package altk.comm.engine.postback;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;

import org.apache.commons.httpclient.ConnectTimeoutException;
import org.apache.commons.httpclient.DefaultHttpMethodRetryHandler;
import org.apache.commons.httpclient.Header;
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.HttpURL;
import org.apache.commons.httpclient.methods.PostMethod;
import org.apache.commons.httpclient.methods.StringRequestEntity;
import org.apache.commons.httpclient.params.HttpMethodParams;
import org.apache.log4j.Logger;
import org.w3c.dom.Document;
import org.w3c.dom.Node;

import altk.comm.engine.CommonLogger;


/**
 * Queues JobReports to be posted back to attribute postBackURL.
 * Multiple internal class Sender members consume this postQueue, sending items
 * in postQueue to postBackURL.  
 * 
 * In the future, if postBackURL has problem, or if
 * length of postQueue is more than a MAX_QUEUE_LENGTH, then it starts writing
 * everything to backingFile.
 * 
 * @author Kwong
 *
 */
public class PostBack
{
    private static final String XML_VERSION_1_0_ENCODING_UTF_8 = "<?xml version=\"1.0\" encoding=\"utf-8\"?>";
    
    private static final int QUEUE_WAIT = 300; // seconds
    private static final int POSTBACK_SERVER_WAIT_TIME = 10; // seconds
    
    private final String postBackURL;
    private final String xmlTopElement;
    private Queue<String> postQueue;
    private final int maxQueueSize;
    private List<Sender> senderPool;
    private final String myName;
    private int maxBatchSize;

    private static Logger myLogger = Logger.getLogger(PostBack.class);

    public enum PostBackStatus
    {
        SUCCESS,
        SERVER_IO_ERROR,
        IRRECOVERABLE_ERROR,
        HTTP_STATUS_ERROR
    }
    
    class Sender extends Thread
    {
        private boolean threadShouldStop;

        private Sender(String name)
        {
            setName(name);
            start();
        }
        
        public void run()
        {
            threadShouldStop = false;
            
            myLogger.info(getName() + " started");
           
            String report;
            
            for (;;)   // Each iteration sends a batch
            {
                if (threadShouldStop)
                {
                    myLogger.info(getName() + " terminating");
                    System.out.println(getName() + " terminating");
                    return;
                }
                
                List<String> reportList = null;
                synchronized(postQueue)
                {
                    // Each iteration examines the queue for a batch to send
                    for (;;) 
                    {
                        reportList = new ArrayList<String>();
                        for (int i = 0; i < maxBatchSize ; i++)
                        {
                            report = postQueue.poll();
                            if (report == null) break;
                            reportList.add(report);
                        }
                        if (reportList.size() > 0)
                        {
                            postQueue.notify();
                            break;  // break out to do the work.
                        }
                        
                        // Nothing to do, so wait a while, and look at the
                        // queue again.
                        try
                        {
                            postQueue.wait(QUEUE_WAIT * 1000);
                        }
                        catch (InterruptedException e)
                        {
                            CommonLogger.alarm.info(getName() + ": Postback queue interrupted while waiting: " + e);
                            break;
                        }
                        CommonLogger.health.info(getName() + " surfacing from wait");
                        System.out.println(getName() + " surfacing from wait");
                        continue;
                    }
                } // synchronized()
                if (reportList != null && reportList.size() > 0)
                {
                    switch (post(reportList))
                    {
                        case IRRECOVERABLE_ERROR:
                        case SUCCESS:
                            break;
                            
                        case SERVER_IO_ERROR:
                            // TODO: Limit retries, using rate limiting.  Posting can be recovered using the activity log.
                            // Re-queue these reports
                            for (String rpt : reportList)
                            {
                                queueReport(rpt);
                            }
                            // Sleep for a while before retrying this PostBack server.
                            CommonLogger.alarm.warn(getName() + ": Caught server IO error.  sleep for " + POSTBACK_SERVER_WAIT_TIME + " seconds");
                            try
                            {
                                Thread.sleep(POSTBACK_SERVER_WAIT_TIME * 1000);
                            }
                            catch (InterruptedException e)
                            {
                                CommonLogger.alarm.warn(getName() + ": Caught while PostBack thread sleeps: " + e);
                            }
                        default:
                    }
                }
            }
        }
        
        /**
         * 
         * @param reportList
         * @return SUCCESS,  
         *         SERVER_IO_ERROR, when postback receiver has problem
         *         IRRECOVERABLE_ERROR
         */
        private PostBackStatus post(List<String> reportList)
        {
            StringBuffer xml = new StringBuffer(XML_VERSION_1_0_ENCODING_UTF_8);
            xml.append("<"); xml.append(xmlTopElement); xml.append(">");
            for (String report : reportList)
            {
                xml.append(report);
            }
            xml.append("</"); xml.append(xmlTopElement); xml.append(">");
            
            PostMethod post = new PostMethod();
            String responseBody = null;
            StringRequestEntity requestEntity = null;
            try
            {
                requestEntity = new StringRequestEntity(xml.toString(), "application/xml", "utf-8");
            }
            catch (UnsupportedEncodingException e)
            {
                CommonLogger.alarm.warn(getName() + ": While adding this application/xml content to PostBack: " + xml + " -- " + e);
                return PostBackStatus.IRRECOVERABLE_ERROR;
            }
            post.setRequestEntity(requestEntity);
            post.getParams().setParameter(HttpMethodParams.RETRY_HANDLER, 
                new DefaultHttpMethodRetryHandler(3, false));
            /*
            CommonLogger.activity.debug("Before calling setFolloweRedirects()");
            post.setFollowRedirects(false);
            CommonLogger.activity.debug("After calling setFolloweRedirects()");
            */
            HttpClient client = new HttpClient();
            String url = postBackURL;
            for (int redirectCount = 0; redirectCount < 3; redirectCount++)
            {
                try
                {
                    client.getHttpConnectionManager().getParams().setConnectionTimeout(5 * 1000);
                    post.setURI(new HttpURL(url));
                    if (redirectCount == 0)
                    {
                        CommonLogger.activity.info(getName() + ": posting " + xml.toString() + " to " + url);
                    }
                    else
                    {
                        CommonLogger.activity.info(getName() + ": redirected to " + url);
                    }
                    int statusCode = client.executeMethod(post);
    
                    if (statusCode == 302)
                    {
                        Header locationHeader = post.getResponseHeader("Location");
                        if (locationHeader != null)
                        {
                            url = locationHeader.getValue();
                            post.releaseConnection();
                            continue;
                        }
                        else
                        {
                            CommonLogger.alarm.warn(getName() + ": When posting to \"" + url + "\": " + " received status 302 but without location header");
                            return PostBackStatus.IRRECOVERABLE_ERROR;
                        }
                    }
                    else if (statusCode != 200)
                    {
                        CommonLogger.alarm.warn(getName() + ": Received problem status code " + statusCode + " from posting to \"" + url + "\": " + xml);
                        return PostBackStatus.HTTP_STATUS_ERROR;
                    }
                    responseBody = post.getResponseBodyAsString().trim();
                    post.releaseConnection();
                    CommonLogger.activity.info(getName() + ": Received response: " + (responseBody.length() == 0? "[empty]" : responseBody));
                    if (responseBody.trim().length() == 0) return PostBackStatus.SUCCESS;
                    break;
                }
                catch (ConnectTimeoutException e)
                {
                    CommonLogger.alarm.warn(getName() + ": IO problem while posting to \"" + url + "\": " + xml + " -- " + e.getMessage());
                    return PostBackStatus.SERVER_IO_ERROR;                
                }
                catch (IOException e)
                {
                    CommonLogger.alarm.warn(getName() + ": IO problem while posting to \"" + url + "\": " + xml + " -- " + e.getMessage());
                    return PostBackStatus.SERVER_IO_ERROR;
                }
                catch (IllegalArgumentException e)
                {
                    CommonLogger.alarm.warn(getName() + ": When posting to \"" + url + "\": " + e.getMessage());
                    return PostBackStatus.IRRECOVERABLE_ERROR;
                }
            }
            if (responseBody == null)
            {
                CommonLogger.alarm.warn(getName() + ": When posting to \"" + url + "\": " + " Exhausted allowable redirects");
                return PostBackStatus.IRRECOVERABLE_ERROR;
            }
            // parse into xml doc
            Document xmlDoc = null;
            try
            {
                DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
                DocumentBuilder builder = factory.newDocumentBuilder();
                xmlDoc = builder.parse(new ByteArrayInputStream(responseBody.getBytes()));
            }
            catch (Exception e)
            {
                CommonLogger.alarm.warn(getName() + ": xml parse problem on received response from " + postBackURL + ": " + responseBody);
                return PostBackStatus.IRRECOVERABLE_ERROR;
            }
            if (!xmlDoc.getDocumentElement().getNodeName().startsWith(xmlTopElement))
            {
                CommonLogger.alarm.warn(getName() + ": xml response from " + postBackURL + " not a <" + xmlTopElement + "> response: " + responseBody);
                return PostBackStatus.IRRECOVERABLE_ERROR;
            }
            XPath xpathEngine = XPathFactory.newInstance().newXPath();
            String xpath = null;
            try
            {
                xpath = "@error";
                Node errorNode = (Node)xpathEngine.evaluate(xpath, xmlDoc.getDocumentElement(), XPathConstants.NODE);
                if (errorNode != null)
                {
                    String errorCode = errorNode.getNodeValue();
                    xpath = "error_text";
                    String errorText = (String)xpathEngine.evaluate(xpath,
                            xmlDoc.getDocumentElement(), XPathConstants.STRING);
                    CommonLogger.alarm.warn(getName() + ": Error response to <" + xmlTopElement + "> post back to "
                            + postBackURL + " -- error code=\"" + errorCode + "\", error text = \""
                            + errorText + "\"");
                    return PostBackStatus.IRRECOVERABLE_ERROR;
                }
            }
            catch (XPathExpressionException e)
            {
                CommonLogger.alarm.warn("Bad xpath: " + xpath);
                return PostBackStatus.IRRECOVERABLE_ERROR;
            }
            catch (Exception e)
            {
                CommonLogger.alarm.warn(getName() + ": While decoding post back response from server: " + e);
                return PostBackStatus.IRRECOVERABLE_ERROR;
            }
            return PostBackStatus.SUCCESS;
        }

        public void terminate()
        {
            if (threadShouldStop) return;
            
            threadShouldStop = true;
            
            //Wait for at most 100 ms for thread to stop
            interrupt();
        }
        
    }
    
    /**
     * Constructs a pool of threads doing posting from a common job queue,
     * to the supplied postBackURL.  The top element of the XML that gets
     * posted back has the give name.
     * 
     * Requires these System properties:
     *     postback_max_queue_size
     *     postback_threadpool_size
     *     
     * @param postBackURL
     * @param xmlTopElementName
     * @throws IllegalArgumentException if either postBackURL or xmlTopElementName is
     *         not supplied nor valid.
     */
    public PostBack(String postBackURL, String xmlTopElementName,
            int maxQueueSize, int senderPoolSize, int maxBatchSize)
    throws IllegalArgumentException
    {
        if (postBackURL == null || postBackURL.length() == 0)
        {
            throw new IllegalArgumentException("PostBack class given null postBackURL");
        }
        myName = "Postback-" + postBackURL;
        if (xmlTopElementName == null || xmlTopElementName.length() == 0)
        {
            throw new IllegalArgumentException(myName + ": PostBack class given null xmlTopElement");
        }
        this.postBackURL = postBackURL;
        this.xmlTopElement = xmlTopElementName;
        this.maxQueueSize = maxQueueSize;
        this.maxBatchSize = maxBatchSize;
        postQueue = new LinkedList<String>();
        
        senderPool = new ArrayList<Sender>();
        for (int i = 0; i < senderPoolSize; i++)
        {
            Sender sender = new Sender(myName + '-' + i);
            senderPool.add(sender);
        }
    }
    
    /**
     * Queues report to postQueue only if the queue size has not reached the
     * maxQueueSize.
     * @param report
     * @return true if report is added to queue, false otherwise (queue full)
     */
    public boolean queueReport(String report)
    {
        // Log for recovery in case of problem in posting report.
        CommonLogger.activity.info(myName + " queing report: " + report);
        
        myLogger.debug(myName + ": postQueue size: " + postQueue.size());
        synchronized(postQueue)
        {
            for (;;)
            {
                if (postQueue.size() < maxQueueSize)
                {    
                    postQueue.add(report);
                    postQueue.notify();
                    return true;
                }
                else
                {
                    myLogger.debug("Waiting for space in postQueue to queue report");
                    try
                    {
                        postQueue.wait();
                    }
                    catch (InterruptedException e)
                    {
                        break;
                    }
                }
            }
        }
        myLogger.error("Interrupted while waiting for space to queue report");
        return false;
    }
    
    /**
     * Queues reports to postQueue only if the queue size has not reached the
     * maxQueueSize.
     * @param reports to be added back to postQueue
     * @return true if all jobs have been added to queue, false otherwise (queue full)
     */
    /*
    @Deprecated
    public boolean queueReports(List<String> reports)
    {
        myLogger.debug(myName + ": postQueue size: " + postQueue.size());
        synchronized(postQueue)
        {
            Iterator<String> iter = reports.iterator();
            int count = 0; // Number of reports added back to postQueue
            while (iter.hasNext())
            {
                String report = iter.next();
                if (postQueue.size() < maxQueueSize)
                {    
                    postQueue.add(report);
                    count++;
                }
            }
            if (count > 0) postQueue.notify();
            boolean returnValue = (count == reports.size());
            if (!returnValue)
            {
                CommonLogger.alarm.warn(myName
                        + ".queueReport method returning false, having queued "
                        + count + " out of " + reports.size());
            }
            return returnValue;
        }
    }
    */

    public void terminate()
    {
        for (Sender sender : senderPool)
        {
            sender.terminate();
        }
        
    }
    
}