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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.sling.servlets.post;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.Writer;

import javax.servlet.http.HttpServletResponse;

import org.apache.sling.api.request.ResponseUtil;

/**
 * The HtmlResponse is an {@link AbstractPostResponse} preparing
 * the response in HTML (actually XHTML) such that it can be interpreted
 * as a plain response in a browser or as XML response in an Ajax request.
 */
public class HtmlResponse extends AbstractPostResponse {

    /**
     * Name of the property into which the change log is gathered to be
     * sent back by the {@link #doSend(HttpServletResponse)} method. This
     * property is only sent before replacing all variables in the HTML
     * response remplate.
     */
    private static final String PN_CHANGE_LOG = "changeLog";

    /**
     * name of the html template
     */
    private static final String TEMPLATE_NAME = "HtmlResponse.html";

    /**
     * name of the html safe referer template
     */
    private static final String NO_GO_BACK_TEMPLATE_NAME = "HtmlNoGoBackResponse.html";
    
    /**
     * list of changes
     */
    private final StringBuilder changes = new StringBuilder();

    /**
     * Records a generic change of the given type.
     * 
     * The change is added to the internal list of changes with the syntax of a
     * method call, where the type is the method name and the
     * arguments are the string arguments to the method enclosed in
     * double quotes. For example, the the call
     *
     * 
     * onChange("sameple", "arg1", "arg2");
     * 
     *
     * is aded as
     *
     *      * sample("arg1", "arg2")
     * 
     *
     * to the internal list of changes.
     *
     * @param type The type of the modification
     * @param arguments The arguments to the modifications
     */
    public void onChange(String type, String... arguments) {
        changes.append(type);
        String delim = "(";
        for (String a : arguments) {
            changes.append(delim);
            changes.append('\"');
            changes.append(a);
            changes.append('\"');
            delim = ", ";
        }
        changes.append(");
");
    }

    // ---------- Response Generation ------------------------------------------

    /**
     * Writes the response to the given writer and replaces all ${var} patterns
     * by the value of the respective property. if the property is not defined
     * the pattern is not modified.
     *
     * @param response to send to
     * @throws IOException if an i/o exception occurs
     */
    @Override
    protected void doSend(HttpServletResponse response)
            throws IOException {

        response.setContentType("text/html");
        response.setCharacterEncoding("UTF-8");

        // get changelog
        changes.insert(0, "");
        changes.append("");
        if (getError() == null) {
            setProperty(PN_CHANGE_LOG, changes.toString());
        } else {
            setProperty(PN_CHANGE_LOG, "");
        }

        Writer out = response.getWriter();
        
        String templateName;
        if(isSafeReferer()) {
            templateName = TEMPLATE_NAME;
        } else {
            templateName = NO_GO_BACK_TEMPLATE_NAME;
        }
        
        InputStream template = getClass().getResourceAsStream(templateName);
        Reader in = new BufferedReader(new InputStreamReader(template));
        StringBuilder varBuffer = new StringBuilder();
        int state = 0;
        int read;
        while ((read = in.read()) >= 0) {
            char c = (char) read;
            switch (state) {
                // initial
                case 0:
                    if (c == '$') {
                        state = 1;
                    } else {
                        out.write(c);
                    }
                    break;
                // $ read
                case 1:
                    if (c == '{') {
                        state = 2;
                    } else {
                        state = 0;
                        out.write('$');
                        out.write(c);
                    }
                    break;
                // { read
                case 2:
                    if (c == '}') {
                        state = 0;
                        Object prop = getProperty(varBuffer.toString());
                        if (prop != null) {
                            out.write(ResponseUtil.escapeXml(prop.toString()));
                        }
                        varBuffer.setLength(0);
                    } else {
                        varBuffer.append(c);
                    }
            }
        }
        in.close();
        out.flush();
    }

}