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package org.wings.resource;

import java.io.IOException;
import java.util.Iterator;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.wings.ReloadManager;
import org.wings.SFrame;
import org.wings.plaf.Update;
import org.wings.plaf.css.Utils;
import org.wings.io.Device;
import org.wings.script.ScriptListener;
import org.wings.session.ScriptManager;
import org.wings.session.SessionManager;

/**
 * This resource is responsible for incremental page updates using AJAX. While requests sent to the
 * {@link ReloadResource} always entail a full rewrite of the frame's complete component hierarchy,
 * requests received by the {@link UpdateResource} will result in preferably small data chunks being
 * sent back to the client. These so called "incremental updates" encapsulate all informations the
 * client needs in order to synchronize its page with the server's state. Because this resource is
 * typically requested from an XMLHttpRequest object, it returns a well-formed XML document with MIME
 * type "text/xml". The updates in this document will be processed by according JavaScript functions.
 *
 * The XML structure looks as follows:
 *
 *  * 
 * 
 *   
 *   
 *   
 *   ...
 * 
 * 
 *
 * @author Stephan Schuster
 */
public class UpdateResource extends DynamicResource {

    private static final transient Logger log = LoggerFactory.getLogger(UpdateResource.class);

    public UpdateResource(final SFrame f) {
        super(f);
        this.extension = "xml";
        this.mimeType = "text/xml; charset=" + SessionManager.getSession().getCharacterEncoding();
    }

    @Override
    public void write(Device out) throws IOException {
        try {
            final SFrame frame = getFrame();
            final ReloadManager reloadManager = frame.getSession().getReloadManager();
            final ScriptManager scriptManager = frame.getSession().getScriptManager();

            writeHeader(out);
            if (reloadManager.isReloadRequired(frame)) {
                writeUpdate(out, "wingS.request.reloadFrame()");
            } else {
                // update components
                for (Update update : reloadManager.getUpdates()) {
                    if (update == null) {
                        continue;
                    }
                    writeUpdate(out, update);
                }

                // update scripts
                ScriptListener[] scriptListeners = scriptManager.getScriptListeners();
                for (ScriptListener scriptListener : scriptListeners) {
                    if (scriptListener.getScript() != null) {
                        writeUpdate(out, scriptListener.getScript());
                    }
                }
                scriptManager.clearScriptListeners();
			}
            writeFooter(out);

        } catch (IOException e) {
            throw e;
        } catch (Exception e) {
            log.error("resource: " + getId(), e);
            throw new IOException(e.getMessage());
        }
    }

    public static void writeHeader(Device out) throws IOException {
        String encoding = SessionManager.getSession().getCharacterEncoding();
        out.print("");
        out.print("\n");

        if (log.isDebugEnabled()) {
            SFrame frame = SessionManager.getSession().getRootFrame();
            log.debug("Request: " + (frame != null ? frame.getEventEpoch() : "x"));
        }
    }

    public static void writeFooter(Device out) throws IOException {
        out.print("\n");
    }

    public static void writeUpdate(Device out, Update update) throws IOException {
        Update.Handler handler = update.getHandler();

        writePrefix(out);
    	out.print(handler.getName()).print('(');
        Iterator parameters = handler.getParameters();
        boolean isFirst = true;
        while (parameters.hasNext()) {
            if (!isFirst) out.print(',');
            Utils.encodeJS(out, parameters.next());
            isFirst = false;
        }
        out.print(')');
        writePostfix(out);

        if (log.isDebugEnabled()) {
            log.debug(update.getClass().getName() + ':');
            StringBuilder builder = new StringBuilder();
            builder.append(handler.getName()).append('(');
            parameters = handler.getParameters();
            if (parameters.hasNext())
                builder.append(parameters.next());
            while (parameters.hasNext())
                builder.append(',').append(parameters.next());
            builder.append(')');
            log.debug(builder.toString());
        }
    }

    public static void writeUpdate(Device out, String update) throws IOException {
        writePrefix(out);
        out.print(update);
        writePostfix(out);
    }

    private static void writePrefix(Device out) throws IOException {
        out.print("\n  ");
    }
}