import java.nio.*;
import java.nio.channels.*;
import java.nio.charset.*;
import java.io.*;
import java.net.InetSocketAddress;
import java.sql.*;
import java.util.*;

public class Pro2JdbcServer {

    private Charset charset = null;
    ServerSocketChannel channel = null;
    SocketChannel sc = null;
    Connection con = null;
    String queryString = null;
    int portNum;

    public void start() {

        ResourceBundle rb = ResourceBundle.getBundle("pro2jdbc");

        charset = Charset.forName(rb.getString("fileEncoding"));
        portNum = Integer.parseInt(rb.getString("portNum"));

        try {
			Class.forName("org.postgresql.Driver");
			con = DriverManager.getConnection(rb.getString("url"), 
					rb.getString("user"), rb.getString("password"));

            openChannel();
            waitForConnection();
            closeChannel();

			con.close();
        } catch (IOException e) {
            e.printStackTrace();
        } catch(SQLException ex) {
            System.err.print("SQLException: ");
            System.err.println(ex.getMessage());
		} catch(java.lang.ClassNotFoundException e) {
			System.err.print("ClassNotFoundException: ");
			System.err.println(e.getMessage());
        }	
    }

    private void openChannel() throws IOException {
        channel = ServerSocketChannel.open();
        channel.socket().bind(new InetSocketAddress(portNum));
        while (!channel.isOpen()) {
        }
        System.out.println("Channel is open...");
    }

    private void closeChannel() throws IOException {
        channel.socket().close();
        channel.close();
        System.out.println("...channel is closed.");
    }

    private void waitForConnection() throws IOException {
        while (queryString == null || !queryString.equals("END_PROCESSING")) {
            sc = channel.accept();
            if (sc != null) {
                System.out.println("A connection is added...");
                while(processRequest()) {
                }
                sc.close();
            }
        }
    }

    private boolean processRequest() throws IOException {
        boolean stillProcessing;
        ByteBuffer buffer = ByteBuffer.allocate(10000);

        buffer.clear();
        sc.read(buffer);
        buffer.flip();
        queryString = charset.decode(buffer).toString();
        System.out.println("Received request: " + queryString);
        if (queryString == null ||
            queryString.equals("LAST_REQUEST") ||
            queryString.equals("END_PROCESSING")) {
            stillProcessing = false;
        } else {
            stillProcessing = true;

            try {
                // execute query
                Statement stmt = con.createStatement();							
                ResultSet rs = stmt.executeQuery(queryString);
                ResultSetMetaData rsmd = rs.getMetaData();
                int numberOfColumns = rsmd.getColumnCount();
                // retrieve records
                while (rs.next()) {
                    String recordAsString = "";
                    for (int i = 1; i <= numberOfColumns; i++) {
                        String colString = rs.getString(i);
                        if (colString == null) colString = "?";
                        if (i > 1) recordAsString += "\t";
                        recordAsString += colString;
                    }
                    writeRecord( recordAsString );
                }
                stmt.close();
            } catch(SQLException ex) {
                writeRecord("SQL_EXCEPTION " + ex.getMessage());
            }	
            // write empty record at the end
            writeRecord( null );
        }

        return stillProcessing;
    }

    private void writeRecord( String recordAsString ) throws IOException {
        /* record size */
        ByteBuffer writeBuffer = ByteBuffer.allocate(4);
        IntBuffer intBuffer = writeBuffer.asIntBuffer();
        if (recordAsString == null) {
            intBuffer.put(0,0);
        } else {
            if (recordAsString.equals("")) recordAsString = " ";
            intBuffer.put(0,recordAsString.length());
        }
        sc.write(writeBuffer);

        if (recordAsString != null) {
            /* record itself */
            writeBuffer = charset.encode(recordAsString);
            sc.write(writeBuffer);
            System.out.println( "Return record: " + recordAsString );
        }
    }

    public static void main(String[] args) {
        new Pro2JdbcServer().start();
    }
}