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Common components for jEaSSE: java EAsy Server-Sent Events
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/*
Copyright 2016 - Mario Macias Lloret

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 info.macias.sse.events;

/**
 * This class encapsulates a SSE Message Event. It may specify the next optional fields:
 *
 * 
 *     event: an arbitrary name describing an event type (e.g. "message", "error", "newEvent", etc...)
 *     data: string data to be transmitted with the event
 *     id: a string that provides an unique identifier for this event
 *     retry: a number representing the timeout (in milliseconds) that the client must wait before
 *         reconnecting again to the server, after the event has been received
 * 
 * @author Mario Macías
 */
public class MessageEvent {
    private final String data;
    private final String event;
    private final Integer retry;
    private final String id;

    private final String toStringCache;

    private MessageEvent(String event, String data, Integer retry, String id, String toStringCache) {
        this.data = data;
        this.event = event;
        this.toStringCache = toStringCache;
        this.retry = retry;
        this.id = id;

    }

    /**
     * Returns the 'data' field: string data to be transmitted with the event
     * @return the value of the 'data' field
     */
    public final String getData() {
        return data;
    }

    /**
     * Returns the 'event' field: an arbitrary name describing an event type (e.g. "message", "error", "newEvent", etc...)
     * @return the value of the 'event' field
     */
    public final String getEvent() {
        return event;
    }

    /**
     * Returns the 'retry' field: a number representing the timeout (in milliseconds) that the client must wait before
     *         reconnecting again to the server, after the event has been received
     * @return the value of the 'retry' field
     */
    public Integer getRetry() {
        return retry;
    }

    /**
     * Returns the 'id' field: a string that provides an unique identifier for this event
     * @return the 'id' field
     */
    public String getId() {
        return id;
    }

    /**
     * Converts the MessageEvent to a String in the format to be transmitted to the listener clients. E.g.:
     *      *     event: message
     *     id: ea23-234a-f334-c899
     *     retry: 10000
     *     data: This is a multi-line
     *     data: text that must be transmitted
     * 
     * @return the string representation of the MessageEvent. Ready to be transmitted.
     */
    public String toString() {
        return toStringCache;
    }

    /**
     * Helper class used to build a {@link MessageEvent} instance.
     */
    public static class Builder {
        private String data = null;
        private String event = null;
        private Integer retry = null;
        private String id = null;

        /**
         * Sets the information of the 'data' field: string data to be transmitted with the event
         * @param data string data to be transmitted with the event
         * @return The same target instance where the method has been invoked on.
         */
        public Builder setData(String data) {
            this.data = data;
            return this;
        }

        /**
         * Sets the information of the 'event' field: an arbitrary name describing an event type (e.g. "message", "error", "newEvent", etc...)
         * @param event an arbitrary name describing an event type
         * @return The same target instance where the method has been invoked on.
         */
        public Builder setEvent(String event) {
            this.event = event;
            return this;
        }

        /**
         * Sets the information of the 'retry' field: a number representing the timeout (in milliseconds) that the client
         * must wait before reconnecting again to the server, after the event has been received
         * @param retry a number representing the timeout (in milliseconds) that the client
         * must wait before reconnecting again to the server
         * @return The same target instance where the method has been invoked on.
         */
        public Builder setRetry(int retry) {
            this.retry = retry;
            return this;
        }

        /**
         * Sets the information of the 'id' field: a string that provides an unique identifier for this event
         * @param id A string that provides an unique identifier for this event string data to be transmitted with the event
         * @return The same target instance where the method has been invoked on.
         */
        public Builder setId(String id) {
            this.id = id;
            return this;
        }

        /**
         * Instantiates a {@link MessageEvent} object with the same attributes as the Builder object.
         * @return the {@link MessageEvent} instance
         */
        public MessageEvent build() {
            StringBuilder sb = new StringBuilder();
            if(event != null) {
                sb.append("event: ").append(event.replace("\n", "")).append('\n');
            }
            if(data != null) {
                for(String s : data.split("\n")) {
                    sb.append("data: ").append(s).append('\n');
                }
            }
            if(retry != null) {
                sb.append("retry: ").append(retry).append('\n');
            }
            if(id != null) {
                sb.append("id: ").append(id.replace("\n","")).append('\n');
            }

            // an empty line dispatches the event
            sb.append('\n');
            return new MessageEvent(event,data,retry,id,sb.toString());
        }
    }
}