/*
 * Copyright (c) 2013 Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions 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 Oracle nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * This source code is provided to illustrate the usage of a given feature
 * or technique and has been deliberately simplified. Additional steps
 * required for a production-quality application, such as security checks,
 * input validation and proper error handling, might not be present in
 * this sample code.
 */
package stream.data;

import java.io.File;
import java.util.ArrayList;
import java.util.List;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

/**
 * DataUtilities is a singleton helper class that creates test data. This class
 * uses jaxws API to read xml into java object, which includes 3 list of data 1.
 * Customers 2. Products 3. Vendors Note in this demo here we don't use stream
 * API to change data, if we use stream API to populate source data, we should
 * be aware this is not free and not thread-safe.
 */
interface XMLList<E> {

    public List<E> getList();
}

/**
 * class for PRODUCTS_XML's root
 */
@XmlRootElement(name = "products")
class Products implements XMLList<Product> {

    /**
     * node products only contains product list
     */
    @XmlElement(name = "product")
    private ArrayList<Product> products;

    /**
     * product list
     */
    @Override
    public List<Product> getList() {
        return products;
    }
}

/**
 * class for VENDORS_XML's root
 */
@XmlRootElement(name = "vendors")
class Vendors implements XMLList<Vendor> {

    /**
     * node Vendors only contains vendor list
     */

    @Override
    public List<Vendor> getList() {
        return vendors;
    }

    /**
     * vendor list
     */
    @XmlElement(name = "vendor")
    private ArrayList<Vendor> vendors;
}

/**
 * class for CUSTOMERS_XML's root
 */
@XmlRootElement(name = "customers")
class Customers implements XMLList<Customer> {

    /**
     * node customers only contains customer list
     */
    @Override
    public List<Customer> getList() {
        return customers;
    }

    /**
     * customer list
     */
    @XmlElement(name = "customer")
    private ArrayList<Customer> customers;
}

public class DataUtilities {

    /**
     * xml file name for Customers object
     */

    private final static String CUSTOMERS_XML = "Customers.xml";

    /**
     * xml file name for Products object
     */
    private final static String PRODUCTS_XML = "Products.xml";

    /**
     * xml file name for Products object
     */
    private final static String VENDORS_XML = "Vendors.xml";

    /**
     * Lazy initiate static inner class for
     */
    private static class UtilitiesHolder {

        static DataUtilities instance = new DataUtilities();
    }

    /**
     * private constructor is needed for singleton
     */
    private DataUtilities() {
    }

    //products
    private List<Product> productList;

    //customer
    private List<Customer> customerList;

    //vendors
    private List<Vendor> vendorList;

    /**
     * Lazy initial to get product list
     *
     * @return initiated product list
     */
    public List<Product> getProductList() {
        if (productList == null) {
            createLists();
        }
        return productList;
    }

    /**
     * Lazy initial to get customer list
     *
     * @return initiated customer list
     */
    public List<Customer> getCustomerList() {
        if (customerList == null) {
            createLists();
        }
        return customerList;
    }

    /**
     * Lazy initial to get vendor list
     *
     * @return initiated vendor list
     */
    public List<Vendor> getVendorList() {
        if (vendorList == null) {
            createLists();
        }
        return vendorList;
    }

    /**
     * convert xml files to java objects
     */
    private void createLists() {
        customerList = xmlToObject(Customers.class, CUSTOMERS_XML);
        productList = xmlToObject(Products.class, PRODUCTS_XML);
        vendorList = xmlToObject(Vendors.class, VENDORS_XML);
    }

    /**
     * Convert a xml file to instance of class by given file name
     *
     * @param clazz to be converted java object's class
     * @param file xml file name
     * @return a list of object that xml's root contains
     */
    private <U, V extends XMLList<U>> List<U> xmlToObject(Class<V> clazz,
            String file) {
        try {
            JAXBContext context = JAXBContext.newInstance(clazz);
            Unmarshaller um = context.createUnmarshaller();
            @SuppressWarnings("unchecked")
            V cs = (V) um.unmarshal(new File(file));
            return cs.getList();
        } catch (JAXBException ex) {
            throw new RuntimeException(ex);
        }
    }

    /**
     * static factory method for singleton
     *
     * @return a DataUtitlities signgleton instance
     */
    public static DataUtilities getUtilities() {
        return UtilitiesHolder.instance;
    }
}