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#
# xts: eXtensible time-series
#
# Copyright (C) 2008 Jeffrey A. Ryan jeff.a.ryan @ gmail.com
#
# Contributions from Joshua M. Ulrich
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
# This function corresponds to the ISO 8601 standard
# for specifying dates and times as described in
# the ISO 8601:2004e standard.
#
# See:
# http://en.wikipedia.org/wiki/ISO_8601
# http://www.iso.org/iso/support/faqs/faqs_widely_used_standards/widely_used_standards_other/date_and_time_format.htm
#
# This implementation is currently restricted
# to interval based parsing, with basic or
# extended formats, and duration strings.
# Currently the duration must be in basic format
# e.g. PnnYnnMnnDTnnHnnMnnS
#
# The return value is a list of start and
# end times, in POSIXt space.
#
# Copyright 2009. Jeffrey A. Ryan. All rights reserved.
# This is licensed under the GPL version 2 or later
#
#' Create an ISO8601 string from a time series object
#'
#' This function uses the `start()` and `end()` of a time series object to
#' create an ISO8601 string that spans the time range of the object.
#'
#' This is not exported an therefore not part of the official xts API.
#'
#' @param x A time series object with `start()` and `end()` methods.
#'
#' @return A character vector of length one describing the ISO-style format
#' for the range of a given time series object.
#'
#' @noRd
#' @examples
#'
#' data(sample_matrix)
#' x <- as.xts(sample_matrix)
#' .makeISO8601(x)
#'
.makeISO8601 <- function(x) {
paste(start(x), end(x), sep = "/")
}
#' Internal ISO 8601:2004(e) Time Parser
#'
#' This function replicates most of the ISO standard for parsing times and
#' time-based ranges in a universally accepted way. The best documentation is
#' the official ISO page as well as the Wikipedia entry for ISO 8601:2004.
#'
#' The basic idea is to create the endpoints of a range, given a string
#' representation. These endpoints are aligned in POSIXct time to the zero
#' second of the day at the beginning, and the 59.9999th second of the 59th
#' minute of the 23rd hour of the final day.
#'
#' For dates prior to the epoch (1970-01-01) the ending time is aligned to the
#' 59.0000 second. This is due to a bug/feature in the \R implementation of
#' `as.POSIXct()` and `mktime0()` at the C-source level. This limits the
#' precision of ranges prior to 1970 to 1 minute granularity with the current
#' \pkg{xts} workaround.
#'
#' Recurring times over multiple days may be specified using the "T" notation.
#' See the examples for details.
#'
#' @param x A character string conforming to the ISO 8601:2004(e) rules.
#' @param start Lower constraint on range.
#' @param end Upper constraint of range
#' @param tz Timezone (tzone) to use internally.
#'
#' @return A two element list with an entry named \sQuote{first.time} and
#' one named \sQuote{last.time}.
#'
#' @note There is no checking done to test for a properly constructed ISO
#' format string. This must be correctly entered by the user.
#'
#' When using durations, it is important to note that the time of the duration
#' specified is not necessarily the same as the realized periods that may be
#' returned when applied to an irregular time series. This is not a bug, it is
#' a standards and implementation gotcha.
#'
#' @author Jeffrey A. Ryan
#'
#' @references <https://en.wikipedia.org/wiki/ISO_8601>\cr
#' <https://www.iso.org/iso-8601-date-and-time-format.html>
#'
#' @aliases ISO8601 parseISO8601
#' @rdname parseISO8601
#'
#' @keywords utilities
#' @examples
#'
#' # the start and end of 2000
#' .parseISO8601('2000')
#'
#' # the start of 2000 and end of 2001
#' .parseISO8601('2000/2001')
#'
#' # May 1, 2000 to Dec 31, 2001
#' .parseISO8601('2000-05/2001')
#'
#' # May 1, 2000 to end of Feb 2001
#' .parseISO8601('2000-05/2001-02')
#'
#' # Jan 1, 2000 to Feb 29, 2000; note the truncated time on the LHS
#' .parseISO8601('2000-01/02')
#'
#' # 8:30 to 15:00 (used in xts subsetting to extract recurring times)
#' .parseISO8601('T08:30/T15:00')
#'
.parseISO8601 <- function(x, start, end, tz="") {
# x: character vector of length 1 in ISO8601:2004(e) format
# start: optional earliest time
# end: optional latest time
# tz: optional tzone to create with
as_numeric <- function(.x) {
# simple helper function
if(gsub(" ","",.x)=="")
NULL
else as.numeric(.x)
}
x <- gsub("NOW",format(Sys.time(),"%Y%m%dT%H%M%S"),x)
x <- gsub("TODAY",format(Sys.Date(),"%Y%m%d"),x)
if(identical(grep("/|(--)|(::)", x), integer(0))) {
x <- paste(x,x,sep="/")
}
intervals <- unlist(strsplit(x, "/|(--)|(::)"))
# e.g. "/2009": "" "xxx" end of defined, needs context
# e.g. "2009/": "xxx" start of defined, needs context
# check for duration specification
DURATION <- ""
if(length(intervals)==2L) {
if(substr(intervals[1],0,1)=="P") {
# duration on LHS
DURATION <- intervals[1]
DURATION_LHS <- TRUE
intervals[1] <- ""
}
if(substr(intervals[2],0,1)=="P") {
# duration on RHS
DURATION <- intervals[2]
DURATION_LHS <- FALSE
intervals <- intervals[1]
}
# leave alone if no duration
}
parse.side <- function(x, startof) {
if( is.na(x) || !nzchar(x))
return(c(NULL))
basic <- gsub(":|-", "", x, perl=TRUE) #, extended=TRUE)
date.time <- unlist(strsplit(basic, " |T"))
# dates
date <- date.time[1]
if(!missing(startof) && nchar(basic)==2L) {
startof <- gsub(":|-", "", startof, perl=TRUE) #, extended=TRUE)
if(nchar(startof) - nchar(date) >= 4) {
# FIXME 200901/2009 needs to work, fix is ex-post now
# pad to last place of startof
# with startof values
sstartof <- substr(startof,0,nchar(startof)-nchar(date))
date <- paste(sstartof,date,sep="")
}
}
date <- sprintf("%-8s", date)
YYYY <- substr(date,0,4)
MM <- substr(date,5,6)
DD <- substr(date,7,8)
# times
time <- date.time[2]
if( !is.na(time)) {
time <- sprintf("%-6s", time)
H <- substr(time,0,2)
M <- substr(time,3,4)
S <- substr(time,5,10000L)
} else H<-M<-S<-""
# return as list
c(as.list(c(
year=as_numeric(YYYY),
month=as_numeric(MM),
day=as_numeric(DD),
hour=as_numeric(H),
min=as_numeric(M),
sec=as_numeric(S)
)
),tz=tz)
}
s <- e <- NA
if(nzchar(intervals[1])) # LHS
s <- as.POSIXlt(do.call(firstof, parse.side(intervals[1])))
if(length(intervals) == 2L) { # RHS
e <- as.POSIXlt(do.call(lastof, parse.side(intervals[2],intervals[1])))
if(is.na(e))
e <- as.POSIXlt(do.call(lastof, parse.side(intervals[2])))
}
if(is.na(s) && is.na(e) && !nzchar(DURATION) && intervals[1L] != "") {
warning("cannot determine first and last time from ", x)
return(list(first.time=NA_real_,last.time=NA_real_))
}
if(!missing(start)) {
start <- as.numeric(start)
#s <- as.POSIXlt(structure(max(start, as.numeric(s), na.rm=TRUE),
# class=c("POSIXct","POSIXt"),tz=tz))
s <- as.POSIXlt(.POSIXct(max(start, as.numeric(s), na.rm=TRUE),tz=tz))
}
if(!missing(end)) {
end <- as.numeric(end)
#e <- as.POSIXlt(structure(min(end, as.numeric(e), na.rm=TRUE),
# class=c("POSIXct","POSIXt"),tz=tz))
e <- as.POSIXlt(.POSIXct(min(end, as.numeric(e), na.rm=TRUE),tz=tz))
}
if(nzchar(DURATION)) {
parse_duration <- function(P) {
# TODO:
# strip leading P from string
# convert second M (min) to 'm' IFF following a T
# remove/ignore T
# convert extended format (PYYYYMMDD) to basic format (PnnYnnMnnD)
P <- gsub("P","",P)
P <- gsub("T(.*)M","\\1m",P)
n <- unlist(strsplit(P, "[[:alpha:]]"))
d <- unlist(strsplit(gsub("[[:digit:]]", "", P),""))
dur.vec <- list(as.numeric(n),unname(c(Y=6,M=5,D=4,H=3,m=2,S=1)[d]))
init.vec <- rep(0, 9)
init.vec[dur.vec[[2]]] <- dur.vec[[1]]
init.vec
}
if(DURATION_LHS) {
s <- as.POSIXct(structure(as.list(mapply(`-`,e,parse_duration(DURATION))),
class=c("POSIXlt","POSIXt"), tzone=attr(e,"tzone")))
} else {
e <- as.POSIXct(structure(as.list(mapply(`+`,s,parse_duration(DURATION))),
class=c("POSIXlt","POSIXt"), tzone=attr(e,"tzone")))
}
}
list(first.time=as.POSIXct(s),last.time=as.POSIXct(e))
}
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