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eXist-db XQuery File Module
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/*
 * eXist-db Open Source Native XML Database
 * Copyright (C) 2001 The eXist-db Authors
 *
 * [email protected]
 * http://www.exist-db.org
 *
 * 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 Street, Fifth Floor, Boston, MA  02110-1301  USA
 */
package org.exist.xquery.modules.file;

import java.nio.file.Files;
import java.nio.file.LinkOption;
import java.nio.file.Path;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

import org.exist.dom.QName;
import org.exist.xquery.BasicFunction;
import org.exist.xquery.Cardinality;
import org.exist.xquery.FunctionSignature;
import org.exist.xquery.XPathException;
import org.exist.xquery.XQueryContext;
import org.exist.xquery.value.BooleanValue;
import org.exist.xquery.value.FunctionReturnSequenceType;
import org.exist.xquery.value.FunctionParameterSequenceType;
import org.exist.xquery.value.Sequence;
import org.exist.xquery.value.SequenceType;
import org.exist.xquery.value.Type;

/**
 * @see java.nio.file.Files#exists(Path, LinkOption...)
 *
 * @author Andrzej Taramina
 *
 */
public class FileExists extends BasicFunction { 
	
	private final static Logger logger = LogManager.getLogger(FileExists.class);
	
	public final static FunctionSignature signatures[] = {
		new FunctionSignature(
			new QName( "exists", FileModule.NAMESPACE_URI, FileModule.PREFIX ),
			"Tests if a file or directory exists.  This method is only available to the DBA role.",
			new SequenceType[] {				
				new FunctionParameterSequenceType( "path", Type.ITEM, 
                        Cardinality.EXACTLY_ONE, "The full path or URI to the file in the file system" )
				},				
			new FunctionReturnSequenceType(Type.BOOLEAN, 
                    Cardinality.EXACTLY_ONE, "the boolean value true if the file exists, false otherwise" ) )
		};

	public FileExists(final XQueryContext context, final FunctionSignature signature )
	{
		super( context, signature );
	}
	
	@Override
	public Sequence eval(final Sequence[] args, final Sequence contextSequence) throws XPathException
	{
		if (!context.getSubject().hasDbaRole()) {
			XPathException xPathException = new XPathException(this, "Permission denied, calling user '" + context.getSubject().getName() + "' must be a DBA to call this function.");
			logger.error("Invalid user", xPathException);
			throw xPathException;
		}

		final String inputPath = args[0].getStringValue();
		final Path file = FileModuleHelper.getFile(inputPath, this);

		return BooleanValue.valueOf(Files.exists(file));
	}
}