/*
 * Copyright 2002-2018 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.reactive.config;

import java.util.ArrayList;
import java.util.Arrays;
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.ObjectUtils;
import org.springframework.web.reactive.result.view.HttpMessageWriterView;
import org.springframework.web.reactive.result.view.UrlBasedViewResolver;
import org.springframework.web.reactive.result.view.View;
import org.springframework.web.reactive.result.view.ViewResolver;
import org.springframework.web.reactive.result.view.freemarker.FreeMarkerConfigurer;
import org.springframework.web.reactive.result.view.freemarker.FreeMarkerViewResolver;
import org.springframework.web.reactive.result.view.script.ScriptTemplateConfigurer;
import org.springframework.web.reactive.result.view.script.ScriptTemplateViewResolver;

/**
 * Assist with the configuration of a chain of {@link ViewResolver}'s supporting
 * different template mechanisms.
 *
 * <p>In addition, you can also configure {@link #defaultViews(View...)
 * defaultViews} for rendering according to the requested content type, e.g.
 * JSON, XML, etc.
 *
 * @author Rossen Stoyanchev
 * @author Sebastien Deleuze
 * @since 5.0
 */
public class ViewResolverRegistry {

        @Nullable
        private final ApplicationContext applicationContext;

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

        private final List<View> defaultViews = new ArrayList<>(4);

        @Nullable
        private Integer order;


        public ViewResolverRegistry(@Nullable ApplicationContext applicationContext) {
                this.applicationContext = applicationContext;
        }


        /**
         * Register a {@code FreeMarkerViewResolver} with a ".ftl" suffix.
         * <p><strong>Note</strong> that you must also configure FreeMarker by
         * adding a {@link 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();
                UrlBasedViewResolver resolver = registration.getViewResolver();
                if (this.applicationContext != null) {
                        resolver.setApplicationContext(this.applicationContext);
                }
                this.viewResolvers.add(resolver);
                return registration;
        }

        /**
         * Register a script template view resolver with an empty default view name prefix and suffix.
         * <p><strong>Note</strong> that you must also configure script templating by
         * adding a {@link ScriptTemplateConfigurer} bean.
         * @since 5.0.4
         */
        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();
                UrlBasedViewResolver resolver = registration.getViewResolver();
                if (this.applicationContext != null) {
                        resolver.setApplicationContext(this.applicationContext);
                }
                this.viewResolvers.add(resolver);
                return registration;
        }

        /**
         * Register a {@link ViewResolver} bean instance. This may be useful to
         * configure a 3rd party resolver implementation or 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) {
                this.viewResolvers.add(viewResolver);
        }

        /**
         * Set default views associated with any view name and selected based on the
         * best match for the requested content type.
         * <p>Use {@link HttpMessageWriterView
         * HttpMessageWriterView} to adapt and use any existing
         * {@code HttpMessageWriter} (e.g. JSON, XML) as a {@code View}.
         */
        public void defaultViews(View... defaultViews) {
                this.defaultViews.addAll(Arrays.asList(defaultViews));
        }

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

        /**
         * Set the order for the
         * {@link org.springframework.web.reactive.result.view.ViewResolutionResultHandler
         * ViewResolutionResultHandler}.
         * <p>By default this property is not set, which means the result handler is
         * ordered at {@link Ordered#LOWEST_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() {
                return this.viewResolvers;
        }

        protected List<View> getDefaultViews() {
                return this.defaultViews;
        }


        private static class FreeMarkerRegistration extends UrlBasedViewResolverRegistration {

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

        private static class ScriptRegistration extends UrlBasedViewResolverRegistration {

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

}