src/net/instaweb/rewriter/public/critical_css_filter.h

/*
 * Copyright 2013 Google Inc.
 *
 * 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.
 */

// Author: slamm@google.com (Stephen Lamm)
//
// Replace link tags with the inline CSS that is resolved on initial load.
// Move the link tags to the bottom (usually CSS is placed in HEAD). Also,
// copy existing inline style blocks to the bottom to maintain the original
// rule order.
//
// TODO(slamm): Consider prioritizing the rules in inline style blocks too.
//
// This lessons the extern resources in the HEAD and allows the page to load
// sooner.
//

#ifndef NET_INSTAWEB_REWRITER_PUBLIC_CRITICAL_CSS_FILTER_H_
#define NET_INSTAWEB_REWRITER_PUBLIC_CRITICAL_CSS_FILTER_H_

#include <map>
#include <vector>

#include "net/instaweb/rewriter/critical_css.pb.h"
#include "net/instaweb/rewriter/public/common_filter.h"
#include "net/instaweb/rewriter/public/css_tag_scanner.h"
#include "pagespeed/kernel/base/basictypes.h"
#include "pagespeed/kernel/base/string.h"

namespace net_instaweb {

class CriticalCssFinder;
class CriticalCssResult;
class CriticalCssResult_LinkRules;
class HtmlCharactersNode;
class HtmlElement;
class RewriteDriver;

class CriticalCssFilter : public CommonFilter {
 public:
  explicit CriticalCssFilter(RewriteDriver* rewrite_driver,
                             CriticalCssFinder* finder);
  virtual ~CriticalCssFilter();

  static const char kAddStylesScript[];
  static const char kStatsScriptTemplate[];

  // Overridden from CommonFilter:
  virtual void DetermineEnabled(GoogleString* disabled_reason);
  virtual void StartDocumentImpl();
  virtual void EndDocument();
  virtual void StartElementImpl(HtmlElement* element);
  virtual void EndElementImpl(HtmlElement* element);
  virtual void Characters(HtmlCharactersNode* characters);

  virtual const char* Name() const { return "CriticalCss"; }

 private:
  // Decodes the link tag into a valid url.
  GoogleString DecodeUrl(const GoogleString& url);

  // Returns the critical CSS rules for the |decoded_url| of a <link> tag.
  // If data is unavailable (e.g., not yet determined, or flushed from
  //     page property cache), the returned value is NULL.
  const CriticalCssResult_LinkRules* GetLinkRules(
      const GoogleString& decoded_url);

  // Log the status of an attempt to rewrite.
  // TODO(gee): This probably belongs in an ancestor class.
  void LogRewrite(int status);

  CriticalCssFinder* finder_;

  CriticalCssResult* critical_css_result_;

  // Map link URLs to indexes in the critical CSS result.
  typedef std::map<GoogleString, int> UrlIndexes;
  UrlIndexes url_indexes_;

  bool has_critical_css_;
  bool is_move_link_script_added_;

  class CssElement;
  class CssStyleElement;
  typedef std::vector<CssElement*> CssElementVector;
  CssElementVector css_elements_;
  CssStyleElement* current_style_element_;

  // TODO(slamm): Are these just for logging, or do you want to export these
  // to varz as well.  Just in general, I think someone intimately familiar with
  // this filter needs to make a pass and figure out what we should be
  // monitoring.
  int total_critical_size_;
  int total_original_size_;
  int repeated_style_blocks_size_;
  int num_repeated_style_blocks_;
  int num_links_;
  int num_replaced_links_;

  DISALLOW_COPY_AND_ASSIGN(CriticalCssFilter);
};

}  // namespace net_instaweb

#endif  // NET_INSTAWEB_REWRITER_PUBLIC_CRITICAL_CSS_FILTER_H_