/*
 * eXist Open Source Native XML Database
 * Copyright (C) 2001-2009 The eXist Project
 * http://exist-db.org
 *
 * This program 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
 * of the License, or (at your option) any later version.
 *  
 * This program 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 program; if not, write to the Free Software Foundation
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *  
 *  $Id$
 */
package org.exist.xquery.functions;

import org.exist.dom.QName;
import org.exist.xquery.Cardinality;
import org.exist.xquery.Dependency;
import org.exist.xquery.Function;
import org.exist.xquery.FunctionSignature;
import org.exist.xquery.Profiler;
import org.exist.xquery.XPathException;
import org.exist.xquery.XQueryContext;
import org.exist.xquery.value.DoubleValue;
import org.exist.xquery.value.FunctionParameterSequenceType;
import org.exist.xquery.value.FunctionReturnSequenceType;
import org.exist.xquery.value.Item;
import org.exist.xquery.value.Sequence;
import org.exist.xquery.value.SequenceType;
import org.exist.xquery.value.Type;

/**
 * xpath-library function: number(object)
 *
 */
public class FunNumber extends Function {

	protected static final String FUNCTION_DESCRIPTION_0_PARAM =    
        "Returns the value of the context item after atomization, " + 
        "converted to an xs:double.\n\n" +
        "If the context item cannot be " +
		"converted to an xs:double, the xs:double value NaN is returned. " +
        "If the context item is undefined an error is raised: " + 
        "[err:XPDY0002]XP.\n\n";	
	protected static final String FUNCTION_DESCRIPTION_1_PARAM =
		"Returns the value indicated by $arg or, if $arg is not specified, " +
		"the context item after atomization, converted to an xs:double.\n\n" +
		"Calling the zero-argument version of the function is defined to " +
		"give the same result as calling the single-argument version with " +
		"the context item (.). That is, fn:number() is equivalent to fn:number(.).\n\n" +
		"If $arg is the empty sequence or if $arg or the context item cannot be " +
		"converted to an xs:double, the xs:double value NaN is returned. " +
        "If the " +
		"context item is undefined an error is raised: [err:XPDY0002]XP.\n\n" +
		"If $arg is the empty sequence, NaN is returned. Otherwise, $arg, or " +
		"the context item after atomization, is converted to an xs:double " +
		"following the rules of 17.1.3.2 Casting to xs:double. If the conversion " +
		"to xs:double fails, the xs:double value NaN is returned.";

	protected static final FunctionParameterSequenceType ARG_PARAM = new FunctionParameterSequenceType("arg", Type.ATOMIC, Cardinality.ZERO_OR_ONE, "The input item");
	protected static final FunctionReturnSequenceType RETURN_TYPE = new FunctionReturnSequenceType(Type.DOUBLE, Cardinality.EXACTLY_ONE, "the numerical value");
	
	public final static FunctionSignature signatures[] = {
		new FunctionSignature(
				new QName("number", Function.BUILTIN_FUNCTION_NS),
				FUNCTION_DESCRIPTION_0_PARAM,
				new SequenceType[0],
				RETURN_TYPE
		),
		new FunctionSignature(
			new QName("number", Function.BUILTIN_FUNCTION_NS),
			FUNCTION_DESCRIPTION_1_PARAM,
			new SequenceType[] { ARG_PARAM },
			RETURN_TYPE
		)
	};

	public FunNumber(XQueryContext context, FunctionSignature signature) {
		super(context, signature);
	}

	public Sequence eval(Sequence contextSequence, Item contextItem) throws XPathException {
        if (context.getProfiler().isEnabled()) {
            context.getProfiler().start(this);       
            context.getProfiler().message(this, Profiler.DEPENDENCIES, "DEPENDENCIES", Dependency.getDependenciesName(this.getDependencies()));
            if (contextSequence != null)
                context.getProfiler().message(this, Profiler.START_SEQUENCES, "CONTEXT SEQUENCE", contextSequence);
            if (contextItem != null)
                context.getProfiler().message(this, Profiler.START_SEQUENCES, "CONTEXT ITEM", contextItem.toSequence());
        }
        
		if (contextItem != null)
			contextSequence = contextItem.toSequence();
        
        Sequence result;
		Sequence arg = null;
		if(getSignature().getArgumentCount() == 1)
			arg = getArgument(0).eval(contextSequence);
		else
			arg = contextSequence;
		
		if (arg == null)
			throw new XPathException(this, "XPDY0002: Undefined context item");
		        
		if(arg.isEmpty())
			result = DoubleValue.NaN;
		else {
            try {
                result = arg.convertTo(Type.DOUBLE);
            } catch(XPathException e) {
                result = DoubleValue.NaN;
            }
        }
        
        if (context.getProfiler().isEnabled()) 
            context.getProfiler().end(this, "", result); 
        
        return result; 
        
	}
}