/*
 * @(#)BagAttribute.java
 *
 * Copyright 2003-2004 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistribution of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 * 
 *   2. Redistribution in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * 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
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MICROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
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 */

package com.sun.xacml.attr;

import java.net.URI;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;


/**
 * Represents a bag used in the XACML spec as return values from functions
 * and designators/selectors that provide more than one value. All values in
 * the bag are of the same type, and the bag may be empty. The bag is
 * immutable, although its contents may not be.
 * <p>
 * NOTE: This is the one standard attribute type that can't be created from
 * the factory, since you can't have this in an XML block (it is used only
 * in return values & dynamic inputs). I think this is right, but we may need
 * to add some functionality to let this go into the factory.
 *
 * @since 1.0
 * @author Seth Proctor
 * @author Steve Hanna
 */
public class BagAttribute extends AttributeValue
{

    // The Collection of AttributeValues that this object encapsulates
    private Collection bag;

    /**
     * Creates a new <code>BagAttribute</code> that represents
     * the <code>Collection</code> of <code>AttributeValue</code>s supplied.
     * If the set is null or empty, then the new bag is empty.
     *
     * @param type the data type of all the attributes in the set
     * @param bag a <code>Collection</code> of <code>AttributeValue</code>s
     */
    public BagAttribute(URI type, Collection bag) {
        super(type);

        if (type == null)
            throw new IllegalArgumentException("Bags require a non-null " +
                                               "type be provided");

        // see if the bag is empty/null
        if ((bag == null) || (bag.size() == 0)) {
            // empty bag
            this.bag = new ArrayList();
        } else {
            // go through the collection to make sure it's a valid bag
            Iterator it = bag.iterator();
            
            while (it.hasNext()) {
                AttributeValue attr = (AttributeValue)(it.next());

                // a bag cannot contain other bags, so make sure that each
                // value isn't actually another bag
                if (attr.isBag())
                    throw new IllegalArgumentException("bags cannot contain " +
                                                       "other bags");
                    
                // make sure that they're all the same type
                if (! type.equals(attr.getType()))
                    throw new
                        IllegalArgumentException("Bag items must all be of " +
                                                 "the same type");
            }

            // if we get here, then they're all the same type
            this.bag = bag;
        }
    }

    /**
     * Overrides the default method to always return true.
     *
     * @return a value of true
     */
    public boolean isBag() {
        return true;
    }

    /**
     * Convenience function that returns a bag with no elements
     *
     * @param type the types contained in the bag
     *
     * @return a new empty bag
     */
    public static BagAttribute createEmptyBag(URI type) {
        return new BagAttribute(type, null);
    }

    /**
     * A convenience function that returns whether or not the bag is empty
     * (ie, whether or not the size of the bag is zero)
     *
     * @return whether or not the bag is empty
     */
    public boolean isEmpty() {
        return (bag.size() == 0);
    }

    /**
     * Returns the number of elements in this bag
     *
     * @return the number of elements in this bag
     */
    public int size() {
        return bag.size();
    }

    /**
     * Returns true if this set contains the specified value. More formally,
     * returns true if and only if this bag contains a value v such that
     * (value==null ? v==null : value.equals(v)). Note that this will only
     * work correctly if the <code>AttributeValue</code> has overridden the
     * <code>equals</code> method.
     *
     * @param value the value to look for
     *
     * @return true if the value is in the bag
     */
    public boolean contains(AttributeValue value) {
        return bag.contains(value);
    }

    /**
     * Returns true if this bag contains all of the values of the specified bag.
     * Note that this will only work correctly if the
     * <code>AttributeValue</code> type contained in the bag has overridden
     * the <code>equals</code> method.
     *
     * @param bag the bag to compare
     *
     * @return true if the input is a subset of this bag
     */
    public boolean containsAll(BagAttribute bag) {
        return this.bag.containsAll(bag.bag);
    }


    /**
     * Returns an iterator over te 
     */
    public Iterator iterator() {
        return new ImmutableIterator(bag.iterator());
    }

    /**
     * This is a version of Iterator that overrides the <code>remove</code>
     * method so that items can't be taken out of the bag.
     */
    private class ImmutableIterator implements Iterator {

        // the iterator we're wrapping
        private Iterator iterator;

        /**
         * Create a new ImmutableIterator
         */
        public ImmutableIterator(Iterator iterator) {
            this.iterator = iterator;
        }
        
        /**
         * Standard hasNext method
         */
        public boolean hasNext() {
            return iterator.hasNext();
        }

        /**
         * Standard next method
         */
        public Object next() throws NoSuchElementException {
            return iterator.next();
        }

        /**
         * Makes sure that no one can remove any elements from the bag
         */
        public void remove() throws UnsupportedOperationException {
            throw new UnsupportedOperationException();
        }
        
    }

    /**
     * Because a bag cannot be included in a request/response or a 
     * policy, this will always throw an
     * <code>UnsupportedOperationException</code>.
     */
    public String encode() {
        throw new UnsupportedOperationException("Bags cannot be encoded");
    }

}