Date comparison & timezone offset help

Alexander_Hobday · July 16, 2020, 5:38pm

Can someone help me with this date comparison?

Is it possible to work out if this is before or after now?

Tue Oct 13 2020 10:00 AM PT

eg {{ if gt .date now }}

Anyway interested there is an excellent explanation of timezones with Hugo at the bottom of this thread.

jmooring · July 16, 2020, 7:51pm

How accurate does it have to be? Can we round down to the nearest day, or do you need hour:min granularity?

AdamSpann · July 17, 2020, 10:59am

convert to unix time.

Alexander_Hobday · July 17, 2020, 2:47pm

I tried the unix timestamp conversion but I’m getting the following error:

at <$date.Unix>: can’t evaluate field Unix in type string

I think the issue is my date field is coming from a data file so I guess Hugo is considering it a string and not a date. How do I make sure it gets converted?

Here’s the data file:

data:
- Tue Jul 21 2020 10:00 AM PT
- Tue Aug 11 2020 10:00 AM PT
- Tue Sep 15 2020 10:00 AM PT
- Tue Oct 13 2020 10:00 AM PT

Here’s my code:

{{ $datafile := index $fields “data” }}
{{ range $datafile }}
{{ $date := . }}
{{ if gt $date.Unix now.Unix }}
{{ . }}
{{ end }}
{{ end }}

moorereason · July 17, 2020, 2:51pm

Try

{{ if gt (time .date) now }}

Alexander_Hobday · July 17, 2020, 3:05pm

Partially worked, no error but now the condition never evaluates to true.

jmooring · July 17, 2020, 3:13pm

Back to my original question:

Alexander_Hobday · July 17, 2020, 3:13pm

Nearest day works.

jmooring · July 17, 2020, 3:21pm

You have to wrangle the date from your external source into a format understood by go. The partial referenced below uses an inline partial, so you’ll need Hugo 0.74.1.

content/foo,md:

{{< test "Tue Oct 13 2020 10:12 PM PT" >}}

layouts/shortcodes/test.html:

{{- $input := "" -}}
{{- with .Get 0 -}}
  {{- $input = . -}}
{{- else -}}
  {{- $msg1 := printf "The '%s' shortcode requires one positional parameter, a timestamp" .Name -}}
  {{- $msg2 := printf "formatted as follows: Tue Oct 13 2020 10:12 PM PT. See %s" .Position -}}
  {{- errorf "%s %s" $msg1 $msg2 -}}
{{- end -}}

{{- $timestamp := partial "convert-date.html" $input -}}

{{- $str_timestamp := $timestamp.Format "2006-01-02T15:04:05-07:00" -}}
{{- $str_now := now.Format "2006-01-02T15:04:05-07:00" -}}

<pre>
Input:     {{ $input }} (time zone will be ignored)<br>
Converted: {{ $str_timestamp }}<br>
Now:       {{ $str_now }}
</pre>

<br>

{{- if gt $timestamp now -}}
<pre>The input date is greater than now.</pre>
{{- else -}}
<pre>The input date is less than or equal to now.</pre>
{{- end -}}
</p>

layouts/partials/convert-date.html:

{{/*
@param string timestamp
  Example: Tue Oct 13 2020 10:12 PM PT

@returns time converted_timestamp
  Example: 2020-10-13T22:12:00

The time zone is ignored.
*/}}
{{- $time_parts := split . " " -}}

{{- $year := index $time_parts 3 -}}
{{- $month := partial "get-month-number" (index $time_parts 1) -}}
{{- $day := index $time_parts 2 -}}
{{- $hour := index (split (index $time_parts 4) ":") 0 -}}
{{- $min := index (split (index $time_parts 4) ":") 1 -}}
{{- $sec := "00" -}}
{{- $period := index $time_parts 5 -}}
{{- $tz := index $time_parts 6 -}}
{{- $offset := "00:00" }}

{{- if eq (lower (index $time_parts 5)) "pm" -}}
  {{ $hour = string (add (int $hour) 12) }}
{{- end -}}

{{- $converted_timestamp := printf "%s-%s-%sT%s:%s:%s-%s" $year $month $day $hour $min $sec $offset -}}

{{- return time $converted_timestamp  }}

{{/*
@param string month_name
  Examples: mar, march, Mar, March

@returns string month_number
  Example: 03
*/}}
{{- define "partials/get-month-number" -}}
  {{- $months := dict -}}

  {{- $months = merge $months (dict "jan" "01") -}}
  {{- $months = merge $months (dict "feb" "02") -}}
  {{- $months = merge $months (dict "mar" "03") -}}
  {{- $months = merge $months (dict "apr" "04") -}}
  {{- $months = merge $months (dict "may" "05") -}}
  {{- $months = merge $months (dict "jun" "06") -}}
  {{- $months = merge $months (dict "jul" "07") -}}
  {{- $months = merge $months (dict "aug" "08") -}}
  {{- $months = merge $months (dict "sep" "09") -}}
  {{- $months = merge $months (dict "oct" "10") -}}
  {{- $months = merge $months (dict "nov" "11") -}}
  {{- $months = merge $months (dict "dec" "12") -}}

  {{- $month_name := substr . 0 3 | lower -}}
  {{- $month_number := index $months $month_name -}}

  {{- return $month_number -}}
{{- end -}}

Alexander_Hobday · July 17, 2020, 3:23pm

OK let me take a look through. I do have the option of changing the date in the date file to some other format if that would help Go view it as a date object?

jmooring · July 17, 2020, 3:26pm

Yes, it would. For example:

2020-07-17T11:26:14-04:00

Alexander_Hobday · July 17, 2020, 3:34pm

That did the trick, my condition is now evaluating correctly

For reference:

Data file:

data:
- 2020-07-21T10:00:00-08:00
- 2020-08-11T10:00:00-08:00
- 2020-09-15T10:00:00-08:00
- 2020-10-13T10:00:00-08:00

Code:

Only issue I have now is formatting the date back to what I need:

This: {{ dateFormat “Tue Jul 21 2020 10:00 AM PT” . date}}

Outputs: Tue Jul 118 11110 80:00 AM PT

jmooring · July 17, 2020, 3:45pm

dateFormat "Mon Jan 2 2006 3:04 PM MST"

Note that “PT” is not a valid time zone. On the west coast of the United States, the time zone is either PST or PDT.

Alexander_Hobday · July 17, 2020, 3:48pm

Thank you, that mostly did it, but the timezone isn’t getting translated:

Tue Aug 11 2020 10:00 AM -0800

jmooring · July 17, 2020, 3:53pm

What is the current offset of your system? I suspect it is not -08:00. Please confirm.

Alexander_Hobday · July 17, 2020, 4:08pm

I’m just testing locally, How would I find that out?

jmooring · July 17, 2020, 4:10pm

On Linux:

date -Iseconds

Alexander_Hobday · July 17, 2020, 4:45pm

Ahh, sorry you meant my machine. I’m GMT -6 currently.

Alexander_Hobday · July 17, 2020, 4:49pm

I actually don’t know how Hugo processes timezones. If you have any pointers, appreciated.

jmooring · July 17, 2020, 5:17pm

Short Answer

If you want to ignore the offset in your dates, and always print PT, do this:

dateFormat "Mon Jan 2 2006 3:04 PM PT"

Medium Answer

Don’t display the time zone abbreviation. Display the offset instead. Why? Because time zone abbreviations are essentially useless.

dateFormat "Mon Jan 2 2006 15:04 -07:00"

Long Answer

There is a N:N relationship between time zone abbreviations and offsets. For example:

Different offsets with the same time zone abbreviation:

Time Zone Abbreviation	Description	Offset
CST	Central Standard Time (North America)	-06:00
CST	China Standard Time	+08:00
CST	Cuba Standard Time	-05:00

Different time zone abbreviations with the same offset:

Offset	Description	Time Zone Abbreviation
-06:00	Central Standard Time (North America)	CST
-06:00	Mountain Daylight Time (North America)	MDT
-06:00	Easter Island Standard Time	EAST
-06:00	Galápagos Time	GALT

So, when the timestamp is 2020-07-17T12:49:12-04:00, which time zone abbreviation should be displayed? It depends on where you are. Similarly, if you say you eat dinner at 5 PM CST, I have no idea when you actually eat dinner.

With Hugo, if you use the Mon Jan 2 2006 3:04 PM MST format string:

When the offset of the date to be formatted is the same as your local offset, the local time zone abbreviation for the offset is displayed, based on the TZ environment variable on your machine. If you change the TZ environment variable on your machine to America/Los_Angeles and rebuild the site, you will get different results.
When the offset of the date to be formatted is different than your local offset, we have no idea what time zone abbreviation to display, so we display the offset instead.

So what to do?

Don’t display the time zone abbreviation. Display the offset instead.

References:

Topic		Replies	Views
Parsing dates yields different results support	6	601	February 7, 2022
Hugo Date and Time system support	1	387	September 17, 2023
String to Time object function? support	0	646	May 1, 2015
Converting time variable between timezones feature dateformats	0	573	December 18, 2022
Document Dates in Front matter support	8	2047	June 11, 2019

Date comparison & timezone offset help

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