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/*
 * Copyright 2004-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.springframework.faces.webflow;

import java.io.IOException;
import java.io.Writer;

import javax.faces.context.FacesContext;
import javax.faces.context.ResponseWriter;
import javax.faces.render.RenderKitFactory;
import javax.faces.render.ResponseStateManager;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.faces.support.ResponseStateManagerWrapper;
import org.springframework.webflow.execution.RequestContext;
import org.springframework.webflow.execution.RequestContextHolder;

/**
 * A custom ResponseStateManager that writes JSF state to a Web Flow managed view-scoped variable. This class is plugged
 * in via {@link FlowRenderKit}.
 *
 * @author Rossen Stoyanchev
 * @author Phillip Webb
 *
 * @since 2.2.0
 */
public class FlowResponseStateManager extends ResponseStateManagerWrapper {

	private static final Log logger = LogFactory.getLog(FlowResponseStateManager.class);

	static final String FACES_VIEW_STATE = "facesViewState";

	private static final char[] STATE_FIELD_START = ("".toCharArray();

	private final ResponseStateManager wrapped;

	public FlowResponseStateManager(ResponseStateManager wrapped) {
		this.wrapped = wrapped;
	}

	@Override
	public ResponseStateManager getWrapped() {
		return this.wrapped;
	}

	@Override
	public void writeState(FacesContext facesContext, Object state) throws IOException {
		if (!JsfUtils.isFlowRequest()) {
			super.writeState(facesContext, state);
		} else {
			saveState(state);
			ResponseWriter writer = facesContext.getResponseWriter();
			writeViewStateField(facesContext, writer);
			writeRenderKitIdField(facesContext, writer);
		}
	}

	@Override
	public Object getState(FacesContext facesContext, String viewId) {
		if (!JsfUtils.isFlowRequest()) {
			return super.getState(facesContext, viewId);
		}
		RequestContext requestContext = RequestContextHolder.getRequestContext();
		Object state = requestContext.getViewScope().get(FACES_VIEW_STATE);
		if (state == null) {
			logger.debug("No matching view in view scope");
		}
		return state;
	}

	/**
	 * This method returns the flow execution key to be used as the value for the "javax.faces.ViewState" hidden input
	 * field. The value of this key is not important because JSF state is stored in a Web Flow managed view scoped
	 * variable. However the presence of the view state parameter alone is important for triggering actions. Hence we
	 * return the most logical value, which is the flow execution key.
	 */
	@Override
	public String getViewState(FacesContext facesContext, Object state) {
		if (!JsfUtils.isFlowRequest()) {
			return super.getViewState(facesContext, state);
		}
		saveState(state);
		return getFlowExecutionKey();
	}

	private void saveState(Object state) {
		RequestContext requestContext = RequestContextHolder.getRequestContext();
		requestContext.getViewScope().put(FACES_VIEW_STATE, state);
	}

	private String getFlowExecutionKey() {
		RequestContext requestContext = RequestContextHolder.getRequestContext();
		return requestContext.getFlowExecutionContext().getKey().toString();
	}

	/**
	 * See comments on {@link ResponseStateManager#VIEW_STATE_PARAM}.
	 *
	 * @param context the FacesContext for the current request
	 * @param writer the ResponseWriter to write to
	 * @throws IOException if an error occurs writing to the client
	 */
	private void writeViewStateField(FacesContext context, Writer writer) throws IOException {
		writer.write(STATE_FIELD_START);
		writer.write(getFlowExecutionKey());
		writer.write(STATE_FIELD_END);
	}

	/**
	 * See comments on ResponseStateManager.RENDER_KIT_ID_PARAM in
	 * {@link ResponseStateManager#writeState(FacesContext, Object)}.
	 *
	 * @param context the FacesContext for the current request
	 * @param writer the ResponseWriter to write to
	 * @throws IOException if an error occurs writing to the client
	 */
	private void writeRenderKitIdField(FacesContext context, ResponseWriter writer) throws IOException {
		String result = context.getApplication().getDefaultRenderKitId();
		if (result != null && !RenderKitFactory.HTML_BASIC_RENDER_KIT.equals(result)) {
			writer.startElement("input", context.getViewRoot());
			writer.writeAttribute("type", "hidden", "type");
			writer.writeAttribute("name", ResponseStateManager.RENDER_KIT_ID_PARAM, "name");
			writer.writeAttribute("value", result, "value");
			writer.endElement("input");
		}
	}
}