#' @title dateIndexToInteger
#'
#' @description Transform a (potential) date index into an integer (relative to data)
#'
#' @param index Date (or integer) index
#' @param data Object of class \code{Data}
#'
#' @export
dateIndexToInteger = function(index, data)
{
	index = index[1]
	if (is.numeric(index))
		index = as.integer(index)
	if (is.integer(index))
		return (index)
	if (inherits(index, "Date") || is.character(index))
	{
		tryCatch(dt <- as.POSIXct(index), error=function(e) stop("Unrecognized index format"))
		#TODO: tz arg to difftime ?
		integerIndex <- round( (as.numeric( difftime(dt, data$getTime(1)) ))[1] ) + 1
		if (integerIndex > 0 && integerIndex <= data$getSize())
		{
			#WARNING: if series start at date >0h, result must be shifted
			date1 = as.POSIXlt(data$getTime(1)[1])
			date2 = as.POSIXlt(data$getTime(2)[1])
			shift = (date1$year==date2$year && date1$mon==date2$mon && date1$mday==date2$mday)
			return (integerIndex + ifelse(shift,1,0))
		}
		stop("Date outside data range")
	}
	stop("Unrecognized index format")
}

#' @title integerIndexToDate
#'
#' @description Transform an integer index to date index (relative to data)
#'
#' @param index Date (or integer) index
#' @param data Object of class \code{Data}
#'
#' @export
integerIndexToDate = function(index, data)
{
	index = index[1]
	if (is.numeric(index))
		index = as.integer(index)
	if (!is.integer(index))
		stop("'index' should be an integer")
	as.Date( data$getTime(index)[1] )
}

#' @title getSimilarDaysIndices
#'
#' @description Find similar days indices in the past
#'
#' @param index Day index (numeric or date)
#' @param limit Maximum number of indices to return
#' @param same_seaon Should the indices correspond to day in same season?
#'
#' @export
getSimilarDaysIndices = function(index, limit, same_season)
{
	index = dateIndexToInteger(index)

	#TODO: mardi similaire à lundi mercredi jeudi aussi ...etc
	if (!same_season)
	{
		#take all similar days in recent past
		nb_days = min( (index-1) %/% 7, limit)
		return ( rep(index,nb_days) - 7*seq_len(nb_days) )
	}

	#Look for similar days in similar season (+/- 30 days)
	days = c()
	i = index
	while (i >= 1 && length(days) < limit)
	{
		if (i < index)
		{
			days = c(days, i)
			#look in the "future of the past"
			for (j in 1:4)
				days = c(days, i+7*j)
		}
		#...and in the "past of the past"
		for (j in 1:4)
		{
			if (i - 7*j >= 1)
				days = c(days, i-7*j)
		}
		# TODO: exact computation instead of -364
		# 364 = closest multiple of 7 to 365 - drift along the years... but not so many years so OK
		i = i - 364
	}

	return ( days[1:min(limit,length(days))] )
}