/*
 * Copyright 2002-2016 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.http.server;

import java.io.IOException;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import javax.servlet.http.HttpServletResponse;

import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.CollectionUtils;

/**
 * {@link ServerHttpResponse} implementation that is based on a {@link HttpServletResponse}.
 *
 * @author Arjen Poutsma
 * @author Rossen Stoyanchev
 * @since 3.0
 */
public class ServletServerHttpResponse implements ServerHttpResponse {

        /** Checking for Servlet 3.0+ HttpServletResponse.getHeader(String) */
        private static final boolean servlet3Present =
                        ClassUtils.hasMethod(HttpServletResponse.class, "getHeader", String.class);


        private final HttpServletResponse servletResponse;

        private final HttpHeaders headers;

        private boolean headersWritten = false;

        private boolean bodyUsed = false;


        /**
         * Construct a new instance of the ServletServerHttpResponse based on the given {@link HttpServletResponse}.
         * @param servletResponse the servlet response
         */
        public ServletServerHttpResponse(HttpServletResponse servletResponse) {
                Assert.notNull(servletResponse, "HttpServletResponse must not be null");
                this.servletResponse = servletResponse;
                this.headers = (servlet3Present ? new ServletResponseHttpHeaders() : new HttpHeaders());
        }


        /**
         * Return the {@code HttpServletResponse} this object is based on.
         */
        public HttpServletResponse getServletResponse() {
                return this.servletResponse;
        }

        @Override
        public void setStatusCode(HttpStatus status) {
                Assert.notNull(status, "HttpStatus must not be null");
                this.servletResponse.setStatus(status.value());
        }

        @Override
        public HttpHeaders getHeaders() {
                return (this.headersWritten ? HttpHeaders.readOnlyHttpHeaders(this.headers) : this.headers);
        }

        @Override
        public OutputStream getBody() throws IOException {
                this.bodyUsed = true;
                writeHeaders();
                return this.servletResponse.getOutputStream();
        }

        @Override
        public void flush() throws IOException {
                writeHeaders();
                if (this.bodyUsed) {
                        this.servletResponse.flushBuffer();
                }
        }

        @Override
        public void close() {
                writeHeaders();
        }

        private void writeHeaders() {
                if (!this.headersWritten) {
                        for (Map.Entry<String, List<String>> entry : this.headers.entrySet()) {
                                String headerName = entry.getKey();
                                for (String headerValue : entry.getValue()) {
                                        this.servletResponse.addHeader(headerName, headerValue);
                                }
                        }
                        // HttpServletResponse exposes some headers as properties: we should include those if not already present
                        if (this.servletResponse.getContentType() == null && this.headers.getContentType() != null) {
                                this.servletResponse.setContentType(this.headers.getContentType().toString());
                        }
                        if (this.servletResponse.getCharacterEncoding() == null && this.headers.getContentType() != null &&
                                        this.headers.getContentType().getCharset() != null) {
                                this.servletResponse.setCharacterEncoding(this.headers.getContentType().getCharset().name());
                        }
                        this.headersWritten = true;
                }
        }


        /**
         * Extends HttpHeaders with the ability to look up headers already present in
         * the underlying HttpServletResponse.
         *
         * <p>The intent is merely to expose what is available through the HttpServletResponse
         * i.e. the ability to look up specific header values by name. All other
         * map-related operations (e.g. iteration, removal, etc) apply only to values
         * added directly through HttpHeaders methods.
         *
         * @since 4.0.3
         */
        private class ServletResponseHttpHeaders extends HttpHeaders {

                private static final long serialVersionUID = 3410708522401046302L;

                @Override
                public boolean containsKey(Object key) {
                        return (super.containsKey(key) || (get(key) != null));
                }

                @Override
                public String getFirst(String headerName) {
                        String value = servletResponse.getHeader(headerName);
                        if (value != null) {
                                return value;
                        }
                        else {
                                return super.getFirst(headerName);
                        }
                }

                @Override
                public List<String> get(Object key) {
                        Assert.isInstanceOf(String.class, key, "Key must be a String-based header name");

                        Collection<String> values1 = servletResponse.getHeaders((String) key);
                        boolean isEmpty1 = CollectionUtils.isEmpty(values1);

                        List<String> values2 = super.get(key);
                        boolean isEmpty2 = CollectionUtils.isEmpty(values2);

                        if (isEmpty1 && isEmpty2) {
                                return null;
                        }

                        List<String> values = new ArrayList<String>();
                        if (!isEmpty1) {
                                values.addAll(values1);
                        }
                        if (!isEmpty2) {
                                values.addAll(values2);
                        }
                        return values;
                }
        }

}