package com.bigdata.gom.web;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;

import org.openrdf.repository.RepositoryException;

import com.bigdata.gom.om.ObjectManager;
import com.bigdata.journal.ITx;
import com.bigdata.rdf.sail.BigdataSail;
import com.bigdata.rdf.sail.BigdataSailRepository;
import com.bigdata.rdf.sail.webapp.BigdataRDFContext;
import com.bigdata.rdf.sail.webapp.BigdataRDFServlet;
import com.bigdata.rdf.store.AbstractTripleStore;

/**
 * A simple utility class that can be initialized with a ServletRequest and used
 * to simplify dynamic web pages.
 * 
 * @author Martyn Cutcher
 */
public class GOMWebUtil {

    /**
     * The name of the request attribute to which we attach the
     * {@link ObjectManager} scoped to that request.
     */
    static private final String ATTRIBUTE_OM = ObjectManager.class.getName();

    /**
     * Return an {@link ITx#UNISOLATED} {@link ObjectManager} instance that is
     * scoped to the <code>request</code>. The same {@link ObjectManager}
     * instance will be returned each time this method is invoked for the same
     * <code>request</code>. A distinct {@link ObjectManager} instance is
     * returned for each distinct <code>request</code>.
     * 
     * @param request
     *            The request.
     * 
     * @return The {@link ObjectManager}.
     * 
     * @throws Exception
     */
    public static ObjectManager getObjectManager(
            final HttpServletRequest request) throws Exception {

        return newObjectManager(request, ITx.UNISOLATED);

	}


    /**
     * Return an {@link ObjectManager} instance that is scoped to the
     * <code>request</code>. The same {@link ObjectManager} instance will be
     * returned each time this method is invoked for the same
     * <code>request</code>. A distinct {@link ObjectManager} instance is
     * returned for each distinct <code>request</code>.
     * 
     * @param request
     *            The request.
     * @param timestamp
     *            The timestamp of the view.
     *            
     * @return The {@link ObjectManager}.
     * 
     * @throws Exception
     */
    public static ObjectManager newObjectManager(
            final HttpServletRequest request, final long timestamp)
            throws RepositoryException {

        ObjectManager om = (ObjectManager) request.getAttribute(ATTRIBUTE_OM);
        
        if (om != null) {

            return om;

        }

        final ServletContext servletContext = request.getSession()
                .getServletContext();

        final BigdataRDFContext rdfContext = getBigdataRDFContext(servletContext);

        // The SPARQL endpoint.
        final String endpoint = request.getRequestURL().toString();
        
        final String namespace = rdfContext.getConfig().namespace;
        
        final AbstractTripleStore tripleStore = (AbstractTripleStore) rdfContext
                .getIndexManager().getResourceLocator()
                .locate(namespace, timestamp);

        if (tripleStore == null) {

            throw new RuntimeException("Not found: namespace=" + namespace);

        }

        // Wrap with SAIL.
        final BigdataSail sail = new BigdataSail(tripleStore);

        final BigdataSailRepository repo = new BigdataSailRepository(sail);

        repo.initialize();

        om = new ObjectManager(endpoint, repo);

        request.setAttribute(ATTRIBUTE_OM, om);

        return om;

    }

    static final protected BigdataRDFContext getBigdataRDFContext(
            final ServletContext servletContext) {

        return getRequiredServletContextAttribute(servletContext,
                BigdataRDFServlet.ATTRIBUTE_RDF_CONTEXT);

    }

    static protected <T> T getRequiredServletContextAttribute(
            final ServletContext servletContext, final String name) {

        @SuppressWarnings("unchecked")
        final T v = (T) servletContext.getAttribute(name);

        if (v == null)
            throw new RuntimeException("Not set: " + name);

        return v;

    }

}