Pattern match on Timex date

Questions / Help
1

I’m generating custom time select fields in my form and that’s the only way that comes to my mind how to do this.
But I’m sure there is a pattern match for that
I want to show only current year
unless it is the first of january then I want to show also the previous year.
or when its the end of year I want to show the next year

now = Timex.now
  defp year_select(now) do
    year = [now.year]
    year = if now.month == 1 and now.day == 1, do: [now.year - 1, now.year], else: year
    year = if now.month == 12 and now.day > Timex.shift(now, days: +4).day, do: [now.year, now.year + 1], else: year
    year
  end

now looks like:
~U[2019-10-23 19:57:12.649300Z]

2 
defp year_select(%{year: y, month: 1, day: 1}, do: [y - 1, y]
defp year_select(%{year: y, month: 12, day: d), when d in 28..31, do: [y, y + 1]
defp year_select(%{year: y}, do: [y]

I hope I got the “end of year” match correct… I’m not quite sure what Timex.shift does, but it looks like you were checking for an overflow on the days when adding 4 days… Thats why I used 28..31, the last 4 days of december…

Perhaps that line would have been more obvious as now.year < Timex.shift(now, days: 4).year.

You could even use %DateTime{…} to make sure you get an actual date time, and not just a map with a :year key…

3 Likes
3

Thanks, with the end of year it’s exactly what I meant. I was confused by the ~U sygil that timex returns. With a map it makes more sense to me

4

sigil_U is just a pretty printed %DateTime{}.

i/1 and h/1 in iex are your friends.

2 Likes
5

Thanks - It helped me a lot