import java.sql.*;

public class MySQLConnection
{
    // Default database connection info.
    private static final String SERVER = "localhost",
                                DATABASE = "test",
                                USERNAME = "root",
                                PASSWORD = "";

    private static final String ATTRIBUTE_SEPARATOR = ", ";

    private Connection con;

    /**
     * Default constructor.
     * Uses the static default server, database, username and password.
     */
    public MySQLConnection()
    {
        this(SERVER, DATABASE, USERNAME, PASSWORD);
    }

    /**
     * Custom constructor.
     * Uses the input strings to connect to a custom database.
     * @param server The server IP
     * @param db The database
     * @param user A username
     * @param pass A password
     */
    public MySQLConnection(String server, String db, String user, String pass)
    {
        try
        {
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            con = java.sql.DriverManager.getConnection("jdbc:mysql://" + server + "/" + db, user, pass);
        }
        catch (Exception e)
        {
            System.out.println("An error occurred: " + e);
            System.exit(0);
        }
        System.out.println("Connection OK.");
    }

    /**
     * Get the Connection object of this MySQLConnection
     * @return A Connection
     */
    public Connection getConnection()
    {
        return con;
    }

    /**
     * Execute the input string as a query.
     * @param sql The query
     * @return A ResultSet if the query was successful, null otherwise
     */
    public ResultSet query(String sql)
    {
        try
        {
            PreparedStatement s = con.prepareStatement(sql);
            return s.executeQuery();
        }
        catch (Exception e)
        {
            System.out.println("An error occurred: " + e);
        }
        return null;
    }

    /**
     * Execute a select query with the input variables.
     * @param select The SELECT clause
     * @param from The FROM clause
     * @param where The WHERE clause
     * @return A ResultSet, if the query was successful, null otherwise.
     */
    public ResultSet select(String select, String from, String where)
    {
        String query = "SELECT " + select +
                       "FROM "   + from +
                       "WHERE "  + where;

        return query(query);
    }

    /**
     * Execute an update using the input SQL statement
     * @param sql An update statement
     * @return The row count or 0 for successful updates, -1 otherwise
     */
    public int update(String sql)
    {
        try
        {
            PreparedStatement s = con.prepareStatement(sql);
            return s.executeUpdate();
        }
        catch (Exception e)
        {
            System.out.println("An error occurred: " + e);
        }
        return -1;
    }

    /**
     * Given a ResultSet, print all the attribute values of the attributes in the String array
     * @param r A ResultSet
     * @param attrs An arbitrary list of attributes
     */
    public void printValues(ResultSet r, String... attrs)
    {
        try
        {
            while(r.next())
            {
                StringBuffer buffy = new StringBuffer();
                for (int i = 0; i < attrs.length; i++)
                {
                    buffy.append(r.getString(attrs[i]));
                    if (i < attrs.length - 1)
                        buffy.append(ATTRIBUTE_SEPARATOR);
                }
                System.out.println(buffy);
            }
        }
        catch (Exception e)
        {
            System.out.println("Brown donkey.");
        }
    }
}