package helper;

import webutil.Args;
import javax.servlet.ServletConfig;
import java.util.Properties;
import java.util.logging.*;

import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.AddressException;
import javax.mail.internet.MimeMessage;

import webutil.Util;
import webutil.Webmaster;

/**
* Send simple email from the {@link Webmaster} to a receiver.
*
* <P>The emails sent by this class include sender, receiver, subject, and 
* body. No features such as attachments are supported by this class. If more 
* flexibity is needed, please use {@link javax.mail} directly.
* 
* <P>See <tt>web.xml</tt> for more email configuration information.
*
* @used.By 
* {@link TroubleTicket},
* {@link hirondelle.exampleA.user.AddUser}
* {@link hirondelle.exampleA.user.User},
* {@link hirondelle.web4j.Controller}.
*
* @author <a href="http://www.javapractices.com/">javapractices.com</a>
* @to.do Is {@link javax.mail.Transport#send} thread-safe? The documentation is not 
* clear.
*/
public final class Mailer {

  /**
  * Called upon startup, to allow this class to extract mail server 
  * config information from <code>web.xml</code>.
  */
  public static void init(ServletConfig aConfig){
    fConfig = aConfig;
  }
  
  /**
  * Validate the form of an email address.
  *
  * <P>Return <code>true</code> only if 
  *<ul> 
  * <li> <code>aEmailAddress</code> can successfully construct an 
  * {@link javax.mail.internet.InternetAddress} 
  * <li> when parsed with a "@" delimiter, <code>aEmailAddress</code> contains 
  * two tokens which satisfy {@link hirondelle.web4j.util.Util#textHasContent}.
  *</ul>
  *
  *<P> The second condition arises since local email addresses, simply of the form
  * "<tt>albert</tt>", for example, are valid but almost always undesired.
  */
  public static boolean isValidEmailAddress(String aEmailAddress){
    if (aEmailAddress == null) return false;
    
    boolean result = true;
    try {
      InternetAddress emailAddr = new InternetAddress(aEmailAddress);
      if ( ! hasNameAndDomain(aEmailAddress) ) {
        result = false;
      }
    }
    catch (AddressException ex){
      result = false;
    }
    return result;
  }
  
  /**
  * Send an email to a single recipient, using the the {@link Webmaster} address 
  * configured in <code>web.xml</code> as the "from" address.
  *
  * @param aToAddress satisfies {@link #isValidEmailAddress}.
  * @param aSubject satisfies {@link hirondelle.web4j.util.Util#textHasContent}.
  * @param aBody satisfies {@link hirondelle.web4j.util.Util#textHasContent}.
  */
  public void send(String aToAddress, String aSubject, String aBody){
    Args.checkForContent(aSubject);
    Args.checkForContent(aBody);
    if ( isMailDisabled() ){
      fLogger.fine("Mailing is disabled.");
      return;
    }
    
    Session session = Session.getDefaultInstance( getMailServerConfig(), null );
    MimeMessage message = new MimeMessage( session );
    try {
      message.setFrom( new InternetAddress(new Webmaster().getEmailAddress()) );
      message.addRecipient(Message.RecipientType.TO, new InternetAddress(aToAddress));
      message.setSubject( aSubject );
      message.setText( aBody );
      Transport.send( message ); //thread-safe?
    }
    catch (MessagingException ex){
      fLogger.severe("CANNOT SEND EMAIL." + ex);
    }
    fLogger.fine("Mail is sent.");
  }
  
  // PRIVATE //
  
  private static ServletConfig fConfig;
  
  /**
  * Identifies the item in web.xml which contains the configured 
  * mail server.
  */
  private static final String fMAIL_SERVER = "MailServer";
  
  /**
  * Identifies the lack of any configured mail server in web.xml.
  * If fMAIL_SERVER takes this value, then mailing is disabled, and 
  * this class will abort all attempts to send email.
  */
  private static final String fNONE = "NONE";
  
  private static final Logger fLogger = Util.getLogger(Mailer.class);  

  private String getMailServer(){
    return fConfig.getServletContext().getInitParameter(fMAIL_SERVER);
  }
  
  private boolean isMailDisabled(){
    return getMailServer().equalsIgnoreCase(fNONE);
  }

  /**
  * Return the configured mail server in the form of a Properties object.
  */
  private Properties getMailServerConfig(){
    Properties result = new Properties();
    result.put("mail.host", getMailServer() );
    return result;
  }
  
  private static boolean hasNameAndDomain(String aEmailAddress){
    String[] tokens = aEmailAddress.split("@");
    return 
     tokens.length == 2 &&
     Util.textHasContent( tokens[0] ) && 
     Util.textHasContent( tokens[1] ) ;
  }
}