// Copyright 2000-2005 the Contributors, as shown in the revision logs.
// Licensed under the Apache Public Source License 2.0 ("the License").
// You may not use this file except in compliance with the License.

package org.ibex.mail;
import org.ibex.mail.target.*;
import org.ibex.util.*;
import org.ibex.net.*;
import org.ibex.io.*;
import java.net.*;
import java.io.*;
import java.util.*;
import java.text.*;
import javax.naming.*;
import javax.naming.directory.*;

// FIXME: inbound throttling/ratelimiting

// "Address enumeration detection" -- notice when it looks like somebody
// is trying a raft of addresses.

// RFC's implemented
// RFC2554: SMTP Service Extension for Authentication
//     - did not implement section 5, though
// RFC4616: SASL PLAIN

// Note: we can't actually use status codes for feedback if we accept
// multiple destination addresses...  a failure on one and success on
// the other...

// FIXME: logging: current logging sucks
// FIXME: loop prevention
// FIXME: probably need some throttling on outbound mail

// FEATURE: public static boolean validate(Address a)
// FEATURE: rate-limiting

// FEATURE: infer messageid, date, if not present (?)
// FEATURE: exponential backoff on retry time?
// FEATURE: RFC2822, section 4.5.1: special "postmaster" address
// FEATURE: RFC2822, section 4.5.4.1: retry strategies
// FEATURE: RFC2822, section 5, multiple MX records, preferences, ordering
// FEATURE: RFC2822, end of 4.1.2: backslashes in headers
public class SMTP {

    public static final SimpleDateFormat dateFormat = new SimpleDateFormat("EEE, d MMM yyyy HH:mm:ss Z");
    public static final int numOutgoingThreads = 5;

    private static final SqliteMailbox allmail =
        (SqliteMailbox)FileBasedMailbox
        .getFileBasedMailbox("/afs/megacz.com/mail/user/megacz/allmail", false);

    public static final int GRAYLIST_MINWAIT =  1000 * 60 * 60;           // one hour
    public static final int GRAYLIST_MAXWAIT =  1000 * 60 * 60 * 24 * 5;  // five days

    public static final int RETRY_TIME = 1000 * 60 * 30;

    public static final Graylist graylist;
    public static final Whitelist whitelist;
    static {
        try {
            graylist =  new Graylist(Mailbox.STORAGE_ROOT+"/db/graylist.sqlite");
            whitelist = new Whitelist(Mailbox.STORAGE_ROOT+"/db/whitelist.sqlite");
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public static final int MAX_MESSAGE_SIZE =
        Integer.parseInt(System.getProperty("org.ibex.mail.smtp.maxMessageSize", "-1"));

    private static final Mailbox spool =
        FileBasedMailbox.getFileBasedMailbox(Mailbox.STORAGE_ROOT,false).slash("spool",true).slash("smtp",true).getMailbox();

    static {
        for(int i=0; i<numOutgoingThreads; i++)
            new Outgoing().start();
    }

    public static void enqueue(Message m) throws IOException {
        if (!m.envelopeTo.isLocal()) Outgoing.enqueue(m);
        else {
            try {
                allmail.accept(m);
            } catch (Exception e) {
                // FIXME incredibly gross hack
                if (e.toString().indexOf("attempt to insert two messages with identical messageid")==-1)
                    Log.error(SMTP.class, e);
            }
            Target.root.accept(m);
        }
    }

    public static class SMTPException extends MailException {
        int code;
        String message;
        public SMTPException(String s) {
            try {
                code = Integer.parseInt(s.substring(0, s.indexOf(' ')));
                message = s.substring(s.indexOf(' ')+1);
            } catch (NumberFormatException nfe) {
                code = -1;
                message = s;
            }
        }
        public String toString() { return "SMTP " + code + ": " + message; }
        public String getMessage() { return toString(); }
    }

    // Server //////////////////////////////////////////////////////////////////////////////

    public static class Server {
        public void handleRequest(Connection conn) throws IOException {
            conn.setTimeout(5 * 60 * 1000);
            conn.setNewline("\r\n");
            conn.println("220 " + conn.vhost + " ESMTP " + this.getClass().getName());
            Address from = null;
            Vector to = new Vector();
            boolean ehlo = false;
            String remotehost = null;
            String authenticatedAs = null;
            int failedRcptCount = 0;
            for(String command = conn.readln(); ; command = conn.readln()) try {
                if (command == null) return;
                Log.warn("**"+conn.getRemoteAddress()+"**", command);
                String c = command.toUpperCase();
                if (c.startsWith("HELO"))        {
                    remotehost = c.substring(5).trim();
                    conn.println("250 HELO " + conn.vhost);
                    from = null; to = new Vector();
                } else if (c.startsWith("EHLO")) {
                    remotehost = c.substring(5).trim();
                    conn.println("250-"+conn.vhost);
                    //conn.println("250-AUTH");
                    conn.println("250-AUTH PLAIN");
                    //conn.println("250-STARTTLS");
                    conn.println("250 HELP");
                    ehlo = true;     
                    from = null; to = new Vector();
                } else if (c.startsWith("RSET")) { conn.println("250 reset ok");           from = null; to = new Vector();
                } else if (c.startsWith("HELP")) { conn.println("214 you are beyond help.  see a trained professional.");
                } else if (c.startsWith("VRFY")) { conn.println("502 VRFY not supported");
                } else if (c.startsWith("EXPN")) { conn.println("502 EXPN not supported");
                } else if (c.startsWith("NOOP")) { conn.println("250 OK");
                } else if (c.startsWith("QUIT")) { conn.println("221 " + conn.vhost + " closing connection"); return;
                } else if (c.startsWith("STARTTLS")) {
                    conn.println("220 starting TLS...");
                    conn.flush();
                    conn = conn.negotiateSSL(true);
                    from = null; to = new Vector();
                } else if (c.startsWith("AUTH")) {
                    if (authenticatedAs != null) {
                        conn.println("503 you are already authenticated; you must reconnect to reauth");
                    } else {
                        String mechanism = command.substring(4).trim();
                        String rest = "";
                        if (mechanism.indexOf(' ')!=-1) {
                            rest      = mechanism.substring(mechanism.indexOf(' ')+1).trim();
                            mechanism = mechanism.substring(0, mechanism.indexOf(' '));
                        }
                        if (mechanism.equals("PLAIN")) {
                            // 538 Encryption required for requested authentication mechanism?
                            byte[] bytes = Encode.fromBase64(rest);
                            String authenticateUser = null;
                            String authorizeUser = null;
                            String password = null;
                            int start = 0;
                            for(int i=0; i<=bytes.length; i++) {
                                if (i<bytes.length && bytes[i]!=0) continue;
                                String result = new String(bytes, start, i-start, "UTF-8");
                                if (authenticateUser==null)   authenticateUser = result;
                                else if (authorizeUser==null) authorizeUser = result;
                                else if (password==null)      password = result;
                                start = i+1;
                            }
                            // FIXME: be smarter here
                            if (Main.auth.login(authorizeUser, password)!=null)
                                authenticatedAs = authenticateUser;
                            conn.println("235 Authentication successful");
                            /*
                        } else if (mechanism.equals("CRAM-MD5")) {
                            String challenge = ;
                            conn.println("334 "+challenge);
                            String resp = conn.readln();
                            if (resp.equals("*")) {
                                conn.println("501 client requested AUTH cancellation");
                            }
                        } else if (mechanism.equals("ANONYMOUS")) {
                        } else if (mechanism.equals("EXTERNAL")) {
                        } else if (mechanism.equals("DIGEST-MD5")) {
                            */
                        } else {
                            conn.println("504 unrecognized authentication type");
                        }
                        // on success, reset to initial state; client will EHLO again
                        from = null; to = new Vector();
                    }
                } else if (c.startsWith("MAIL FROM:")) {
                    command = command.substring(10).trim();
                    from = command.equals("<>") ? null : new Address(command);
                    conn.println("250 " + from + " is syntactically correct");
                    // Don't perform SAV; discouraged here
                    //   http://blog.fastmail.fm/2007/12/05/sending-email-servers-best-practice/
                } else if (c.startsWith("RCPT TO:")) {
                    // some clients are broken and put RCPT first; we will tolerate this
                    command = command.substring(8).trim();
                    if(command.indexOf(' ') != -1) command = command.substring(0, command.indexOf(' '));
                    Address addr = new Address(command);
                    if (conn.getRemoteAddress().isLoopbackAddress() || (from!=null&&from.toString().indexOf("johnw")!=-1)) {
                        conn.println("250 you are connected locally, so I will let you send");
                        to.addElement(addr);
                        if (!whitelist.isWhitelisted(addr))
                            whitelist.addWhitelist(addr);
                    } else if (authenticatedAs!=null) {
                        conn.println("250 you are authenticated as "+authenticatedAs+", so I will let you send");
                        to.addElement(addr);
                        if (!whitelist.isWhitelisted(addr))
                            whitelist.addWhitelist(addr);
                    } else if (addr.isLocal()) {
                        if (to.size() > 3) {
                            conn.println("536 sorry, limit on 3 RCPT TO's per DATA");
                        } else {
                            // FEATURE: should check the address further and give 550 if undeliverable
                            conn.println("250 " + addr + " is on this machine; I will deliver it");
                            to.addElement(addr);
                        }
                    } else {
                        conn.println("535 sorry, " + addr + " is not on this machine, you are not connected from localhost, and I will not relay without SMTP AUTH");
                        Log.warn("","535 sorry, " + addr + " is not on this machine, you are not connected from localhost, and I will not relay without SMTP AUTH");
                        failedRcptCount++;
                        if (failedRcptCount > 3) {
                            conn.close();
                            return;
                        }
                    }
                    conn.flush();
                } else if (c.startsWith("DATA")) {
                    //if (from == null) { conn.println("503 MAIL FROM command must precede DATA"); continue; }
                    if (to == null || to.size()==0) { conn.println("503 RCPT TO command must precede DATA"); continue; }
                    if (!graylist.isWhitelisted(conn.getRemoteAddress()) && !conn.getRemoteAddress().isLoopbackAddress() && authenticatedAs==null) {
                        long when = graylist.getGrayListTimestamp(conn.getRemoteAddress(), from+"", to+"");
                        if (when == 0 || System.currentTimeMillis() - when > GRAYLIST_MAXWAIT) {
                            graylist.setGrayListTimestamp(conn.getRemoteAddress(), from+"", to+"",  System.currentTimeMillis());
                            conn.println("451 you are graylisted; please try back in one hour to be whitelisted");
                            Log.warn(conn.getRemoteAddress().toString(), "451 you are graylisted; please try back in one hour to be whitelisted");
                            conn.flush();
                            continue;
                        } else if (System.currentTimeMillis() - when > GRAYLIST_MINWAIT) {
                            graylist.addWhitelist(conn.getRemoteAddress());
                            conn.println("354 (you have been whitelisted) Enter message, ending with \".\" on a line by itself");
                            Log.warn(conn.getRemoteAddress().toString(), "has been whitelisted");
                        } else {
                            conn.println("451 you are still graylisted (since "+new java.util.Date(when)+")");
                            conn.flush();
                            Log.warn(conn.getRemoteAddress().toString(), "451 you are still graylisted (since "+new java.util.Date(when)+")");
                            continue;
                        }
                    } else {
                        conn.println("354 Enter message, ending with \".\" on a line by itself");
                    }
                    conn.flush();
                    try {
                        // FIXME: deal with messages larger than memory here?
                        StringBuffer buf = new StringBuffer();
                        buf.append("Received: from " + conn.getRemoteHostname() + " (" + remotehost + ")\r\n");
                        buf.append("          by "+conn.vhost+" ("+SMTP.class.getName()+") with "+(ehlo?"ESMTP":"SMTP") + "\r\n");
                        buf.append("          for ");
                        // FIXME: this is leaking BCC addrs
                        // for(int i=0; i<to.size(); i++) buf.append(to.elementAt(i) + " ");
                        buf.append("; " + dateFormat.format(new Date()) + "\r\n");

                        // FIXME: some sort of stream transformer here?
                        while(true) {
                            String s = conn.readln();
                            if (s == null) throw new RuntimeException("connection closed");
                            if (s.equals(".")) break;
                            if (s.startsWith(".")) s = s.substring(1);
                            buf.append(s + "\r\n");
                            if (MAX_MESSAGE_SIZE != -1 && buf.length() > MAX_MESSAGE_SIZE && (from+"").indexOf("paperless")==-1) {
                                Log.error("**"+conn.getRemoteAddress()+"**",
                                          "sorry, this mail server only accepts messages of less than " +
                                          ByteSize.toString(MAX_MESSAGE_SIZE));
                                throw new MailException.Malformed("sorry, this mail server only accepts messages of less than " +
                                                                  ByteSize.toString(MAX_MESSAGE_SIZE));
                            }
                        }
                        String message = buf.toString();
                        Message m = null;
                        for(int i=0; i<to.size(); i++)
                            enqueue(m = Message.newMessage(Fountain.Util.create(message)).withEnvelope(from, (Address)to.elementAt(i)));
                        if (m != null) Log.info(SMTP.class, "accepted message: " + m.summary());
                        conn.println("250 message accepted");
                        conn.flush();
                        from = null; to = new Vector();
                    } catch (MailException.Malformed mfe) {    conn.println("501 " + mfe.toString());
                    } catch (MailException.MailboxFull mbf) {  conn.println("452 " + mbf);
                    } catch (Script.Later.LaterException le) { conn.println("453 try again later");
                    } catch (Script.Reject.RejectException re) {
			Log.warn(SMTP.class, "rejecting message due to: " + re.reason + "\n   " + re.m.summary());
			conn.println("501 " + re.reason);
                    }
                } else                    { conn.println("500 unrecognized command"); }                    
            } catch (Message.Malformed e) { conn.println("501 " + e.toString()); }
        }
    }


    // Outgoing Mail Thread //////////////////////////////////////////////////////////////////////////////

    public static class Outgoing extends Thread {

        private static final HashMap deadHosts = new HashMap();
        public static void enqueue(Message m) throws IOException {
            if (m == null) { Log.warn(Outgoing.class, "attempted to enqueue(null)"); return; }
            String traces = m.headers.get("Received");
            if (traces!=null) {
                int lines = 0;
                for(int i=0; i<traces.length(); i++)
                    if (traces.charAt(i)=='\n' || traces.charAt(i)=='\r')
                        lines++;
                if (lines > 100) { // required by rfc
                    Log.warn(SMTP.Outgoing.class, "Message with " + lines + " trace hops; dropping\n" + m.summary());
                    return;
                }
            }
            synchronized(Outgoing.class) {
                spool.insert(m, Mailbox.Flag.defaultFlags);
                Outgoing.class.notifyAll();
            }
        }

        public static boolean attempt(Message m) throws IOException { return attempt(m, false); }
        public static boolean attempt(Message m, boolean noBounces) throws IOException {
            if (m.envelopeTo == null) {
                Log.warn(SMTP.Outgoing.class, "aieeee, null envelopeTo: " + m.summary());
                return false;
            }
            InetAddress[] mx = getMailExchangerIPs(m.envelopeTo.host);
            if (mx.length == 0) {
		if (!noBounces) {
		    enqueue(m.bounce("could not resolve " + m.envelopeTo.host));
		    return true;
		} else {
		    Log.warn(SMTP.Outgoing.class, "could not resolve " + m.envelopeTo.host);
		    return false;
		}
            }
            if (new Date().getTime() - m.arrival.getTime() > 1000 * 60 * 60 * 24 * 5) {
		if (!noBounces) {
		    enqueue(m.bounce("could not send for 5 days"));
		    return true;
		} else {
		    Log.warn(SMTP.Outgoing.class, "could not send for 5 days: " + m.summary());
		    return false;
		}
            }
            for(int i=0; i<mx.length; i++) {
                //if (deadHosts.contains(mx[i])) continue;
                if (attempt(m, mx[i])) return true;
            }
            return false;
        }

        private static void check(String s, Connection conn) {
            if (s==null) return;
            while (s.length() > 3 && s.charAt(3) == '-') s = conn.readln();
            //if (s.startsWith("4")||s.startsWith("5")) throw new SMTPException(s);
            if (!s.startsWith("2")&&!s.startsWith("3")) throw new SMTPException(s);
        }
        private static boolean attempt(final Message m, final InetAddress mx) {
            boolean accepted = false;
            Connection conn = null;
            try {
                conn = new Connection(new Socket(mx, 25), InetAddress.getLocalHost().getHostName());
                InetAddress localAddress = conn.getSocket().getLocalAddress();
                String reverse = DNSUtil.reverseLookup(localAddress);
                Log.info(SMTP.Outgoing.class,
                         "outbound connection to " + mx + " uses " + localAddress + " [reverse: " + reverse + "]");
                InetAddress relookup = InetAddress.getByName(reverse);
                if (!relookup.equals(localAddress))
                    Log.error(SMTP.Outgoing.class,
                              "Warning: local machine fails forward-confirmed-reverse; " +
                              reverse + " resolves to " + localAddress);
                conn.setNewline("\r\n");
                conn.setTimeout(60 * 1000);
                check(conn.readln(), conn);  // banner
                try {
                    conn.println("EHLO " + reverse);
                    check(conn.readln(), conn);
                } catch (SMTPException smtpe) {
                    conn.println("HELO " + reverse);
                    check(conn.readln(), conn);
                }
                String envelopeFrom = m.envelopeFrom==null ? "" : m.envelopeFrom.toString();
                conn.println("MAIL FROM:<" + envelopeFrom +">");            check(conn.readln(), conn);
                conn.println("RCPT TO:<"   + m.envelopeTo.toString()+">");  check(conn.readln(), conn);
                conn.println("DATA");                                       check(conn.readln(), conn);

                Headers head = new Headers(m.headers,
                                           new String[] {
                                               "return-path", null,
                                               "bcc", null
                                           });
                Stream stream = head.getStream();
                for(String s = stream.readln(); s!=null; s=stream.readln()) {
                    if (s.startsWith(".")) conn.print(".");
                    conn.println(s);
                }
                conn.println("");
                stream = m.getBody().getStream();
                for(String s = stream.readln(); s!=null; s=stream.readln()) {
                    if (s.startsWith(".")) conn.print(".");
                    conn.println(s);
                }
                conn.println(".");
                String resp = conn.readln();
                if (resp == null)
                    throw new SMTPException("server " + mx + " closed connection without accepting message");
                check(resp, conn);
                Log.warn(SMTP.Outgoing.class, "success: " + mx + " accepted " + m.summary() + "\n["+resp+"]");
                accepted = true;
                conn.close();
            } catch (SMTPException e) {
                if (accepted) return true;
                Log.warn(SMTP.Outgoing.class, "    unable to send; error=" + e);
                Log.warn(SMTP.Outgoing.class, "      message: " + m.summary());
                Log.warn(SMTP.Outgoing.class, e);
                /*
                  // FIXME: we should not be bouncing here!
                if (e.code >= 500 && e.code <= 599) {
                    try {
                        attempt(m.bounce("unable to deliver: " + e), true);
                    } catch (Exception ex) {
                        Log.error(SMTP.Outgoing.class, "exception while trying to deliver bounce; giving up completely");
                        Log.error(SMTP.Outgoing.class, ex);
                    }
                    return true;
                }
                */
                return false;
            } catch (Exception e) {
                if (accepted) return true;
                Log.warn(SMTP.Outgoing.class, "    unable to send; error=" + e);
                Log.warn(SMTP.Outgoing.class, "      message: " + m.summary());
                Log.warn(SMTP.Outgoing.class, e);
                //if (conn != null) Log.warn(SMTP.Outgoing.class, conn.dumpLog());
                return false;
            } finally {
                if (conn != null) conn.close();
            }
            return accepted;
        }

        private static HashSet<Outgoing> threads = new HashSet<Outgoing>();
        private static int serials = 1;
        private int serial = serials++;
        private Mailbox.Iterator it;

        private static Map<String,Long> nextTry = Collections.synchronizedMap(new HashMap<String,Long>());

        public Outgoing() {
            synchronized(Outgoing.class) {
                threads.add(this);
            }
        }

        public void wake() {
            int count = spool.count(Query.all());
            Log.info(SMTP.Outgoing.class, "outgoing thread #"+serial+" woke up; " + count + " messages to send");
            try {
                while(true) {
                    boolean good = false;
                    synchronized(Outgoing.class) {
                        it = spool.iterator();
                        OUTER: for(; it.next(); ) {
                            for(Outgoing o : threads)
                                if (o!=this && o.it != null && o.it.uid()==it.uid())
                                    continue OUTER;
                            good = true;
                            break;
                        }
                    }
                    if (!good) break;
		    try {
                        String messageid = it.cur().messageid;
                        if (nextTry.get(messageid) == null || System.currentTimeMillis() > nextTry.get(messageid)) {
                            boolean ok = attempt(it.cur());
                            if (ok) it.delete();
                            else nextTry.put(messageid, System.currentTimeMillis() + RETRY_TIME);
                        }
		    } catch (Exception e) {
			Log.error(SMTP.Outgoing.class, e);
		    }
                    Log.info(this, "sleeping for 3s...");
                    Thread.sleep(3000);
                }
            } catch (Exception e) {
                //if (e instanceof InterruptedException) throw e;
                Log.error(SMTP.Outgoing.class, e);
            }
            Log.info(SMTP.Outgoing.class, "outgoing thread #"+serial+" going back to sleep");
            it = null;
        }

        public void run() {
            try {
                while(true) {
                    Log.setThreadAnnotation("[outgoing #"+serial+"] ");
                    wake();
                    Thread.sleep(1000);
                    synchronized(Outgoing.class) {
                        Outgoing.class.wait(5 * 60 * 1000);
                    }
                }
            } catch (InterruptedException e) { Log.warn(this, e); }
        }
    }

    public static InetAddress[] getMailExchangerIPs(String hostName) {
        InetAddress[] ret;
        try {
            Hashtable env = new Hashtable();
            env.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");
            DirContext ictx = new InitialDirContext(env);
            Attributes attrs = ictx.getAttributes(hostName, new String[] { "MX" });
            Attribute attr = attrs.get("MX");
            if (attr == null) {
                ret = new InetAddress[1];
                try {
                    ret[0] = InetAddress.getByName(hostName);
                    if (ret[0].equals(IP.getIP(127,0,0,1)) || ret[0].isLoopbackAddress()) throw new UnknownHostException();
                    return ret;
                } catch (UnknownHostException uhe) {
                    Log.warn(SMTP.class, "no MX hosts or A record for " + hostName);
                    return new InetAddress[0];
                }
            } else {
                ret = new InetAddress[attr.size()];
                NamingEnumeration ne = attr.getAll();
                for(int i=0; ne.hasMore();) {
                    String mx = (String)ne.next();
                    // FIXME we should be sorting here
                    mx = mx.substring(mx.indexOf(" ") + 1);
                    if (mx.charAt(mx.length() - 1) == '.') mx = mx.substring(0, mx.length() - 1);
                    InetAddress ia = InetAddress.getByName(mx);
                    if (ia.equals(IP.getIP(127,0,0,1)) || ia.isLoopbackAddress()) continue;
                    ret[i++] = ia;
                }
            }
        } catch (Exception e) {
            Log.warn(SMTP.class, "couldn't find MX host for " + hostName + " due to");
            Log.warn(SMTP.class, e);
            return new InetAddress[0];
        }
        return ret;
    }
}