package com.waldura.mail;

import java.io.InputStream;
import java.io.IOException;
import java.util.Properties;

// JavaMail
import javax.mail.*;
import javax.mail.internet.*;


/**
 * Facade for JavaMail. Also Singleton.
 * <p>
 * This class declared <code>final</code> because I don't see any
 * good reason why anyone would want to extend it. If you need more
 * functionality than this class provides, either use JavaMail directly
 * or modify the Facade itself to include that functionality.
 *
 * @author Renaud Waldura, 6/26/2001
 */

public final class Mailer
{
    /**
     * The name of the default configuration file for this object.
     * It is looked up in this classloader's resources using
     * {@link Class#getResource(String)}.
     */
    public static final String DEFAULT_CONFIG_FILE = "/Mailer.properties";

    /**
     * Debug JavaMail? Set this property to <code>true</code> to have the
     * JavaMail library print debugging statements to <code>System.err</code>.
     */
    private static final String DEBUG_JAVAMAIL_PROPERTY = "mail.debug";

    // singleton instance
    private static Mailer instance = null;

    // the JavaMail session
    private Session session;

    /**
     * Private constructor prevents instantiation.
     */
    private Mailer() {}

    /**
     * Configure the mailing sub-system from the given stream.
     * It is advised you use
     * {@link #configure(String)}
     * instead.
     *
     * @param is a stream the configuration is read from
     *
     * @throws IOException if failed to read the configuration data from
     * file
     */
    private void configure(final InputStream is)
        throws IOException
    {
        // load properties from stream
        Properties p = new Properties();
        p.load(is);

        session = Session.getDefaultInstance(p, null);

        // debugging?
        String debug = p.getProperty( DEBUG_JAVAMAIL_PROPERTY );
        session.setDebug( "true".equals(debug) );
    }

    /**
     * Configure the mailing sub-system from the given file.
     * The file is looked up in the same directory as the compiled class
     * file, using
     * {@link Class#getResourceAsStream}.
     *
     * @param configFile the name of the configuration file
     *
     * @throws IOException if failed to read the configuration data from
     * file
     */
    public void configure(final String configFile)
        throws IOException
    {
        configure( getClass().getResourceAsStream(configFile) );
    }

    /**
     * Configure the mailing sub-system.
     * The {@link #DEFAULT_CONFIG_FILE DEFAULT_CONFIG_FILE} is used
     * for the configuration data.
     *
     * @throws MailingException if the sub-system configuration failed
     */
    public void configure()
        throws MailingException
    {
        try
        {
            configure(DEFAULT_CONFIG_FILE);
        }
        catch (IOException ioe)
        {
            // re-type and propagate
            throw new MailingException("Configuration failed", ioe);
        }
    }

    /**
     * Implementation of the Singleton pattern.
     *
     * @throws MailingException if initializing the sub-system failed
     */
    public static synchronized Mailer getInstance()
        throws MailingException
    {
        if (instance == null)
        {
            instance = new Mailer();
            instance.configure();
        }

        return instance;
    }

    /**
     * Parse a list of addresses into an array of
     * <code>Address</code> objects.
     *
     * @returns an array of <code>Address</code> objects
     *
     * @throws AddressException if failed
     */
    private Address[] parseAddresses(final String addressList)
        throws AddressException
    {
        return InternetAddress.parse(addressList, true); // strict parsing?
    }

    /**
     * Sends an e-mail message.
     *
     * @param mail the e-mail message to send
     *
     * @throws IllegalArgumentException if the message to send is invalid
     * in some way
     *
     * @throws MailingException if anything else went wrong
     */
    public void send(final MailMessage mail)
        throws MailingException
    {
        Address from = null;
        Address[] to = null;
        Address[] cc = null;
        String subject, body;

        try    // pre-conditions
        {
            String addr = null;

            // From is required
            addr = mail.getFrom();
            if (addr == null) throw new IllegalArgumentException("Email \"from\" address is undefined");
            from = parseAddresses(addr)[0];

            // To is required
            addr = mail.getTo();
            if (addr == null) throw new IllegalArgumentException("Email \"to\" address is undefined");
            to = parseAddresses(addr);

            // Cc is optional
            addr = mail.getCc();
            if (addr != null) cc = parseAddresses(addr);

            // Subject is required
            subject = mail.getSubject();
            if (subject == null) throw new IllegalArgumentException("No e-mail subject");

            // Body is required
            body = mail.getBody();
            if (body == null) throw new IllegalArgumentException("No e-mail body");
        }
        catch (AddressException ae)
        {
            throw new MailingException("One or more addresses of the message are invalid", ae);
        }

        try
        {
            // prepare message to be sent
            Message m = new MimeMessage(session);

            // set "From" address
            m.setFrom( from );

            // set "To" addresses
            m.setRecipients(Message.RecipientType.TO, to);

            // set "Cc" addresses
            if (cc != null)
               m.setRecipients(Message.RecipientType.CC, cc);

            // set subject
            m.setSubject(subject);

            // set body
            m.setText(body);

            // send it now
            Transport.send(m);
        }
        catch (MessagingException me)
        {
            throw new MailingException("Unable to send the message", me);
        }
    }
}