/*
 * Copyright 2005 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.wamblee.crawler.impl;

import java.io.InputStream;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.apache.commons.httpclient.NameValuePair;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import org.wamblee.crawler.Configuration;
import org.wamblee.crawler.GetPageRequest;
import org.wamblee.crawler.PageRequest;
import org.wamblee.crawler.PostPageRequest;
import org.wamblee.xml.XslTransformer;

/**
 * Parsing of the configuration from an XML file.
 */
public class ConfigurationParser {

    private static final String ELEM_URL = "url";

    private static final String ELEM_TYPE = "type";

    private static final String ELEM_PATTERN = "pattern";

    private static final String ELEM_METHOD = "method";

    private static final String ELEM_XSLT = "xslt";

    private static final String ELEM_PARAM = "param";
    
    private static final String ELEM_HEADER = "header";

    private static final String AT_NAME = "name";

    private static final String AT_VALUE = "value";

    private static final String METHOD_POST = "post";

    private static final String METHOD_GET = "get";

    private static final int MAX_TRIES = 3;

    private static final int MAX_DELAY = 5000;
    
    private XslTransformer _transformer;

    /**
     * Constructs the configuration parser. 
     */
    public ConfigurationParser(XslTransformer aTransformer) {
        _transformer = aTransformer; 
    }

    /**
     * Parses the configuration from an input stream.
     * @param aStream Input file. 
     * @return Configuration. 
     */
    public Configuration parse(InputStream aStream) {
        try {
            SAXReader reader = new SAXReader();
            Document document = reader.read(aStream);

            Element root = document.getRootElement();
            List<UrlConfig> urlConfigs = parseUrlConfigs(root);
            List<PageTypeConfig> pageTypeConfigs = parsePageTypeConfigs(root);
            return new ConfigurationImpl(urlConfigs, pageTypeConfigs);
        } catch (DocumentException e) {
            throw new RuntimeException("Problem parsing config file", e);
        }
    }

    /**
     * Parses the URL-based configuration. 
     * @param aRoot Root of the configuration file document. 
     * @return List of URL-based configurations. 
     */
    private List<UrlConfig> parseUrlConfigs(Element aRoot) {
        List<UrlConfig> configs = new ArrayList<UrlConfig>();
        for (Iterator i = aRoot.elementIterator(ELEM_URL); i.hasNext();) {
            Element url = (Element) i.next();
            UrlConfig config = parseUrlConfig(url);
            configs.add(config);
        }
        return configs;
    }

    /**
     * Parses the page type based configurations. 
     * @param aRoot Root of the configuration file document. 
     * @return LIst of page type based configurations. 
     */
    private List<PageTypeConfig> parsePageTypeConfigs(Element aRoot) {
        List<PageTypeConfig> configs = new ArrayList<PageTypeConfig>();
        for (Iterator i = aRoot.elementIterator(ELEM_TYPE); i.hasNext();) {
            Element url = (Element) i.next();
            PageTypeConfig config = parsePageTypeConfig(url);
            configs.add(config);
        }
        return configs;
    }

    /**
     * Parses a URL-based configuration. 
     * @param aUrlElem Configuration element. 
     * @return Configuration. 
     */
    private UrlConfig parseUrlConfig(Element aUrlElem) {
        String pattern = aUrlElem.elementText(ELEM_PATTERN);
        PageRequest request = parseRequestConfig(aUrlElem);
        return new UrlConfig(pattern, request);
    }

    /**
     * Parses a page type based configuration. 
     * @param aTypeElem Configuration element. 
     * @return Configuration. 
     */
    private PageTypeConfig parsePageTypeConfig(Element aTypeElem) {
        String pattern = aTypeElem.elementText(ELEM_PATTERN);
        PageRequest request = parseRequestConfig(aTypeElem);
        return new PageTypeConfig(pattern, request);
    }

    /**
     * Parses a request configuration describing how to execute requests. 
     * @param aElem Configuration element. 
     * @return Page request. 
     */
    private PageRequest parseRequestConfig(Element aElem) {
        String method = aElem.elementText(ELEM_METHOD);
        String xslt = aElem.elementText(ELEM_XSLT);
        List<NameValuePair> params = parseNameValuePairs(aElem, ELEM_PARAM); 
        List<NameValuePair> headers = parseNameValuePairs(aElem, ELEM_HEADER);
        
        NameValuePair[] paramsArray = params.toArray(new NameValuePair[0]);
        NameValuePair[] headersArray = headers.toArray(new NameValuePair[0]);
        PageRequest request;
        if (METHOD_POST.equals(method)) {
            request = new PostPageRequest(MAX_TRIES, MAX_DELAY, paramsArray, headersArray,
                    xslt, _transformer);
        } else if (METHOD_GET.equals(method) || method == null) {
            request = new GetPageRequest(MAX_TRIES, MAX_DELAY, paramsArray, headersArray,
                    xslt, _transformer);
        } else {
            throw new RuntimeException("Unknown request method '" + method
                    + "'. Only " + METHOD_GET + " and " + METHOD_POST
                    + " are supported");
        }
        return request;
    }

    /**
     * @param aElem
     * @return
     */
    private List<NameValuePair> parseNameValuePairs(Element aElem, String aElemName) {
        List<NameValuePair> headers = new ArrayList<NameValuePair>();
        for (Iterator i = aElem.elementIterator(aElemName); i.hasNext();) {
            Element paramElem = (Element) i.next();
            NameValuePair header = parseParameter(paramElem);
            headers.add(header);
        }
        return headers;
    }

    /**
     * Parses a parameter definition. 
     * @param aParam Parameter. 
     * @return Name value pair describing a parameter. 
     */
    private NameValuePair parseParameter(Element aParam) {
        String name = aParam.attributeValue(AT_NAME);
        String value = aParam.attributeValue(AT_VALUE);
        return new NameValuePair(name, value);
    }
}