/*
 * Copyright 2012-2017 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
 *
 *      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.springframework.boot.web.servlet.support;

import java.util.Collections;

import javax.servlet.Filter;
import javax.servlet.Servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.builder.ParentContextApplicationContextInitializer;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.web.servlet.ServletContextInitializer;
import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.util.Assert;
import org.springframework.web.WebApplicationInitializer;
import org.springframework.web.context.ContextLoaderListener;
import org.springframework.web.context.WebApplicationContext;

/**
 * An opinionated {@link WebApplicationInitializer} to run a {@link SpringApplication}
 * from a traditional WAR deployment. Binds {@link Servlet}, {@link Filter} and
 * {@link ServletContextInitializer} beans from the application context to the server.
 * <p>
 * To configure the application either override the
 * {@link #configure(SpringApplicationBuilder)} method (calling
 * {@link SpringApplicationBuilder#sources(Class...)}) or make the initializer itself a
 * {@code @Configuration}. If you are using {@link SpringBootServletInitializer} in
 * combination with other {@link WebApplicationInitializer WebApplicationInitializers} you
 * might also want to add an {@code @Ordered} annotation to configure a specific startup
 * order.
 * <p>
 * Note that a WebApplicationInitializer is only needed if you are building a war file and
 * deploying it. If you prefer to run an embedded web server then you won't need this at
 * all.
 *
 * @author Dave Syer
 * @author Phillip Webb
 * @author Andy Wilkinson
 * @since 2.0.0
 * @see #configure(SpringApplicationBuilder)
 */
public abstract class SpringBootServletInitializer implements WebApplicationInitializer {

	protected Log logger; // Don't initialize early

	private boolean registerErrorPageFilter = true;

	/**
	 * Set if the {@link ErrorPageFilter} should be registered. Set to {@code false} if
	 * error page mappings should be handled via the server and not Spring Boot.
	 * @param registerErrorPageFilter if the {@link ErrorPageFilter} should be registered.
	 */
	protected final void setRegisterErrorPageFilter(boolean registerErrorPageFilter) {
		this.registerErrorPageFilter = registerErrorPageFilter;
	}

	@Override
	public void onStartup(ServletContext servletContext) throws ServletException {
		// Logger initialization is deferred in case a ordered
		// LogServletContextInitializer is being used
		this.logger = LogFactory.getLog(getClass());
		WebApplicationContext rootAppContext = createRootApplicationContext(
				servletContext);
		if (rootAppContext != null) {
			servletContext.addListener(new ContextLoaderListener(rootAppContext) {
				@Override
				public void contextInitialized(ServletContextEvent event) {
					// no-op because the application context is already initialized
				}
			});
		}
		else {
			this.logger.debug("No ContextLoaderListener registered, as "
					+ "createRootApplicationContext() did not "
					+ "return an application context");
		}
	}

	protected WebApplicationContext createRootApplicationContext(
			ServletContext servletContext) {
		SpringApplicationBuilder builder = createSpringApplicationBuilder();
		builder.main(getClass());
		ApplicationContext parent = getExistingRootWebApplicationContext(servletContext);
		if (parent != null) {
			this.logger.info("Root context already created (using as parent).");
			servletContext.setAttribute(
					WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, null);
			builder.initializers(new ParentContextApplicationContextInitializer(parent));
		}
		builder.initializers(
				new ServletContextApplicationContextInitializer(servletContext));
		builder.listeners(new ServletContextApplicationListener(servletContext));
		builder.contextClass(AnnotationConfigServletWebServerApplicationContext.class);
		builder = configure(builder);
		SpringApplication application = builder.build();
		if (application.getAllSources().isEmpty() && AnnotationUtils
				.findAnnotation(getClass(), Configuration.class) != null) {
			application.addPrimarySources(Collections.singleton(getClass()));
		}
		Assert.state(!application.getAllSources().isEmpty(),
				"No SpringApplication sources have been defined. Either override the "
						+ "configure method or add an @Configuration annotation");
		// Ensure error pages are registered
		if (this.registerErrorPageFilter) {
			application.addPrimarySources(
					Collections.singleton(ErrorPageFilterConfiguration.class));
		}
		return run(application);
	}

	/**
	 * Returns the {@code SpringApplicationBuilder} that is used to configure and create
	 * the {@link SpringApplication}. The default implementation returns a new
	 * {@code SpringApplicationBuilder} in its default state.
	 * @return the {@code SpringApplicationBuilder}.
	 * @since 1.3.0
	 */
	protected SpringApplicationBuilder createSpringApplicationBuilder() {
		return new SpringApplicationBuilder();
	}

	/**
	 * Called to run a fully configured {@link SpringApplication}.
	 * @param application the application to run
	 * @return the {@link WebApplicationContext}
	 */
	protected WebApplicationContext run(SpringApplication application) {
		return (WebApplicationContext) application.run();
	}

	private ApplicationContext getExistingRootWebApplicationContext(
			ServletContext servletContext) {
		Object context = servletContext.getAttribute(
				WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
		if (context instanceof ApplicationContext) {
			return (ApplicationContext) context;
		}
		return null;
	}

	/**
	 * Configure the application. Normally all you would need to do is to add sources
	 * (e.g. config classes) because other settings have sensible defaults. You might
	 * choose (for instance) to add default command line arguments, or set an active
	 * Spring profile.
	 * @param builder a builder for the application context
	 * @return the application builder
	 * @see SpringApplicationBuilder
	 */
	protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
		return builder;
	}

}
