Parser for RFC 3339

[DavisVaughan]

This is basically an even saner ISO 8601
https://datatracker.ietf.org/doc/html/rfc3339#page-4

It is stricter, and basically just offers 4 formats (plus optional fractional seconds)

%Y-%m-%dT%H:%M:%SZ
%Y-%m-%d %H:%M:%SZ # replace T with space

%Y-%m-%dT%H:%M:%S+00:00 # replace Z with offset from UTC
%Y-%m-%d %H:%M:%S+00:00 # replace T with space

So we can do:

library(clock)
library(rlang)

sys_time_parse_rfc3339 <- function(x, 
                                   ...,
                                   separator = "T",
                                   offset = "Z",
                                   precision = "second") {
  separator <- arg_match0(separator, values = c("T", "t", " "), arg_nm = "separator")
  offset <- arg_match0(offset, values = c("Z", "z", "%z"), arg_nm = "offset")
  format <- paste0("%Y-%m-%d", separator, "%H:%M:%S", offset)
  sys_time_parse(x, ..., format = format, precision = precision)
}

date_time_parse_rfc3339 <- function(x,
                                    ...,
                                    separator = "T",
                                    offset = "Z") {
  x <- sys_time_parse_rfc3339(x, ..., separator = separator, offset = offset, precision = "second")
  as.POSIXct(x, tz = "UTC")
}

foo <- c("2019-09-07T15:14:24Z", "2014-06-02T08:52:46Z", "2014-06-16T08:36:43Z")

date_time_parse_rfc3339(foo)
#> [1] "2019-09-07 15:14:24 UTC" "2014-06-02 08:52:46 UTC"
#> [3] "2014-06-16 08:36:43 UTC"

foo <- c("2019-09-07T15:14:24+01:00", "2014-06-02T08:52:46+01:00", "2014-06-16T08:36:43+01:30")

date_time_parse_rfc3339(foo, offset = "%z")
#> [1] "2019-09-07 14:14:24 UTC" "2014-06-02 07:52:46 UTC"
#> [3] "2014-06-16 07:36:43 UTC"

It nicely doesn't allow for local time in any way, so we can safely return UTC time stamps.

From my understanding in reading the RFC, the only optional part is fractional seconds, so we don't need to try and support a ton of formats that we have to guess through, which I really like