import java.util.*;
import java.io.*;
import javax.swing.*;
import java.lang.*;

public class Main {
	private static File file = new File ("Users.txt");
    public static void main(String args[]) throws Exception {
	 CreateUser();



    }
	public static void CreateUser() throws Exception{			//login method
        String WriteToFile;
		FileWriter fw = new FileWriter(file,true);//writes to admins.txt all in one chunk
        PrintWriter pw = new PrintWriter(fw);//allows u to write to filewriter
        FileReader fr= new FileReader(file);
		LineNumberReader lnr = new LineNumberReader(fr);
		int LineNumber=lnr.getLineNumber();
		String UserID = Integer.toString(LineNumber);
		String s,username,password,DetailsConfirm;
		username="";
		boolean ValidEmail=false;
		boolean CorrectFormat=false;
		boolean IsInUse=false;
		while (ValidEmail==false)
		{
			ValidEmail=(CorrectFormat && IsInUse);
		username = JOptionPane.showInputDialog(null,"Please enter a valid email address");	// enter user and pass

		 CorrectFormat=isValidEmailAddress(username);
		 if (CorrectFormat==true)
		 IsInUse=	isEmailInUse(username);

		}



		 password = RandomPassword();


		 DetailsConfirm=("Your username is "+username+      "Your Password is "+password);
		  JOptionPane.showMessageDialog(null, DetailsConfirm);
          WriteToFile =("\n"+username + "," + password+","+UserID);		// creates string to be stored in file
          pw.println(WriteToFile);//printwriter will write the account details to filewriter
          pw.close();//at this point it is printed to the text file
	}


		static String RandomPassword() throws Exception {
		 String alphabet= "abcdefghijklmnopqrstuvwxyz1234567890";
        String GeneratedString = "";
        Random random = new Random();
        int randomLen = 5+random.nextInt(8);		// between 5 and 12
        for (int i = 0; i < randomLen; i++) {
            char c = alphabet.charAt(random.nextInt(36));
            GeneratedString+=c;
        }

		return GeneratedString;
    }
	  private static boolean isValidEmailAddress(String email) {
           String ePattern = "^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@((\\[[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\])|(([a-zA-Z\\-0-9]+\\.)+[a-zA-Z]{2,}))$";
           java.util.regex.Pattern p = java.util.regex.Pattern.compile(ePattern);
           java.util.regex.Matcher m = p.matcher(email);
           return m.matches();

}

public static boolean isEmailInUse(String email) throws IOException {

        boolean found = false;
        File aFile = new File("Users.txt");

            Scanner in = new Scanner(aFile);
            String fileElements[];
            while (in.hasNext()) {
                fileElements = (in.nextLine()).split(",");
                if ((fileElements[0]).equals(email))
                    found = true;


        }
        if (found==true)
		{JOptionPane.showMessageDialog(null, "Email already in use");
            return false;
		}
        else
            return true;
    }


}