////////////////////////////////////////////////////////////////////////////////
   // 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.whitespace;
  
  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.utils.CommonUtil;
  
  /**
   * <p>
   * Checks that non-whitespace characters are separated by no more than one
   * whitespace. Separating characters by tabs or multiple spaces will be
   * reported. Currently the check doesn't permit horizontal alignment. To inspect
   * whitespaces before and after comments, set the property
   * <b>validateComments</b> to true.
   * </p>
   *
   * <p>
   * Setting <b>validateComments</b> to false will ignore cases like:
   * </p>
   *
   * <pre>
   * int i;  &#47;&#47; Multiple whitespaces before comment tokens will be ignored.
   * private void foo(int  &#47;* whitespaces before and after block-comments will be
   * ignored *&#47;  i) {
   * </pre>
   *
   * <p>
   * Sometimes, users like to space similar items on different lines to the same
   * column position for easier reading. This feature isn't supported by this
   * check, so both braces in the following case will be reported as violations.
   * </p>
   *
   * <pre>
   * public long toNanos(long d)  { return d;             }  &#47;&#47; 2 violations
   * public long toMicros(long d) { return d / (C1 / C0); }
   * </pre>
   *
   * <p>
   * Check have following options:
   * </p>
   *
   * <ul>
   * <li>validateComments - Boolean when set to {@code true}, whitespaces
   * surrounding comments will be ignored. Default value is {@code false}.</li>
   * </ul>
   *
   * <p>
   * To configure the check:
   * </p>
   *
   * <pre>
   * &lt;module name=&quot;SingleSpaceSeparator&quot;/&gt;
   * </pre>
   *
   * <p>
   * To configure the check so that it validates comments:
   * </p>
   *
   * <pre>
   * &lt;module name=&quot;SingleSpaceSeparator&quot;&gt;
   * &lt;property name=&quot;validateComments&quot; value=&quot;true&quot;/&gt;
   * &lt;/module&gt;
   * </pre>
   *
   */
  @StatelessCheck
  public class SingleSpaceSeparatorCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "single.space.separator";
  
      /** Indicates if whitespaces surrounding comments will be ignored. */
      private boolean validateComments;
  
      /**
       * Sets whether or not to validate surrounding whitespaces at comments.
       *
      * @param validateComments {@code true} to validate surrounding whitespaces at comments.
      */
     public void setValidateComments(boolean validateComments) {
         this.validateComments = validateComments;
     }
 
     @Override
     public int[] getDefaultTokens() {
         return getRequiredTokens();
     }
 
     @Override
     public int[] getAcceptableTokens() {
         return getRequiredTokens();
     }
 
     @Override
     public int[] getRequiredTokens() {
         return CommonUtil.EMPTY_INT_ARRAY;
     }
 
     // -@cs[SimpleAccessorNameNotation] Overrides method from base class.
     // Issue: https://github.com/sevntu-checkstyle/sevntu.checkstyle/issues/166
     @Override
     public boolean isCommentNodesRequired() {
         return validateComments;
     }
 
     @Override
     public void beginTree(DetailAST rootAST) {
         if (rootAST != null) {
             visitEachToken(rootAST);
         }
     }
 
     /**
      * Examines every sibling and child of {@code node} for violations.
      *
      * @param node The node to start examining.
      */
     private void visitEachToken(DetailAST node) {
         DetailAST sibling = node;
 
         do {
             final int columnNo = sibling.getColumnNo() - 1;
 
             // in such expression: "j  =123", placed at the start of the string index of the second
             // space character will be: 2 = 0(j) + 1(whitespace) + 1(whitespace). It is a minimal
             // possible index for the second whitespace between non-whitespace characters.
             final int minSecondWhitespaceColumnNo = 2;
 
             if (columnNo >= minSecondWhitespaceColumnNo
                     && !isTextSeparatedCorrectlyFromPrevious(getLine(sibling.getLineNo() - 1),
                             columnNo)) {
                 log(sibling, MSG_KEY);
             }
             if (sibling.getChildCount() >= 1) {
                 visitEachToken(sibling.getFirstChild());
             }
 
             sibling = sibling.getNextSibling();
         } while (sibling != null);
     }
 
     /**
      * Checks if characters in {@code line} at and around {@code columnNo} has
      * the correct number of spaces. to return {@code true} the following
      * conditions must be met:<br />
      * - the character at {@code columnNo} is the first in the line.<br />
      * - the character at {@code columnNo} is not separated by whitespaces from
      * the previous non-whitespace character. <br />
      * - the character at {@code columnNo} is separated by only one whitespace
      * from the previous non-whitespace character.<br />
      * - {@link #validateComments} is disabled and the previous text is the
      * end of a block comment.
      *
      * @param line The line in the file to examine.
      * @param columnNo The column position in the {@code line} to examine.
      * @return {@code true} if the text at {@code columnNo} is separated
      *         correctly from the previous token.
      */
     private boolean isTextSeparatedCorrectlyFromPrevious(String line, int columnNo) {
         return isSingleSpace(line, columnNo)
                 || !isWhitespace(line, columnNo)
                 || isFirstInLine(line, columnNo)
                 || !validateComments && isBlockCommentEnd(line, columnNo);
     }
 
     /**
      * Checks if the {@code line} at {@code columnNo} is a single space, and not
      * preceded by another space.
      *
      * @param line The line in the file to examine.
      * @param columnNo The column position in the {@code line} to examine.
      * @return {@code true} if the character at {@code columnNo} is a space, and
      *         not preceded by another space.
      */
     private static boolean isSingleSpace(String line, int columnNo) {
         return isSpace(line, columnNo) && !Character.isWhitespace(line.charAt(columnNo - 1));
     }
 
     /**
      * Checks if the {@code line} at {@code columnNo} is a space.
      *
      * @param line The line in the file to examine.
      * @param columnNo The column position in the {@code line} to examine.
      * @return {@code true} if the character at {@code columnNo} is a space.
      */
     private static boolean isSpace(String line, int columnNo) {
         return line.charAt(columnNo) == ' ';
     }
 
     /**
      * Checks if the {@code line} at {@code columnNo} is a whitespace character.
      *
      * @param line The line in the file to examine.
      * @param columnNo The column position in the {@code line} to examine.
      * @return {@code true} if the character at {@code columnNo} is a
      *         whitespace.
      */
     private static boolean isWhitespace(String line, int columnNo) {
         return Character.isWhitespace(line.charAt(columnNo));
     }
 
     /**
      * Checks if the {@code line} up to and including {@code columnNo} is all
      * non-whitespace text encountered.
      *
      * @param line The line in the file to examine.
      * @param columnNo The column position in the {@code line} to examine.
      * @return {@code true} if the column position is the first non-whitespace
      *         text on the {@code line}.
      */
     private static boolean isFirstInLine(String line, int columnNo) {
         return CommonUtil.isBlank(line.substring(0, columnNo));
     }
 
     /**
      * Checks if the {@code line} at {@code columnNo} is the end of a comment,
      * '*&#47;'.
      *
      * @param line The line in the file to examine.
      * @param columnNo The column position in the {@code line} to examine.
      * @return {@code true} if the previous text is a end comment block.
      */
     private static boolean isBlockCommentEnd(String line, int columnNo) {
         return line.substring(0, columnNo).trim().endsWith("*/");
     }
 
 }