/*
 * Copyright  2000-2004 The Apache Software Foundation
 *
 *  Licensed 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.bcel.verifier;

import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Vector;

/**
 * This class produces instances of the Verifier class. Its purpose is to make
 * sure that they are singleton instances with respect to the class name they
 * operate on. That means, for every class (represented by a unique fully qualified
 * class name) there is exactly one Verifier.
 *
 * @version $Id: VerifierFactory.java 386056 2006-03-15 11:31:56Z tcurdt $
 * @author Enver Haase
 * @see org.apache.bcel.verifier.Verifier
 */
public class VerifierFactory {

    /**
     * The HashMap that holds the data about the already-constructed Verifier instances.
     */
    private static Map hashMap = new HashMap();
    /**
     * The VerifierFactoryObserver instances that observe the VerifierFactory.
     */
    private static List observers = new Vector();


    /**
     * The VerifierFactory is not instantiable.
     */
    private VerifierFactory() {
    }


    /**
     * Returns the (only) verifier responsible for the class with the given name.
     * Possibly a new Verifier object is transparently created.
     * @return the (only) verifier responsible for the class with the given name.
     */
    public static Verifier getVerifier( String fully_qualified_classname ) {
        Verifier v = (Verifier) (hashMap.get(fully_qualified_classname));
        if (v == null) {
            v = new Verifier(fully_qualified_classname);
            hashMap.put(fully_qualified_classname, v);
            notify(fully_qualified_classname);
        }
        return v;
    }


    /**
     * Notifies the observers of a newly generated Verifier.
     */
    private static void notify( String fully_qualified_classname ) {
        // notify the observers
        Iterator i = observers.iterator();
        while (i.hasNext()) {
            VerifierFactoryObserver vfo = (VerifierFactoryObserver) i.next();
            vfo.update(fully_qualified_classname);
        }
    }


    /**
     * Returns all Verifier instances created so far.
     * This is useful when a Verifier recursively lets
     * the VerifierFactory create other Verifier instances
     * and if you want to verify the transitive hull of
     * referenced class files.
     */
    public static Verifier[] getVerifiers() {
        Verifier[] vs = new Verifier[hashMap.values().size()];
        return (Verifier[]) (hashMap.values().toArray(vs)); // Because vs is big enough, vs is used to store the values into and returned!
    }


    /**
     * Adds the VerifierFactoryObserver o to the list of observers.
     */
    public static void attach( VerifierFactoryObserver o ) {
        observers.add(o);
    }


    /**
     * Removes the VerifierFactoryObserver o from the list of observers.
     */
    public static void detach( VerifierFactoryObserver o ) {
        observers.remove(o);
    }
}