package org.codemonkey.simplejavamail;

import java.io.UnsupportedEncodingException;
import java.util.Date;
import java.util.Map;
import java.util.Properties;

import javax.activation.DataHandler;
import javax.activation.DataSource;
import javax.mail.Address;
import javax.mail.Authenticator;
import javax.mail.BodyPart;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Part;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeBodyPart;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMultipart;
import javax.mail.internet.MimeUtility;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Mailing tool aimed for simplicity, for sending e-mails of any complexity. This includes e-mails with plain text and/or html content,
 * embedded images and separate attachments, SMTP, SMTPS / SSL and SMTP + SSL<br>
 * <br>
 * This mailing tool abstracts the javax.mail API to a higher level easy to use API. For public use, this tool only works with {@link Email}
 * instances. <br>
 * <br>
 * The e-mail message structure is built to work with all e-mail clients and has been tested with many different webclients as well as some
 * mainstream client applications such as MS Outlook or Mozilla Thunderbird.<br>
 * <br>
 * Technically, the resulting email structure is as follows:<br>
 * 
 * <pre>
 * - root
 *      - related
 *              - alternative
 *                      - mail text
 *                      - mail html text
 *              - embedded images
 *      - attachments
 * </pre>
 * 
 * <br>
 * Usage example:<br>
 * 
 * <pre>
 * Email email = new Email();
 * email.setFromAddress(&quot;lollypop&quot;, &quot;lolly.pop@somemail.com&quot;);
 * email.addRecipient(&quot;Sugar Cane&quot;, &quot;sugar.cane@candystore.org&quot;, RecipientType.TO);
 * email.setText(&quot;We should meet up!!&quot;);
 * email.setTextHTML(&quot;&lt;b&gt;We should meet up!&lt;/b&gt;&quot;);
 * email.setSubject(&quot;Hey&quot;);
 * new Mailer(preconfiguredMailSession).sendMail(email);
 * // or:
 * new Mailer(&quot;smtp.someserver.com&quot;, 25, &quot;username&quot;, &quot;password&quot;).sendMail(email);
 * </pre>
 * 
 * @author Benny Bottema
 * @see MimeEmailMessageWrapper
 * @see Email
 */
public class Mailer {

        private static final Logger logger = LoggerFactory.getLogger(Mailer.class);

        /**
         * Encoding used for setting body text, email address, headers, reply-to fields etc. ({@value #CHARACTER_ENCODING}).
         */
        private static final String CHARACTER_ENCODING = "UTF-8";

        /**
         * Used to actually send the email. This session can come from being passed in the default constructor, or made by <code>Mailer</code>
         * directly, when no <code>Session</code> instance was provided.
         * 
         * @see #Mailer(Session)
         * @see #Mailer(String, Integer, String, String, TransportStrategy)
         */
        private final Session session;

        /**
         * The transport protocol strategy enum that actually handles the session configuration. Session configuration meaning setting the right
         * properties for the appropriate transport type (ie. <em>"mail.smtp.host"</em> for SMTP, <em>"mail.smtps.host"</em> for SMTPS).
         */
        private TransportStrategy transportStrategy;

        /**
         * Email address restriction flags set either by constructor or overridden by getter by user.
         * 
         * @see EmailAddressValidationCriteria
         */
        private EmailAddressValidationCriteria emailAddressValidationCriteria;

        /**
         * Default constructor, stores the given mail session for later use. Assumes that *all* properties used to make a connection are
         * configured (host, port, authentication and transport protocol settings).
         * <p>
         * Also leaves email address validation criteria empty so that no validation is being performed. Validation errors will come from the
         * smtp server instead.
         * 
         * @param session A preconfigured mail {@link Session} object with which a {@link Message} can be produced.
         */
        public Mailer(final Session session) {
                this.session = session;
                this.emailAddressValidationCriteria = null;
        }

        /**
         * Overloaded constructor which produces a new {@link Session} on the fly. Use this if you don't have a mail session configured in your
         * web container, or Spring context etc.
         * <p>
         * Also leaves email address validation criteria empty so that no validation is being performed. Validation errors will come from the
         * smtp server instead.
         * 
         * @param host The address URL of the SMTP server to be used.
         * @param port The port of the SMTP server.
         * @param username An optional username, may be <code>null</code>.
         * @param password An optional password, may be <code>null</code>, but only if username is <code>null</code> as well.
         * @param transportStrategy The transport protocol configuration type for handling SSL or TLS (or vanilla SMTP)
         */
        public Mailer(final String host, final Integer port, final String username, final String password,
                        final TransportStrategy transportStrategy) {
                // we're doing these validations manually instead of using Apache Commons to avoid another dependency
                if (host == null || host.trim().equals("")) {
                        throw new MailException(MailException.MISSING_HOST);
                } else if ((password != null && !password.trim().equals("")) && (username == null || username.trim().equals(""))) {
                        throw new MailException(MailException.MISSING_USERNAME);
                }
                this.transportStrategy = transportStrategy;
                this.session = createMailSession(host, port, username, password);
                this.emailAddressValidationCriteria = null;
        }

        /**
         * Actually instantiates and configures the {@link Session} instance. Delegates resolving transport protocol specific properties to the
         * {@link #transportStrategy} in two ways:
         * <ol>
         * <li>request an initial property list which the strategy may pre-populate</li>
         * <li>by requesting the property names according to the respective transport protocol it handles (for the host property for example it
         * would be <em>"mail.smtp.host"</em> for SMTP and <em>"mail.smtps.host"</em> for SMTPS)</li>
         * </ol>
         * 
         * @param host The address URL of the SMTP server to be used.
         * @param port The port of the SMTP server.
         * @param username An optional username, may be <code>null</code>.
         * @param password An optional password, may be <code>null</code>.
         * @return A fully configured <code>Session</code> instance complete with transport protocol settings.
         * @see TransportStrategy#generateProperties()
         * @see TransportStrategy#propertyNameHost()
         * @see TransportStrategy#propertyNamePort()
         * @see TransportStrategy#propertyNameUsername()
         * @see TransportStrategy#propertyNameAuthenticate()
         */
        protected Session createMailSession(final String host, final Integer port, final String username, final String password) {
                if (transportStrategy == null) {
                        logger.warn("Transport Strategy not set, using plain SMTP strategy instead!");
                        transportStrategy = TransportStrategy.SMTP_PLAIN;
                }
                Properties props = transportStrategy.generateProperties();
                props.put(transportStrategy.propertyNameHost(), host);
                if (port != null) {
                        props.put(transportStrategy.propertyNamePort(), String.valueOf(port));
                } else {
                        // let JavaMail's Transport objects determine deault port base don the used protocol
                }

                if (username != null) {
                        props.put(transportStrategy.propertyNameUsername(), username);
                }

                if (password != null) {
                        props.put(transportStrategy.propertyNameAuthenticate(), "true");
                        return Session.getInstance(props, new Authenticator() {
                                @Override
                                protected PasswordAuthentication getPasswordAuthentication() {
                                        return new PasswordAuthentication(username, password);
                                }
                        });
                } else {
                        return Session.getInstance(props);
                }
        }

        /**
         * Overloaded constructor which produces a new {@link Session} on the fly, using default vanilla SMTP transport protocol.
         * 
         * @param host The address URL of the SMTP server to be used.
         * @param port The port of the SMTP server.
         * @param username An optional username, may be <code>null</code>.
         * @param password An optional password, may be <code>null</code>, but only if username is <code>null</code> as well.
         * @see #Mailer(String, Integer, String, String, TransportStrategy)
         */
        public Mailer(final String host, final Integer port, final String username, final String password) {
                this(host, port, username, password, TransportStrategy.SMTP_PLAIN);
        }

        /**
         * In case Simple Java Mail falls short somehow, you can get a hold of the internal {@link Session} instance to debug or tweak. Please
         * let us know why you are needing this on https://github.com/bbottema/simple-java-mail/issues.
         */
        public Session getSession() {
                logger.warn("Providing access to Session instance for emergency fall-back scenario. Please let us know why you need it.");
                logger.warn("\t>https://github.com/bbottema/simple-java-mail/issues");
                return session;
        }

        /**
         * Actually sets {@link Session#setDebug(boolean)} so that it generates debug information.
         * 
         * @param debug Flag to indicate debug mode yes/no.
         */
        public void setDebug(final boolean debug) {
                session.setDebug(debug);
        }

        /**
         * Copies all property entries into the {@link Session} using {@link Session#getProperties()}.
         * 
         * @param properties The source properties to add or override in the internal {@link Session} instance.
         */
        public void applyProperties(final Properties properties) {
                session.getProperties().putAll(properties);
        }

        /**
         * Processes an {@link Email} instance into a completely configured {@link Message}.
         * <p>
         * Sends the Sun JavaMail {@link Message} object using {@link Session#getTransport()}. It will call {@link Transport#connect()} assuming
         * all connection details have been configured in the provided {@link Session} instance.
         * <p>
         * Performs a call to {@link Message#saveChanges()} as the Sun JavaMail API indicates it is needed to configure the message headers and
         * providing a message id.
         * 
         * @param email The information for the email to be sent.
         * @throws MailException Can be thrown if an email isn't validating correctly, or some other problem occurs during connection, sending
         *             etc.
         * @see #validate(Email)
         * @see #prepareMessage(Email, MimeEmailMessageWrapper)
         * @see #setRecipients(Email, Message)
         * @see #setTexts(Email, MimeMultipart)
         * @see #setEmbeddedImages(Email, MimeMultipart)
         * @see #setAttachments(Email, MimeMultipart)
         */
        public final void sendMail(final Email email)
                        throws MailException {
                if (validate(email)) {
                        try {
                                // create new wrapper for each mail being sent (enable sending multiple emails with one mailer)
                                final MimeEmailMessageWrapper messageRoot = new MimeEmailMessageWrapper();
                                // fill and send wrapped mime message parts
                                final Message message = prepareMessage(email, messageRoot);
                                logSession(session, transportStrategy);
                                message.saveChanges(); // some headers and id's will be set for this specific message
                                Transport transport = session.getTransport();
                                transport.connect();
                                transport.sendMessage(message, message.getAllRecipients());
                                transport.close();
                        } catch (final UnsupportedEncodingException e) {
                                logger.error(e.getMessage(), e);
                                throw new MailException(String.format(MailException.INVALID_ENCODING, e.getMessage()));
                        } catch (final MessagingException e) {
                                logger.error(e.getMessage(), e);
                                throw new MailException(String.format(MailException.GENERIC_ERROR, e.getMessage()), e);
                        }
                }
        }

        /**
         * Simply logs host details, credentials used and whether authentication will take place and finally the transport protocol used.
         */
        private void logSession(Session session, TransportStrategy transportStrategy) {
                Properties properties = session.getProperties();
                final String specifics;
                if (transportStrategy != null) {
                        final String logmsg = "starting mail session (host: %s, port: %s, username: %s, authenticate: %s, transport: %s)";
                        specifics = String.format(logmsg, properties.get(transportStrategy.propertyNameHost()),
                                        properties.get(transportStrategy.propertyNamePort()), properties.get(transportStrategy.propertyNameUsername()),
                                        properties.get(transportStrategy.propertyNameAuthenticate()), transportStrategy);
                } else {
                        specifics = properties.toString();
                }
                logger.debug(String.format("starting mail session (%s)", specifics));
        }

        /**
         * Validates an {@link Email} instance. Validation fails if the subject is missing, content is missing, or no recipients are defined.
         * 
         * @param email The email that needs to be configured correctly.
         * @return Always <code>true</code> (throws a {@link MailException} exception if validation fails).
         * @throws MailException Is being thrown in any of the above causes.
         * @see EmailValidationUtil
         */
        public boolean validate(final Email email)
                        throws MailException {
                if (email.getText() == null && email.getTextHTML() == null) {
                        throw new MailException(MailException.MISSING_CONTENT);
                } else if (email.getSubject() == null || email.getSubject().equals("")) {
                        throw new MailException(MailException.MISSING_SUBJECT);
                } else if (email.getRecipients().size() == 0) {
                        throw new MailException(MailException.MISSING_RECIPIENT);
                } else if (email.getFromRecipient() == null) {
                        throw new MailException(MailException.MISSING_SENDER);
                } else if (emailAddressValidationCriteria != null) {
                        if (!EmailValidationUtil.isValid(email.getFromRecipient().getAddress(), emailAddressValidationCriteria)) {
                                throw new MailException(String.format(MailException.INVALID_SENDER, email));
                        }
                        for (final Recipient recipient : email.getRecipients()) {
                                if (!EmailValidationUtil.isValid(recipient.getAddress(), emailAddressValidationCriteria)) {
                                        throw new MailException(String.format(MailException.INVALID_RECIPIENT, email));
                                }
                        }
                        if (email.getReplyToRecipient() != null) {
                                if (!EmailValidationUtil.isValid(email.getReplyToRecipient().getAddress(), emailAddressValidationCriteria)) {
                                        throw new MailException(String.format(MailException.INVALID_REPLYTO, email));
                                }
                        }
                }
                return true;
        }

        /**
         * Creates a new {@link MimeMessage} instance and prepares it in the email structure, so that it can be filled and send.
         * <p>
         * Fills subject, from,reply-to, content, sent-date, recipients, texts, embedded images, attachments, content and adds all headers.
         * 
         * @param email The email message from which the subject and From-address are extracted.
         * @param messageRoot The root of the email which holds everything (filled with some email data).
         * @return A fully preparated {@link Message} instance, ready to be sent.
         * @throws MessagingException May be thrown when the message couldn't be processed by JavaMail.
         * @throws UnsupportedEncodingException Zie {@link InternetAddress#InternetAddress(String, String)}.
         */
        private Message prepareMessage(final Email email, final MimeEmailMessageWrapper messageRoot)
                        throws MessagingException, UnsupportedEncodingException {
                final MimeMessage message = new MimeMessage(session);
                // set basic email properties
                message.setSubject(email.getSubject(), CHARACTER_ENCODING);
                message.setFrom(new InternetAddress(email.getFromRecipient().getAddress(), email.getFromRecipient().getName(), CHARACTER_ENCODING));
                setReplyTo(email, message);
                setRecipients(email, message);
                // fill multipart structure
                setTexts(email, messageRoot.multipartAlternativeMessages);
                setEmbeddedImages(email, messageRoot.multipartRelated);
                setAttachments(email, messageRoot.multipartRoot);
                message.setContent(messageRoot.multipartRoot);
                setHeaders(email, message);
                message.setSentDate(new Date());
                return message;
        }

        /**
         * Fills the {@link Message} instance with recipients from the {@link Email}.
         * 
         * @param email The message in which the recipients are defined.
         * @param message The javax message that needs to be filled with recipients.
         * @throws UnsupportedEncodingException See {@link InternetAddress#InternetAddress(String, String)}.
         * @throws MessagingException See {@link Message#addRecipient(javax.mail.Message.RecipientType, Address)}
         */
        private void setRecipients(final Email email, final Message message)
                        throws UnsupportedEncodingException, MessagingException {
                for (final Recipient recipient : email.getRecipients()) {
                        final Address address = new InternetAddress(recipient.getAddress(), recipient.getName(), CHARACTER_ENCODING);
                        message.addRecipient(recipient.getType(), address);
                }
        }

        /**
         * Fills the {@link Message} instance with reply-to address.
         * 
         * @param email The message in which the recipients are defined.
         * @param message The javax message that needs to be filled with reply-to address.
         * @throws UnsupportedEncodingException See {@link InternetAddress#InternetAddress(String, String)}.
         * @throws MessagingException See {@link Message#setReplyTo(Address[])}
         */
        private void setReplyTo(final Email email, final Message message)
                        throws UnsupportedEncodingException, MessagingException {
                final Recipient replyToRecipient = email.getReplyToRecipient();
                if (replyToRecipient != null) {
                        InternetAddress replyToAddress = new InternetAddress(replyToRecipient.getAddress(), replyToRecipient.getName(),
                                        CHARACTER_ENCODING);
                        message.setReplyTo(new Address[] { replyToAddress });
                }
        }

        /**
         * Fills the {@link Message} instance with the content bodies (text and html).
         * 
         * @param email The message in which the content is defined.
         * @param multipartAlternativeMessages See {@link MimeMultipart#addBodyPart(BodyPart)}
         * @throws MessagingException See {@link BodyPart#setText(String)}, {@link BodyPart#setContent(Object, String)} and
         *             {@link MimeMultipart#addBodyPart(BodyPart)}.
         */
        private void setTexts(final Email email, final MimeMultipart multipartAlternativeMessages)
                        throws MessagingException {
                if (email.getText() != null) {
                        final MimeBodyPart messagePart = new MimeBodyPart();
                        messagePart.setText(email.getText(), CHARACTER_ENCODING);
                        multipartAlternativeMessages.addBodyPart(messagePart);
                }
                if (email.getTextHTML() != null) {
                        final MimeBodyPart messagePartHTML = new MimeBodyPart();
                        messagePartHTML.setContent(email.getTextHTML(), "text/html; charset=\"" + CHARACTER_ENCODING + "\"");
                        multipartAlternativeMessages.addBodyPart(messagePartHTML);
                }
        }

        /**
         * Fills the {@link Message} instance with the embedded images from the {@link Email}.
         * 
         * @param email The message in which the embedded images are defined.
         * @param multipartRelated The branch in the email structure in which we'll stuff the embedded images.
         * @throws MessagingException See {@link MimeMultipart#addBodyPart(BodyPart)} and
         *             {@link #getBodyPartFromDatasource(AttachmentResource, String)}
         */
        private void setEmbeddedImages(final Email email, final MimeMultipart multipartRelated)
                        throws MessagingException {
                for (final AttachmentResource embeddedImage : email.getEmbeddedImages()) {
                        multipartRelated.addBodyPart(getBodyPartFromDatasource(embeddedImage, Part.INLINE));
                }
        }

        /**
         * Fills the {@link Message} instance with the attachments from the {@link Email}.
         * 
         * @param email The message in which the attachments are defined.
         * @param multipartRoot The branch in the email structure in which we'll stuff the attachments.
         * @throws MessagingException See {@link MimeMultipart#addBodyPart(BodyPart)} and
         *             {@link #getBodyPartFromDatasource(AttachmentResource, String)}
         */
        private void setAttachments(final Email email, final MimeMultipart multipartRoot)
                        throws MessagingException {
                for (final AttachmentResource resource : email.getAttachments()) {
                        multipartRoot.addBodyPart(getBodyPartFromDatasource(resource, Part.ATTACHMENT));
                }
        }

        /**
         * Sets all headers on the {@link Message} instance. Since we're not using a high-level JavaMail method, the JavaMail library says we
         * need to do some encoding and 'folding' manually, to get the value right for the headers (see {@link MimeUtility}.
         * 
         * @param email The message in which the headers are defined.
         * @param message The {@link Message} on which to set the raw, encoded and folded headers.
         * @throws UnsupportedEncodingException See {@link MimeUtility#encodeText(String, String, String)}
         * @throws MessagingException See {@link Message#addHeader(String, String)}
         * @see {@link MimeUtility#encodeText(String, String, String)}
         * @see MimeUtility#fold(int, String)
         */
        private void setHeaders(final Email email, final Message message)
                        throws UnsupportedEncodingException, MessagingException {
                // add headers (for raw message headers we need to 'fold' them using MimeUtility
                for (Map.Entry<String, String> header : email.getHeaders().entrySet()) {
                        String headerName = header.getKey();
                        String headerValue = MimeUtility.encodeText(header.getValue(), CHARACTER_ENCODING, null);
                        String foldedHeaderValue = MimeUtility.fold(headerName.length() + 2, headerValue);
                        message.addHeader(header.getKey(), foldedHeaderValue);
                }
        }

        /**
         * Helper method which generates a {@link BodyPart} from an {@link AttachmentResource} (from its {@link DataSource}) and a disposition
         * type ({@link Part#INLINE} or {@link Part#ATTACHMENT}). With this the attachment data can be converted into objects that fit in the
         * email structure. <br>
         * <br>
         * For every attachment and embedded image a header needs to be set.
         * 
         * @param resource An object that describes the attachment and contains the actual content data.
         * @param dispositionType The type of attachment, {@link Part#INLINE} or {@link Part#ATTACHMENT} .
         * @return An object with the attachment data read for placement in the email structure.
         * @throws MessagingException All BodyPart setters.
         */
        private BodyPart getBodyPartFromDatasource(final AttachmentResource resource, final String dispositionType)
                        throws MessagingException {
                final BodyPart attachmentPart = new MimeBodyPart();
                final DataSource ds = resource.getDataSource();
                // setting headers isn't working nicely using the javax mail API, so let's do that manually
                attachmentPart.setDataHandler(new DataHandler(resource.getDataSource()));
                attachmentPart.setFileName(resource.getName());
                attachmentPart.setHeader("Content-Type", ds.getContentType() + "; filename=" + ds.getName() + "; name=" + ds.getName());
                attachmentPart.setHeader("Content-ID", String.format("<%s>", ds.getName()));
                attachmentPart.setDisposition(dispositionType + "; size=0");
                return attachmentPart;
        }

        /**
         * This class conveniently wraps all necessary mimemessage parts that need to be filled with content, attachments etc. The root is
         * ultimately sent using JavaMail.<br>
         * <br>
         * The constructor creates a new email message constructed from {@link MimeMultipart} as follows:
         * 
         * <pre>
         * - root
         *      - related
         *              - alternative
         *                      - mail tekst
         *                      - mail html tekst
         *              - embedded images
         *      - attachments
         * </pre>
         * 
         * @author Benny Bottema
         */
        private class MimeEmailMessageWrapper {

                private final MimeMultipart multipartRoot;

                private final MimeMultipart multipartRelated;

                private final MimeMultipart multipartAlternativeMessages;

                /**
                 * Creates an email skeleton structure, so that embedded images, attachments and (html) texts are being processed properly.
                 */
                MimeEmailMessageWrapper() {
                        multipartRoot = new MimeMultipart("mixed");
                        final MimeBodyPart contentRelated = new MimeBodyPart();
                        multipartRelated = new MimeMultipart("related");
                        final MimeBodyPart contentAlternativeMessages = new MimeBodyPart();
                        multipartAlternativeMessages = new MimeMultipart("alternative");
                        try {
                                // construct mail structure
                                multipartRoot.addBodyPart(contentRelated);
                                contentRelated.setContent(multipartRelated);
                                multipartRelated.addBodyPart(contentAlternativeMessages);
                                contentAlternativeMessages.setContent(multipartAlternativeMessages);
                        } catch (final MessagingException e) {
                                logger.error(e.getMessage(), e);
                                throw new RuntimeException(e.getMessage(), e);
                        }
                }
        }

        /**
         * Overrides the default email address validation restrictions when validating and sending emails using the current <code>Mailer</code>
         * instance. By default no validation will be performed by simple-java-mail, until a criteria object has been set.
         * 
         * @param emailAddressValidationCriteria Refer to
         *            {@link EmailAddressValidationCriteria#EmailAddressValidationCriteria(boolean, boolean)}.
         */
        public void setEmailAddressValidationCriteria(EmailAddressValidationCriteria emailAddressValidationCriteria) {
                this.emailAddressValidationCriteria = emailAddressValidationCriteria;
        }
}