code: /* LanguageTool, a natural language style checker 
   * Copyright (C) 2016 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.dev.bigdata;
  
  import org.languagetool.AnalyzedTokenReadings;
  
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * @since 3.3
   */
  public class ContextBuilder {
  
    private final String startMarker;
    private final String endMarker;
  
    public ContextBuilder() {
      this.startMarker = "_START_";
      this.endMarker = "_END_";
    }
    
    public ContextBuilder(String startMarker, String endMarker) {
      this.startMarker = startMarker;
      this.endMarker = endMarker;
    }
    
    public List<String> getContext(AnalyzedTokenReadings[] tokens, int pos, int contextSize) {
      List<String> l = new ArrayList<>();
      int i = 0;
      for (AnalyzedTokenReadings token : tokens) {
        if (i == pos) {
          l.addAll(getLeftContext(tokens, pos, contextSize));
          l.add(token.getToken());
          l.addAll(getRightContext(tokens, pos, contextSize));
          break;
        }
        i++;
      }
      return l;
    }
  
    private List<String> getLeftContext(AnalyzedTokenReadings[] tokens, int pos, int contextSize) {
      List<String> l = new ArrayList<>();
      for (int i = pos - 1; i >= 0 && l.size() < contextSize; i--) {
        if (i == 0) {
          l.add(0, startMarker);
        } else {
          l.add(0, tokens[i].getToken());
        }
      }
      return l;
    }
  
    private List<String> getRightContext(AnalyzedTokenReadings[] tokens, int pos, int contextSize) {
      List<String> l = new ArrayList<>();
      for (int i = pos + 1; i <= tokens.length && l.size() < contextSize; i++) {
        if (i == tokens.length) {
          l.add(endMarker);
        } else {
          l.add(tokens[i].getToken());
        }
      }
      return l;
    }
  }
  