public static void main(String[] args)throws Exception {

// see if we do not use default server port

int serverPort = 1502;

/* change above port number this if required */

if (args.length >= 1)

serverPort = Integer.parseInt(args[0]);

// System.out.println(serverPort);

// create server socket

ServerSocket welcomeSocket = new ServerSocket(serverPort);

while (true){

// accept connection from connection queue

Socket connectionSocket = welcomeSocket.accept();

System.out.println("connection from " + connectionSocket);

// create read stream to get input

BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));

String clientSentence;

clientSentence = inFromClient.readLine();

// process input

// send reply

DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());

StringTokenizer LineBreaker = new StringTokenizer(clientSentence);

String FirstName = LineBreaker.nextToken("&");

String FamilyName = LineBreaker.nextToken("&");

String Cardnumber = LineBreaker.nextToken("&");

int Spending = Integer.parseInt(LineBreaker.nextToken("&"));

Pattern namePattern = Pattern.compile("/[^a-z0-9 ]/gi");

// System.out.println(FirstName+FamilyName+Cardnumber+Spending);

String Info = FirstName.concat("\t").concat(FamilyName).concat("\t").concat(Cardnumber);

// System.out.println(Info);

java.util.regex.Matcher match = namePattern.matcher(Info);

String matchInfo = String.valueOf(fileReader("credit.txt" , Info));

// System.out.println(matchInfo + matchInfo.length());

if(FirstName.length() == 0 || FamilyName.length() == 0 || Cardnumber.length() < 8 || match.matches() ){

//System.out.println("this is a hacker!!!! stop him!!");

outToClient.writeBytes("nouser");

}

else if (matchInfo.length() == 0 || matchInfo.equals("null")){

// System.out.println("no info for this client"); //debug

outToClient.writeBytes("nouser");

}else{

StringTokenizer TempBreaker = new StringTokenizer(matchInfo);

String TempReader = TempBreaker.nextToken("\t");

TempReader = TempBreaker.nextToken("\t");

TempReader = TempBreaker.nextToken("\t");

TempReader = TempBreaker.nextToken("\t");

int balance =Integer.parseInt(TempReader);

TempReader = TempBreaker.nextToken("\t");

int credit = Integer.parseInt(TempReader);

// System.out.println(balance + "+" + credit);

if(credit < Spending){

System.out.println("insufficient");

outToClient.writeBytes("insufficient\r\n");

}else{

System.out.println("approved");

outToClient.writeBytes("approved");

credit = credit - Spending;

balance = balance + Spending;

String newInfo = Info.concat("\t").concat(String.valueOf(balance)).concat("\t").concat(String.valueOf(credit)).concat("\n");

RandomAccessFile f = new RandomAccessFile("credit.txt", "rw");

while (f.readLine().startsWith(Info) == false);

f.seek(f.getFilePointer()-matchInfo.length()-1);

f.writeBytes(newInfo);

}

}

connectionSocket.close();

} // end of while (true)

}

static String fileReader(String filename,String key){

String t = null;

try{

FileInputStream tempfile = new FileInputStream(filename);

DataInputStream tempdata = new DataInputStream(tempfile);

BufferedReader buffer = new BufferedReader(new InputStreamReader(tempdata));

while ((t = buffer.readLine()).startsWith(key) == false);

tempdata.close();

}catch (Exception error){//Catch exception if any

//do nothing

}

return t;

}// end of main()