001    /**
002     * =========================================
003     * LibFormula : a free Java formula library
004     * =========================================
005     *
006     * Project Info:  http://reporting.pentaho.org/libformula/
007     *
008     * (C) Copyright 2006-2007, by Pentaho Corporation and Contributors.
009     *
010     * This library is free software; you can redistribute it and/or modify it under the terms
011     * of the GNU Lesser General Public License as published by the Free Software Foundation;
012     * either version 2.1 of the License, or (at your option) any later version.
013     *
014     * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
015     * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
016     * See the GNU Lesser General Public License for more details.
017     *
018     * You should have received a copy of the GNU Lesser General Public License along with this
019     * library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
020     * Boston, MA 02111-1307, USA.
021     *
022     * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
023     * in the United States and other countries.]
024     *
025     *
026     * ------------
027     * $Id: LeftFunction.java 2752 2007-04-10 14:10:41Z taqua $
028     * ------------
029     * (C) Copyright 2006-2007, by Pentaho Corporation.
030     */
031    package org.jfree.formula.function.text;
032    
033    import org.jfree.formula.EvaluationException;
034    import org.jfree.formula.FormulaContext;
035    import org.jfree.formula.LibFormulaErrorValue;
036    import org.jfree.formula.function.Function;
037    import org.jfree.formula.function.ParameterCallback;
038    import org.jfree.formula.lvalues.TypeValuePair;
039    import org.jfree.formula.typing.Type;
040    import org.jfree.formula.typing.TypeRegistry;
041    import org.jfree.formula.typing.coretypes.TextType;
042    
043    /**
044     * This function returns a selected number of text characters from the left.<br/>
045     * This function depends on <code>MidFunction</code>.
046     *
047     * @see MidFunction
048     *
049     * @author Cedric Pronzato
050     *
051     */
052    public class LeftFunction implements Function
053    {
054      public LeftFunction()
055      {
056      }
057    
058      public TypeValuePair evaluate(final FormulaContext context,
059                                    final ParameterCallback parameters) throws EvaluationException
060      {
061        final int parameterCount = parameters.getParameterCount();
062        if (parameterCount < 1 || parameterCount > 2)
063        {
064          throw new EvaluationException(LibFormulaErrorValue.ERROR_ARGUMENTS_VALUE);
065        }
066        final TypeRegistry typeRegistry = context.getTypeRegistry();
067    
068        final Type textType = parameters.getType(0);
069        final Object textValue = parameters.getValue(0);
070    
071        final String text = typeRegistry.convertToText(textType, textValue);
072        final int length;
073        if(parameterCount == 2)
074        {
075          final Type lengthType = parameters.getType(1);
076          final Object lengthValue = parameters.getValue(1);
077          final Number lengthConv = typeRegistry.convertToNumber(lengthType, lengthValue);
078          if(lengthConv.doubleValue() < 0)
079          {
080            throw new EvaluationException(LibFormulaErrorValue.ERROR_INVALID_ARGUMENT_VALUE);
081          }
082    
083          length = lengthConv.intValue();
084        }
085        else
086        {
087          length = 1;
088        }
089    
090        if(text == null)
091        {
092          throw new EvaluationException(LibFormulaErrorValue.ERROR_INVALID_ARGUMENT_VALUE);
093        }
094    
095        // Note that MID(T;1;Length) produces the same results as LEFT(T;Length).
096        final MidFunction function = new MidFunction();
097        return new TypeValuePair(TextType.TYPE, function.process(text, new Integer(1), new Integer(length)));
098      }
099    
100      public String getCanonicalName()
101      {
102        return "LEFT";
103      }
104    
105    }