/*
 * Copyright 2002-2017 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.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.util.Assert;
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;

/**
 * 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
 * @since 5.0
 */
public class ViewResolverRegistry {

	private final ApplicationContext applicationContext;

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

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

	private Integer order;


	public ViewResolverRegistry(ApplicationContext applicationContext) {
		Assert.notNull(applicationContext, "ApplicationContext must not be null");
		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 (this.applicationContext != null && !hasBeanOfType(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();
		resolver.setApplicationContext(this.applicationContext);
		this.viewResolvers.add(resolver);
		return registration;
	}

	protected boolean hasBeanOfType(Class<?> beanType) {
		return !ObjectUtils.isEmpty(BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
				this.applicationContext, beanType, false, false));
	}

	/**
	 * 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;
	}

	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");
		}
	}

}