# UsesInstance.java

    /*
     * Copyright (c) 2008, Rickard Öberg. All Rights Reserved.
     *
     * 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.qi4j.runtime.composite;

    import java.util.Arrays;
    import java.util.Collections;
    import java.util.HashSet;
    import java.util.Set;
    import org.qi4j.functional.Iterables;

    /**
     * JAVADOC
     */
    public final class UsesInstance
    {
        public static final UsesInstance EMPTY_USES;
        private final Set<Object> uses;

        static
        {
            EMPTY_USES = new UsesInstance( new HashSet<>() );
        }

        private UsesInstance( HashSet<Object> uses )
        {
            this.uses = Collections.unmodifiableSet( uses );
        }

        public UsesInstance use( Object... objects )
        {
            HashSet<Object> useObjects = new HashSet<>();
            if( !uses.isEmpty() )
            {
                useObjects.addAll( uses );
                for( Object object : objects )
                {
                    Object oldUseForType = useForType( object.getClass() );
                    if( oldUseForType != null )
                    {
                        useObjects.remove( oldUseForType );
                    }
                }
            }
            useObjects.addAll( Arrays.asList( objects ) );
            return new UsesInstance( useObjects );
        }

        public Object useForType( Class<?> type )
        {
            // Check instances first
            for( Object use : uses )
            {
                if( type.isInstance( use ) )
                {
                    return use;
                }
            }

            return null;
        }

        public Object[] toArray()
        {
            return Iterables.toArray( uses );
        }

        @Override
        public boolean equals( Object o )
        {
            if( this == o )
            {
                return true;
            }
            if( o == null || getClass() != o.getClass() )
            {
                return false;
            }
            UsesInstance that = (UsesInstance) o;
            return uses.equals( that.uses );
        }

        @Override
        public int hashCode()
        {
            return uses.hashCode();
        }

        @Override
        public String toString()
        {
            return "UsesInstance{" +
                   "uses=" + uses +
                   '}';
        }
    }