/*
 * Copyright (c) 2010 Mysema Ltd.
 * All rights reserved.
 *
 */
package com.mysema.rdfbean.rdb;

import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;

import com.mysema.rdfbean.CORE;
import com.mysema.rdfbean.model.LIT;
import com.mysema.rdfbean.model.NODE;
import com.mysema.rdfbean.model.Nodes;
import com.mysema.rdfbean.model.RDF;
import com.mysema.rdfbean.model.RDFS;
import com.mysema.rdfbean.model.RepositoryException;
import com.mysema.rdfbean.model.UID;
import com.mysema.rdfbean.owl.OWL;

/**
 * MD5IdFactory is a MD5 hash based implementation of the IdFactory interface
 * 
 * @author tiwe
 * @version $Id$
 */
public class MD5IdFactory implements IdFactory {

    private final Map<UID, String> uid2string = new HashMap<UID, String>();

    public MD5IdFactory() {
        register("rdf", Nodes.get(RDF.NS));
        register("rdfs", Nodes.get(RDFS.NS));
        register("owl", Nodes.get(OWL.NS));
        register("xsd", Nodes.get(RDF.NS));
        register("core", Arrays.asList(CORE.localId));
    }

    private void register(String prefix, Collection<UID> all) {
        for (UID id : all) {
            uid2string.put(id, prefix + ":" + id.ln());
        }
    }

    private String getReadableURI(UID uid) {
        String rv = uid2string.get(uid);
        if (rv == null) {
            rv = uid.getId();
        }
        return rv;
    }

    @Override
    public Long getId(NODE node) {
        int mask;
        String value;
        if (node.isLiteral()) {
            LIT literal = node.asLiteral();
            if (literal.getLang() != null) {
                mask = 0;
                value = literal.getValue() + literal.getLang();
            } else {
                mask = 1;
                value = literal.getValue() + getReadableURI(literal.getDatatype());
            }
        } else if (node.isBNode()) {
            mask = 2;
            value = node.getValue();
        } else {
            mask = 3;
            value = getReadableURI(node.asURI());
        }
        try {
            MessageDigest digest = MessageDigest.getInstance("MD5");
            digest.update(value.getBytes("UTF-8"));
            byte[] hash = digest.digest();
            byte[] longBytes = new byte[8];
            System.arraycopy(hash, 0, longBytes, 0, longBytes.length);
            longBytes[0] = (byte) (mask(longBytes[0], mask));
            return new BigInteger(longBytes).longValue();
        } catch (NoSuchAlgorithmException e) {
            throw new RepositoryException(e);
        } catch (UnsupportedEncodingException e) {
            throw new RepositoryException(e);
        }

    }

    int mask(byte b, int mask) {
        switch (mask) {
        case 0:
            return (b & ~3); // 00
        case 1:
            return (b & ~3) | 1; // 10
        case 2:
            return (b & ~3) | 2; // 01
        default:
            return (b & ~3) | 3; // 11
        }
    }

    @Override
    public Integer getId(Locale locale) {
        try {
            MessageDigest digest = MessageDigest.getInstance("MD5");
            digest.update(locale.toString().getBytes("UTF-8"));
            byte[] hash = digest.digest();
            byte[] intBytes = new byte[4];
            System.arraycopy(hash, 0, intBytes, 0, intBytes.length);
            return new BigInteger(intBytes).intValue();
        } catch (NoSuchAlgorithmException e) {
            throw new RepositoryException(e);
        } catch (UnsupportedEncodingException e) {
            throw new RepositoryException(e);
        }
    }

}