import java.net.*;
import java.io.*;
import java.util.LinkedList;
import java.util.Iterator;

/**
 * Simulates a trivial SMTP server; calls Evolution (or another program)
 * to enable the user to edit and send the mail.
 *
 * Call: java SMTPEvolutionAdapter [port [mailCommand]]
 */
public class SMTPEvolutionAdapter {

    // the default port where the smtp server is listening
    private static final int DEFAULT_PORT = 25;
    
    // the default command line for the mail program
    // %r is replaced by the recipients, %s by the subject,
    // %c by the ccs, %b by the bccs and %t by the text of the mail
    private static final String DEFAULT_COMMAND 
        = "evolution mailto:%r?subject=%s&cc=%c&bcc=%b&body=%t";

    private String command = null;
    private ServerSocket theSocket = null;

    /**
     * 'main' function. Command line arguments can be:
     * - the port where the adapter shall listen
     * - the command to start the mail program
     * if the command is given, the port must be given, too.
     */
    public static void main (String[] args) {
	int portNr = DEFAULT_PORT;
	if (args.length > 0) try {
	    portNr = Integer.parseInt(args[0]);
	}
	catch (NumberFormatException e) {
	    System.out.println(args[0] + " is not a valid port.");
	    System.exit(1);
	}
	String cmd = DEFAULT_COMMAND;
	if (args.length > 1) cmd = args[1];
	try {
	    SMTPEvolutionAdapter sea = new SMTPEvolutionAdapter(portNr, cmd);
	    System.out.println("SMTPEvolutionAdapter listening on port " 
			       + portNr + ".");
	    sea.listen();
	}
	catch (IOException e) {
	    e.printStackTrace();
	    System.exit(2);
	}
    }

    /** Simple constructor. Creates the ServerSocket. */
    public SMTPEvolutionAdapter(int portNr, String cmd) throws IOException {
	theSocket = new ServerSocket(portNr);
	command = cmd;
    }

    /**
     * Listens for clients. Each client is handled by an instance of 
     * MailSession in a separate thread, allowing multiple clients to 
     * connect concurrently.
     */
    public void listen() throws IOException {
	while (true) {
	    Socket clientSocket = theSocket.accept();
	    (new Thread(new MailSession(clientSocket))).start();
	}
    }

    /**
     * Handles an SMTP session with a client. See RFC 821 (SMTP) for details.
     * At the end of the mail session, the external mail program is called.
     */
    class MailSession implements Runnable {

	// states of the session; will normally by run through in this order
	private static final int NOT_CONNECTED = 0;
	private static final int CONNECTED = 1;
	private static final int MAIL_CMD = 2;
	private static final int DATA_HEADER = 3;
	private static final int DATA_TEXT = 4;
	
	// command names, see RFC 821
	private static final String MAIL = "MAIL FROM:";
	private static final String RCPT = "RCPT TO:";
	private static final String NOOP = "NOOP";
	private static final String DATA = "DATA";
	private static final String HELO = "HELO";
	private static final String QUIT = "QUIT";
	private static final String RSET = "RSET";

	// important informations in the mail
	private LinkedList recipients = new LinkedList();
	private LinkedList ccs = new LinkedList();
	private LinkedList bccs = new LinkedList();
	private String subject = "";
	private String body = "";

	private int state = NOT_CONNECTED; // state of session
	private Socket mySocket = null; // the client socket

	/** Simple Constructor */
	public MailSession(Socket socket) {
	    mySocket = socket;
	    state = CONNECTED;
	}

	/** Resets the session, so that no mail information is kept */
	private void reset() {
	    recipients.clear();
	    ccs.clear();
	    bccs.clear();
	    subject = "";
	    body = "";
	}
	
	/**
	 * Calls the external mail program.
	 * At least for Evolution, special characters must be masked URL-like;
	 * though spaces must also be masked in UTF-8 (%20), not as '+'.
	 */
	private void callExternalMailer() throws IOException {
	    // concatenate the recipients
	    String recipientsString = "";
	    Iterator it = recipients.iterator();
	    while(it.hasNext()) {
		recipientsString += it.next();
		if (it.hasNext()) recipientsString += ",";
	    }
	    // the same for ccs and bccs
	    String ccsString = "";
	    it = ccs.iterator();
	    while(it.hasNext()) {
		ccsString += it.next();
		if (it.hasNext()) ccsString += ",";
	    }
	    String bccsString = "";
	    it = bccs.iterator();
	    while(it.hasNext()) {
		bccsString += it.next();
		if (it.hasNext()) bccsString += ",";
	    }
	    // encode special characters, using java.net.URLEncoder
	    try {
		subject = URLEncoder.encode(subject, "UTF-8");
		body = URLEncoder.encode(body, "UTF-8");
	    }
	    catch (UnsupportedEncodingException e) {
		// won't happen
		e.printStackTrace();
	    }
	    // replace '+' by '%20' (space). Each '+' must mean a space, 
	    // since orginal '+' chars were replaced by the URLEncoder
	    // '+' is a special char in regexps and must be masked. The 
            // '\' must then be masked again for the java compiler. 
	    subject = subject.replaceAll("\\+", "%20");
	    body = body.replaceAll("\\+", "%20");
	    // insert the recipients, subject and body. '%' chars in 
	    // subject or body were replaced by the URLEncoder, so no
	    // problem there.
	    String cmd = command.replaceAll("%r", recipientsString);
	    cmd = cmd.replaceAll("%c", ccsString);
	    cmd = cmd.replaceAll("%b", bccsString);
	    cmd = cmd.replaceAll("%s", subject);
	    cmd = cmd.replaceAll("%t", body);
	    //System.out.println(cmd);
	    Runtime.getRuntime().exec(cmd);
	}

	/**
	 * Communication with client.
	 */
	public void run() {
	    try {
		BufferedReader in = new BufferedReader(
		    new InputStreamReader(mySocket.getInputStream()));
		PrintWriter out = new PrintWriter(new BufferedWriter(
		    new OutputStreamWriter(mySocket.getOutputStream())));
		out.println("220 SMTPEvolutionAdapter ready");
		// each time after print, a flush is necessary to ensure
		// that the client gets the message
		out.flush();
		String line = null;
		while (state != NOT_CONNECTED &&
		       (line = in.readLine()) != null) {
		    if (state == MAIL_CMD) { // control commands
			if (line.toUpperCase().startsWith(MAIL)) {
			    // ignore, since 'from' isn't important here
			    out.println("250 OK");
			    out.flush();
			}
			else if (line.toUpperCase().startsWith(RCPT)) {
			    // trim(): remove spaces at start and end
			    recipients.addLast((line.substring(
				RCPT.length(), line.length())).trim());
			    out.println("250 OK");
			    out.flush();
			}
			else if (line.toUpperCase().startsWith(DATA)) {
			    if (!recipients.isEmpty()) {
				state = DATA_HEADER;
				out.println("354 Start mail input; end with "
					    + "<CRLF>.<CRLF>");
				out.flush();
			    }
			    else {
				out.println("503 Recipient missing");
				out.flush();
			    }
			}
			else if (line.toUpperCase().startsWith(HELO)) {
			    reset();
			    out.println("250 SMTPEvolutionAdapter");
			    out.flush();
			}
			else if (line.toUpperCase().startsWith(RSET)) {
			    reset();
			    out.println("250 Ok");
			    out.flush();
			}
			else if (line.toUpperCase().startsWith(NOOP)) {
			    out.println("250 Ok");
			    out.flush();
			}
			else if (line.toUpperCase().startsWith(QUIT)) {
			    out.println("221 Closing Connection");
			    out.flush();
			    in.close();
			    out.close();
			    mySocket.close();
			    state = NOT_CONNECTED; // breaks the loop
			}
			else {
			    out.println("500 Syntax Error");
			    out.flush();
			}
		    }
		    else if (state == CONNECTED) {
			if (line.toUpperCase().startsWith(HELO)) {
			    reset();
			    out.println("250 SMTPEvolutionAdapter");
			    out.flush();
			    state = MAIL_CMD;
			}
			else if (line.toUpperCase().startsWith(QUIT)) {
			    out.println("221 Closing Connection");
			    out.flush();
			    in.close();
			    out.close();
			    mySocket.close();
			    state = NOT_CONNECTED; // breaks the loop
			}
			else if (line.toUpperCase().startsWith(NOOP)) {
			    out.println("250 Ok");
			    out.flush();
			}
			else if (line.toUpperCase().startsWith(DATA) ||
				 line.toUpperCase().startsWith(RCPT) ||
				 line.toUpperCase().startsWith(MAIL) ||
				 line.toUpperCase().startsWith(RSET)) {
			    out.println("503 Say hello first");
			    out.flush();
			}
			else {
			    out.println("500 Syntax Error");
			    out.flush();
			}
		    }
		    // else must be DATA_XXXX
		    else if (line.equals(".")) { // end of Data section
			try {
			    callExternalMailer();
			    out.println("250 OK");
			    out.flush();
			}
			catch (IOException e) {
			    e.printStackTrace();
			    out.println("550 " + e.getMessage());
			    out.flush();
			}
			reset();
			state = MAIL_CMD;
		    }
		    else if (state == DATA_HEADER) {
			// the only relevant headers are 'Subject', 'CC' 
			// and 'BCC'
			if (line.startsWith("Subject:")) {
			    subject = line.substring(8, line.length()).trim();
			}
			else if (line.toUpperCase().startsWith("CC:")) {
			    ccs.addLast(line.substring(
				3, line.length()).trim());
			}
			else if (line.toUpperCase().startsWith("BCC:")) {
			    bccs.addLast(line.substring(
				4, line.length()).trim());
			}
			// empty line means end of headers
			else if (line.trim().length() == 0) {
			    state = DATA_TEXT;
			}
			// all other lines are ignored
		    }
		    else { // DATA_TEXT
			// remove leading points
			if (line.startsWith("..")) {
			    line = line.substring(1, line.length());
			}
			body = body + line + "\n";
		    }
		}
	    }
	    catch (IOException e) {
		e.printStackTrace();
	    }
	}
    }

}