/*
 * 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.http.codec;

import java.time.Duration;

import org.springframework.lang.Nullable;

/**
 * Representation for a Server-Sent Event for use with Spring's reactive Web support.
 * {@code Flux<ServerSentEvent>} or {@code Observable<ServerSentEvent>} is the
 * reactive equivalent to Spring MVC's {@code SseEmitter}.
 *
 * @author Sebastien Deleuze
 * @author Arjen Poutsma
 * @since 5.0
 * @param <T> the type of data that this event contains
 * @see ServerSentEventHttpMessageWriter
 * @see <a href="https://www.w3.org/TR/eventsource/">Server-Sent Events W3C recommendation</a>
 */
public final class ServerSentEvent<T> {

        @Nullable
        private final String id;

        @Nullable
        private final String event;

        @Nullable
        private final Duration retry;

        @Nullable
        private final String comment;

        @Nullable
        private final T data;


        private ServerSentEvent(@Nullable String id, @Nullable String event, @Nullable Duration retry,
                        @Nullable String comment, @Nullable T data) {

                this.id = id;
                this.event = event;
                this.retry = retry;
                this.comment = comment;
                this.data = data;
        }


        /**
         * Return the {@code id} field of this event, if available.
         */
        @Nullable
        public String id() {
                return this.id;
        }

        /**
         * Return the {@code event} field of this event, if available.
         */
        @Nullable
        public String event() {
                return this.event;
        }

        /**
         * Return the {@code retry} field of this event, if available.
         */
        @Nullable
        public Duration retry() {
                return this.retry;
        }

        /**
         * Return the comment of this event, if available.
         */
        @Nullable
        public String comment() {
                return this.comment;
        }

        /**
         * Return the {@code data} field of this event, if available.
         */
        @Nullable
        public T data() {
                return this.data;
        }


        @Override
        public String toString() {
                return ("ServerSentEvent [id = '" + this.id + "\', event='" + this.event + "\', retry=" +
                                this.retry + ", comment='" + this.comment + "', data=" + this.data + ']');
        }


        /**
         * Return a builder for a {@code SseEvent}.
         * @param <T> the type of data that this event contains
         * @return the builder
         */
        public static <T> Builder<T> builder() {
                return new BuilderImpl<>();
        }

        /**
         * Return a builder for a {@code SseEvent}, populated with the give {@linkplain #data() data}.
         * @param <T> the type of data that this event contains
         * @return the builder
         */
        public static <T> Builder<T> builder(T data) {
                return new BuilderImpl<>(data);
        }


        /**
         * A mutable builder for a {@code SseEvent}.
         *
         * @param <T> the type of data that this event contains
         */
        public interface Builder<T> {

                /**
                 * Set the value of the {@code id} field.
                 * @param id the value of the id field
                 * @return {@code this} builder
                 */
                Builder<T> id(String id);

                /**
                 * Set the value of the {@code event} field.
                 * @param event the value of the event field
                 * @return {@code this} builder
                 */
                Builder<T> event(String event);

                /**
                 * Set the value of the {@code retry} field.
                 * @param retry the value of the retry field
                 * @return {@code this} builder
                 */
                Builder<T> retry(Duration retry);

                /**
                 * Set SSE comment. If a multi-line comment is provided, it will be turned into multiple
                 * SSE comment lines as defined in Server-Sent Events W3C recommendation.
                 * @param comment the comment to set
                 * @return {@code this} builder
                 */
                Builder<T> comment(String comment);

                /**
                 * Set the value of the {@code data} field. If the {@code data} argument is a multi-line
                 * {@code String}, it will be turned into multiple {@code data} field lines as defined
                 * in the Server-Sent Events W3C recommendation. If {@code data} is not a String, it will
                 * be {@linkplain org.springframework.http.codec.json.Jackson2JsonEncoder encoded} into JSON.
                 * @param data the value of the data field
                 * @return {@code this} builder
                 */
                Builder<T> data(@Nullable T data);

                /**
                 * Builds the event.
                 * @return the built event
                 */
                ServerSentEvent<T> build();
        }


        private static class BuilderImpl<T> implements Builder<T> {

                @Nullable
                private String id;

                @Nullable
                private String event;

                @Nullable
                private Duration retry;

                @Nullable
                private String comment;

                @Nullable
                private T data;

                public BuilderImpl() {
                }

                public BuilderImpl(T data) {
                        this.data = data;
                }

                @Override
                public Builder<T> id(String id) {
                        this.id = id;
                        return this;
                }

                @Override
                public Builder<T> event(String event) {
                        this.event = event;
                        return this;
                }

                @Override
                public Builder<T> retry(Duration retry) {
                        this.retry = retry;
                        return this;
                }

                @Override
                public Builder<T> comment(String comment) {
                        this.comment = comment;
                        return this;
                }

                @Override
                public Builder<T> data(@Nullable T data) {
                        this.data = data;
                        return this;
                }

                @Override
                public ServerSentEvent<T> build() {
                        return new ServerSentEvent<>(this.id, this.event, this.retry, this.comment, this.data);
                }
        }

}