant: n is the number of lines read thus far, NOT
        //    counting the last line read, line.
        while (line != null) {
            n= n+1;
            line= br.readLine();
        }
        br.close();
        return n;
    }

    /** Print the first 30 lines of the html file given by URL */
    public static void URLlines(int n, URL url) throws IOException {
        InputStreamReader isr= new InputStreamReader(url.openStream());
        BufferedReader br = new BufferedReader(isr);
        String line= br.readLine();
        int h= 0;
        // invariant: h lines have been printed and line is the next
        //            one to print (if not null)
        while (h < n  &&  line != null) {
            System.out.println(line);
            h= h+1;
            line= br.readLine();
        }
        br.close();
    }


    /** Obtain a file name from the user using a JFileChooser)
      and return a reader that is linked to it. If the user cancels the
      dialog window and thus does not give a file name, return null.
      Parameter p can be a path on the hard drive or null. If p is not null,
      start the JFileChooser at the path given by p.*/
    public static BufferedReader getReader(String p) throws IOException {
        try {
            JFileChooser jd;
            if (p == null) {
                jd= new JFileChooser();
            }
            else {
                jd= new JFileChooser(p);
            }

            jd.setDialogTitle("Choose input file");
            int returnVal= jd.showOpenDialog(null);

            if (returnVal != JFileChooser.APPROVE_OPTION) {
                System.out.println("Dialog window canceled, or IO error");
                return null;
            }

            System.out.println("You chose file " + jd.getSelectedFile());
            FileReader fr= new FileReader(jd.getSelectedFile());
            return new BufferedReader(fr);
        }
        catch (IOException e) {
            return null;
        }
    }

    /** Obtain a file name from the user, using a JFileChooser, and return
      a PrintStream that is linked to it. Return null if the user cancels. */
    public static PrintStream getWriter() throws IOException {
        JFileChooser jd= new JFileChooser();
        jd.setDialogTitle("Choose output file");
        jd.showSaveDialog(null);
        File f= jd.getSelectedFile();
        if (f == null) {
            return null;
        }
        return new PrintStream(new FileOutputStream(f));
    }

    /** Obtain from the user an input file, expected to be a .java file (using a JFileChooser).
      * Obtain from the user an output file name to write (using a JFileChooser)
      * Write on the output file all lines of the input file that have "//" in them. */
    public static void extract() throws IOException {

        // store in input a BufferedReader for the input file.
        BufferedReader input= getReader(null);

        // Store in output a PrintStream out for the output file.
        PrintStream output= getWriter();

        // Write to output all lines of input that have "//" in them
        String line= input.readLine();
        // invariant: All input lines before the one in line that
        //            contain "//" have been placed in output
        while (line != null) {
            if (line.contains("//")) {
                output.println(line);
            }
            line= input.readLine();
        }

        // Close streams
        input.close();
        output.close();


    }

}