/*
 * Copyright 2002-2020 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.web.servlet.config.annotation;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.beans.factory.BeanInitializationException;
import org.springframework.context.ApplicationContext;
import org.springframework.core.Ordered;
import org.springframework.lang.Nullable;
import org.springframework.util.CollectionUtils;
import org.springframework.util.ObjectUtils;
import org.springframework.web.accept.ContentNegotiationManager;
import org.springframework.web.servlet.View;
import org.springframework.web.servlet.ViewResolver;
import org.springframework.web.servlet.view.BeanNameViewResolver;
import org.springframework.web.servlet.view.ContentNegotiatingViewResolver;
import org.springframework.web.servlet.view.InternalResourceViewResolver;
import org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer;
import org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver;
import org.springframework.web.servlet.view.groovy.GroovyMarkupConfigurer;
import org.springframework.web.servlet.view.groovy.GroovyMarkupViewResolver;
import org.springframework.web.servlet.view.script.ScriptTemplateConfigurer;
import org.springframework.web.servlet.view.script.ScriptTemplateViewResolver;
import org.springframework.web.servlet.view.tiles3.TilesConfigurer;
import org.springframework.web.servlet.view.tiles3.TilesViewResolver;

Assist with the configuration of a chain of ViewResolver instances. This class is expected to be used via WebMvcConfigurer.configureViewResolvers. 
Author:
Sebastien Deleuze, Rossen Stoyanchev
Since:
4.1/**
 * Assist with the configuration of a chain of
 * {@link org.springframework.web.servlet.ViewResolver ViewResolver} instances.
 * This class is expected to be used via {@link WebMvcConfigurer#configureViewResolvers}.
 *
 * @author Sebastien Deleuze
 * @author Rossen Stoyanchev
 * @since 4.1
 */
public class ViewResolverRegistry {

	@Nullable
	private ContentNegotiationManager contentNegotiationManager;

	@Nullable
	private ApplicationContext applicationContext;

	@Nullable
	private ContentNegotiatingViewResolver contentNegotiatingResolver;

	private final List<ViewResolver> viewResolvers = new ArrayList<>(4);

	@Nullable
	private Integer order;


	
Class constructor with ContentNegotiationManager and ApplicationContext. 
Since:
4.3.12/**
	 * Class constructor with {@link ContentNegotiationManager} and {@link ApplicationContext}.
	 * @since 4.3.12
	 */
	public ViewResolverRegistry(
			ContentNegotiationManager contentNegotiationManager, @Nullable ApplicationContext context) {

		this.contentNegotiationManager = contentNegotiationManager;
		this.applicationContext = context;
	}


	
Whether any view resolvers have been registered.
/**
	 * Whether any view resolvers have been registered.
	 */
	public boolean hasRegistrations() {
		return (this.contentNegotiatingResolver != null || !this.viewResolvers.isEmpty());
	}

	
Enable use of a ContentNegotiatingViewResolver to front all other configured view resolvers and select among all selected Views based on media types requested by the client (e.g. in the Accept header). 
If invoked multiple times the provided default views will be added to
any other default views that may have been configured already.
See Also:
ContentNegotiatingViewResolver.setDefaultViews/**
	 * Enable use of a {@link ContentNegotiatingViewResolver} to front all other
	 * configured view resolvers and select among all selected Views based on
	 * media types requested by the client (e.g. in the Accept header).
	 * <p>If invoked multiple times the provided default views will be added to
	 * any other default views that may have been configured already.
	 * @see ContentNegotiatingViewResolver#setDefaultViews
	 */
	public void enableContentNegotiation(View... defaultViews) {
		initContentNegotiatingViewResolver(defaultViews);
	}

	
Enable use of a ContentNegotiatingViewResolver to front all other configured view resolvers and select among all selected Views based on media types requested by the client (e.g. in the Accept header). 
If invoked multiple times the provided default views will be added to
any other default views that may have been configured already.
See Also:
ContentNegotiatingViewResolver.setDefaultViews/**
	 * Enable use of a {@link ContentNegotiatingViewResolver} to front all other
	 * configured view resolvers and select among all selected Views based on
	 * media types requested by the client (e.g. in the Accept header).
	 * <p>If invoked multiple times the provided default views will be added to
	 * any other default views that may have been configured already.
	 * @see ContentNegotiatingViewResolver#setDefaultViews
	 */
	public void enableContentNegotiation(boolean useNotAcceptableStatus, View... defaultViews) {
		ContentNegotiatingViewResolver vr = initContentNegotiatingViewResolver(defaultViews);
		vr.setUseNotAcceptableStatusCode(useNotAcceptableStatus);
	}

	private ContentNegotiatingViewResolver initContentNegotiatingViewResolver(View[] defaultViews) {
		// ContentNegotiatingResolver in the registry: elevate its precedence!
		this.order = (this.order != null ? this.order : Ordered.HIGHEST_PRECEDENCE);

		if (this.contentNegotiatingResolver != null) {
			if (!ObjectUtils.isEmpty(defaultViews) &&
					!CollectionUtils.isEmpty(this.contentNegotiatingResolver.getDefaultViews())) {
				List<View> views = new ArrayList<>(this.contentNegotiatingResolver.getDefaultViews());
				views.addAll(Arrays.asList(defaultViews));
				this.contentNegotiatingResolver.setDefaultViews(views);
			}
		}
		else {
			this.contentNegotiatingResolver = new ContentNegotiatingViewResolver();
			this.contentNegotiatingResolver.setDefaultViews(Arrays.asList(defaultViews));
			this.contentNegotiatingResolver.setViewResolvers(this.viewResolvers);
			if (this.contentNegotiationManager != null) {
				this.contentNegotiatingResolver.setContentNegotiationManager(this.contentNegotiationManager);
			}
		}
		return this.contentNegotiatingResolver;
	}

	
Register JSP view resolver using a default view name prefix of "/WEB-INF/"
and a default suffix of ".jsp".
When this method is invoked more than once, each call will register a
new ViewResolver instance. Note that since it's not easy to determine
if a JSP exists without forwarding to it, using multiple JSP-based view
resolvers only makes sense in combination with the "viewNames" property
on the resolver indicating which view names are handled by which resolver.
/**
	 * Register JSP view resolver using a default view name prefix of "/WEB-INF/"
	 * and a default suffix of ".jsp".
	 * <p>When this method is invoked more than once, each call will register a
	 * new ViewResolver instance. Note that since it's not easy to determine
	 * if a JSP exists without forwarding to it, using multiple JSP-based view
	 * resolvers only makes sense in combination with the "viewNames" property
	 * on the resolver indicating which view names are handled by which resolver.
	 */
	public UrlBasedViewResolverRegistration jsp() {
		return jsp("/WEB-INF/", ".jsp");
	}

	
Register JSP view resolver with the specified prefix and suffix.
When this method is invoked more than once, each call will register a
new ViewResolver instance. Note that since it's not easy to determine
if a JSP exists without forwarding to it, using multiple JSP-based view
resolvers only makes sense in combination with the "viewNames" property
on the resolver indicating which view names are handled by which resolver.
/**
	 * Register JSP view resolver with the specified prefix and suffix.
	 * <p>When this method is invoked more than once, each call will register a
	 * new ViewResolver instance. Note that since it's not easy to determine
	 * if a JSP exists without forwarding to it, using multiple JSP-based view
	 * resolvers only makes sense in combination with the "viewNames" property
	 * on the resolver indicating which view names are handled by which resolver.
	 */
	public UrlBasedViewResolverRegistration jsp(String prefix, String suffix) {
		InternalResourceViewResolver resolver = new InternalResourceViewResolver();
		resolver.setPrefix(prefix);
		resolver.setSuffix(suffix);
		this.viewResolvers.add(resolver);
		return new UrlBasedViewResolverRegistration(resolver);
	}

	
Register Tiles 3.x view resolver.
Note that you must also configure Tiles by adding a TilesConfigurer bean. /**
	 * Register Tiles 3.x view resolver.
	 * <p><strong>Note</strong> that you must also configure Tiles by adding a
	 * {@link org.springframework.web.servlet.view.tiles3.TilesConfigurer} bean.
	 */
	public UrlBasedViewResolverRegistration tiles() {
		if (!checkBeanOfType(TilesConfigurer.class)) {
			throw new BeanInitializationException("In addition to a Tiles view resolver " +
					"there must also be a single TilesConfigurer bean in this web application context " +
					"(or its parent).");
		}
		TilesRegistration registration = new TilesRegistration();
		this.viewResolvers.add(registration.getViewResolver());
		return registration;
	}

	
Register a FreeMarker view resolver with an empty default view name
prefix and a default suffix of ".ftl".
Note that you must also configure FreeMarker by adding a FreeMarkerConfigurer bean. /**
	 * Register a FreeMarker view resolver with an empty default view name
	 * prefix and a default suffix of ".ftl".
	 * <p><strong>Note</strong> that you must also configure FreeMarker by adding a
	 * {@link org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer} bean.
	 */
	public UrlBasedViewResolverRegistration freeMarker() {
		if (!checkBeanOfType(FreeMarkerConfigurer.class)) {
			throw new BeanInitializationException("In addition to a FreeMarker view resolver " +
					"there must also be a single FreeMarkerConfig bean in this web application context " +
					"(or its parent): FreeMarkerConfigurer is the usual implementation. " +
					"This bean may be given any name.");
		}
		FreeMarkerRegistration registration = new FreeMarkerRegistration();
		this.viewResolvers.add(registration.getViewResolver());
		return registration;
	}

	
Register a Groovy markup view resolver with an empty default view name
prefix and a default suffix of ".tpl".
/**
	 * Register a Groovy markup view resolver with an empty default view name
	 * prefix and a default suffix of ".tpl".
	 */
	public UrlBasedViewResolverRegistration groovy() {
		if (!checkBeanOfType(GroovyMarkupConfigurer.class)) {
			throw new BeanInitializationException("In addition to a Groovy markup view resolver " +
					"there must also be a single GroovyMarkupConfig bean in this web application context " +
					"(or its parent): GroovyMarkupConfigurer is the usual implementation. " +
					"This bean may be given any name.");
		}
		GroovyMarkupRegistration registration = new GroovyMarkupRegistration();
		this.viewResolvers.add(registration.getViewResolver());
		return registration;
	}

	
Register a script template view resolver with an empty default view name prefix and suffix.
Since:
4.2/**
	 * Register a script template view resolver with an empty default view name prefix and suffix.
	 * @since 4.2
	 */
	public UrlBasedViewResolverRegistration scriptTemplate() {
		if (!checkBeanOfType(ScriptTemplateConfigurer.class)) {
			throw new BeanInitializationException("In addition to a script template view resolver " +
					"there must also be a single ScriptTemplateConfig bean in this web application context " +
					"(or its parent): ScriptTemplateConfigurer is the usual implementation. " +
					"This bean may be given any name.");
		}
		ScriptRegistration registration = new ScriptRegistration();
		this.viewResolvers.add(registration.getViewResolver());
		return registration;
	}

	
Register a bean name view resolver that interprets view names as the names of View beans. /**
	 * Register a bean name view resolver that interprets view names as the names
	 * of {@link org.springframework.web.servlet.View} beans.
	 */
	public void beanName() {
		BeanNameViewResolver resolver = new BeanNameViewResolver();
		this.viewResolvers.add(resolver);
	}

	
Register a ViewResolver bean instance. This may be useful to configure a custom (or 3rd party) resolver implementation. It may also be used as an alternative to other registration methods in this class when they don't expose some more advanced property that needs to be set. /**
	 * Register a {@link ViewResolver} bean instance. This may be useful to
	 * configure a custom (or 3rd party) resolver implementation. It may also be
	 * used as an alternative to other registration methods in this class when
	 * they don't expose some more advanced property that needs to be set.
	 */
	public void viewResolver(ViewResolver viewResolver) {
		if (viewResolver instanceof ContentNegotiatingViewResolver) {
			throw new BeanInitializationException(
					"addViewResolver cannot be used to configure a ContentNegotiatingViewResolver. " +
					"Please use the method enableContentNegotiation instead.");
		}
		this.viewResolvers.add(viewResolver);
	}

	
ViewResolver's registered through this registry are encapsulated in an instance of 
ViewResolverComposite and follow the order of registration. This property determines the order of the ViewResolverComposite itself relative to any additional ViewResolver's (not registered here) present in the Spring configuration 
By default this property is not set, which means the resolver is ordered at Ordered.LOWEST_PRECEDENCE unless content negotiation is enabled in which case the order (if not set explicitly) is changed to Ordered.HIGHEST_PRECEDENCE. /**
	 * ViewResolver's registered through this registry are encapsulated in an
	 * instance of {@link org.springframework.web.servlet.view.ViewResolverComposite
	 * ViewResolverComposite} and follow the order of registration.
	 * This property determines the order of the ViewResolverComposite itself
	 * relative to any additional ViewResolver's (not registered here) present in
	 * the Spring configuration
	 * <p>By default this property is not set, which means the resolver is ordered
	 * at {@link Ordered#LOWEST_PRECEDENCE} unless content negotiation is enabled
	 * in which case the order (if not set explicitly) is changed to
	 * {@link Ordered#HIGHEST_PRECEDENCE}.
	 */
	public void order(int order) {
		this.order = order;
	}


	private boolean checkBeanOfType(Class<?> beanType) {
		return (this.applicationContext == null ||
				!ObjectUtils.isEmpty(BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
						this.applicationContext, beanType, false, false)));
	}

	protected int getOrder() {
		return (this.order != null ? this.order : Ordered.LOWEST_PRECEDENCE);
	}

	protected List<ViewResolver> getViewResolvers() {
		if (this.contentNegotiatingResolver != null) {
			return Collections.singletonList(this.contentNegotiatingResolver);
		}
		else {
			return this.viewResolvers;
		}
	}


	private static class TilesRegistration extends UrlBasedViewResolverRegistration {

		public TilesRegistration() {
			super(new TilesViewResolver());
		}
	}

	private static class FreeMarkerRegistration extends UrlBasedViewResolverRegistration {

		public FreeMarkerRegistration() {
			super(new FreeMarkerViewResolver());
			getViewResolver().setSuffix(".ftl");
		}
	}


	private static class GroovyMarkupRegistration extends UrlBasedViewResolverRegistration {

		public GroovyMarkupRegistration() {
			super(new GroovyMarkupViewResolver());
			getViewResolver().setSuffix(".tpl");
		}
	}


	private static class ScriptRegistration extends UrlBasedViewResolverRegistration {

		public ScriptRegistration() {
			super(new ScriptTemplateViewResolver());
			getViewResolver();
		}
	}

}