package org.daisy.pipeline.file.saxon.impl;
   
   import java.net.URI;
   import java.net.URISyntaxException;
   import java.nio.file.Files;
   
   import net.sf.saxon.expr.XPathContext;
   import net.sf.saxon.lib.ExtensionFunctionCall;
   import net.sf.saxon.lib.ExtensionFunctionDefinition;
  import net.sf.saxon.om.Sequence;
  import net.sf.saxon.om.StructuredQName;
  import net.sf.saxon.trans.XPathException;
  import net.sf.saxon.type.BuiltInAtomicType;
  import net.sf.saxon.value.BooleanValue;
  import net.sf.saxon.value.SequenceType;
  
  import org.daisy.common.file.URLs;
  import org.daisy.pipeline.file.FileUtils;
  
  import org.osgi.service.component.annotations.Component;
  
  @Component(
  	name = "pf:file-exists",
  	service = { ExtensionFunctionDefinition.class }
  )
  @SuppressWarnings("serial")
  public class FileExists extends ExtensionFunctionDefinition {
  
  	private static final StructuredQName funcname = new StructuredQName(
  		"pf",
  		"http://www.daisy.org/ns/pipeline/functions",
  		"file-exists");
  
  	@Override
  	public SequenceType[] getArgumentTypes() {
  		return new SequenceType[] { SequenceType.SINGLE_STRING };
  	}
  
  	@Override
  	public StructuredQName getFunctionQName() {
  		return funcname;
  	}
  
  	@Override
  	public SequenceType getResultType(SequenceType[] arg0) {
  		return SequenceType.SINGLE_BOOLEAN;
  	}
  
  	@Override
  	public ExtensionFunctionCall makeCallExpression() {
  		return new ExtensionFunctionCall() {
  
  			@SuppressWarnings({ "unchecked", "rawtypes" })
  			public Sequence call(XPathContext context, Sequence[] arguments) throws XPathException {
  				try {
  					String uri = arguments[0].head().getStringValue();
  					return new BooleanValue(exists(URLs.asURI(uri)), BuiltInAtomicType.BOOLEAN);
  				} catch (Throwable e) {
  					throw new XPathException("Unexpected error in pf:file-exists", e);
  				}
  			}
  		};
  	}
  
  	/**
  	 * Whether the file or ZIP entry denoted by this absolute URI exists.
  	 */
  	private static boolean exists(URI uri) throws URISyntaxException {
  		try {
  			return Files.exists(FileUtils.asPath(uri));
  		} catch (IllegalArgumentException e) {
  			return false;
  		}
  	}
  }