/*
 * 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.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

import org.apache.commons.httpclient.NameValuePair;
import org.dom4j.DocumentHelper;
import org.dom4j.Element;
import org.dom4j.XPath;
import org.wamblee.crawler.Action;
import org.wamblee.crawler.Crawler;
import org.wamblee.crawler.Page;
import org.wamblee.crawler.PageType;

/**
 * Page implementation.
 *
 * @author Erik Brakkee
 */
public class PageImpl implements Page {

    private static final String ELEM_NAME = "action";

    private static final String ATT_NAME = "name";

    private static final String ATT_HREF = "reference";

    private static final String ATT_TYPE = "type";
    
    private static final String ELEM_PARAM = "param"; 
    
    private static final String ATT_VALUE = "value";

    private String _href; 
    
    private Crawler _crawler;

    private Element _content;

    private Action[] _actions;

    /**
     * Constructs a page.
     * 
     * @param aContent
     */
    public PageImpl(String aHref, Crawler aCrawler, Element aContent) {
        _href = aHref;
        _crawler = aCrawler;
        _content = aContent;
        _actions = computeActions();
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.wamblee.crawler.Page#getLinkNames()
     */
    private Action[] computeActions() {
        XPath xpath = DocumentHelper.createXPath(ELEM_NAME);
        List<Element> results = (List<Element>) xpath.selectNodes(_content);
        List<Action> names = new ArrayList<Action>();
        for (Element elem : results) {
            String name = elem.attributeValue(ATT_NAME);
            String href = elem.attributeValue(ATT_HREF);
            String type = elem.attributeValue(ATT_TYPE);
            NameValuePair[] params = getMandatoryParameters(elem);
            href = absolutizeHref(_href, href); 
            if (type == null) {
                names.add(new ActionImpl(_crawler, elem, name, href, params));
            } else {
                names.add(new ActionImpl(_crawler, elem, name, href,
                        new PageType(type), params));
            }
        }
        return names.toArray(new Action[0]);
    }
    
    /**
     * Absolutize the hyperlink 
     * @param aPageHref Absolute page reference.
     * @param aLinkHref Possibly relative link reference.
     * @return Absolute hyperlink. 
     */
    private String absolutizeHref(String aPageHref, String aLinkHref) {
        
        try {
            URL pageUrl = new URL(aPageHref);
            URL newUrl = new URL(pageUrl, aLinkHref); 
            return newUrl.toString(); // TODO need to use URL instead of String throughout the code. 
        } catch (MalformedURLException e) {
            throw new RuntimeException("Malformed URL", e); 
        }
    }

    private NameValuePair[] getMandatoryParameters(Element aAction) {
        List<NameValuePair> result = new ArrayList<NameValuePair>();
        for (Element param: (List<Element>)aAction.elements(ELEM_PARAM)) { 
            String name = param.attributeValue(ATT_NAME); 
            String value = param.attributeValue(ATT_VALUE); 
            result.add(new NameValuePair(name, value));
        }
        return result.toArray(new NameValuePair[0]);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.wamblee.crawler.Page#getContent()
     */
    public Element getContent() {
        return _content;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.wamblee.crawler.Page#getActions()
     */
    public Action[] getActions() {
        return _actions;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.wamblee.crawler.Page#getAction(java.lang.String)
     */
    public Action getAction(String aName) {
        List<Action> results = new ArrayList<Action>();
        for (Action action : _actions) {
            if (action.getName().equals(aName)) {
                results.add(action);
            }
        }
        if (results.size() == 0) {
            return null;
        }
        if (results.size() > 1) {
            throw new RuntimeException("Duplicate action '" + aName + "'");
        }
        return results.get(0);
    }
}