/*
    * Copyright 2007 Sebastien Brunot (sbrunot@gmail.com)
    * 
    * 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 net.sourceforge.buildmonitor.utils;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.net.URL;
  import java.text.DateFormat;
  import java.text.ParseException;
  
  import org.xml.sax.Attributes;
  import org.xml.sax.InputSource;
  import org.xml.sax.SAXException;
  import org.xml.sax.XMLReader;
  import org.xml.sax.helpers.DefaultHandler;
  import org.xml.sax.helpers.XMLReaderFactory;
  
  /**
   * A class that can parse an RSS feed and return a Feed object.
   * @author sbrunot
   *
   */
  public class RssFeedReader
  {
  	/////////////////////////////////
  	// Nested classes
  	/////////////////////////////////
  
  	public class RssFeedContentHandler extends DefaultHandler
  	{
  		///////////////////////////////
  		// Constants
  		///////////////////////////////
  
  		private static final int TITLE_ATTRIBUTE = 1;
  		private static final int DESCRIPTION_ATTRIBUTE = 2;
  		private static final int PUBDATE_ATTRIBUTE = 3;
  		private static final int LINK_ATTRIBUTE = 4;
  		
  		///////////////////////////////
  		// Attributes
  		///////////////////////////////
  
  		RssFeedDocument rssFeedDocument = null;
  		RssFeedItem currentItem = null;
  		int currentItemAttributeToSet = -1;
  		DateFormat rssFeedDateFormat = null;
  		
  		///////////////////////////////
  		// Constructor
  		///////////////////////////////
  
  		public RssFeedContentHandler(DateFormat theRssFeedDateFormat)
  		{
  			if (theRssFeedDateFormat == null)
  			{
  				throw new IllegalArgumentException("The RSS Feed date format cannot be null !");
  			}
  			this.rssFeedDateFormat = theRssFeedDateFormat;
  		}
  		
  		///////////////////////////////
  		// ContentHandler implementation
  		///////////////////////////////
  		
  		public void startDocument()
  		{
  			this.rssFeedDocument = new RssFeedDocument();
  		}
  
  		public void startElement(String theNameSpace, String theLocalName, String theQName, Attributes theAttributes)
  		{
  			if ("item".equals(theLocalName))
  			{
  				// this is a new Item
  				this.currentItem = new RssFeedItem();
  			}
  			else if ("title".equals(theLocalName))
  			{
  				this.currentItemAttributeToSet = TITLE_ATTRIBUTE;
  			}
  			else if ("link".equals(theLocalName))
  			{
  				this.currentItemAttributeToSet = LINK_ATTRIBUTE;
  			}
  			else if ("description".equals(theLocalName))
 			{
 				this.currentItemAttributeToSet = DESCRIPTION_ATTRIBUTE;
 			}
 			else if ("pubDate".equals(theLocalName))
 			{
 				this.currentItemAttributeToSet = PUBDATE_ATTRIBUTE;
 			}
 			else
 			{
 				this.currentItemAttributeToSet = -1;
 			}
 		}
 
 		public void endElement(String theNameSpace, String theLocalName, String theQName)
 		{
 			if ("item".equals(theLocalName))
 			{
 				// end of the item: add it to the document
 				this.rssFeedDocument.add(this.currentItem);
 				this.currentItem = null;
 			}
 		}
 
 		public void characters(char[] theCharacters, int theStartIndex, int theLength)
 		{
 			String characters = new String(theCharacters, theStartIndex, theLength).trim();
 			String trimedCharacters = characters.replace("\n", "");
 			if (!"".equals(trimedCharacters))
 			{
 				setCurrentItemAttribute(characters);
 			}
 		}
 
 		///////////////////////////////
 		// Public methods
 		///////////////////////////////
 
 		public RssFeedDocument getDocument()
 		{
 			return this.rssFeedDocument;
 		}
 
 		///////////////////////////////
 		// Private methods
 		///////////////////////////////
 
 		private void setCurrentItemAttribute(String theValueOfTheAttribute)
 		{
 			if (this.currentItem != null && this.currentItemAttributeToSet != -1)
 			{
 				if (this.currentItemAttributeToSet == TITLE_ATTRIBUTE)
 				{
 					this.currentItem.setTitle(theValueOfTheAttribute);
 				}
 				else if (this.currentItemAttributeToSet == DESCRIPTION_ATTRIBUTE)
 				{
 					this.currentItem.setDescription(theValueOfTheAttribute);
 				}
 				else if (this.currentItemAttributeToSet == LINK_ATTRIBUTE)
 				{
 					this.currentItem.setLink(theValueOfTheAttribute);
 				}
 				else if (this.currentItemAttributeToSet == PUBDATE_ATTRIBUTE)
 				{
 					// TODO: USE A DateFormat
 					try
 					{
 						this.currentItem.setPubDate(this.rssFeedDateFormat.parse(theValueOfTheAttribute));
 					}
 					catch (ParseException e)
 					{
 						this.currentItem.setPubDate(null);
 						// TODO: ADD A LOG INSTEAD OF SYSTEM.ERR OUTPUT
 						System.err.println("WARNING: publication date <" + theValueOfTheAttribute + "> does not follow the expected date format.");
 					}
 				}
 				else
 				{
 					throw new RuntimeException("Error discovered in RssFeedContentHandler: please contact sbrunot@gmail.com");
 				}
 			}
 		}
 	}
 	
 	/////////////////////////////////
 	// Attributes
 	/////////////////////////////////
 
 	private URL rssFeedUrl;
 	
 	private DateFormat rssFeedDateFormat;
 	
 	/////////////////////////////////
 	// Constructor
 	/////////////////////////////////
 	
 	public RssFeedReader(URL theRssFeedUrl, DateFormat theRssFeedDateFormat)
 	{
 		if (theRssFeedUrl == null)
 		{
 			throw new IllegalArgumentException("URL of the RSS feed cannot be null.");
 		}
 		if (theRssFeedDateFormat == null)
 		{
 			throw new IllegalArgumentException("Date format for the RSS feed cannot be null.");
 		}
 		this.rssFeedUrl = theRssFeedUrl;
 		this.rssFeedDateFormat = theRssFeedDateFormat;
 	}
 
 	/////////////////////////////////
 	// Public methods
 	/////////////////////////////////
 
 	public RssFeedDocument getRssFeedDocument() throws IOException, SAXException
 	{
 		InputStream rssDocumentInputStream = null;
 		try
 		{
 			rssDocumentInputStream = this.rssFeedUrl.openStream();
 			XMLReader rssDocumentReader = XMLReaderFactory.createXMLReader();
 			RssFeedContentHandler contentHandler = new RssFeedContentHandler(this.rssFeedDateFormat);
 			rssDocumentReader.setContentHandler(contentHandler);
 			rssDocumentReader.parse(new InputSource(rssDocumentInputStream));
 			return contentHandler.getDocument();
 		}
 		finally
 		{
 			if (rssDocumentInputStream != null)
 			{
 				try
 				{
 					rssDocumentInputStream.close();
 				}
 				catch (IOException e)
 				{
 					// do nothing here: it may mask a previous exception ? (to be verified in java spec)
 				}
 			}
 		}
 	}
 }