# LibraryService.java

    /*
     * Licensed to the Apache Software Foundation (ASF) under one
     * or more contributor license agreements.  See the NOTICE file
     * distributed with this work for additional information
     * regarding copyright ownership.  The ASF licenses this file
     * to you 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.tutorials.services.step5;

    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.StringTokenizer;
    import org.qi4j.api.configuration.Configuration;
    import org.qi4j.api.configuration.ConfigurationComposite;
    import org.qi4j.api.injection.scope.Structure;
    import org.qi4j.api.injection.scope.This;
    import org.qi4j.api.mixin.Mixins;
    import org.qi4j.api.property.Property;
    import org.qi4j.api.service.ServiceComposite;
    import org.qi4j.api.value.ValueBuilder;
    import org.qi4j.api.value.ValueBuilderFactory;

    @Mixins( LibraryService.LibraryMixin.class )
    public interface LibraryService
        extends Library, ServiceComposite
    {
        public static interface LibraryConfiguration
            extends ConfigurationComposite
        {
            Property<String> titles();

            Property<String> authors();

            Property<Integer> copies();
        }

        public static class LibraryMixin
            implements Library
        {

            private HashMap<String, ArrayList<Book>> books;

            public LibraryMixin( @This Configuration<LibraryConfiguration> config,
                                 @Structure ValueBuilderFactory factory
            )
            {
                books = new HashMap<String, ArrayList<Book>>();
                String titles = config.get().titles().get();
                String authors = config.get().authors().get();
                int copies = config.get().copies().get();
                StringTokenizer titlesSt = new StringTokenizer( titles, ",", false );
                StringTokenizer authorSt = new StringTokenizer( authors, ",", false );
                while( titlesSt.hasMoreTokens() )
                {
                    String title = titlesSt.nextToken();
                    String author = authorSt.nextToken();
                    createBook( factory, author, title, copies );
                }
            }

            @Override
            public Book borrowBook( String author, String title )
            {
                String key = constructKey( author, title );
                ArrayList<Book> copies = books.get( key );
                if( copies == null )
                {
                    System.out.println( "Book not available." );
                    return null; // Indicate that book is not available.
                }
                Book book = copies.remove( 0 );
                if( book == null )
                {
                    System.out.println( "Book not available." );
                    return null; // Indicate that book is not available.
                }
                System.out.println( "Book borrowed: " + book.title().get() + " by " + book.author().get() );
                return book;
            }

            @Override
            public void returnBook( Book book )
            {
                System.out.println( "Book returned: " + book.title().get() + " by " + book.author().get() );
                String key = constructKey( book.author().get(), book.title().get() );
                ArrayList<Book> copies = books.get( key );
                if( copies == null )
                {
                    throw new IllegalStateException( "Book " + book + " was not borrowed here." );
                }
                copies.add( book );
            }

            private void createBook( ValueBuilderFactory factory, String author, String title, int copies )
            {
                ArrayList<Book> bookCopies = new ArrayList<Book>();
                String key = constructKey( author, title );
                books.put( key, bookCopies );

                for( int i = 0; i < copies; i++ )
                {
                    ValueBuilder<Book> builder = factory.newValueBuilder( Book.class );
                    Book prototype = builder.prototype();
                    prototype.author().set( author );
                    prototype.title().set( title );

                    Book book = builder.newInstance();
                    System.out.println( "Book created: " + book );
                    bookCopies.add( book );
                }
            }

            private String constructKey( String author, String title )
            {
                return author + "::" + title;
            }
        }
    }