package de.unisiegen.tpml.core.languages ;


import java.io.IOException ;
import de.unisiegen.tpml.core.prettyprinter.PrettyStyle ;


/**
 * Abstract base class for classes that implement the
 * {@link de.unisiegen.tpml.core.languages.LanguageScanner} interface.
 * 
 * @author Benedikt Meurer
 * @version $Rev:380 $
 * @see de.unisiegen.tpml.core.languages.LanguageScanner
 */
public abstract class AbstractLanguageScanner implements LanguageScanner
{
  /**
   * Allocates a new <code>AbstractLanguageScanner</code>, which implements
   * the <code>LanguageScanner</code> interface and should be used as base
   * class for all scanners generated by JFlex.
   */
  protected AbstractLanguageScanner ( )
  {
    super ( ) ;
  }


  //
  // Symbol allocation (protected)
  //
  /**
   * Allocates a new {@link LanguageSymbol} with the specified <code>name</code>
   * and symbol <code>id</code>. The remaining parameters are optional, see
   * the documentation of the {@link LanguageSymbol} class for details.
   * 
   * @param name the name of the symbol.
   * @param id the unique identifier of the symbol.
   * @param left the left position of the symbol, or <code>-1</code>.
   * @param right the right position of the symbol, or <code>-1</code>.
   * @param value the value of the symbol.
   * @return the generated {@link LanguageSymbol}.
   */
  protected final LanguageSymbol symbol ( String name , int id , int left ,
      int right , Object value )
  {
    return new LanguageSymbol ( name , id , left , right , value ) ;
  }


  /**
   * {@inheritDoc}
   * 
   * @see LanguageScanner#getStyleBySymbol(LanguageSymbol)
   */
  public final PrettyStyle getStyleBySymbol ( LanguageSymbol symbol )
  {
    return getStyleBySymbolId ( symbol.getId ( ) ) ;
  }


  /**
   * Returns the {@link PrettyStyle} for the specified symbol <code>id</code>,
   * for example {@link PrettyStyle#KEYWORD} if the <code>id</code> refers to
   * the token <code>"let"</code>. This method must be implemented by all
   * lexers generated by JFlex.
   * 
   * @param id the unique identifier of a symbol.
   * @return the {@link PrettyStyle} for the symbol <code>id</code>.
   * @see #getStyleBySymbol(LanguageSymbol)
   */
  public abstract PrettyStyle getStyleBySymbolId ( int id ) ;


  /**
   * Implementation of the <code>next_token()</code> interface of the
   * {@link java_cup.runtime.Scanner} interface. This is a simple wrapper around
   * the <code>nextSymbol()</code> method, which automatically skips all
   * symbols that should be ignored by the parser.
   * 
   * @return the next symbol from the scanner, skipping all tokens that should
   *         be ignored by the parser, or <code>null</code> on end-of-file.
   * @see java_cup.runtime.Scanner#next_token()
   * @throws IOException if an error occurs while reading characters from the
   *           input source stream.
   * @throws LanguageScannerException if a syntax error occurred while trying to
   *           scan the input stream.
   */
  public final LanguageSymbol next_token ( ) throws IOException ,
      LanguageScannerException
  {
    for ( ; ; )
    {
      // return the next symbol, skipping comments
      LanguageSymbol symbol = nextSymbol ( ) ;
      if ( symbol != null && getStyleBySymbol ( symbol ) == PrettyStyle.COMMENT )
        continue ;
      return symbol ;
    }
  }
}