package net.sf.xsshtmlfilter;
   
   import java.util.ArrayList;
   import java.util.Collections;
   import java.util.HashMap;
   import java.util.List;
   import java.util.Map;
   import java.util.concurrent.ConcurrentHashMap;
   import java.util.concurrent.ConcurrentMap;
  import java.util.logging.Logger;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  /**
   *
   * HTML filtering utility for protecting against XSS (Cross Site Scripting).
   *
   * This code is licensed LGPLv3
   *
   * This code is a Java port of the original work in PHP by Cal Hendersen.
   * http://code.iamcal.com/php/lib_filter/
   *
   * The trickiest part of the translation was handling the differences in regex handling
   * between PHP and Java.  These resources were helpful in the process:
   *
   * http://java.sun.com/j2se/1.4.2/docs/api/java/util/regex/Pattern.html
   * http://us2.php.net/manual/en/reference.pcre.pattern.modifiers.php
   * http://www.regular-expressions.info/modifiers.html
   *
   * A note on naming conventions: instance variables are prefixed with a "v"; global
   * constants are in all caps.
   *
   * Sample use:
   * String input = ...
   * String clean = new HTMLFilter().filter( input );
   *
   * The class is not thread safe. Create a new instance if in doubt.
   *
   * If you find bugs or have suggestions on improvement (especially regarding
   * performance), please contact us.  The latest version of this
   * source, and our contact details, can be found at http://xss-html-filter.sf.net
   *
   * @author Joseph O'Connell
   * @author Cal Hendersen
   * @author Michael Semb Wever
   */
  public final class HTMLFilter {
  
      /** regex flag union representing /si modifiers in php **/
      private static final int REGEX_FLAGS_SI = Pattern.CASE_INSENSITIVE | Pattern.DOTALL;
      private static final Pattern P_COMMENTS = Pattern.compile("<!--(.*?)-->", Pattern.DOTALL);
      private static final Pattern P_COMMENT = Pattern.compile("^!--(.*)--$", REGEX_FLAGS_SI);
      private static final Pattern P_TAGS = Pattern.compile("<(.*?)>", Pattern.DOTALL);
      private static final Pattern P_END_TAG = Pattern.compile("^/([a-z0-9]+)", REGEX_FLAGS_SI);
      private static final Pattern P_START_TAG = Pattern.compile("^([a-z0-9]+)(.*?)(/?)$", REGEX_FLAGS_SI);
      private static final Pattern P_QUOTED_ATTRIBUTES = Pattern.compile("([a-z0-9]+)=([\"'])(.*?)\\2", REGEX_FLAGS_SI);
      private static final Pattern P_UNQUOTED_ATTRIBUTES = Pattern.compile("([a-z0-9]+)(=)([^\"\\s']+)", REGEX_FLAGS_SI);
      private static final Pattern P_PROTOCOL = Pattern.compile("^([^:]+):", REGEX_FLAGS_SI);
      private static final Pattern P_ENTITY = Pattern.compile("&#(\\d+);?");
      private static final Pattern P_ENTITY_UNICODE = Pattern.compile("&#x([0-9a-f]+);?");
      private static final Pattern P_ENCODE = Pattern.compile("%([0-9a-f]{2});?");
      private static final Pattern P_VALID_ENTITIES = Pattern.compile("&([^&;]*)(?=(;|&|$))");
      private static final Pattern P_VALID_QUOTES = Pattern.compile("(>|^)([^<]+?)(<|$)", Pattern.DOTALL);
      private static final Pattern P_END_ARROW = Pattern.compile("^>");
      private static final Pattern P_BODY_TO_END = Pattern.compile("<([^>]*?)(?=<|$)");
      private static final Pattern P_XML_CONTENT = Pattern.compile("(^|>)([^<]*?)(?=>)");
      private static final Pattern P_STRAY_LEFT_ARROW = Pattern.compile("<([^>]*?)(?=<|$)");
      private static final Pattern P_STRAY_RIGHT_ARROW = Pattern.compile("(^|>)([^<]*?)(?=>)");
      private static final Pattern P_AMP = Pattern.compile("&");
      private static final Pattern P_QUOTE = Pattern.compile("\"");
      private static final Pattern P_LEFT_ARROW = Pattern.compile("<");
      private static final Pattern P_RIGHT_ARROW = Pattern.compile(">");
      private static final Pattern P_BOTH_ARROWS = Pattern.compile("<>");
  
      // @xxx could grow large... maybe use sesat's ReferenceMap
      private static final ConcurrentMap<String,Pattern> P_REMOVE_PAIR_BLANKS = new ConcurrentHashMap<String, Pattern>();
      private static final ConcurrentMap<String,Pattern> P_REMOVE_SELF_BLANKS = new ConcurrentHashMap<String, Pattern>();
  
      /** set of allowed html elements, along with allowed attributes for each element **/
      private final Map<String, List<String>> vAllowed;
      /** counts of open tags for each (allowable) html element **/
      private final Map<String, Integer> vTagCounts = new HashMap<String, Integer>();
  
      /** html elements which must always be self-closing (e.g. "<img />") **/
      private final String[] vSelfClosingTags;
      /** html elements which must always have separate opening and closing tags (e.g. "<b></b>") **/
      private final String[] vNeedClosingTags;
      /** set of disallowed html elements **/
      private final String[] vDisallowed;
      /** attributes which should be checked for valid protocols **/
      private final String[] vProtocolAtts;
      /** allowed protocols **/
      private final String[] vAllowedProtocols;
      /** tags which should be removed if they contain no content (e.g. "<b></b>" or "<b />") **/
      private final String[] vRemoveBlanks;
      /** entities allowed within html markup **/
      private final String[] vAllowedEntities;
      /** flag determining whether comments are allowed in input String. */
      private final boolean stripComment;
     private final boolean encodeQuotes;
     private boolean vDebug = false;
     /**
      * flag determining whether to try to make tags when presented with "unbalanced"
      * angle brackets (e.g. "<b text </b>" becomes "<b> text </b>").  If set to false,
      * unbalanced angle brackets will be html escaped.
      */
     private final boolean alwaysMakeTags;
 
     /** Default constructor.
      *
      */
     public HTMLFilter() {
         vAllowed = new HashMap<String, List<String>>();
 
         final ArrayList<String> a_atts = new ArrayList<String>();
         a_atts.add("href");
         a_atts.add("target");
         vAllowed.put("a", a_atts);
 
         final ArrayList<String> img_atts = new ArrayList<String>();
         img_atts.add("src");
         img_atts.add("width");
         img_atts.add("height");
         img_atts.add("alt");
         vAllowed.put("img", img_atts);
 
         final ArrayList<String> no_atts = new ArrayList<String>();
         vAllowed.put("b", no_atts);
         vAllowed.put("strong", no_atts);
         vAllowed.put("i", no_atts);
         vAllowed.put("em", no_atts);
 
         vSelfClosingTags = new String[]{"img"};
         vNeedClosingTags = new String[]{"a", "b", "strong", "i", "em"};
         vDisallowed = new String[]{};
         vAllowedProtocols = new String[]{"http", "mailto"}; // no ftp.
         vProtocolAtts = new String[]{"src", "href"};
         vRemoveBlanks = new String[]{"a", "b", "strong", "i", "em"};
         vAllowedEntities = new String[]{"amp", "gt", "lt", "quot"};
         stripComment = true;
         encodeQuotes = true;
         alwaysMakeTags = true;
     }
 
     /** Set debug flag to true. Otherwise use default settings. See the default constructor.
      *
      * @param debug turn debug on with a true argument
      */
     public HTMLFilter(final boolean debug) {
         this();
         vDebug = debug;
 
     }
 
     /** Map-parameter configurable constructor.
      *
      * @param conf map containing configuration. keys match field names.
      */
     public HTMLFilter(final Map<String,Object> conf) {
 
         assert conf.containsKey("vAllowed") : "configuration requires vAllowed";
         assert conf.containsKey("vSelfClosingTags") : "configuration requires vSelfClosingTags";
         assert conf.containsKey("vNeedClosingTags") : "configuration requires vNeedClosingTags";
         assert conf.containsKey("vDisallowed") : "configuration requires vDisallowed";
         assert conf.containsKey("vAllowedProtocols") : "configuration requires vAllowedProtocols";
         assert conf.containsKey("vProtocolAtts") : "configuration requires vProtocolAtts";
         assert conf.containsKey("vRemoveBlanks") : "configuration requires vRemoveBlanks";
         assert conf.containsKey("vAllowedEntities") : "configuration requires vAllowedEntities";
 
         vAllowed = Collections.unmodifiableMap((HashMap<String, List<String>>) conf.get("vAllowed"));
         vSelfClosingTags = (String[]) conf.get("vSelfClosingTags");
         vNeedClosingTags = (String[]) conf.get("vNeedClosingTags");
         vDisallowed = (String[]) conf.get("vDisallowed");
         vAllowedProtocols = (String[]) conf.get("vAllowedProtocols");
         vProtocolAtts = (String[]) conf.get("vProtocolAtts");
         vRemoveBlanks = (String[]) conf.get("vRemoveBlanks");
         vAllowedEntities = (String[]) conf.get("vAllowedEntities");
         stripComment =  conf.containsKey("stripComment") ? (Boolean) conf.get("stripComment") : true;
         encodeQuotes = conf.containsKey("encodeQuotes") ? (Boolean) conf.get("encodeQuotes") : true;
         alwaysMakeTags = conf.containsKey("alwaysMakeTags") ? (Boolean) conf.get("alwaysMakeTags") : true;
     }
 
     private void reset() {
         vTagCounts.clear();
     }
 
     private void debug(final String msg) {
         if (vDebug) {
             Logger.getAnonymousLogger().info(msg);
         }
     }
 
     //---------------------------------------------------------------
     // my versions of some PHP library functions
     public static String chr(final int decimal) {
         return String.valueOf((char) decimal);
     }
 
     public static String htmlSpecialChars(final String s) {
         String result = s;
         result = regexReplace(P_AMP, "&amp;", result);
         result = regexReplace(P_QUOTE, "&quot;", result);
         result = regexReplace(P_LEFT_ARROW, "&lt;", result);
         result = regexReplace(P_RIGHT_ARROW, "&gt;", result);
         return result;
     }
 
     //---------------------------------------------------------------
     /**
      * given a user submitted input String, filter out any invalid or restricted
      * html.
      *
      * @param input text (i.e. submitted by a user) than may contain html
      * @return "clean" version of input, with only valid, whitelisted html elements allowed
      */
     public String filter(final String input) {
         reset();
         String s = input;
 
         debug("************************************************");
         debug("              INPUT: " + input);
 
         s = escapeComments(s);
         debug("     escapeComments: " + s);
 
         s = balanceHTML(s);
         debug("        balanceHTML: " + s);
 
         s = checkTags(s);
         debug("          checkTags: " + s);
 
         s = processRemoveBlanks(s);
         debug("processRemoveBlanks: " + s);
 
         s = validateEntities(s);
         debug("    validateEntites: " + s);
 
         debug("************************************************\n\n");
         return s;
     }
 
     public boolean isAlwaysMakeTags(){
         return alwaysMakeTags;
     }
 
     public boolean isStripComments(){
         return stripComment;
     }
 
     private String escapeComments(final String s) {
         final Matcher m = P_COMMENTS.matcher(s);
         final StringBuffer buf = new StringBuffer();
         if (m.find()) {
             final String match = m.group(1); //(.*?)
             m.appendReplacement(buf, Matcher.quoteReplacement("<!--" + htmlSpecialChars(match) + "-->"));
         }
         m.appendTail(buf);
 
         return buf.toString();
     }
 
     private String balanceHTML(String s) {
         if (alwaysMakeTags) {
             //
             // try and form html
             //
             s = regexReplace(P_END_ARROW, "", s);
             s = regexReplace(P_BODY_TO_END, "<$1>", s);
             s = regexReplace(P_XML_CONTENT, "$1<$2", s);
 
         } else {
             //
             // escape stray brackets
             //
             s = regexReplace(P_STRAY_LEFT_ARROW, "&lt;$1", s);
             s = regexReplace(P_STRAY_RIGHT_ARROW, "$1$2&gt;<", s);
 
             //
             // the last regexp causes '<>' entities to appear
             // (we need to do a lookahead assertion so that the last bracket can
             // be used in the next pass of the regexp)
             //
             s = regexReplace(P_BOTH_ARROWS, "", s);
         }
 
         return s;
     }
 
     private String checkTags(String s) {
         Matcher m = P_TAGS.matcher(s);
 
         final StringBuffer buf = new StringBuffer();
         while (m.find()) {
             String replaceStr = m.group(1);
             replaceStr = processTag(replaceStr);
             m.appendReplacement(buf, Matcher.quoteReplacement(replaceStr));
         }
         m.appendTail(buf);
 
         s = buf.toString();
 
         // these get tallied in processTag
         // (remember to reset before subsequent calls to filter method)
         for (String key : vTagCounts.keySet()) {
             for (int ii = 0; ii < vTagCounts.get(key); ii++) {
                 s += "</" + key + ">";
             }
         }
 
         return s;
     }
 
     private String processRemoveBlanks(final String s) {
         String result = s;
         for (String tag : vRemoveBlanks) {
             if(!P_REMOVE_PAIR_BLANKS.containsKey(tag)){
                 P_REMOVE_PAIR_BLANKS.putIfAbsent(tag, Pattern.compile("<" + tag + "(\\s[^>]*)?></" + tag + ">"));
             }
             result = regexReplace(P_REMOVE_PAIR_BLANKS.get(tag), "", result);
             if(!P_REMOVE_SELF_BLANKS.containsKey(tag)){
                 P_REMOVE_SELF_BLANKS.putIfAbsent(tag, Pattern.compile("<" + tag + "(\\s[^>]*)?/>"));
             }
             result = regexReplace(P_REMOVE_SELF_BLANKS.get(tag), "", result);
         }
 
         return result;
     }
 
     private static String regexReplace(final Pattern regex_pattern, final String replacement, final String s) {
         Matcher m = regex_pattern.matcher(s);
         return m.replaceAll(replacement);
     }
 
     private String processTag(final String s) {
         // ending tags
         Matcher m = P_END_TAG.matcher(s);
         if (m.find()) {
             final String name = m.group(1).toLowerCase();
             if (allowed(name)) {
                 if (!inArray(name, vSelfClosingTags)) {
                     if (vTagCounts.containsKey(name)) {
                         vTagCounts.put(name, vTagCounts.get(name) - 1);
                         return "</" + name + ">";
                     }
                 }
             }
         }
 
         // starting tags
         m = P_START_TAG.matcher(s);
         if (m.find()) {
             final String name = m.group(1).toLowerCase();
             final String body = m.group(2);
             String ending = m.group(3);
 
             //debug( "in a starting tag, name='" + name + "'; body='" + body + "'; ending='" + ending + "'" );
             if (allowed(name)) {
                 String params = "";
 
                 final Matcher m2 = P_QUOTED_ATTRIBUTES.matcher(body);
                 final Matcher m3 = P_UNQUOTED_ATTRIBUTES.matcher(body);
                 final List<String> paramNames = new ArrayList<String>();
                 final List<String> paramValues = new ArrayList<String>();
                 while (m2.find()) {
                     paramNames.add(m2.group(1)); //([a-z0-9]+)
                     paramValues.add(m2.group(3)); //(.*?)
                 }
                 while (m3.find()) {
                     paramNames.add(m3.group(1)); //([a-z0-9]+)
                     paramValues.add(m3.group(3)); //([^\"\\s']+)
                 }
 
                 String paramName, paramValue;
                 for (int ii = 0; ii < paramNames.size(); ii++) {
                     paramName = paramNames.get(ii).toLowerCase();
                     paramValue = paramValues.get(ii);
 
 //          debug( "paramName='" + paramName + "'" );
 //          debug( "paramValue='" + paramValue + "'" );
 //          debug( "allowed? " + vAllowed.get( name ).contains( paramName ) );
 
                     if (allowedAttribute(name, paramName)) {
                         if (inArray(paramName, vProtocolAtts)) {
                             paramValue = processParamProtocol(paramValue);
                         }
                         params += " " + paramName + "=\"" + paramValue + "\"";
                     }
                 }
 
                 if (inArray(name, vSelfClosingTags)) {
                     ending = " /";
                 }
 
                 if (inArray(name, vNeedClosingTags)) {
                     ending = "";
                 }
 
                 if (ending == null || ending.length() < 1) {
                     if (vTagCounts.containsKey(name)) {
                         vTagCounts.put(name, vTagCounts.get(name) + 1);
                     } else {
                         vTagCounts.put(name, 1);
                     }
                 } else {
                     ending = " /";
                 }
                 return "<" + name + params + ending + ">";
             } else {
                 return "";
             }
         }
 
         // comments
         m = P_COMMENT.matcher(s);
         if (!stripComment && m.find()) {
             return  "<" + m.group() + ">";
         }
 
         return "";
     }
 
     private String processParamProtocol(String s) {
         s = decodeEntities(s);
         final Matcher m = P_PROTOCOL.matcher(s);
         if (m.find()) {
             final String protocol = m.group(1);
             if (!inArray(protocol, vAllowedProtocols)) {
                 // bad protocol, turn into local anchor link instead
                 s = "#" + s.substring(protocol.length() + 1, s.length());
                 if (s.startsWith("#//")) {
                     s = "#" + s.substring(3, s.length());
                 }
             }
         }
 
         return s;
     }
 
     private String decodeEntities(String s) {
         StringBuffer buf = new StringBuffer();
 
         Matcher m = P_ENTITY.matcher(s);
         while (m.find()) {
             final String match = m.group(1);
             final int decimal = Integer.decode(match).intValue();
             m.appendReplacement(buf, Matcher.quoteReplacement(chr(decimal)));
         }
         m.appendTail(buf);
         s = buf.toString();
 
         buf = new StringBuffer();
         m = P_ENTITY_UNICODE.matcher(s);
         while (m.find()) {
             final String match = m.group(1);
             final int decimal = Integer.valueOf(match, 16).intValue();
             m.appendReplacement(buf, Matcher.quoteReplacement(chr(decimal)));
         }
         m.appendTail(buf);
         s = buf.toString();
 
         buf = new StringBuffer();
         m = P_ENCODE.matcher(s);
         while (m.find()) {
             final String match = m.group(1);
             final int decimal = Integer.valueOf(match, 16).intValue();
             m.appendReplacement(buf, Matcher.quoteReplacement(chr(decimal)));
         }
         m.appendTail(buf);
         s = buf.toString();
 
         s = validateEntities(s);
         return s;
     }
 
     private String validateEntities(final String s) {
         StringBuffer buf = new StringBuffer();
 
         // validate entities throughout the string
         Matcher m = P_VALID_ENTITIES.matcher(s);
         while (m.find()) {
             final String one = m.group(1); //([^&;]*)
             final String two = m.group(2); //(?=(;|&|$))
             m.appendReplacement(buf, Matcher.quoteReplacement(checkEntity(one, two)));
         }
         m.appendTail(buf);
 
         return encodeQuotes(buf.toString());
     }
 
     private String encodeQuotes(final String s){
         if(encodeQuotes){
             StringBuffer buf = new StringBuffer();
             Matcher m = P_VALID_QUOTES.matcher(s);
             while (m.find()) {
                 final String one = m.group(1); //(>|^)
                 final String two = m.group(2); //([^<]+?)
                 final String three = m.group(3); //(<|$)
                 m.appendReplacement(buf, Matcher.quoteReplacement(one + regexReplace(P_QUOTE, "&quot;", two) + three));
             }
             m.appendTail(buf);
             return buf.toString();
         }else{
             return s;
         }
     }
 
     private String checkEntity(final String preamble, final String term) {
 
         return ";".equals(term) && isValidEntity(preamble)
                 ? '&' + preamble
                 : "&amp;" + preamble;
     }
 
     private boolean isValidEntity(final String entity) {
         return inArray(entity, vAllowedEntities);
     }
 
     private static boolean inArray(final String s, final String[] array) {
         for (String item : array) {
             if (item != null && item.equals(s)) {
                 return true;
             }
         }
         return false;
     }
 
     private boolean allowed(final String name) {
         return (vAllowed.isEmpty() || vAllowed.containsKey(name)) && !inArray(name, vDisallowed);
     }
 
     private boolean allowedAttribute(final String name, final String paramName) {
         return allowed(name) && (vAllowed.isEmpty() || vAllowed.get(name).contains(paramName));
     }
 }