///////////////////////////////////////////////////////////////////////////////////////////////
   // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
   // Copyright (C) 2001-2026 the original author or authors.
   //
   // This library is free software; you can redistribute it and/or
   // modify it under the terms of the GNU Lesser General Public
   // License as published by the Free Software Foundation; either
   // version 2.1 of the License, or (at your option) any later version.
   //
  // This library is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  // Lesser General Public License for more details.
  //
  // You should have received a copy of the GNU Lesser General Public
  // License along with this library; if not, write to the Free Software
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  ///////////////////////////////////////////////////////////////////////////////////////////////
  
  package com.puppycrawl.tools.checkstyle.checks;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
  import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
  import com.puppycrawl.tools.checkstyle.api.DetailAST;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  import com.puppycrawl.tools.checkstyle.utils.CheckUtil;
  
  /**
   * <div>
   * Restricts using
   * <a href = "https://docs.oracle.com/javase/specs/jls/se11/html/jls-3.html#jls-3.3">
   * Unicode escapes</a>
   * (such as &#92;u221e). It is possible to allow using escapes for
   * <a href="https://en.wiktionary.org/wiki/Appendix:Control_characters">
   * non-printable, control characters</a>.
   * Also, this check can be configured to allow using escapes
   * if trail comment is present. By the option it is possible to
   * allow using escapes if literal contains only them.
   * </div>
   *
   * @since 5.8
   */
  @FileStatefulCheck
  public class AvoidEscapedUnicodeCharactersCheck
      extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "forbid.escaped.unicode.char";
  
      /** Regular expression for Unicode chars. */
      private static final Pattern UNICODE_REGEXP = Pattern.compile("\\\\u+[a-fA-F\\d]{4}");
  
      /**
       * Regular expression Unicode control characters.
       *
       * @see <a href="https://en.wiktionary.org/wiki/Appendix:Control_characters">
       *     Appendix:Control characters</a>
       */
      private static final Pattern UNICODE_CONTROL = Pattern.compile("\\\\u+"
              + "(00[0-1][\\dA-Fa-f]"
              + "|00[8-9][\\dA-Fa-f]"
              + "|00[aA][dD]"
              + "|034[fF]"
              + "|070[fF]"
              + "|180[eE]"
              + "|200[b-fB-F]"
              + "|202[a-eA-E]"
              + "|206[0-4a-fA-F]"
              + "|[fF]{3}[9a-bA-B]"
              + "|[fF][eE][fF]{2})");
  
      /**
       * Regular expression for all escaped chars.
       * See <a href="https://docs.oracle.com/javase/specs/jls/se15/html/jls-3.html#jls-3.10.7">
       * EscapeSequence</a>
       */
      private static final Pattern ALL_ESCAPED_CHARS = Pattern.compile("^("
              + UNICODE_REGEXP.pattern()
              + "|\""
              + "|'"
              + "|\\\\"
              + "|\\\\b"
              + "|\\\\f"
              + "|\\\\n"
              + "|\\R"
              + "|\\\\r"
              + "|\\\\s"
              + "|\\\\t"
              + ")+$");
 
     /** Regular expression for escaped backslash. */
     private static final Pattern ESCAPED_BACKSLASH = Pattern.compile("\\\\\\\\");
 
     /** Regular expression for non-printable unicode chars. */
     private static final Pattern NON_PRINTABLE_CHARS = Pattern.compile("\\\\u0000"
             + "|\\\\u0009"
             + "|\\\\u000[bB]"
             + "|\\\\u000[cC]"
             + "|\\\\u0020"
             + "|\\\\u007[fF]"
             + "|\\\\u0085"
             + "|\\\\u009[fF]"
             + "|\\\\u00[aA]0"
             + "|\\\\u00[aA][dD]"
             + "|\\\\u04[fF]9"
             + "|\\\\u05[bB][eE]"
             + "|\\\\u05[dD]0"
             + "|\\\\u05[eE][aA]"
             + "|\\\\u05[fF]3"
             + "|\\\\u05[fF]4"
             + "|\\\\u0600"
             + "|\\\\u0604"
             + "|\\\\u061[cC]"
             + "|\\\\u06[dD]{2}"
             + "|\\\\u06[fF]{2}"
             + "|\\\\u070[fF]"
             + "|\\\\u0750"
             + "|\\\\u077[fF]"
             + "|\\\\u0[eE]00"
             + "|\\\\u0[eE]7[fF]"
             + "|\\\\u1680"
             + "|\\\\u180[eE]"
             + "|\\\\u1[eE]00"
             + "|\\\\u2000"
             + "|\\\\u2001"
             + "|\\\\u2002"
             + "|\\\\u2003"
             + "|\\\\u2004"
             + "|\\\\u2005"
             + "|\\\\u2006"
             + "|\\\\u2007"
             + "|\\\\u2008"
             + "|\\\\u2009"
             + "|\\\\u200[aA]"
             + "|\\\\u200[fF]"
             + "|\\\\u2025"
             + "|\\\\u2028"
             + "|\\\\u2029"
             + "|\\\\u202[fF]"
             + "|\\\\u205[fF]"
             + "|\\\\u2064"
             + "|\\\\u2066"
             + "|\\\\u2067"
             + "|\\\\u2068"
             + "|\\\\u2069"
             + "|\\\\u206[aA]"
             + "|\\\\u206[fF]"
             + "|\\\\u20[aA][fF]"
             + "|\\\\u2100"
             + "|\\\\u213[aA]"
             + "|\\\\u3000"
             + "|\\\\u[dD]800"
             + "|\\\\u[fF]8[fF]{2}"
             + "|\\\\u[fF][bB]50"
             + "|\\\\u[fF][dD][fF]{2}"
             + "|\\\\u[fF][eE]70"
             + "|\\\\u[fF][eE][fF]{2}"
             + "|\\\\u[fF]{2}0[eE]"
             + "|\\\\u[fF]{2}61"
             + "|\\\\u[fF]{2}[dD][cC]"
             + "|\\\\u[fF]{3}9"
             + "|\\\\u[fF]{3}[aA]"
             + "|\\\\u[fF]{3}[bB]"
             + "|\\\\u[fF]{4}");
 
     /**
      * Map of Pending Violations.
      * Key: Line number of the violation.
      * Value: List of literal AST nodes on that line pending validation.
      */
     private final Map<Integer, List<DetailAST>> pendingViolations = new HashMap<>();
 
     /** Allow use escapes for non-printable, control characters. */
     private boolean allowEscapesForControlCharacters;
 
     /** Allow use escapes if trail comment is present. */
     private boolean allowByTailComment;
 
     /** Allow if all characters in literal are escaped. */
     private boolean allowIfAllCharactersEscaped;
 
     /** Allow use escapes for non-printable, whitespace characters. */
     private boolean allowNonPrintableEscapes;
 
     /**
      * Setter to allow use escapes for non-printable, control characters.
      *
      * @param allow user's value.
      * @since 5.8
      */
     public final void setAllowEscapesForControlCharacters(boolean allow) {
         allowEscapesForControlCharacters = allow;
     }
 
     /**
      * Setter to allow use escapes if trail comment is present.
      *
      * @param allow user's value.
      * @since 5.8
      */
     public final void setAllowByTailComment(boolean allow) {
         allowByTailComment = allow;
     }
 
     /**
      * Setter to allow if all characters in literal are escaped.
      *
      * @param allow user's value.
      * @since 5.8
      */
     public final void setAllowIfAllCharactersEscaped(boolean allow) {
         allowIfAllCharactersEscaped = allow;
     }
 
     /**
      * Setter to allow use escapes for non-printable, whitespace characters.
      *
      * @param allow user's value.
      * @since 5.8
      */
     public final void setAllowNonPrintableEscapes(boolean allow) {
         allowNonPrintableEscapes = allow;
     }
 
     @Override
     public int[] getDefaultTokens() {
         return getRequiredTokens();
     }
 
     @Override
     public int[] getAcceptableTokens() {
         return getRequiredTokens();
     }
 
     @Override
     public int[] getRequiredTokens() {
         return new int[] {
             TokenTypes.STRING_LITERAL,
             TokenTypes.CHAR_LITERAL,
             TokenTypes.TEXT_BLOCK_CONTENT,
             TokenTypes.SINGLE_LINE_COMMENT,
             TokenTypes.BLOCK_COMMENT_BEGIN,
         };
     }
 
     @Override
     public boolean isCommentNodesRequired() {
         return true;
     }
 
     @Override
     public void beginTree(DetailAST rootAST) {
         pendingViolations.clear();
     }
 
     @Override
     public void visitToken(DetailAST ast) {
         if (ast.getType() == TokenTypes.SINGLE_LINE_COMMENT
                 || ast.getType() == TokenTypes.BLOCK_COMMENT_BEGIN) {
             checkComment(ast);
         }
         else {
             checkLiteral(ast);
         }
     }
 
     @Override
     public void finishTree(DetailAST rootAST) {
         for (List<DetailAST> asts : pendingViolations.values()) {
             for (DetailAST ast : asts) {
                 log(ast, MSG_KEY);
             }
         }
     }
 
     /**
      * Checks if the literal has Unicode char and should be reported.
      * If violation is found, it is added to pendingViolations.
      *
      * @param ast literal token.
      */
     private void checkLiteral(DetailAST ast) {
         final String literal =
             CheckUtil.stripIndentAndInitialNewLineFromTextBlock(ast.getText());
 
         if (hasUnicodeChar(literal) && !(isAllCharactersEscaped(literal)
                 || allowEscapesForControlCharacters
                         && isOnlyUnicodeValidChars(literal, UNICODE_CONTROL)
                 || allowNonPrintableEscapes
                         && isOnlyUnicodeValidChars(literal, NON_PRINTABLE_CHARS))) {
 
             if (allowByTailComment) {
                 int lineNo = ast.getLineNo();
                 if (ast.getType() == TokenTypes.TEXT_BLOCK_CONTENT) {
                     lineNo = ast.getNextSibling().getLineNo();
                 }
                 pendingViolations.computeIfAbsent(lineNo, key -> new ArrayList<>()).add(ast);
             }
             else {
                 log(ast, MSG_KEY);
             }
         }
     }
 
     /**
      * Checks if a comment clears any pending violations on the same line.
      *
      * @param comment comment token.
      */
     private void checkComment(DetailAST comment) {
         if (isTrailingComment(comment)) {
             pendingViolations.remove(comment.getLineNo());
         }
     }
 
     /**
      * Checks if a comment is trailing (has no code after it on the same line).
      *
      * @param commentNode the comment AST node
      * @return true if it is trailing
      */
     private static boolean isTrailingComment(DetailAST commentNode) {
         final DetailAST nextSibling = commentNode.getNextSibling();
         return nextSibling == null || nextSibling.getLineNo() != commentNode.getLineNo();
     }
 
     /**
      * Checks if literal has Unicode chars.
      *
      * @param literal String literal.
      * @return true if literal has Unicode chars.
      */
     private static boolean hasUnicodeChar(String literal) {
         final String literalWithoutEscapedBackslashes =
                 ESCAPED_BACKSLASH.matcher(literal).replaceAll("");
         return UNICODE_REGEXP.matcher(literalWithoutEscapedBackslashes).find();
     }
 
     /**
      * Check if String literal contains Unicode control chars.
      *
      * @param literal String literal.
      * @param pattern RegExp for valid characters.
      * @return true, if String literal contains Unicode control chars.
      */
     private static boolean isOnlyUnicodeValidChars(String literal, Pattern pattern) {
         final int unicodeMatchesCounter =
                 countMatches(UNICODE_REGEXP, literal);
         final int unicodeValidMatchesCounter =
                 countMatches(pattern, literal);
         return unicodeMatchesCounter - unicodeValidMatchesCounter == 0;
     }
 
     /**
      * Count regexp matches into String literal.
      *
      * @param pattern pattern.
      * @param target String literal.
      * @return count of regexp matches.
      */
     private static int countMatches(Pattern pattern, String target) {
         int matcherCounter = 0;
         final Matcher matcher = pattern.matcher(target);
         while (matcher.find()) {
             matcherCounter++;
         }
         return matcherCounter;
     }
 
     /**
      * Checks if all characters in String literal is escaped.
      *
      * @param literal current literal.
      * @return true if all characters in String literal is escaped.
      */
     private boolean isAllCharactersEscaped(String literal) {
         return allowIfAllCharactersEscaped
                 && ALL_ESCAPED_CHARS.matcher(literal).find();
     }
 }