/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

package org.apache.harmony.luni.util;


import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;

public class OIDDatabase {

    private static OIDDatabase instance = new OIDDatabase();

    private Set<DBEntry> oids = new HashSet<DBEntry>();

    private Set<DBEntry> algorithms = new HashSet<DBEntry>();

    /**
     * Private constructor to enforce singleton pattern
     */
    private OIDDatabase() {
        // First, encryption algorithms...

        // MD2withRSA
        DBEntry oid = new DBEntry("1.2.840.113549.1.1.2");
        DBEntry alg = new DBEntry("MD2withRSA");
        wireTogether(oid, alg);

        // MD5withRSA
        oid = new DBEntry("1.2.840.113549.1.1.4");
        alg = new DBEntry("MD5withRSA");
        wireTogether(oid, alg);

        // SHA1withRSA
        oid = new DBEntry("1.2.840.113549.1.1.5");
        alg = new DBEntry("SHA1withRSA");
        wireTogether(oid, alg);

        // SHA1withDSA
        oid = new DBEntry("1.2.840.10040.4.3");
        alg = new DBEntry("SHA1withDSA");
        wireTogether(oid, alg);

        // message digest algorithms

        // SHA and SHA-1
        oid = new DBEntry("1.3.14.3.2.26");
        alg = new DBEntry("SHA");
        DBEntry alg2 = new DBEntry("SHA-1");
        wireTogether(oid, alg);
        wireTogether(oid, alg2);

        // MD5
        oid = new DBEntry("1.2.840.113549.2.5");
        alg = new DBEntry("MD5");
        wireTogether(oid, alg);

        // key factories

        // RSA
        oid = new DBEntry("1.2.840.113549.1.1.1");
        alg = new DBEntry("RSA");
        wireTogether(oid, alg);

        // DSA
        oid = new DBEntry("1.2.840.10040.4.1");
        DBEntry oid2 = new DBEntry("1.3.14.3.2.12");
        alg = new DBEntry("DSA");
        wireTogether(oid, alg);
        wireTogether(oid2, alg);

        // DiffieHellman
        oid = new DBEntry("1.2.840.10046.2.1");
        alg = new DBEntry("DiffieHellman");
        wireTogether(oid, alg);
    }

    private void wireTogether(DBEntry oidValue, DBEntry algorithmValue) {
        oids.add(oidValue);
        algorithms.add(algorithmValue);
        oidValue.addEquivalent(algorithmValue);
        algorithmValue.addEquivalent(oidValue);
    }

    public static OIDDatabase getInstance() {
        return instance;
    }

    public String getFirstAlgorithmForOID(String oid) {
        String result = null;
        Iterator<String> it = this.getAllAlgorithmsForOID(oid).iterator();
        if (it.hasNext()) {
            result = (it.next());
        }
        return result;
    }

    public Set<String> getAllAlgorithmsForOID(String oid) {
        Set<String> result = null;
        Iterator<DBEntry> it = this.oids.iterator();
        result = getAllEquivalents(oid, it);
        if (result == null) {
            throw new IllegalArgumentException("Unknown OID : " + oid);
        }
        return result;
    }

    public String getFirstOIDForAlgorithm(String algorithm) {
        String result = null;
        Iterator<String> it = this.getAllOIDsForAlgorithm(algorithm).iterator();
        if (it.hasNext()) {
            result = (it.next());
        }
        return result;
    }

    public Set<String> getAllOIDsForAlgorithm(String algorithm) {
        Set<String> result = null;
        Iterator<DBEntry> it = this.algorithms.iterator();
        result = getAllEquivalents(algorithm, it);
        if (result == null) {
            throw new IllegalArgumentException("Unsupported algorithm : "
                    + algorithm);
        }
        return result;
    }

    private Set<String> getAllEquivalents(String value, Iterator<DBEntry> it) {
        Set<String> result = null;
        while (it.hasNext()) {
            DBEntry element = it.next();
            if (element.getValue().equals(value)) {
                Set<DBEntry> allMatchingDBEntries = element.getAllEquivalents();
                result = new HashSet<String>();
                Iterator<DBEntry> dbIt = allMatchingDBEntries.iterator();
                while (dbIt.hasNext()) {
                    DBEntry matchingEntry = dbIt.next();
                    result.add(matchingEntry.getValue());
                }
            }
        }
        return result;
    }

    static class DBEntry {
        private final List<DBEntry> equivalents = new LinkedList<DBEntry>();

        private final String value;

        DBEntry(String value) {
            this.value = value;
        }

        void addEquivalent(DBEntry entry) {
            this.equivalents.add(entry);
        }

        String getValue() {
            return this.value;
        }

        Set<DBEntry> getAllEquivalents() {
            return new HashSet<DBEntry>(this.equivalents);
        }
    }
}