/*
 * 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.apache.tamaya.metamodel;

import org.apache.tamaya.base.ServiceContext;
import org.apache.tamaya.metamodel.spi.MetaConfigReader;
import org.apache.tamaya.base.ServiceContextManager;
import org.w3c.dom.Document;
import org.xml.sax.SAXException;

import javax.config.Config;
import javax.config.spi.ConfigBuilder;
import javax.config.spi.ConfigProviderResolver;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import java.io.File;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Objects;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Accessor singleton for accessing/loading meta-configuration.
 */
public final class MetaConfig {

    private static final String CONFIG_RESOURCE = "tamaya-config.xml";

    private static final Logger LOG = Logger.getLogger(MetaConfig.class.getName());

    /**
     * Singleton constructor.
     */
    private MetaConfig(){}

    /**
     * Creates a new {@link Config} using {@link #createConfig(URL)}
     * and applies it as default configuration using {@link ConfigProviderResolver#registerConfig(Config, ClassLoader)} .
     */
    public static void configure(ClassLoader classLoader){
        LOG.info("TAMAYA: Checking for meta-configuration...");
        URL configFile = getDefaultMetaConfig();
        if(configFile==null){
            LOG.warning("TAMAYA: No " + CONFIG_RESOURCE + " found, using defaults.");
        }
        configure(configFile, classLoader);
    }

    /**
     * Creates a new {@link Config} using {@link #createConfig(URL)}
     * and applies it as default configuration using {@link ConfigProviderResolver#registerConfig(Config, ClassLoader)} .
     * @param metaConfig URL for loading the {@code tamaya-config.xml} meta-configuration.
     */
    public static void configure(URL metaConfig, ClassLoader classloader){
        try {
            // Let readers do their work
            Config config = createConfig(metaConfig);
            ConfigProviderResolver.instance().registerConfig(config, classloader);
        }catch(Exception e){
            LOG.log(Level.SEVERE, "TAMAYA: Error loading configuration.", e);
        }
    }

    private static URL getDefaultMetaConfig() {
        // 1: check tamaya-config system property
        String tamayaConfig = System.getProperty("tamaya-config");
        if(tamayaConfig!=null){
            File file = new File(tamayaConfig);
            if(!file.exists() || !file.canRead() || !file.isFile()){
                LOG.severe("TAMAYA: Not a valid config file: " + tamayaConfig);
            }else{
                try {
                    return file.toURI().toURL();
                } catch (MalformedURLException e) {
                    LOG.severe("TAMAYA: Invalid file name: " + tamayaConfig);
                }
            }
        }
        return MetaConfig.class.getClassLoader().getResource(CONFIG_RESOURCE);
    }

    /**
     * Performs initialization of a new configuration
     * context to the {@link MetaConfigReader} instances found in the current
     * {@link ServiceContext} and returns the corresponding builder
     * instance.
     * @param metaConfig URL for loading the {@code tamaya-config.xml} meta-configuration.
     * @return a new configuration context builder, never null.
     * @throws IllegalStateException If the URL cannot be read.
     */
    public static ConfigBuilder createConfigBuilder(URL metaConfig){
        URL configFile = Objects.requireNonNull(metaConfig);
        LOG.info("TAMAYA: Loading tamaya-config.xml...");
        Document document = null;
        try {
            document = DocumentBuilderFactory.newInstance()
                    .newDocumentBuilder().parse(configFile.openStream());
            ConfigBuilder builder = ConfigProviderResolver.instance().getBuilder();
            for(MetaConfigReader reader: ServiceContextManager.getServiceContext().getServices(
                    MetaConfigReader.class
            )){
                LOG.fine("TAMAYA: Executing MetaConfig-Reader: " + reader.getClass().getName() + "...");
                reader.read(document, builder);
            }
            return builder;
        } catch (SAXException | IOException | ParserConfigurationException e) {
            throw new IllegalStateException("Cannot read meta-config from " + metaConfig, e);
        }
    }

    /**
     * Reads the meta-configuration and delegates initialization of the current configuration
     * context to the {@link MetaConfigReader} instances found in the current
     * {@link ServiceContext}.
     * @param metaConfig URL for loading the {@code tamaya-config.xml} meta-configuration.
     * @return the new configuration instance.
     */
    public static Config createConfig(URL metaConfig){
        return createConfigBuilder(metaConfig).build();
    }

}