path: root/JLanguageTool/src/java/de/danielnaber/languagetool/rules/en/AvsAnRule.java

/* 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 de.danielnaber.languagetool.rules.en;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import java.util.ResourceBundle;
import java.util.TreeSet;

import de.danielnaber.languagetool.AnalyzedSentence;
import de.danielnaber.languagetool.AnalyzedTokenReadings;
import de.danielnaber.languagetool.JLanguageTool;
import de.danielnaber.languagetool.rules.Category;
import de.danielnaber.languagetool.rules.RuleMatch;
import de.danielnaber.languagetool.tools.StringTools;

/**
 * Check if the determiner (if any) preceding a word is:
 * <ul>
 *   <li><i>an</i> if the next word starts with a vowel
 *   <li><i>a</i> if the next word does not start with a vowel
 * </ul>
 *  This rule loads some exceptions from external files (e.g. <i>an hour</i>).
 *   
 * @author Daniel Naber
 */
public class AvsAnRule extends EnglishRule {

  private static final String FILENAME_A = "/en/det_a.txt";
  private static final String FILENAME_AN = "/en/det_an.txt";

  private final TreeSet<String> requiresA;
  private final TreeSet<String> requiresAn;
  
  public AvsAnRule(final ResourceBundle messages) throws IOException {
    if (messages != null) {
      super.setCategory(new Category(messages.getString("category_misc")));
    }
    requiresA = loadWords(JLanguageTool.getDataBroker().getFromRulesDirAsStream(FILENAME_A));
    requiresAn = loadWords(JLanguageTool.getDataBroker().getFromRulesDirAsStream(FILENAME_AN));
  }
  
  @Override
  public String getId() {
    return "EN_A_VS_AN";
  }

  @Override
  public String getDescription() {
    return "Use of 'a' vs. 'an'";
  }

  @Override
  public RuleMatch[] match(final AnalyzedSentence text) {
    final List<RuleMatch> ruleMatches = new ArrayList<RuleMatch>();
    final AnalyzedTokenReadings[] tokens = text.getTokensWithoutWhitespace();
    String prevToken = "";
    int prevPos = 0;
    //ignoring token 0, i.e., SENT_START
    for (int i = 1; i < tokens.length; i++) {
      String token = tokens[i].getToken();
        boolean doesRequireA = false;
        boolean doesRequireAn = false;
        // check for exceptions:
        boolean isException = false;
        final String[] parts = token.split("[-']");  // for example, in "one-way" only "one" is relevant
        if (parts.length >= 1 &&
            !parts[0].equalsIgnoreCase("a")) {  // avoid false alarm on "A-levels are..."
          token = parts[0];
        }
        token = token.replaceAll("[^a-zA-Z0-9\\.']", "");         // e.g. >>an "industry party"<<
        if (StringTools.isEmpty(token)) {          
          continue;
        }
        final char tokenFirstChar = token.charAt(0);
        if (requiresA.contains(token.toLowerCase()) || requiresA.contains(token)) {
          isException = true;
          doesRequireA = true;
        }
        if (requiresAn.contains(token.toLowerCase()) || requiresAn.contains(token)) {
          if (isException) {
            throw new IllegalStateException(token + " is listed in both det_a.txt and det_an.txt");
          }
          isException = true;
          doesRequireAn = true;
        }
                
        if (!isException) {
          if (StringTools.isAllUppercase(token) || StringTools.isMixedCase(token)) {
            // we don't know how all-uppercase and mixed case words (often abbreviations) are pronounced, 
            // so never complain about these:
            doesRequireAn = false;
            doesRequireA = false;
          } else if (isVowel(tokenFirstChar)) {
            doesRequireAn = true;
          } else {
            doesRequireA = true;
          }
        }
        //System.err.println(prevToken + " " +token + ", a="+doesRequireA + ", an="+doesRequireAn);
        String msg = null;        
        if (prevToken.equalsIgnoreCase("a") && doesRequireAn) {
          String replacement = "an";
          if (prevToken.equals("A")) {
            replacement = "An";
          }
          msg = "Use <suggestion>" +replacement+ "</suggestion> instead of '" +prevToken+ "' if the following "+
          "word starts with a vowel sound, e.g. 'an article', "
          + "'an hour'";
        } else if (prevToken.equalsIgnoreCase("an") && doesRequireA) {
          String replacement = "a";
          if (prevToken.equals("An")) {
            replacement = "A";
          }
          msg = "Use <suggestion>" +replacement+ "</suggestion> instead of '" +prevToken+ "' if the following "+
          "word doesn't start with a vowel sound, e.g. 'a sentence', "
          + "'a university'";
        }
        if (msg != null) {          
          final RuleMatch ruleMatch = new RuleMatch(this, prevPos, prevPos+prevToken.length(), msg, "Wrong article");
          ruleMatches.add(ruleMatch);
        }
        if (tokens[i].hasPosTag("DT")) {
          prevToken = token;
          prevPos = tokens[i].getStartPos();
        } else {
          prevToken = "";
        }
    }
    return toRuleMatchArray(ruleMatches);
  }

  /**
   * Adds "a" or "an" to the English noun. 
   * Used for suggesting the proper form of the
   * indefinite article.
   * @param noun Word that needs an article.
   * @return String containing the word with a determiner, 
   * or just the word if the word is an abbreviation.
   */
  public final String suggestAorAn(final String noun) {
    String word = noun;
    boolean doesRequireA = false;
    boolean doesRequireAn = false;
    // check for exceptions:
    boolean isException = false;
    final String[] parts = word.split("[-']");  // for example, in "one-way" only "one" is relevant
    if (parts.length >= 1 &&
        !parts[0].equalsIgnoreCase("a")) {  // avoid false alarm on "A-levels are..."
      word = parts[0];
    }
    //html entities!
    word = word.replaceAll("&quot|&amp|&lt|&gt|[^a-zA-Z0-9]", "");         // e.g. >>an "industry party"<<
    if (StringTools.isEmpty(word)) {
      return word;
    }
    final char tokenFirstChar = word.charAt(0);
    if (requiresA.contains(word.toLowerCase()) || requiresA.contains(word)) {
      isException = true;
      doesRequireA = true;
    }
    if (requiresAn.contains(word.toLowerCase()) || requiresAn.contains(word)) {
      if (isException) {
        throw new IllegalStateException(word + " is listed in both det_a.txt and det_an.txt");
      }
      isException = true;
      doesRequireAn = true;
    }
    if (!isException) {
      if (StringTools.isAllUppercase(word) || StringTools.isMixedCase(word)) {
        // we don't know how all-uppercase words (often abbreviations) are pronounced, 
        // so never complain about these:
        doesRequireAn = false;
        doesRequireA = false;
      } else if (isVowel(tokenFirstChar)) {
        doesRequireAn = true;
      } else {
        doesRequireA = true;
      }
    }
    if (doesRequireA) {
      return "a " + noun;
    } else if (doesRequireAn) {
      return "an " + noun;
    } else {
      return noun;
    }
  }
  
  private static boolean isVowel(char c) {
    c = Character.toLowerCase(c);
    return c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u'; 
  }
  
  /**
   * Load words, normalized to lowercase.
   */
  private TreeSet<String> loadWords(final InputStream file) throws IOException {
    BufferedReader br = null;
    final TreeSet<String> set = new TreeSet<String>();
    try {
      br = new BufferedReader(new InputStreamReader(file));
      String line;
      while ((line = br.readLine()) != null) {
        line = line.trim();
        if (line.length() < 1) {
          continue;
        }
        if (line.charAt(0) == '#') {
          continue;
        }
        if (line.charAt(0) == '*') {
          set.add(line.substring(1));
        } else {
          set.add(line.toLowerCase());
        }
      }
    } finally {
      if (br != null) {
        br.close();
      }
    }
    return set;
  }

  @Override
  public void reset() {
    // nothing
  }

}