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Eclipse Ditto is a framework for creating and managing digital twins in the IoT.
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/**
 * Maps the passed parameters which originated from a Ditto Protocol message to an external message.
 * @param {string} namespace - The namespace of the entity in java package notation, e.g.: "org.eclipse.ditto". Or "_"
 * (underscore) for connection announcements.
 * @param {string} name - The name of the entity, e.g.: "device".
 * @param {string} group - The affected group/entity: "things"|"policies"|"connections".
 * @param {string} channel - The channel for the signal: "twin"|"live"|"none"
 * @param {string} criterion - The criterion to apply: "commands"|"events"|"search"|"messages"|"announcements"|"errors".
 * @param {string} action - The action to perform: "create"|"retrieve"|"modify"|"delete". Or the announcement name:
 * "opened"|"closed"|"subjectDeletion". Or the subject of the message.
 * @param {string} path - The path which is affected by the message (e.g.: "/attributes"), or the destination
 * of a message (e.g.: "inbox"|"outbox").
 * @param {Object.} dittoHeaders - The headers Object containing all Ditto Protocol header values.
 * @param {*} [value] - The value to apply / which was applied (e.g. in a "modify" action).
 * @param {number} [status] - The status code that indicates the result of the command. When this field is set,
 * it indicates that the Ditto Protocol Message contains a response.
 * @param {Object} [extra] - The enriched extra fields when selected via "extraFields" option.
 * @returns {(ExternalMessage|Array)} externalMessage - The mapped external message, an array of
 * external messages or null if the message could/should not be mapped.
 */
function mapFromDittoProtocolMsg(
  namespace,
  name,
  group,
  channel,
  criterion,
  action,
  path,
  dittoHeaders,
  value,
  status,
  extra
) {

  // ###
  // Insert your mapping logic here

  // ### example code using the Ditto protocol content type.
  let headers = dittoHeaders;
  let textPayload = JSON.stringify(Ditto.buildDittoProtocolMsg(namespace, name, group, channel, criterion, action,
                                                               path, dittoHeaders, value, status, extra));
  let bytePayload = null;
  let contentType = 'application/vnd.eclipse.ditto+json';

  return Ditto.buildExternalMsg(
      headers, // The external headers Object containing header values
      textPayload, // The external mapped String
      bytePayload, // The external mapped byte[]
      contentType // The returned Content-Type
  );
}

/**
 * Maps the passed Ditto Protocol message to an external message.
 * @param {DittoProtocolMessage} dittoProtocolMsg - The Ditto Protocol message to map
 * @returns {(ExternalMessage|Array)} externalMessage -
 *  The mapped external message,
 *  an array of external messages or
 *  null if the message could/should not be mapped
 */
function mapFromDittoProtocolMsgWrapper(dittoProtocolMsg) {

  let topic = dittoProtocolMsg.topic;
  let splitTopic = topic.split("/");

  let namespace = splitTopic[0];
  let name = splitTopic[1];
  let group = splitTopic[2];

  let channel;
  let criterion;
  let action;
  if (hasChannel(group)) {
    channel = splitTopic[3];
    criterion = splitTopic[4];
    action = splitTopic[5];
  } else {
    channel = 'none';
    criterion = splitTopic[3];
    action = splitTopic[4];
  }

  let path = dittoProtocolMsg.path;
  let dittoHeaders = dittoProtocolMsg.headers;
  let value = dittoProtocolMsg.value;
  let status = dittoProtocolMsg.status;
  let extra = dittoProtocolMsg.extra;

  return mapFromDittoProtocolMsg(namespace, name, group, channel, criterion, action, path, dittoHeaders, value, status, extra);
}

/**
 * Checks if the provided topic group has a channel in the topic.
 * @param group the group to check.
 * @return {boolean} true, if the group supports channels.
 */
function hasChannel(group) {
  return 'things' === group;
}