#' getPersistenceJumpPredict
#'
#' Analog of the PersistenceForecaster: predict the jump after last observed value either
#' by re-applying the last jump between similar day and its follower (if argument
#' "same_day" is TRUE), or by re-using the very last observed jump (when "same_day" =
#' FALSE).
#'
#' @inheritParams computeForecast
#' @inheritParams getZeroJumpPredict
#'
#' @aliases J_Persistence
#'
getPersistenceJumpPredict = function(data, today, memory, horizon, params, ...)
{
	#return gap between end of similar day curve and first day of tomorrow (in the past)
	first_day = max(1, today-memory)
	same_day = ifelse(hasArg("same_day"), list(...)$same_day, TRUE)
	index = today - ifelse(same_day,7,1)
	repeat
	{
		{
			last_serie_end = tail( data$getSerie(index), 1)
			last_tomorrow_begin = head( data$getSerie(index+1), 1)
			index = index - ifelse(same_day,7,1)
		};
		if (!is.na(last_serie_end) && !is.na(last_tomorrow_begin))
			return (last_tomorrow_begin - last_serie_end);
		if (index < first_day)
			return (NA)
	}
}