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/// @startDocuBlock JSF_get_api_replication_applier_state
/// @brief output the current status of the replication
///
/// @RESTHEADER{GET /_api/replication/applier-state, State of the replication applier}
///
/// @RESTDESCRIPTION
/// Returns the state of the replication applier, regardless of whether the
/// applier is currently running or not.
///
/// The response is a JSON object with the following attributes:
///
/// - *state*: a JSON object with the following sub-attributes:
///
///   - *running*: whether or not the applier is active and running
///
///   - *lastAppliedContinuousTick*: the last tick value from the continuous
///     replication log the applier has applied.
///
///   - *lastProcessedContinuousTick*: the last tick value from the continuous
///     replication log the applier has processed.
///
///     Regularly, the last applied and last processed tick values should be
///     identical. For transactional operations, the replication applier will first
///     process incoming log events before applying them, so the processed tick
///     value might be higher than the applied tick value. This will be the case
///     until the applier encounters the *transaction commit* log event for the
///     transaction.
///
///   - *lastAvailableContinuousTick*: the last tick value the logger server can
///     provide.
///
///   - *time*: the time on the applier server.
///
///   - *totalRequests*: the total number of requests the applier has made to the
///     endpoint.
///
///   - *totalFailedConnects*: the total number of failed connection attempts the
///     applier has made.
///
///   - *totalEvents*: the total number of log events the applier has processed.
///
///   - *totalOperationsExcluded*: the total number of log events excluded because
///     of *restrictCollections*.
///
///   - *progress*: a JSON object with details about the replication applier progress.
///     It contains the following sub-attributes if there is progress to report:
///
///     - *message*: a textual description of the progress
///
///     - *time*: the date and time the progress was logged
///
///     - *failedConnects*: the current number of failed connection attempts
///
///   - *lastError*: a JSON object with details about the last error that happened on
///     the applier. It contains the following sub-attributes if there was an error:
///
///     - *errorNum*: a numerical error code
///
///     - *errorMessage*: a textual error description
///
///     - *time*: the date and time the error occurred
///
///     In case no error has occurred, *lastError* will be empty.
///
/// - *server*: a JSON object with the following sub-attributes:
///
///   - *version*: the applier server's version
///
///   - *serverId*: the applier server's id
///
/// - *endpoint*: the endpoint the applier is connected to (if applier is
///   active) or will connect to (if applier is currently inactive)
///
/// - *database*: the name of the database the applier is connected to (if applier is
///   active) or will connect to (if applier is currently inactive)
///
/// @RESTRETURNCODES
///
/// @RESTRETURNCODE{200}
/// is returned if the request was executed successfully.
///
/// @RESTRETURNCODE{405}
/// is returned when an invalid HTTP method is used.
///
/// @RESTRETURNCODE{500}
/// is returned if an error occurred while assembling the response.
///
/// @EXAMPLES
///
/// Fetching the state of an inactive applier:
///
/// @EXAMPLE_ARANGOSH_RUN{RestReplicationApplierStateNotRunning}
///     var re = require("@arangodb/replication");
///     re.applier.shutdown();
///
///     var url = "/_api/replication/applier-state";
///     var response = logCurlRequest('GET', url);
///
///     assert(response.code === 200);
///     logJsonResponse(response);
/// @END_EXAMPLE_ARANGOSH_RUN
///
/// Fetching the state of an active applier:
///
/// @EXAMPLE_ARANGOSH_RUN{RestReplicationApplierStateRunning}
///     var re = require("@arangodb/replication");
///     re.applier.shutdown();
///     re.applier.start();
///
///     var url = "/_api/replication/applier-state";
///     var response = logCurlRequest('GET', url);
///     re.applier.shutdown();
///
///     assert(response.code === 200);
///     logJsonResponse(response);
/// @END_EXAMPLE_ARANGOSH_RUN
/// @endDocuBlock
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