/*
    * #%L
    * wcm.io
    * %%
    * Copyright (C) 2014 wcm.io
    * %%
    * 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.
   * #L%
   */
  package io.wcm.handler.url.rewriter.impl;
  
  import java.net.URLDecoder;
  import java.nio.charset.StandardCharsets;
  
  import org.apache.commons.lang3.StringUtils;
  import org.apache.sling.rewriter.ProcessingComponentConfiguration;
  import org.apache.sling.rewriter.ProcessingContext;
  import org.apache.sling.rewriter.Transformer;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  import org.xml.sax.Attributes;
  import org.xml.sax.ContentHandler;
  import org.xml.sax.Locator;
  import org.xml.sax.SAXException;
  import org.xml.sax.helpers.AttributesImpl;
  import org.xml.sax.helpers.DefaultHandler;
  
  import io.wcm.handler.url.UrlHandler;
  
  /**
   * HTML transformer that rewrites URLs in certain HTML element attributes.
   */
  class UrlExternalizerTransformer implements Transformer {
  
    private UrlExternalizerTransformerConfig transformerConfig;
    private ContentHandler contentHandler = EMPTY_CONTENT_HANDLER;
    private UrlHandler urlHandler;
  
    private static final Logger log = LoggerFactory.getLogger(UrlExternalizerTransformer.class.getName());
    private static final ContentHandler EMPTY_CONTENT_HANDLER = new DefaultHandler();
  
    @Override
    public void init(ProcessingContext pipelineContext, ProcessingComponentConfiguration config) {
      log.trace("Initialize UrlExternalizerTransformer with config: {}", config.getConfiguration());
      transformerConfig = new UrlExternalizerTransformerConfig(config.getConfiguration());
      urlHandler = pipelineContext.getRequest().adaptTo(UrlHandler.class);
    }
  
    @Override
    public void setContentHandler(ContentHandler contentHandler) {
      this.contentHandler = contentHandler;
    }
  
    @Override
    @SuppressWarnings("PMD.UseStringBufferForStringAppends")
    public void startElement(String nsUri, String name, String raw, Attributes attrs) throws SAXException {
  
      // check if for this element an attribute for rewriting is configured
      String rewriteAttr = transformerConfig.getElementAttributeNames().get(name);
      if (rewriteAttr == null) {
        log.trace("Rewrite element {}: Skip - No rewrite attribute configured.", name);
        contentHandler.startElement(nsUri, name, raw, attrs);
        return;
      }
  
      // validate URL handler
      if (urlHandler == null) {
        log.warn("Rewrite element {}: Skip - Unable to get URL handler/Integrator handler instance.", name);
        contentHandler.startElement(nsUri, name, raw, attrs);
        return;
      }
  
      // check if attribute exists
      int attributeIndex = attrs.getIndex(rewriteAttr);
      if (attributeIndex < 0) {
        log.trace("Rewrite element {}: Skip - Attribute does not exist: {}", name, rewriteAttr);
        contentHandler.startElement(nsUri, name, raw, attrs);
        return;
      }
  
      // rewrite URL
      String url = attrs.getValue(attributeIndex);
      if (StringUtils.isEmpty(url)) {
        log.trace("Rewrite element {}: Skip - URL is empty.", name);
        contentHandler.startElement(nsUri, name, raw, attrs);
        return;
      }
  
      // split off query string or fragment that may be appended to the URL
     String urlRemainder = null;
     int urlRemainderPos = StringUtils.indexOfAny(url, '?', '#');
     if (urlRemainderPos >= 0) {
       urlRemainder = url.substring(urlRemainderPos);
       url = url.substring(0, urlRemainderPos);
     }
 
     // decode URL (without URL remainder)
     url = URLDecoder.decode(url, StandardCharsets.UTF_8);
 
     // externalize URL (if it is not already externalized)
     String rewrittenUrl = urlHandler.get(url).buildExternalResourceUrl();
     if (urlRemainder != null) {
       if (rewrittenUrl == null) {
         rewrittenUrl = urlRemainder;
       }
       else {
         rewrittenUrl += urlRemainder;
       }
     }
 
     if (StringUtils.equals(url, rewrittenUrl)) {
       log.debug("Rewrite element {}: Skip - URL is already externalized: {}", name, url);
       contentHandler.startElement(nsUri, name, raw, attrs);
       return;
     }
 
     // set new attribute value
     log.debug("Rewrite element {}: Rewrite URL {} to {}", name, url, rewrittenUrl);
     AttributesImpl newAttrs = new AttributesImpl(attrs);
     newAttrs.setValue(attributeIndex, rewrittenUrl);
     contentHandler.startElement(nsUri, name, raw, newAttrs);
   }
 
   @Override
   public void setDocumentLocator(Locator locator) {
     this.contentHandler.setDocumentLocator(locator);
   }
 
   @Override
   public void startDocument() throws SAXException {
     this.contentHandler.startDocument();
   }
 
   @Override
   public void endDocument() throws SAXException {
     this.contentHandler.endDocument();
   }
 
   @Override
   public void startPrefixMapping(String prefix, String uri) throws SAXException {
     this.contentHandler.startPrefixMapping(prefix, uri);
   }
 
   @Override
   public void endPrefixMapping(String prefix) throws SAXException {
     this.contentHandler.endPrefixMapping(prefix);
   }
 
   @Override
   public void endElement(String uri, String localName, String qName) throws SAXException {
     this.contentHandler.endElement(uri, localName, qName);
   }
 
   @Override
   public void characters(char[] ch, int start, int length) throws SAXException {
     this.contentHandler.characters(ch, start, length);
   }
 
   @Override
   public void ignorableWhitespace(char[] ch, int start, int length) throws SAXException {
     this.contentHandler.ignorableWhitespace(ch, start, length);
   }
 
   @Override
   public void processingInstruction(String target, String data) throws SAXException {
     this.contentHandler.processingInstruction(target, data);
   }
 
   @Override
   public void skippedEntity(String name) throws SAXException {
     this.contentHandler.skippedEntity(name);
   }
 
   @Override
   public void dispose() {
     // nothing to do
   }
 
 }