package org.daisy.pipeline.nlp.impl.matchrules;
   
   import java.util.regex.Matcher;
   import java.util.regex.Pattern;
   
   import org.daisy.pipeline.nlp.TextCategorizer.Category;
   import org.daisy.pipeline.nlp.TextCategorizer.MatchMode;
   import org.daisy.pipeline.nlp.impl.MatchRule;
   
  /**
   * Match text with one regex but return the text matched by another regex.
   * Better use the Negative Lookahead syntax when it is possible.
   */
  public class RegexAheadMatchRule extends MatchRule {
  
  	private Pattern mPattern;
  	private Pattern mPatternForward;
  
  	public RegexAheadMatchRule(Category category, int priority, boolean caseSensitive,
  	        MatchMode matchMode) {
  		super(category, priority, caseSensitive, matchMode);
  	}
  
  	public void init(String regexp, String regexpForward) {
  		int flags = Pattern.UNICODE_CASE | Pattern.MULTILINE;
  
  		// java7: flags |= Pattern.UNICODE_CHARACTER_CLASS;
  
  		if (!mCaseSensitive) {
  			flags |= Pattern.CASE_INSENSITIVE;
  		}
  
  		mPattern = Pattern.compile(regexp, flags);
  		mPatternForward = Pattern.compile(regexpForward, flags);
  	}
  
  	@Override
  	protected String match(String input) {
  		Matcher m = mPattern.matcher(input);
  		switch (mMatchMode) {
  		case FULL_MATCH:
  			if (m.matches()) {
  				return m.group(0);
  			}
  			break;
  		case PREFIX_MATCH:
  			if (m.lookingAt()) {
  				Matcher m2 = mPatternForward.matcher(input);
  				if (m2.lookingAt())
  					return m2.group(0);
  				else {
  					System.err.println("** critical error **: " + mPatternForward.pattern()
  					        + " not included in " + mPattern.pattern());
  				}
  			}
  			break;
  		}
  
  		return null;
  	}
  
  	@Override
  	public boolean threadsafe() {
  		return true;
  	}
  }