package com.ldodds.sparql;

import com.hp.hpl.jena.query.expr.ExprEvalException;
import com.hp.hpl.jena.query.expr.NodeValue;
import com.hp.hpl.jena.query.function.FunctionBase1;

import java.net.*;
import java.text.SimpleDateFormat;
import java.util.*;

public class LastModified extends FunctionBase1 
{
	private static final SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
	
	private Map _cache;
	
	public LastModified()
	{
		_cache = new HashMap();
	}
	
	public NodeValue exec(NodeValue nodeValue) 
	{
		String value = nodeValue.asString();
		if (_cache.containsKey(value))
		{
			return (NodeValue)_cache.get(value);
		}
				
        if ( !nodeValue.asNode().isURI() )
            throw new ExprEvalException("Attempt to get Last-Modified for a literal");
        
        try
		{
        	String lastModified = getLastModified( nodeValue.asString() );
        	
        	NodeValue date = NodeValue.makeDate(lastModified);
        	_cache.put(value, date);
        	return date;
		} catch (Exception e)
		{
			throw new ExprEvalException("Error fetching Last-Modified", e);
		}
	}

	public String getLastModified(String link) throws Exception
	{
		URL url = new URL(link);
		
		URLConnection connection = url.openConnection();
		connection.setAllowUserInteraction(false);
		long secs = connection.getLastModified();
		
		String xsdDate = dateToXSD(secs);
		return xsdDate;
	}
		
	public String dateToXSD(long secs)
	{
		Date date = new Date(secs);		
		return format.format(date);
	}
}