Hugo: Get the week number of the year (tips)

Description

Actually, Hugo (the SSG) is not capable to get a week number!
It’s ‘under consideration’!

However, Go language provides the IsoWeek() method.

Find the week number serves a purpose, whilst uncommon, is certainly useful.
As instance, a weekly newsletter :)

I’m going to show you two differents functions:

• by getIsoWeek
• or with getWeekNumber

getisoweek

First, create a partial template: /func/getIsoWeek:

{{- $date := time.AsTime . -}}
{{- $weekday := $date.Weekday }}
{{/* 1. Normalize Weekday (Mon=1 ... Sun=7) */}}
{{- $isoDay := cond (eq $weekday 0) 7 (int $weekday) -}}
{{/* 2. Find Thursday (ISO Week belongs to the year of its Thursday) */}}
{{- $offset := sub 4 $isoDay -}}
{{- $thursday := $date.AddDate 0 0 $offset -}}
{{/* 3. Calculate Week Number */}}
{{- $isoYear := $thursday.Year -}}
{{- $isoWeek := add (div (sub $thursday.YearDay 1) 7) 1 -}}
{{/* 4. Return the data */}}
{{- $str := dict "week" (printf "%02d" $isoWeek) "year" (printf "%04d" $isoYear) -}}
{{- $data := dict "week" $isoWeek "year" $isoYear "str" $str -}}
{{- return $data -}}

The call:

{{- partial "func/getisoweek" .Date -}}

Or any other varible using Time, such as now.

⇒ Remark about getIsoWeek :

• if I want values as int, I call $data.week and $data.year
• if I want values as str, I call $data.str.week and $data.str.year

Personnaly, I’ve too created another partial template, called utils/formatIsoDate.

The code as follows:

{{- $data := partial "func/getIsoWeek" . -}}
{{- $s := printf "w%s-y%s" $data.str.week $data.str.year -}}
{{- return $s -}}

I can call it either from the default archetypes, or anywhere into the templates or shortcodes, as I wish, such as:
{{ partial "utils/formatIsoDate" .Date }} ou {{ partial "utils/formatIsoDate" now }}.

getweeknumber

This second method for finding the week number is a little trickier!

This time, I have two main files.

⇒ The first function, func/splitNameYMO, is designed to “break down” a standardized date (YYYY-MM-DD) into the corresponding day, month, and year, and return a dictionary.

{{- $str := split . "-" -}}
{{- $d = (int (index $str 2)) -}}
{{- $m = (int (index $str 1)) -}}
{{- $y = (int (index $str 0)) -}}
{{- return (dict "day" $d "month" $m "year" $y) -}}

I created this file because I use it frequently throughout my code…

⇒ The second file is the main function, named func/getWeekNumber

{{- $date := "" -}}
{{- $tz := site.Params.timeZone -}}
{{- $week := 0 -}}

{{ $type := printf "%T" . }}

{{ if eq $type "string" }}

    {{- $data := partial "func/splitNameYMO" . }}
    {{- $date = time (printf "%04d-%02d-%02d" $data.year $data.month $data.day) $tz -}}

{{ else }}

    {{- $date = time . $tz -}}

{{- end -}}

{{/* Calcul 'doy: day of the year', 'dow: day of the week' */}}
{{- $doy := $date.YearDay -}}
{{- $dow := int $date.Weekday -}}
{{- $year := $date.Year -}}

{{/* calcul week number */}}
{{- $week = div (add (sub $doy $dow) 10) 7 -}}
{{- if eq $dow 0 -}}
    {{- $week = sub $week 1 -}}
{{- end -}}

{{- $str := dict "week" (printf "%02d" $week) "year" (printf "%04d" $year) -}}
{{- $data := dict "week" $week "year" $year "str" $str -}}
{{- return $data -}}

Explanations:

• First, I need to determine the type of the value I’m injecting into the file call — whether it’s a string or something else, in this case a timestamp — keep in mind that Hugo doesn’t know how to declare a value type for a timestamp, but in the repository, it is defined as Time.time.

• Next, I determine which day of the year the date ($doy) corresponds to, which day of the week it falls on ($dow), and finally the year, of course.

• Calcul of the week number is known:

  • subtract the day of the week from the day of the year
  • add 10
  • and divide the result by 7
  • and finally, if the day of the week is a Sunday, I subtract 1 from the week number found — this applies to Hugo, where weeks start on Sunday

Voila!

Documentation

• https://gohugo.io/quick-reference/methods/#time

Acknowledgements

• https://discourse.gohugo.io/t/group-content-by-week-number-of-year/11894/6

Enjoy-ID!
Enjoy-IT!