////////////////////////////////////////////////////////////////////////////////
   // checkstyle: Checks Java source code for adherence to a set of rules.
   // Copyright (C) 2001-2019 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.indentation;
  
  import java.util.ArrayDeque;
  import java.util.Deque;
  import java.util.Locale;
  
  import com.puppycrawl.tools.checkstyle.StatelessCheck;
  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.CommonUtil;
  
  /**
   * This Check controls the indentation between comments and surrounding code.
   * Comments are indented at the same level as the surrounding code.
   * Detailed info about such convention can be found
   * <a href=
   * "https://checkstyle.org/styleguides/google-java-style-20170228.html#s4.8.6.1-block-comment-style">
   * here</a>
   * <p>
   * Examples:
   * </p>
   * <p>
   * To configure the Check:
   * </p>
   *
   * <pre>
   * {@code
   * &lt;module name=&quot;CommentsIndentation&quot;/&gt;
   * }
   * {@code
   * /*
   *  * comment
   *  * some comment
   *  *&#47;
   * boolean bool = true; - such comment indentation is ok
   *    /*
   *    * comment
   *    * some comment
   *     *&#47;
   * double d = 3.14; - Block Comment has incorrect indentation level 7, expected 4.
   * // some comment - comment is ok
   * String str = "";
   *     // some comment Comment has incorrect indentation level 8, expected 4.
   * String str1 = "";
   * }
   * </pre>
   *
   */
  @StatelessCheck
  public class CommentsIndentationCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties" file.
       */
      public static final String MSG_KEY_SINGLE = "comments.indentation.single";
  
      /**
       * A key is pointing to the warning message text in "messages.properties" file.
       */
      public static final String MSG_KEY_BLOCK = "comments.indentation.block";
  
      @Override
      public int[] getDefaultTokens() {
          return new int[] {
              TokenTypes.SINGLE_LINE_COMMENT,
              TokenTypes.BLOCK_COMMENT_BEGIN,
          };
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return new int[] {
              TokenTypes.SINGLE_LINE_COMMENT,
              TokenTypes.BLOCK_COMMENT_BEGIN,
          };
      }
  
      @Override
      public int[] getRequiredTokens() {
         return CommonUtil.EMPTY_INT_ARRAY;
     }
 
     @Override
     public boolean isCommentNodesRequired() {
         return true;
     }
 
     @Override
     public void visitToken(DetailAST commentAst) {
         switch (commentAst.getType()) {
             case TokenTypes.SINGLE_LINE_COMMENT:
             case TokenTypes.BLOCK_COMMENT_BEGIN:
                 visitComment(commentAst);
                 break;
             default:
                 final String exceptionMsg = "Unexpected token type: " + commentAst.getText();
                 throw new IllegalArgumentException(exceptionMsg);
         }
     }
 
     /**
      * Checks comment indentations over surrounding code, e.g.:
      * <p>
      * {@code
      * // some comment - this is ok
      * double d = 3.14;
      *     // some comment - this is <b>not</b> ok.
      * double d1 = 5.0;
      * }
      * </p>
      * @param comment comment to check.
      */
     private void visitComment(DetailAST comment) {
         if (!isTrailingComment(comment)) {
             final DetailAST prevStmt = getPreviousStatement(comment);
             final DetailAST nextStmt = getNextStmt(comment);
 
             if (isInEmptyCaseBlock(prevStmt, nextStmt)) {
                 handleCommentInEmptyCaseBlock(prevStmt, comment, nextStmt);
             }
             else if (isFallThroughComment(prevStmt, nextStmt)) {
                 handleFallThroughComment(prevStmt, comment, nextStmt);
             }
             else if (isInEmptyCodeBlock(prevStmt, nextStmt)) {
                 handleCommentInEmptyCodeBlock(comment, nextStmt);
             }
             else if (isCommentAtTheEndOfTheCodeBlock(nextStmt)) {
                 handleCommentAtTheEndOfTheCodeBlock(prevStmt, comment, nextStmt);
             }
             else if (nextStmt != null && !areSameLevelIndented(comment, nextStmt, nextStmt)) {
                 log(comment.getLineNo(), getMessageKey(comment), nextStmt.getLineNo(),
                     comment.getColumnNo(), nextStmt.getColumnNo());
             }
         }
     }
 
     /**
      * Returns the next statement of a comment.
      * @param comment comment.
      * @return the next statement of a comment.
      */
     private static DetailAST getNextStmt(DetailAST comment) {
         DetailAST nextStmt = comment.getNextSibling();
         while (nextStmt != null
                 && isComment(nextStmt)
                 && comment.getColumnNo() != nextStmt.getColumnNo()) {
             nextStmt = nextStmt.getNextSibling();
         }
         return nextStmt;
     }
 
     /**
      * Returns the previous statement of a comment.
      * @param comment comment.
      * @return the previous statement of a comment.
      */
     private DetailAST getPreviousStatement(DetailAST comment) {
         final DetailAST prevStatement;
         if (isDistributedPreviousStatement(comment)) {
             prevStatement = getDistributedPreviousStatement(comment);
         }
         else {
             prevStatement = getOneLinePreviousStatement(comment);
         }
         return prevStatement;
     }
 
     /**
      * Checks whether the previous statement of a comment is distributed over two or more lines.
      * @param comment comment to check.
      * @return true if the previous statement of a comment is distributed over two or more lines.
      */
     private boolean isDistributedPreviousStatement(DetailAST comment) {
         final DetailAST previousSibling = comment.getPreviousSibling();
         return isDistributedExpression(comment)
             || isDistributedReturnStatement(previousSibling)
             || isDistributedThrowStatement(previousSibling);
     }
 
     /**
      * Checks whether the previous statement of a comment is a method call chain or
      * string concatenation statement distributed over two ore more lines.
      * @param comment comment to check.
      * @return true if the previous statement is a distributed expression.
      */
     private boolean isDistributedExpression(DetailAST comment) {
         DetailAST previousSibling = comment.getPreviousSibling();
         while (previousSibling != null && isComment(previousSibling)) {
             previousSibling = previousSibling.getPreviousSibling();
         }
         boolean isDistributed = false;
         if (previousSibling != null) {
             if (previousSibling.getType() == TokenTypes.SEMI
                     && isOnPreviousLineIgnoringComments(comment, previousSibling)) {
                 DetailAST currentToken = previousSibling.getPreviousSibling();
                 while (currentToken.getFirstChild() != null) {
                     currentToken = currentToken.getFirstChild();
                 }
                 if (currentToken.getType() == TokenTypes.COMMENT_CONTENT) {
                     currentToken = currentToken.getParent();
                     while (isComment(currentToken)) {
                         currentToken = currentToken.getNextSibling();
                     }
                 }
                 if (previousSibling.getLineNo() != currentToken.getLineNo()) {
                     isDistributed = true;
                 }
             }
             else {
                 isDistributed = isStatementWithPossibleCurlies(previousSibling);
             }
         }
         return isDistributed;
     }
 
     /**
      * Whether the statement can have or always have curly brackets.
      * @param previousSibling the statement to check.
      * @return true if the statement can have or always have curly brackets.
      */
     private static boolean isStatementWithPossibleCurlies(DetailAST previousSibling) {
         return previousSibling.getType() == TokenTypes.LITERAL_IF
             || previousSibling.getType() == TokenTypes.LITERAL_TRY
             || previousSibling.getType() == TokenTypes.LITERAL_FOR
             || previousSibling.getType() == TokenTypes.LITERAL_DO
             || previousSibling.getType() == TokenTypes.LITERAL_WHILE
             || previousSibling.getType() == TokenTypes.LITERAL_SWITCH
             || isDefinition(previousSibling);
     }
 
     /**
      * Whether the statement is a kind of definition (method, class etc.).
      * @param previousSibling the statement to check.
      * @return true if the statement is a kind of definition.
      */
     private static boolean isDefinition(DetailAST previousSibling) {
         return previousSibling.getType() == TokenTypes.METHOD_DEF
             || previousSibling.getType() == TokenTypes.CLASS_DEF
             || previousSibling.getType() == TokenTypes.INTERFACE_DEF
             || previousSibling.getType() == TokenTypes.ENUM_DEF
             || previousSibling.getType() == TokenTypes.ANNOTATION_DEF;
     }
 
     /**
      * Checks whether the previous statement of a comment is a distributed return statement.
      * @param commentPreviousSibling previous sibling of the comment.
      * @return true if the previous statement of a comment is a distributed return statement.
      */
     private static boolean isDistributedReturnStatement(DetailAST commentPreviousSibling) {
         boolean isDistributed = false;
         if (commentPreviousSibling != null
                 && commentPreviousSibling.getType() == TokenTypes.LITERAL_RETURN) {
             final DetailAST firstChild = commentPreviousSibling.getFirstChild();
             final DetailAST nextSibling = firstChild.getNextSibling();
             if (nextSibling != null) {
                 isDistributed = true;
             }
         }
         return isDistributed;
     }
 
     /**
      * Checks whether the previous statement of a comment is a distributed throw statement.
      * @param commentPreviousSibling previous sibling of the comment.
      * @return true if the previous statement of a comment is a distributed throw statement.
      */
     private static boolean isDistributedThrowStatement(DetailAST commentPreviousSibling) {
         boolean isDistributed = false;
         if (commentPreviousSibling != null
                 && commentPreviousSibling.getType() == TokenTypes.LITERAL_THROW) {
             final DetailAST firstChild = commentPreviousSibling.getFirstChild();
             final DetailAST nextSibling = firstChild.getNextSibling();
             if (nextSibling.getLineNo() != commentPreviousSibling.getLineNo()) {
                 isDistributed = true;
             }
         }
         return isDistributed;
     }
 
     /**
      * Returns the first token of the distributed previous statement of comment.
      * @param comment comment to check.
      * @return the first token of the distributed previous statement of comment.
      */
     private static DetailAST getDistributedPreviousStatement(DetailAST comment) {
         DetailAST currentToken = comment.getPreviousSibling();
         while (isComment(currentToken)) {
             currentToken = currentToken.getPreviousSibling();
         }
         final DetailAST previousStatement;
         if (currentToken.getType() == TokenTypes.SEMI) {
             currentToken = currentToken.getPreviousSibling();
             while (currentToken.getFirstChild() != null) {
                 currentToken = currentToken.getFirstChild();
             }
             previousStatement = currentToken;
         }
         else {
             previousStatement = currentToken;
         }
         return previousStatement;
     }
 
     /**
      * Checks whether case block is empty.
      * @param nextStmt previous statement.
      * @param prevStmt next statement.
      * @return true if case block is empty.
      */
     private static boolean isInEmptyCaseBlock(DetailAST prevStmt, DetailAST nextStmt) {
         return prevStmt != null
             && nextStmt != null
             && (prevStmt.getType() == TokenTypes.LITERAL_CASE
                 || prevStmt.getType() == TokenTypes.CASE_GROUP)
             && (nextStmt.getType() == TokenTypes.LITERAL_CASE
                 || nextStmt.getType() == TokenTypes.LITERAL_DEFAULT);
     }
 
     /**
      * Checks whether comment is a 'fall through' comment.
      * For example:
      * <p>
      * {@code
      *    ...
      *    case OPTION_ONE:
      *        int someVariable = 1;
      *        // fall through
      *    case OPTION_TWO:
      *        int a = 5;
      *        break;
      *    ...
      * }
      * </p>
      * @param prevStmt previous statement.
      * @param nextStmt next statement.
      * @return true if a comment is a 'fall through' comment.
      */
     private static boolean isFallThroughComment(DetailAST prevStmt, DetailAST nextStmt) {
         return prevStmt != null
             && nextStmt != null
             && prevStmt.getType() != TokenTypes.LITERAL_CASE
             && (nextStmt.getType() == TokenTypes.LITERAL_CASE
                 || nextStmt.getType() == TokenTypes.LITERAL_DEFAULT);
     }
 
     /**
      * Checks whether a comment is placed at the end of the code block.
      * @param nextStmt next statement.
      * @return true if a comment is placed at the end of the block.
      */
     private static boolean isCommentAtTheEndOfTheCodeBlock(DetailAST nextStmt) {
         return nextStmt != null
             && nextStmt.getType() == TokenTypes.RCURLY;
     }
 
     /**
      * Checks whether comment is placed in the empty code block.
      * For example:
      * <p>
      * ...
      * {@code
      *  // empty code block
      * }
      * ...
      * </p>
      * Note, the method does not treat empty case blocks.
      * @param prevStmt previous statement.
      * @param nextStmt next statement.
      * @return true if comment is placed in the empty code block.
      */
     private static boolean isInEmptyCodeBlock(DetailAST prevStmt, DetailAST nextStmt) {
         return prevStmt != null
             && nextStmt != null
             && (prevStmt.getType() == TokenTypes.SLIST
                 || prevStmt.getType() == TokenTypes.LCURLY
                 || prevStmt.getType() == TokenTypes.ARRAY_INIT
                 || prevStmt.getType() == TokenTypes.OBJBLOCK)
             && nextStmt.getType() == TokenTypes.RCURLY;
     }
 
     /**
      * Handles a comment which is placed within empty case block.
      * Note, if comment is placed at the end of the empty case block, we have Checkstyle's
      * limitations to clearly detect user intention of explanation target - above or below. The
      * only case we can assume as a violation is when a single line comment within the empty case
      * block has indentation level that is lower than the indentation level of the next case
      * token. For example:
      * <p>
      * {@code
      *    ...
      *    case OPTION_ONE:
      * // violation
      *    case OPTION_TWO:
      *    ...
      * }
      * </p>
      * @param prevStmt previous statement.
      * @param comment single line comment.
      * @param nextStmt next statement.
      */
     private void handleCommentInEmptyCaseBlock(DetailAST prevStmt, DetailAST comment,
                                                DetailAST nextStmt) {
         if (comment.getColumnNo() < prevStmt.getColumnNo()
                 || comment.getColumnNo() < nextStmt.getColumnNo()) {
             logMultilineIndentation(prevStmt, comment, nextStmt);
         }
     }
 
     /**
      * Handles 'fall through' single line comment.
      * Note, 'fall through' and similar comments can have indentation level as next or previous
      * statement.
      * For example:
      * <p>
      * {@code
      *    ...
      *    case OPTION_ONE:
      *        int someVariable = 1;
      *        // fall through - OK
      *    case OPTION_TWO:
      *        int a = 5;
      *        break;
      *    ...
      * }
      * </p>
      * <p>
      * {@code
      *    ...
      *    case OPTION_ONE:
      *        int someVariable = 1;
      *    // then init variable a - OK
      *    case OPTION_TWO:
      *        int a = 5;
      *        break;
      *    ...
      * }
      * </p>
      * @param prevStmt previous statement.
      * @param comment single line comment.
      * @param nextStmt next statement.
      */
     private void handleFallThroughComment(DetailAST prevStmt, DetailAST comment,
                                           DetailAST nextStmt) {
         if (!areSameLevelIndented(comment, prevStmt, nextStmt)) {
             logMultilineIndentation(prevStmt, comment, nextStmt);
         }
     }
 
     /**
      * Handles a comment which is placed at the end of non empty code block.
      * Note, if single line comment is placed at the end of non empty block the comment should have
      * the same indentation level as the previous statement. For example:
      * <p>
      * {@code
      *    if (a == true) {
      *        int b = 1;
      *        // comment
      *    }
      * }
      * </p>
      * @param prevStmt previous statement.
      * @param comment comment to check.
      * @param nextStmt next statement.
      */
     private void handleCommentAtTheEndOfTheCodeBlock(DetailAST prevStmt, DetailAST comment,
                                                      DetailAST nextStmt) {
         if (prevStmt != null) {
             if (prevStmt.getType() == TokenTypes.LITERAL_CASE
                     || prevStmt.getType() == TokenTypes.CASE_GROUP
                     || prevStmt.getType() == TokenTypes.LITERAL_DEFAULT) {
                 if (comment.getColumnNo() < nextStmt.getColumnNo()) {
                     log(comment.getLineNo(), getMessageKey(comment), nextStmt.getLineNo(),
                         comment.getColumnNo(), nextStmt.getColumnNo());
                 }
             }
             else if (isCommentForMultiblock(nextStmt)) {
                 if (!areSameLevelIndented(comment, prevStmt, nextStmt)) {
                     logMultilineIndentation(prevStmt, comment, nextStmt);
                 }
             }
             else if (!areSameLevelIndented(comment, prevStmt, prevStmt)) {
                 final int prevStmtLineNo = prevStmt.getLineNo();
                 log(comment.getLineNo(), getMessageKey(comment), prevStmtLineNo,
                         comment.getColumnNo(), getLineStart(prevStmtLineNo));
             }
         }
     }
 
     /**
      * Whether the comment might have been used for the next block in a multi-block structure.
      * @param endBlockStmt the end of the current block.
      * @return true, if the comment might have been used for the next
      *     block in a multi-block structure.
      */
     private static boolean isCommentForMultiblock(DetailAST endBlockStmt) {
         final DetailAST nextBlock = endBlockStmt.getParent().getNextSibling();
         final int endBlockLineNo = endBlockStmt.getLineNo();
         final DetailAST catchAst = endBlockStmt.getParent().getParent();
         final DetailAST finallyAst = catchAst.getNextSibling();
         return nextBlock != null && nextBlock.getLineNo() == endBlockLineNo
                 || finallyAst != null
                     && catchAst.getType() == TokenTypes.LITERAL_CATCH
                     && finallyAst.getLineNo() == endBlockLineNo;
     }
 
     /**
      * Handles a comment which is placed within the empty code block.
      * Note, if comment is placed at the end of the empty code block, we have Checkstyle's
      * limitations to clearly detect user intention of explanation target - above or below. The
      * only case we can assume as a violation is when a single line comment within the empty
      * code block has indentation level that is lower than the indentation level of the closing
      * right curly brace. For example:
      * <p>
      * {@code
      *    if (a == true) {
      * // violation
      *    }
      * }
      * </p>
      *
      * @param comment comment to check.
      * @param nextStmt next statement.
      */
     private void handleCommentInEmptyCodeBlock(DetailAST comment, DetailAST nextStmt) {
         if (comment.getColumnNo() < nextStmt.getColumnNo()) {
             log(comment.getLineNo(), getMessageKey(comment), nextStmt.getLineNo(),
                 comment.getColumnNo(), nextStmt.getColumnNo());
         }
     }
 
     /**
      * Does pre-order traverse of abstract syntax tree to find the previous statement of the
      * comment. If previous statement of the comment is found, then the traverse will
      * be finished.
      * @param comment current statement.
      * @return previous statement of the comment or null if the comment does not have previous
      *         statement.
      */
     private DetailAST getOneLinePreviousStatement(DetailAST comment) {
         DetailAST root = comment.getParent();
         while (root != null && !isBlockStart(root)) {
             root = root.getParent();
         }
 
         final Deque<DetailAST> stack = new ArrayDeque<>();
         DetailAST previousStatement = null;
         while (root != null || !stack.isEmpty()) {
             if (!stack.isEmpty()) {
                 root = stack.pop();
             }
             while (root != null) {
                 previousStatement = findPreviousStatement(comment, root);
                 if (previousStatement != null) {
                     root = null;
                     stack.clear();
                     break;
                 }
                 if (root.getNextSibling() != null) {
                     stack.push(root.getNextSibling());
                 }
                 root = root.getFirstChild();
             }
         }
         return previousStatement;
     }
 
     /**
      * Whether the ast is a comment.
      * @param ast the ast to check.
      * @return true if the ast is a comment.
      */
     private static boolean isComment(DetailAST ast) {
         final int astType = ast.getType();
         return astType == TokenTypes.SINGLE_LINE_COMMENT
             || astType == TokenTypes.BLOCK_COMMENT_BEGIN
             || astType == TokenTypes.COMMENT_CONTENT
             || astType == TokenTypes.BLOCK_COMMENT_END;
     }
 
     /**
      * Whether the AST node starts a block.
      * @param root the AST node to check.
      * @return true if the AST node starts a block.
      */
     private static boolean isBlockStart(DetailAST root) {
         return root.getType() == TokenTypes.SLIST
                 || root.getType() == TokenTypes.OBJBLOCK
                 || root.getType() == TokenTypes.ARRAY_INIT
                 || root.getType() == TokenTypes.CASE_GROUP;
     }
 
     /**
      * Finds a previous statement of the comment.
      * Uses root token of the line while searching.
      * @param comment comment.
      * @param root root token of the line.
      * @return previous statement of the comment or null if previous statement was not found.
      */
     private DetailAST findPreviousStatement(DetailAST comment, DetailAST root) {
         DetailAST previousStatement = null;
         if (root.getLineNo() >= comment.getLineNo()) {
             // ATTENTION: parent of the comment is below the comment in case block
             // See https://github.com/checkstyle/checkstyle/issues/851
             previousStatement = getPrevStatementFromSwitchBlock(comment);
         }
         final DetailAST tokenWhichBeginsTheLine;
         if (root.getType() == TokenTypes.EXPR
                 && root.getFirstChild().getFirstChild() != null) {
             if (root.getFirstChild().getType() == TokenTypes.LITERAL_NEW) {
                 tokenWhichBeginsTheLine = root.getFirstChild();
             }
             else {
                 tokenWhichBeginsTheLine = findTokenWhichBeginsTheLine(root);
             }
         }
         else if (root.getType() == TokenTypes.PLUS) {
             tokenWhichBeginsTheLine = root.getFirstChild();
         }
         else {
             tokenWhichBeginsTheLine = root;
         }
         if (tokenWhichBeginsTheLine != null
                 && !isComment(tokenWhichBeginsTheLine)
                 && isOnPreviousLineIgnoringComments(comment, tokenWhichBeginsTheLine)) {
             previousStatement = tokenWhichBeginsTheLine;
         }
         return previousStatement;
     }
 
     /**
      * Finds a token which begins the line.
      * @param root root token of the line.
      * @return token which begins the line.
      */
     private static DetailAST findTokenWhichBeginsTheLine(DetailAST root) {
         final DetailAST tokenWhichBeginsTheLine;
         if (isUsingOfObjectReferenceToInvokeMethod(root)) {
             tokenWhichBeginsTheLine = findStartTokenOfMethodCallChain(root);
         }
         else {
             tokenWhichBeginsTheLine = root.getFirstChild().findFirstToken(TokenTypes.IDENT);
         }
         return tokenWhichBeginsTheLine;
     }
 
     /**
      * Checks whether there is a use of an object reference to invoke an object's method on line.
      * @param root root token of the line.
      * @return true if there is a use of an object reference to invoke an object's method on line.
      */
     private static boolean isUsingOfObjectReferenceToInvokeMethod(DetailAST root) {
         return root.getFirstChild().getFirstChild().getFirstChild() != null
             && root.getFirstChild().getFirstChild().getFirstChild().getNextSibling() != null;
     }
 
     /**
      * Finds the start token of method call chain.
      * @param root root token of the line.
      * @return the start token of method call chain.
      */
     private static DetailAST findStartTokenOfMethodCallChain(DetailAST root) {
         DetailAST startOfMethodCallChain = root;
         while (startOfMethodCallChain.getFirstChild() != null
                 && startOfMethodCallChain.getFirstChild().getLineNo() == root.getLineNo()) {
             startOfMethodCallChain = startOfMethodCallChain.getFirstChild();
         }
         if (startOfMethodCallChain.getFirstChild() != null) {
             startOfMethodCallChain = startOfMethodCallChain.getFirstChild().getNextSibling();
         }
         return startOfMethodCallChain;
     }
 
     /**
      * Checks whether the checked statement is on the previous line ignoring empty lines
      * and lines which contain only comments.
      * @param currentStatement current statement.
      * @param checkedStatement checked statement.
      * @return true if checked statement is on the line which is previous to current statement
      *     ignoring empty lines and lines which contain only comments.
      */
     private boolean isOnPreviousLineIgnoringComments(DetailAST currentStatement,
                                                      DetailAST checkedStatement) {
         DetailAST nextToken = getNextToken(checkedStatement);
         int distanceAim = 1;
         if (nextToken != null && isComment(nextToken)) {
             distanceAim += countEmptyLines(checkedStatement, currentStatement);
         }
 
         while (nextToken != null && nextToken != currentStatement && isComment(nextToken)) {
             if (nextToken.getType() == TokenTypes.BLOCK_COMMENT_BEGIN) {
                 distanceAim += nextToken.getLastChild().getLineNo() - nextToken.getLineNo();
             }
             distanceAim++;
             nextToken = nextToken.getNextSibling();
         }
         return currentStatement.getLineNo() - checkedStatement.getLineNo() == distanceAim;
     }
 
     /**
      * Get the token to start counting the number of lines to add to the distance aim from.
      * @param checkedStatement the checked statement.
      * @return the token to start counting the number of lines to add to the distance aim from.
      */
     private DetailAST getNextToken(DetailAST checkedStatement) {
         DetailAST nextToken;
         if (checkedStatement.getType() == TokenTypes.SLIST
                 || checkedStatement.getType() == TokenTypes.ARRAY_INIT
                 || checkedStatement.getType() == TokenTypes.CASE_GROUP) {
             nextToken = checkedStatement.getFirstChild();
         }
         else {
             nextToken = checkedStatement.getNextSibling();
         }
         if (nextToken != null && isComment(nextToken) && isTrailingComment(nextToken)) {
             nextToken = nextToken.getNextSibling();
         }
         return nextToken;
     }
 
     /**
      * Count the number of empty lines between statements.
      * @param startStatement start statement.
      * @param endStatement end statement.
      * @return the number of empty lines between statements.
      */
     private int countEmptyLines(DetailAST startStatement, DetailAST endStatement) {
         int emptyLinesNumber = 0;
         final String[] lines = getLines();
         final int endLineNo = endStatement.getLineNo();
         for (int lineNo = startStatement.getLineNo(); lineNo < endLineNo; lineNo++) {
             if (CommonUtil.isBlank(lines[lineNo])) {
                 emptyLinesNumber++;
             }
         }
         return emptyLinesNumber;
     }
 
     /**
      * Logs comment which can have the same indentation level as next or previous statement.
      * @param comment comment.
      * @param nextStmt next statement.
      * @param prevStmt previous statement.
      */
     private void logMultilineIndentation(DetailAST prevStmt, DetailAST comment,
                                          DetailAST nextStmt) {
         final String multilineNoTemplate = "%d, %d";
         log(comment.getLineNo(), getMessageKey(comment),
             String.format(Locale.getDefault(), multilineNoTemplate, prevStmt.getLineNo(),
                 nextStmt.getLineNo()), comment.getColumnNo(),
             String.format(Locale.getDefault(), multilineNoTemplate,
                     getLineStart(prevStmt.getLineNo()), getLineStart(nextStmt.getLineNo())));
     }
 
     /**
      * Get a message key depending on a comment type.
      * @param comment the comment to process.
      * @return a message key.
      */
     private static String getMessageKey(DetailAST comment) {
         final String msgKey;
         if (comment.getType() == TokenTypes.SINGLE_LINE_COMMENT) {
             msgKey = MSG_KEY_SINGLE;
         }
         else {
             msgKey = MSG_KEY_BLOCK;
         }
         return msgKey;
     }
 
     /**
      * Gets comment's previous statement from switch block.
      * @param comment {@link TokenTypes#SINGLE_LINE_COMMENT single-line comment}.
      * @return comment's previous statement or null if previous statement is absent.
      */
     private static DetailAST getPrevStatementFromSwitchBlock(DetailAST comment) {
         final DetailAST prevStmt;
         final DetailAST parentStatement = comment.getParent();
         if (parentStatement.getType() == TokenTypes.CASE_GROUP) {
             prevStmt = getPrevStatementWhenCommentIsUnderCase(parentStatement);
         }
         else {
             prevStmt = getPrevCaseToken(parentStatement);
         }
         return prevStmt;
     }
 
     /**
      * Gets previous statement for comment which is placed immediately under case.
      * @param parentStatement comment's parent statement.
      * @return comment's previous statement or null if previous statement is absent.
      */
     private static DetailAST getPrevStatementWhenCommentIsUnderCase(DetailAST parentStatement) {
         DetailAST prevStmt = null;
         final DetailAST prevBlock = parentStatement.getPreviousSibling();
         if (prevBlock.getLastChild() != null) {
             DetailAST blockBody = prevBlock.getLastChild().getLastChild();
             if (blockBody.getType() == TokenTypes.SEMI) {
                 blockBody = blockBody.getPreviousSibling();
             }
             if (blockBody.getType() == TokenTypes.EXPR) {
                 if (isUsingOfObjectReferenceToInvokeMethod(blockBody)) {
                     prevStmt = findStartTokenOfMethodCallChain(blockBody);
                 }
                 else {
                     prevStmt = blockBody.getFirstChild().getFirstChild();
                 }
             }
             else {
                 if (blockBody.getType() == TokenTypes.SLIST) {
                     prevStmt = blockBody.getParent().getParent();
                 }
                 else {
                     prevStmt = blockBody;
                 }
             }
             if (isComment(prevStmt)) {
                 prevStmt = prevStmt.getNextSibling();
             }
         }
         return prevStmt;
     }
 
     /**
      * Gets previous case-token for comment.
      * @param parentStatement comment's parent statement.
      * @return previous case-token or null if previous case-token is absent.
      */
     private static DetailAST getPrevCaseToken(DetailAST parentStatement) {
         final DetailAST prevCaseToken;
         final DetailAST parentBlock = parentStatement.getParent();
         if (parentBlock.getParent() != null
                 && parentBlock.getParent().getPreviousSibling() != null
                 && parentBlock.getParent().getPreviousSibling().getType()
                     == TokenTypes.LITERAL_CASE) {
             prevCaseToken = parentBlock.getParent().getPreviousSibling();
         }
         else {
             prevCaseToken = null;
         }
         return prevCaseToken;
     }
 
     /**
      * Checks if comment and next code statement
      * (or previous code stmt like <b>case</b> in switch block) are indented at the same level,
      * e.g.:
      * <p>
      * <pre>
      * {@code
      * // some comment - same indentation level
      * int x = 10;
      *     // some comment - different indentation level
      * int x1 = 5;
      * /*
      *  *
      *  *&#47;
      *  boolean bool = true; - same indentation level
      * }
      * </pre>
      * </p>
      * @param comment {@link TokenTypes#SINGLE_LINE_COMMENT single line comment}.
      * @param prevStmt previous code statement.
      * @param nextStmt next code statement.
      * @return true if comment and next code statement are indented at the same level.
      */
     private boolean areSameLevelIndented(DetailAST comment, DetailAST prevStmt,
                                                 DetailAST nextStmt) {
         return comment.getColumnNo() == getLineStart(nextStmt.getLineNo())
             || comment.getColumnNo() == getLineStart(prevStmt.getLineNo());
     }
 
     /**
      * Get a column number where a code starts.
      * @param lineNo the line number to get column number in.
      * @return the column number where a code starts.
      */
     private int getLineStart(int lineNo) {
         final char[] line = getLines()[lineNo - 1].toCharArray();
         int lineStart = 0;
         while (Character.isWhitespace(line[lineStart])) {
             lineStart++;
         }
         return lineStart;
     }
 
     /**
      * Checks if current comment is a trailing comment.
      * @param comment comment to check.
      * @return true if current comment is a trailing comment.
      */
     private boolean isTrailingComment(DetailAST comment) {
         final boolean isTrailingComment;
         if (comment.getType() == TokenTypes.SINGLE_LINE_COMMENT) {
             isTrailingComment = isTrailingSingleLineComment(comment);
         }
         else {
             isTrailingComment = isTrailingBlockComment(comment);
         }
         return isTrailingComment;
     }
 
     /**
      * Checks if current single line comment is trailing comment, e.g.:
      * <p>
      * {@code
      * double d = 3.14; // some comment
      * }
      * </p>
      * @param singleLineComment {@link TokenTypes#SINGLE_LINE_COMMENT single line comment}.
      * @return true if current single line comment is trailing comment.
      */
     private boolean isTrailingSingleLineComment(DetailAST singleLineComment) {
         final String targetSourceLine = getLine(singleLineComment.getLineNo() - 1);
         final int commentColumnNo = singleLineComment.getColumnNo();
         return !CommonUtil.hasWhitespaceBefore(commentColumnNo, targetSourceLine);
     }
 
     /**
      * Checks if current comment block is trailing comment, e.g.:
      * <p>
      * {@code
      * double d = 3.14; /* some comment *&#47;
      * /* some comment *&#47; double d = 18.5;
      * }
      * </p>
      * @param blockComment {@link TokenTypes#BLOCK_COMMENT_BEGIN block comment begin}.
      * @return true if current comment block is trailing comment.
      */
     private boolean isTrailingBlockComment(DetailAST blockComment) {
         final String commentLine = getLine(blockComment.getLineNo() - 1);
         final int commentColumnNo = blockComment.getColumnNo();
         final DetailAST nextSibling = blockComment.getNextSibling();
         return !CommonUtil.hasWhitespaceBefore(commentColumnNo, commentLine)
             || nextSibling != null && nextSibling.getLineNo() == blockComment.getLineNo();
     }
 
 }