/*
 * @(#)BaseCombiningAlgFactory.java
 *
 * Copyright 2004 Sun Microsystems, Inc. All Rights Reserved.
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 * modification, are permitted provided that the following conditions are met:
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 *      this list of conditions and the following disclaimer.
 * 
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 *
 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
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package org.wso2.balana.combine;

import org.wso2.balana.UnknownIdentifierException;

import java.net.URI;

import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Set;

/**
 * This is a basic implementation of <code>CombiningAlgFactory</code>. It implements the insertion
 * and retrieval methods, but doesn't actually setup the factory with any algorithms.
 * <p>
 * Note that while this class is thread-safe on all creation methods, it is not safe to add support
 * for a new algorithm while creating an instance of an algorithm. This follows from the assumption
 * that most people will initialize these factories up-front, and then start processing without ever
 * modifying the factories. If you need these mutual operations to be thread-safe, then you should
 * write a wrapper class that implements the right synchronization.
 * 
 * @since 1.2
 * @author Seth Proctor
 */
public class BaseCombiningAlgFactory extends CombiningAlgFactory {

    // the map of available combining algorithms
    private HashMap algMap;

    /**
     * Default constructor.
     */
    public BaseCombiningAlgFactory() {
        algMap = new HashMap();
    }

    /**
     * Constructor that configures this factory with an initial set of supported algorithms.
     * 
     * @param algorithms a <code>Set</code> of </code>CombiningAlgorithm</code>s
     * 
     * @throws IllegalArgumentException if any elements of the set are not
     *             </code>CombiningAlgorithm</code>s
     */
    public BaseCombiningAlgFactory(Set algorithms) {
        algMap = new HashMap();

        Iterator it = algorithms.iterator();
        while (it.hasNext()) {
            try {
                CombiningAlgorithm alg = (CombiningAlgorithm) (it.next());
                algMap.put(alg.getIdentifier().toString(), alg);
            } catch (ClassCastException cce) {
                throw new IllegalArgumentException("an element of the set "
                        + "was not an instance of " + "CombiningAlgorithm");
            }
        }
    }

    /**
     * Adds a combining algorithm to the factory. This single instance will be returned to anyone
     * who asks the factory for an algorithm with the id given here.
     * 
     * @param alg the combining algorithm to add
     * 
     * @throws IllegalArgumentException if the algId is already registered
     */
    public void addAlgorithm(CombiningAlgorithm alg) {
        String algId = alg.getIdentifier().toString();

        // check that the id doesn't already exist in the factory
        if (algMap.containsKey(algId))
            throw new IllegalArgumentException("algorithm already registered: " + algId);

        // add the algorithm
        algMap.put(algId, alg);
    }

    /**
     * Returns the algorithm identifiers supported by this factory.
     * 
     * @return a <code>Set</code> of <code>String</code>s
     */
    public Set getSupportedAlgorithms() {
        return Collections.unmodifiableSet(algMap.keySet());
    }

    /**
     * Tries to return the correct combinging algorithm based on the given algorithm ID.
     * 
     * @param algId the identifier by which the algorithm is known
     * 
     * @return a combining algorithm
     * 
     * @throws UnknownIdentifierException algId is unknown
     */
    public CombiningAlgorithm createAlgorithm(URI algId) throws UnknownIdentifierException {
        String id = algId.toString();

        if (algMap.containsKey(id)) {
            return (CombiningAlgorithm) (algMap.get(algId.toString()));
        } else {
            throw new UnknownIdentifierException("unknown combining algId: " + id);
        }
    }

}
