/*
 * Copyright 2005 JBoss Inc
 * 
 * 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.drools.util;

import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;

/**
 * Decorates a collection of other collections to provide a single unified view.
 * <p>
 * Changes made to this collection will actually be made on the decorated
 * collection. Add and remove operations require the use of a pluggable
 * strategy. If no strategy is provided then add and remove are unsupported.
 * 
 * @since Commons Collections 3.0
 * @version $Revision: 1.1 $ $Date: 2005/07/26 01:06:32 $
 * 
 * @author Brian McCallister
 * @author Stephen Colebourne
 * @author Phil Steitz
 */
public class CompositeCollection
    implements
    Collection {

    /** CollectionMutator to handle changes to the collection */
    protected CollectionMutator mutator;

    /** Collections in the composite */
    protected Collection[]      all;

    /**
     * Create an empty CompositeCollection.
     */
    public CompositeCollection() {
        super();
        this.all = new Collection[0];
    }

    /**
     * Create a Composite Collection with only coll composited.
     * 
     * @param coll
     *            a collection to decorate
     */
    public CompositeCollection(final Collection coll) {
        this();
        this.addComposited( coll );
    }

    /**
     * Create a CompositeCollection with colls as the initial list of composited
     * collections.
     * 
     * @param colls
     *            an array of collections to decorate
     */
    public CompositeCollection(final Collection[] colls) {
        this();
        this.addComposited( colls );
    }

    // -----------------------------------------------------------------------
    /**
     * Gets the size of this composite collection.
     * <p>
     * This implementation calls <code>size()</code> on each collection.
     * 
     * @return total number of elements in all contained containers
     */
    public int size() {
        int size = 0;
        for ( int i = this.all.length - 1; i >= 0; i-- ) {
            size += this.all[i].size();
        }
        return size;
    }

    /**
     * Checks whether this composite collection is empty.
     * <p>
     * This implementation calls <code>isEmpty()</code> on each collection.
     * 
     * @return true if all of the contained collections are empty
     */
    public boolean isEmpty() {
        for ( int i = this.all.length - 1; i >= 0; i-- ) {
            if ( this.all[i].isEmpty() == false ) {
                return false;
            }
        }
        return true;
    }

    /**
     * Checks whether this composite collection contains the object.
     * <p>
     * This implementation calls <code>contains()</code> on each collection.
     * 
     * @param obj
     *            the object to search for
     * @return true if obj is contained in any of the contained collections
     */
    public boolean contains(final Object obj) {
        for ( int i = this.all.length - 1; i >= 0; i-- ) {
            if ( this.all[i].contains( obj ) ) {
                return true;
            }
        }
        return false;
    }

    /**
     * Gets an iterator over all the collections in this composite.
     * <p>
     * This implementation uses an <code>IteratorChain</code>.
     * 
     * @return an <code>IteratorChain</code> instance which supports
     *         <code>remove()</code>. Iteration occurs over contained
     *         collections in the order they were added, but this behavior
     *         should not be relied upon.
     * @see IteratorChain
     */
    public Iterator iterator() {
        if ( this.all.length == 0 ) {
            return Collections.EMPTY_LIST.iterator();
        }
        final IteratorChain chain = new IteratorChain();
        for ( int i = 0; i < this.all.length; ++i ) {
            chain.addIterator( this.all[i].iterator() );
        }
        return chain;
    }

    /**
     * Returns an array containing all of the elements in this composite.
     * 
     * @return an object array of all the elements in the collection
     */
    public Object[] toArray() {
        final Object[] result = new Object[this.size()];
        int i = 0;
        for ( final Iterator it = this.iterator(); it.hasNext(); i++ ) {
            result[i] = it.next();
        }
        return result;
    }

    /**
     * Returns an object array, populating the supplied array if possible. See
     * <code>Collection</code> interface for full details.
     * 
     * @param array
     *            the array to use, populating if possible
     * @return an array of all the elements in the collection
     */
    public Object[] toArray(final Object[] array) {
        final int size = this.size();
        Object[] result;
        if ( array.length >= size ) {
            result = array;
        } else {
            result = (Object[]) Array.newInstance( array.getClass().getComponentType(),
                                                   size );
        }

        int offset = 0;
        for ( int i = 0; i < this.all.length; ++i ) {
            for ( final Iterator it = this.all[i].iterator(); it.hasNext(); ) {
                result[offset++] = it.next();
            }
        }
        if ( result.length > size ) {
            result[size] = null;
        }
        return result;
    }

    /**
     * Adds an object to the collection, throwing UnsupportedOperationException
     * unless a CollectionMutator strategy is specified.
     * 
     * @param obj
     *            the object to add
     * @return true if the collection was modified
     * @throws UnsupportedOperationException
     *             if CollectionMutator hasn't been set
     * @throws UnsupportedOperationException
     *             if add is unsupported
     * @throws ClassCastException
     *             if the object cannot be added due to its type
     * @throws NullPointerException
     *             if the object cannot be added because its null
     * @throws IllegalArgumentException
     *             if the object cannot be added
     */
    public boolean add(final Object obj) {
        if ( this.mutator == null ) {
            throw new UnsupportedOperationException( "add() is not supported on CompositeCollection without a CollectionMutator strategy" );
        }
        return this.mutator.add( this,
                                 this.all,
                                 obj );
    }

    /**
     * Removes an object from the collection, throwing
     * UnsupportedOperationException unless a CollectionMutator strategy is
     * specified.
     * 
     * @param obj
     *            the object being removed
     * @return true if the collection is changed
     * @throws UnsupportedOperationException
     *             if removed is unsupported
     * @throws ClassCastException
     *             if the object cannot be removed due to its type
     * @throws NullPointerException
     *             if the object cannot be removed because its null
     * @throws IllegalArgumentException
     *             if the object cannot be removed
     */
    public boolean remove(final Object obj) {
        if ( this.mutator == null ) {
            throw new UnsupportedOperationException( "remove() is not supported on CompositeCollection without a CollectionMutator strategy" );
        }
        return this.mutator.remove( this,
                                    this.all,
                                    obj );
    }

    /**
     * Checks whether this composite contains all the elements in the specified
     * collection.
     * <p>
     * This implementation calls <code>contains()</code> for each element in
     * the specified collection.
     * 
     * @param coll
     *            the collection to check for
     * @return true if all elements contained
     */
    public boolean containsAll(final Collection coll) {
        for ( final Iterator it = coll.iterator(); it.hasNext(); ) {
            if ( this.contains( it.next() ) == false ) {
                return false;
            }
        }
        return true;
    }

    /**
     * Adds a collection of elements to this collection, throwing
     * UnsupportedOperationException unless a CollectionMutator strategy is
     * specified.
     * 
     * @param coll
     *            the collection to add
     * @return true if the collection was modified
     * @throws UnsupportedOperationException
     *             if CollectionMutator hasn't been set
     * @throws UnsupportedOperationException
     *             if add is unsupported
     * @throws ClassCastException
     *             if the object cannot be added due to its type
     * @throws NullPointerException
     *             if the object cannot be added because its null
     * @throws IllegalArgumentException
     *             if the object cannot be added
     */
    public boolean addAll(final Collection coll) {
        if ( this.mutator == null ) {
            throw new UnsupportedOperationException( "addAll() is not supported on CompositeCollection without a CollectionMutator strategy" );
        }
        return this.mutator.addAll( this,
                                    this.all,
                                    coll );
    }

    /**
     * Removes the elements in the specified collection from this composite
     * collection.
     * <p>
     * This implementation calls <code>removeAll</code> on each collection.
     * 
     * @param coll
     *            the collection to remove
     * @return true if the collection was modified
     * @throws UnsupportedOperationException
     *             if removeAll is unsupported
     */
    public boolean removeAll(final Collection coll) {
        if ( coll.isEmpty() ) {
            return false;
        }

        boolean changed = false;
        for ( int i = this.all.length - 1; i >= 0; i-- ) {
            changed |= this.all[i].removeAll( coll );
        }
        return changed;
    }

    /**
     * Retains all the elements in the specified collection in this composite
     * collection, removing all others.
     * <p>
     * This implementation calls <code>retainAll()</code> on each collection.
     * 
     * @param coll
     *            the collection to remove
     * @return true if the collection was modified
     * @throws UnsupportedOperationException
     *             if retainAll is unsupported
     */
    public boolean retainAll(final Collection coll) {
        boolean changed = false;
        for ( int i = this.all.length - 1; i >= 0; i-- ) {
            changed = (this.all[i].retainAll( coll ) || changed);
        }
        return changed;
    }

    /**
     * Removes all of the elements from this collection .
     * <p>
     * This implementation calls <code>clear()</code> on each collection.
     * 
     * @throws UnsupportedOperationException
     *             if clear is unsupported
     */
    public void clear() {
        for ( int i = 0; i < this.all.length; ++i ) {
            this.all[i].clear();
        }
    }

    // -----------------------------------------------------------------------
    /**
     * Specify a CollectionMutator strategy instance to handle changes.
     * 
     * @param mutator
     *            the mutator to use
     */
    public void setMutator(final CollectionMutator mutator) {
        this.mutator = mutator;
    }

    /**
     * Add these Collections to the list of collections in this composite
     * 
     * @param comps
     *            Collections to be appended to the composite
     */
    public void addComposited(final Collection[] comps) {
        final ArrayList list = new ArrayList( Arrays.asList( this.all ) );
        list.addAll( Arrays.asList( comps ) );
        this.all = (Collection[]) list.toArray( new Collection[list.size()] );
    }

    /**
     * Add an additional collection to this composite.
     * 
     * @param c
     *            the collection to add
     */
    public void addComposited(final Collection c) {
        this.addComposited( new Collection[]{c} );
    }

    /**
     * Add two additional collections to this composite.
     * 
     * @param c
     *            the first collection to add
     * @param d
     *            the second collection to add
     */
    public void addComposited(final Collection c,
                              final Collection d) {
        this.addComposited( new Collection[]{c, d} );
    }

    /**
     * Removes a collection from the those being decorated in this composite.
     * 
     * @param coll
     *            collection to be removed
     */
    public void removeComposited(final Collection coll) {
        final ArrayList list = new ArrayList( this.all.length );
        list.addAll( Arrays.asList( this.all ) );
        list.remove( coll );
        this.all = (Collection[]) list.toArray( new Collection[list.size()] );
    }

    /**
     * Returns a new collection containing all of the elements
     * 
     * @return A new ArrayList containing all of the elements in this composite.
     *         The new collection is <i>not </i> backed by this composite.
     */
    public Collection toCollection() {
        return new ArrayList( this );
    }

    /**
     * Gets the collections being decorated.
     * 
     * @return Unmodifiable collection of all collections in this composite.
     */
    public Collection getCollections() {
        return Collections.unmodifiableList( Arrays.asList( this.all ) );
    }

    // -----------------------------------------------------------------------
    /**
     * Pluggable strategy to handle changes to the composite.
     */
    public interface CollectionMutator {

        /**
         * Called when an object is to be added to the composite.
         * 
         * @param composite
         *            the CompositeCollection being changed
         * @param collections
         *            all of the Collection instances in this
         *            CompositeCollection
         * @param obj
         *            the object being added
         * @return true if the collection is changed
         * @throws UnsupportedOperationException
         *             if add is unsupported
         * @throws ClassCastException
         *             if the object cannot be added due to its type
         * @throws NullPointerException
         *             if the object cannot be added because its null
         * @throws IllegalArgumentException
         *             if the object cannot be added
         */
        public boolean add(CompositeCollection composite,
                           Collection[] collections,
                           Object obj);

        /**
         * Called when a collection is to be added to the composite.
         * 
         * @param composite
         *            the CompositeCollection being changed
         * @param collections
         *            all of the Collection instances in this
         *            CompositeCollection
         * @param coll
         *            the collection being added
         * @return true if the collection is changed
         * @throws UnsupportedOperationException
         *             if add is unsupported
         * @throws ClassCastException
         *             if the object cannot be added due to its type
         * @throws NullPointerException
         *             if the object cannot be added because its null
         * @throws IllegalArgumentException
         *             if the object cannot be added
         */
        public boolean addAll(CompositeCollection composite,
                              Collection[] collections,
                              Collection coll);

        /**
         * Called when an object is to be removed to the composite.
         * 
         * @param composite
         *            the CompositeCollection being changed
         * @param collections
         *            all of the Collection instances in this
         *            CompositeCollection
         * @param obj
         *            the object being removed
         * @return true if the collection is changed
         * @throws UnsupportedOperationException
         *             if removed is unsupported
         * @throws ClassCastException
         *             if the object cannot be removed due to its type
         * @throws NullPointerException
         *             if the object cannot be removed because its null
         * @throws IllegalArgumentException
         *             if the object cannot be removed
         */
        public boolean remove(CompositeCollection composite,
                              Collection[] collections,
                              Object obj);

    }

}