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/*
 * Copyright 2012-2023 the original author or authors.
 *
 * 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
 *
 *      https://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.grails.cli.app;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;

/**
 * A launcher for {@code SpringApplication} or a {@code SpringApplication} subclass. The
 * class that is used can be configured using the System property
 * {@code grails.application.class.name} or the {@code GRAILS_APPLICATION_CLASS_NAME}
 * environment variable. Uses reflection to allow the launching code to exist in a
 * separate ClassLoader from the application code.
 *
 * @author Andy Wilkinson
 * @author Michael Yan
 * @see System#getProperty(String)
 * @see System#getenv(String)
 * @since 2022.1.0
 */
public class GrailsApplicationLauncher {

    private static final String DEFAULT_GRAILS_APPLICATION_CLASS = "grails.boot.Grails";

    private final ClassLoader classLoader;

    /**
     * Creates a new launcher that will use the given {@code classLoader} to load the
     * configured {@code SpringApplication} class.
     *
     * @param classLoader the {@code ClassLoader} to use
     */
    public GrailsApplicationLauncher(ClassLoader classLoader) {
        this.classLoader = classLoader;
    }

    /**
     * Launches the application created using the given {@code sources}. The application
     * is launched with the given {@code args}.
     *
     * @param sources the sources for the application
     * @param args    the args for the application
     * @return the application's {@code ApplicationContext}
     * @throws Exception if the launch fails
     */
    public Object launch(Class[] sources, String[] args) throws Exception {
        Map defaultProperties = new HashMap<>();
        defaultProperties.put("spring.groovy.template.check-template-location", "false");
        Class applicationClass = Class.forName(getGrailsApplicationClassName(), false, this.classLoader);
        Constructor constructor = applicationClass.getDeclaredConstructor(Class[].class);
        constructor.setAccessible(true);
        Object application = constructor.newInstance((Object) sources);
        applicationClass.getMethod("setDefaultProperties", Map.class).invoke(application, defaultProperties);
        Method method = applicationClass.getMethod("run", String[].class);
        return method.invoke(application, (Object) args);
    }

    private String getGrailsApplicationClassName() {
        String className = System.getProperty("grails.application.class.name");
        if (className == null) {
            className = getEnvironmentVariable("GRAILS_APPLICATION_CLASS_NAME");
        }
        if (className == null) {
            className = DEFAULT_GRAILS_APPLICATION_CLASS;
        }
        return className;
    }

    protected String getEnvironmentVariable(String name) {
        return System.getenv(name);
    }

}