/*
 * Copyright 2012-2020 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.springframework.boot.web.servlet;

import java.util.AbstractCollection;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.EventListener;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.stream.Collectors;

import javax.servlet.Filter;
import javax.servlet.MultipartConfigElement;
import javax.servlet.Servlet;

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

import org.springframework.aop.scope.ScopedProxyUtils;
import org.springframework.beans.factory.ListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;

A collection ServletContextInitializers obtained from a ListableBeanFactory. Includes all ServletContextInitializer beans and also adapts Servlet, Filter and certain EventListener beans. 
 Items are sorted so that adapted beans are top (Servlet, Filter then EventListener) and direct ServletContextInitializer beans are at the end. Further sorting is applied within these groups using the AnnotationAwareOrderComparator. 
Author:
Dave Syer, Phillip Webb, Brian Clozel
Since:
1.4.0/**
 * A collection {@link ServletContextInitializer}s obtained from a
 * {@link ListableBeanFactory}. Includes all {@link ServletContextInitializer} beans and
 * also adapts {@link Servlet}, {@link Filter} and certain {@link EventListener} beans.
 * <p>
 * Items are sorted so that adapted beans are top ({@link Servlet}, {@link Filter} then
 * {@link EventListener}) and direct {@link ServletContextInitializer} beans are at the
 * end. Further sorting is applied within these groups using the
 * {@link AnnotationAwareOrderComparator}.
 *
 * @author Dave Syer
 * @author Phillip Webb
 * @author Brian Clozel
 * @since 1.4.0
 */
public class ServletContextInitializerBeans extends AbstractCollection<ServletContextInitializer> {

	private static final String DISPATCHER_SERVLET_NAME = "dispatcherServlet";

	private static final Log logger = LogFactory.getLog(ServletContextInitializerBeans.class);

	
Seen bean instances or bean names.
/**
	 * Seen bean instances or bean names.
	 */
	private final Set<Object> seen = new HashSet<>();

	private final MultiValueMap<Class<?>, ServletContextInitializer> initializers;

	private final List<Class<? extends ServletContextInitializer>> initializerTypes;

	private List<ServletContextInitializer> sortedList;

	@SafeVarargs
	@SuppressWarnings("varargs")
	public ServletContextInitializerBeans(ListableBeanFactory beanFactory,
			Class<? extends ServletContextInitializer>... initializerTypes) {
		this.initializers = new LinkedMultiValueMap<>();
		this.initializerTypes = (initializerTypes.length != 0) ? Arrays.asList(initializerTypes)
				: Collections.singletonList(ServletContextInitializer.class);
		addServletContextInitializerBeans(beanFactory);
		addAdaptableBeans(beanFactory);
		List<ServletContextInitializer> sortedInitializers = this.initializers.values().stream()
				.flatMap((value) -> value.stream().sorted(AnnotationAwareOrderComparator.INSTANCE))
				.collect(Collectors.toList());
		this.sortedList = Collections.unmodifiableList(sortedInitializers);
		logMappings(this.initializers);
	}

	private void addServletContextInitializerBeans(ListableBeanFactory beanFactory) {
		for (Class<? extends ServletContextInitializer> initializerType : this.initializerTypes) {
			for (Entry<String, ? extends ServletContextInitializer> initializerBean : getOrderedBeansOfType(beanFactory,
					initializerType)) {
				addServletContextInitializerBean(initializerBean.getKey(), initializerBean.getValue(), beanFactory);
			}
		}
	}

	private void addServletContextInitializerBean(String beanName, ServletContextInitializer initializer,
			ListableBeanFactory beanFactory) {
		if (initializer instanceof ServletRegistrationBean) {
			Servlet source = ((ServletRegistrationBean<?>) initializer).getServlet();
			addServletContextInitializerBean(Servlet.class, beanName, initializer, beanFactory, source);
		}
		else if (initializer instanceof FilterRegistrationBean) {
			Filter source = ((FilterRegistrationBean<?>) initializer).getFilter();
			addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source);
		}
		else if (initializer instanceof DelegatingFilterProxyRegistrationBean) {
			String source = ((DelegatingFilterProxyRegistrationBean) initializer).getTargetBeanName();
			addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source);
		}
		else if (initializer instanceof ServletListenerRegistrationBean) {
			EventListener source = ((ServletListenerRegistrationBean<?>) initializer).getListener();
			addServletContextInitializerBean(EventListener.class, beanName, initializer, beanFactory, source);
		}
		else {
			addServletContextInitializerBean(ServletContextInitializer.class, beanName, initializer, beanFactory,
					initializer);
		}
	}

	private void addServletContextInitializerBean(Class<?> type, String beanName, ServletContextInitializer initializer,
			ListableBeanFactory beanFactory, Object source) {
		this.initializers.add(type, initializer);
		if (source != null) {
			// Mark the underlying source as seen in case it wraps an existing bean
			this.seen.add(source);
		}
		if (logger.isTraceEnabled()) {
			String resourceDescription = getResourceDescription(beanName, beanFactory);
			int order = getOrder(initializer);
			logger.trace("Added existing " + type.getSimpleName() + " initializer bean '" + beanName + "'; order="
					+ order + ", resource=" + resourceDescription);
		}
	}

	private String getResourceDescription(String beanName, ListableBeanFactory beanFactory) {
		if (beanFactory instanceof BeanDefinitionRegistry) {
			BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
			return registry.getBeanDefinition(beanName).getResourceDescription();
		}
		return "unknown";
	}

	@SuppressWarnings("unchecked")
	protected void addAdaptableBeans(ListableBeanFactory beanFactory) {
		MultipartConfigElement multipartConfig = getMultipartConfig(beanFactory);
		addAsRegistrationBean(beanFactory, Servlet.class, new ServletRegistrationBeanAdapter(multipartConfig));
		addAsRegistrationBean(beanFactory, Filter.class, new FilterRegistrationBeanAdapter());
		for (Class<?> listenerType : ServletListenerRegistrationBean.getSupportedTypes()) {
			addAsRegistrationBean(beanFactory, EventListener.class, (Class<EventListener>) listenerType,
					new ServletListenerRegistrationBeanAdapter());
		}
	}

	private MultipartConfigElement getMultipartConfig(ListableBeanFactory beanFactory) {
		List<Entry<String, MultipartConfigElement>> beans = getOrderedBeansOfType(beanFactory,
				MultipartConfigElement.class);
		return beans.isEmpty() ? null : beans.get(0).getValue();
	}

	protected <T> void addAsRegistrationBean(ListableBeanFactory beanFactory, Class<T> type,
			RegistrationBeanAdapter<T> adapter) {
		addAsRegistrationBean(beanFactory, type, type, adapter);
	}

	private <T, B extends T> void addAsRegistrationBean(ListableBeanFactory beanFactory, Class<T> type,
			Class<B> beanType, RegistrationBeanAdapter<T> adapter) {
		List<Map.Entry<String, B>> entries = getOrderedBeansOfType(beanFactory, beanType, this.seen);
		for (Entry<String, B> entry : entries) {
			String beanName = entry.getKey();
			B bean = entry.getValue();
			if (this.seen.add(bean)) {
				// One that we haven't already seen
				RegistrationBean registration = adapter.createRegistrationBean(beanName, bean, entries.size());
				int order = getOrder(bean);
				registration.setOrder(order);
				this.initializers.add(type, registration);
				if (logger.isTraceEnabled()) {
					logger.trace("Created " + type.getSimpleName() + " initializer for bean '" + beanName + "'; order="
							+ order + ", resource=" + getResourceDescription(beanName, beanFactory));
				}
			}
		}
	}

	private int getOrder(Object value) {
		return new AnnotationAwareOrderComparator() {
			@Override
			public int getOrder(Object obj) {
				return super.getOrder(obj);
			}
		}.getOrder(value);
	}

	private <T> List<Entry<String, T>> getOrderedBeansOfType(ListableBeanFactory beanFactory, Class<T> type) {
		return getOrderedBeansOfType(beanFactory, type, Collections.emptySet());
	}

	private <T> List<Entry<String, T>> getOrderedBeansOfType(ListableBeanFactory beanFactory, Class<T> type,
			Set<?> excludes) {
		String[] names = beanFactory.getBeanNamesForType(type, true, false);
		Map<String, T> map = new LinkedHashMap<>();
		for (String name : names) {
			if (!excludes.contains(name) && !ScopedProxyUtils.isScopedTarget(name)) {
				T bean = beanFactory.getBean(name, type);
				if (!excludes.contains(bean)) {
					map.put(name, bean);
				}
			}
		}
		List<Entry<String, T>> beans = new ArrayList<>(map.entrySet());
		beans.sort((o1, o2) -> AnnotationAwareOrderComparator.INSTANCE.compare(o1.getValue(), o2.getValue()));
		return beans;
	}

	private void logMappings(MultiValueMap<Class<?>, ServletContextInitializer> initializers) {
		if (logger.isDebugEnabled()) {
			logMappings("filters", initializers, Filter.class, FilterRegistrationBean.class);
			logMappings("servlets", initializers, Servlet.class, ServletRegistrationBean.class);
		}
	}

	private void logMappings(String name, MultiValueMap<Class<?>, ServletContextInitializer> initializers,
			Class<?> type, Class<? extends RegistrationBean> registrationType) {
		List<ServletContextInitializer> registrations = new ArrayList<>();
		registrations.addAll(initializers.getOrDefault(registrationType, Collections.emptyList()));
		registrations.addAll(initializers.getOrDefault(type, Collections.emptyList()));
		String info = registrations.stream().map(Object::toString).collect(Collectors.joining(", "));
		logger.debug("Mapping " + name + ": " + info);
	}

	@Override
	public Iterator<ServletContextInitializer> iterator() {
		return this.sortedList.iterator();
	}

	@Override
	public int size() {
		return this.sortedList.size();
	}

	
Adapter to convert a given Bean type into a RegistrationBean (and hence a ServletContextInitializer). 
Type parameters:
<T> – the type of the Bean to adapt/**
	 * Adapter to convert a given Bean type into a {@link RegistrationBean} (and hence a
	 * {@link ServletContextInitializer}).
	 *
	 * @param <T> the type of the Bean to adapt
	 */
	@FunctionalInterface
	protected interface RegistrationBeanAdapter<T> {

		RegistrationBean createRegistrationBean(String name, T source, int totalNumberOfSourceBeans);

	}

	
RegistrationBeanAdapter for Servlet beans. /**
	 * {@link RegistrationBeanAdapter} for {@link Servlet} beans.
	 */
	private static class ServletRegistrationBeanAdapter implements RegistrationBeanAdapter<Servlet> {

		private final MultipartConfigElement multipartConfig;

		ServletRegistrationBeanAdapter(MultipartConfigElement multipartConfig) {
			this.multipartConfig = multipartConfig;
		}

		@Override
		public RegistrationBean createRegistrationBean(String name, Servlet source, int totalNumberOfSourceBeans) {
			String url = (totalNumberOfSourceBeans != 1) ? "/" + name + "/" : "/";
			if (name.equals(DISPATCHER_SERVLET_NAME)) {
				url = "/"; // always map the main dispatcherServlet to "/"
			}
			ServletRegistrationBean<Servlet> bean = new ServletRegistrationBean<>(source, url);
			bean.setName(name);
			bean.setMultipartConfig(this.multipartConfig);
			return bean;
		}

	}

	
RegistrationBeanAdapter for Filter beans. /**
	 * {@link RegistrationBeanAdapter} for {@link Filter} beans.
	 */
	private static class FilterRegistrationBeanAdapter implements RegistrationBeanAdapter<Filter> {

		@Override
		public RegistrationBean createRegistrationBean(String name, Filter source, int totalNumberOfSourceBeans) {
			FilterRegistrationBean<Filter> bean = new FilterRegistrationBean<>(source);
			bean.setName(name);
			return bean;
		}

	}

	
RegistrationBeanAdapter for certain EventListener beans. /**
	 * {@link RegistrationBeanAdapter} for certain {@link EventListener} beans.
	 */
	private static class ServletListenerRegistrationBeanAdapter implements RegistrationBeanAdapter<EventListener> {

		@Override
		public RegistrationBean createRegistrationBean(String name, EventListener source,
				int totalNumberOfSourceBeans) {
			return new ServletListenerRegistrationBean<>(source);
		}

	}

}