/**************************************************
Emalia has written a program to collect eMail addresses into
an array.  Now she has improved the program to save the array
in a file on the disk drive.  When the program starts, 
it automatically loads the file's contents into the array.
When the program ends, it automatically saves the contents
of the array back into the disk file.  Now her data is PERSISTENT.
***************************************************/

import java.io.*;

public class EmailsSaved
{

  String[] addresses = new String[1000];
  
  int count = 0;        // the number of addresses in the array
  
  public EmailsSaved()
  {
    loadArray();
    String email="";
    do
    {
      printAllAddresses(); 
      email = input("Type an eMail address (ENTER to quit)");
      if( isValid(email) )
      {
        addToAddresses(email);
        saveArray();
      } 
      else
      {
        output(email + " is not valid");
      } 
    } while(email.length() > 0);      // type nothing to quit
  }
  
  boolean isValid(String email)  // check whether email is valid
  {
    if(email.length() < 5)        // shortest is a@b.c
    { return false; }   
    
    int atsign = email.indexOf("@");    // find the @ sign  
    if(atsign < 0 )                     
    { return false; }                   //  @ is missing
    
    String server = email.substring(atsign+1);  // the rest after @
    int dot = server.indexOf(".");              // find . in server
    
    if( dot < 0)                       
    { return false; }                   // . is missing
    
    return true;                  // if it got this far, it's valid                           
  }
  
  void addToAddresses(String email)
  // pre-condition : COUNT contains number of items in the array
  // post-condition: COUNT is 1 bigger and addresses[count] == email
  {
    addresses[count] = email;
    count = count + 1;
  }
  
  void printAllAddresses()
  {
    for(int c=0; c < count; c = c+1)
    {
      System.out.println(addresses[c]);
    } 
    System.out.println("============");
  }
  
  void saveArray()
  {
    try
    {
      ObjectOutputStream os=new ObjectOutputStream(
        new BufferedOutputStream(new FileOutputStream("addresses.dat")));
      os.writeObject(addresses);
      os.close();
    }
    catch(Exception e)
    {
      System.out.println(e.toString());
    }  
  }
  
  void loadArray()
  {
    try
    {
      ObjectInputStream os=new ObjectInputStream(
           new FileInputStream("addresses.dat"));
      addresses = (String[])os.readObject();
      os.close();
    }
    catch(Exception e)
    {
      System.out.println(e.toString());
    } 
    int p = -1;
    do
    {
      p = p+1;
    } while(addresses[p]!=null);
    count = p;
  }
  
  public static void main(String[] args)
  {  new EmailsSaved(); }
  
  public String input(String prompt)
  { return javax.swing.JOptionPane.showInputDialog(null,prompt); }
  
  public void output(String message)
  {  javax.swing.JOptionPane.showMessageDialog(null,message);  }
}