/*
 * Copyright 2012-2018 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
 *
 *      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;

import java.util.Arrays;
import java.util.Collection;
import java.util.LinkedHashSet;
import java.util.Set;

import javax.servlet.MultipartConfigElement;
import javax.servlet.Servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletRegistration;

import org.springframework.util.Assert;
import org.springframework.util.ObjectUtils;
import org.springframework.util.StringUtils;

/**
 * A {@link ServletContextInitializer} to register {@link Servlet}s in a Servlet 3.0+
 * container. Similar to the {@link ServletContext#addServlet(String, Servlet)
 * registration} features provided by {@link ServletContext} but with a Spring Bean
 * friendly design.
 * <p>
 * The {@link #setServlet(Servlet) servlet} must be specified before calling
 * {@link #onStartup}. URL mapping can be configured used {@link #setUrlMappings} or
 * omitted when mapping to '/*' (unless
 * {@link #ServletRegistrationBean(Servlet, boolean, String...) alwaysMapUrl} is set to
 * {@code false}). The servlet name will be deduced if not specified.
 *
 * @param <T> the type of the {@link Servlet} to register
 * @author Phillip Webb
 * @since 1.4.0
 * @see ServletContextInitializer
 * @see ServletContext#addServlet(String, Servlet)
 */
public class ServletRegistrationBean<T extends Servlet>
                extends DynamicRegistrationBean<ServletRegistration.Dynamic> {

        private static final String[] DEFAULT_MAPPINGS = { "/*" };

        private T servlet;

        private Set<String> urlMappings = new LinkedHashSet<>();

        private boolean alwaysMapUrl = true;

        private int loadOnStartup = -1;

        private MultipartConfigElement multipartConfig;

        /**
         * Create a new {@link ServletRegistrationBean} instance.
         */
        public ServletRegistrationBean() {
        }

        /**
         * Create a new {@link ServletRegistrationBean} instance with the specified
         * {@link Servlet} and URL mappings.
         * @param servlet the servlet being mapped
         * @param urlMappings the URLs being mapped
         */
        public ServletRegistrationBean(T servlet, String... urlMappings) {
                this(servlet, true, urlMappings);
        }

        /**
         * Create a new {@link ServletRegistrationBean} instance with the specified
         * {@link Servlet} and URL mappings.
         * @param servlet the servlet being mapped
         * @param alwaysMapUrl if omitted URL mappings should be replaced with '/*'
         * @param urlMappings the URLs being mapped
         */
        public ServletRegistrationBean(T servlet, boolean alwaysMapUrl,
                        String... urlMappings) {
                Assert.notNull(servlet, "Servlet must not be null");
                Assert.notNull(urlMappings, "UrlMappings must not be null");
                this.servlet = servlet;
                this.alwaysMapUrl = alwaysMapUrl;
                this.urlMappings.addAll(Arrays.asList(urlMappings));
        }

        /**
         * Sets the servlet to be registered.
         * @param servlet the servlet
         */
        public void setServlet(T servlet) {
                Assert.notNull(servlet, "Servlet must not be null");
                this.servlet = servlet;
        }

        /**
         * Return the servlet being registered.
         * @return the servlet
         */
        public T getServlet() {
                return this.servlet;
        }

        /**
         * Set the URL mappings for the servlet. If not specified the mapping will default to
         * '/'. This will replace any previously specified mappings.
         * @param urlMappings the mappings to set
         * @see #addUrlMappings(String...)
         */
        public void setUrlMappings(Collection<String> urlMappings) {
                Assert.notNull(urlMappings, "UrlMappings must not be null");
                this.urlMappings = new LinkedHashSet<>(urlMappings);
        }

        /**
         * Return a mutable collection of the URL mappings, as defined in the Servlet
         * specification, for the servlet.
         * @return the urlMappings
         */
        public Collection<String> getUrlMappings() {
                return this.urlMappings;
        }

        /**
         * Add URL mappings, as defined in the Servlet specification, for the servlet.
         * @param urlMappings the mappings to add
         * @see #setUrlMappings(Collection)
         */
        public void addUrlMappings(String... urlMappings) {
                Assert.notNull(urlMappings, "UrlMappings must not be null");
                this.urlMappings.addAll(Arrays.asList(urlMappings));
        }

        /**
         * Sets the {@code loadOnStartup} priority. See
         * {@link ServletRegistration.Dynamic#setLoadOnStartup} for details.
         * @param loadOnStartup if load on startup is enabled
         */
        public void setLoadOnStartup(int loadOnStartup) {
                this.loadOnStartup = loadOnStartup;
        }

        /**
         * Set the {@link MultipartConfigElement multi-part configuration}.
         * @param multipartConfig the multi-part configuration to set or {@code null}
         */
        public void setMultipartConfig(MultipartConfigElement multipartConfig) {
                this.multipartConfig = multipartConfig;
        }

        /**
         * Returns the {@link MultipartConfigElement multi-part configuration} to be applied
         * or {@code null}.
         * @return the multipart config
         */
        public MultipartConfigElement getMultipartConfig() {
                return this.multipartConfig;
        }

        @Override
        protected String getDescription() {
                Assert.notNull(this.servlet, "Servlet must not be null");
                return "servlet " + getServletName();
        }

        @Override
        protected ServletRegistration.Dynamic addRegistration(String description,
                        ServletContext servletContext) {
                String name = getServletName();
                return servletContext.addServlet(name, this.servlet);
        }

        /**
         * Configure registration settings. Subclasses can override this method to perform
         * additional configuration if required.
         * @param registration the registration
         */
        @Override
        protected void configure(ServletRegistration.Dynamic registration) {
                super.configure(registration);
                String[] urlMapping = StringUtils.toStringArray(this.urlMappings);
                if (urlMapping.length == 0 && this.alwaysMapUrl) {
                        urlMapping = DEFAULT_MAPPINGS;
                }
                if (!ObjectUtils.isEmpty(urlMapping)) {
                        registration.addMapping(urlMapping);
                }
                registration.setLoadOnStartup(this.loadOnStartup);
                if (this.multipartConfig != null) {
                        registration.setMultipartConfig(this.multipartConfig);
                }
        }

        /**
         * Returns the servlet name that will be registered.
         * @return the servlet name
         */
        public String getServletName() {
                return getOrDeduceName(this.servlet);
        }

        @Override
        public String toString() {
                return getServletName() + " urls=" + getUrlMappings();
        }

}