code: /* LanguageTool, a natural language style checker
   * Copyright (C) 2005 Daniel Naber (http://www.danielnaber.de)
   * 
   * 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., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
   * USA
   */
  
  package org.languagetool.rules;
  
  import org.languagetool.AnalyzedSentence;
  import org.languagetool.AnalyzedTokenReadings;
  import org.languagetool.Language;
  import org.languagetool.tools.StringTools;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.ResourceBundle;
  
  /**
   * Check if there is duplicated whitespace in a sentence.
   * Considers two spaces as incorrect, and proposes a single space instead.
   * 
   * @author Marcin Miłkowski
   */
  public class MultipleWhitespaceRule extends TextLevelRule {
  
    public MultipleWhitespaceRule(ResourceBundle messages, Language language) {
      super(messages);
      super.setCategory(Categories.TYPOGRAPHY.getCategory(messages));
      setLocQualityIssueType(ITSIssueType.Whitespace);
    }
  
    @Override
    public String getId() {
      return "WHITESPACE_RULE";
    }
  
    @Override
    public String getDescription() {
      return messages.getString("desc_whitespacerepetition");
    }
    
    // First White space is not a linebreak, function or footnote
    private static boolean isFirstWhite(AnalyzedTokenReadings token) {
      return (token.isWhitespace() || StringTools.isNonBreakingWhitespace(token.getToken())) 
          && !token.isLinebreak()
          && !token.getToken().contains("\u200B") && !token.getToken().contains("\uFEFF") && !token.getToken().contains("\u2060");
    }
  
    // Removable white space are not linebreaks, tabs, functions or footnotes
    private static boolean isRemovableWhite(AnalyzedTokenReadings token) {
      return (token.isWhitespace() || StringTools.isNonBreakingWhitespace(token.getToken())) 
          && !token.isLinebreak() && !token.getToken().equals("\t")
          // exclude invisible spaces:
          && !token.getToken().contains("\u200B") && !token.getToken().contains("\uFEFF") && !token.getToken().contains("\u2060");
    }
  
    @Override
    public RuleMatch[] match(List<AnalyzedSentence> sentences) {
      List<RuleMatch> ruleMatches = new ArrayList<>();
      int pos = 0;
      for (AnalyzedSentence sentence : sentences) {
        AnalyzedTokenReadings[] tokens = sentence.getTokens();
        //note: we start from token 1
        //token no. 0 is guaranteed to be SENT_START
        for (int i = 1; i < tokens.length; i++) {
          if(isFirstWhite(tokens[i])) {
            int nFirst = i;
            for (i++; i < tokens.length && isRemovableWhite(tokens[i]); i++);
            i--;
            if (i > nFirst) {
              String message = messages.getString("whitespace_repetition");
              RuleMatch ruleMatch = new RuleMatch(this, sentence, pos + tokens[nFirst].getStartPos(),
                  pos + tokens[i].getEndPos(), message);
              ruleMatch.setSuggestedReplacement(tokens[nFirst].getToken());
              ruleMatches.add(ruleMatch);
            }
          } else if (tokens[i].isLinebreak()) {
            for (i++; i < tokens.length && isRemovableWhite(tokens[i]); i++);
          }
        }
        pos += sentence.getCorrectedTextLength();
      }
      return toRuleMatchArray(ruleMatches);
    }
  
    @Override
    public int minToCheckParagraph() {
      return 0;
    }
  
  }
  