A source of holidays that Koyomi.Holidays can read, for example the holidays of a region or the days a company is closed.

defmodule MyApp.Closures do
  @behaviour Koyomi.Holidays.Provider

  @impl true
  def holidays(year) do
    [{Date.new!(year, 12, 24), "Fermeture", "Office closed"}]
  end

  @impl true
  def language, do: "fr"
end

Koyomi.Holidays.between(["FR", MyApp.Closures], range)

holidays/1 returns the holidays of one year as {date, name, english} tuples: name in the language of language/0, english in English. Entries with a date in another year are dropped. The order does not matter.

The optional callbacks:

• language/0 - the language of name, a code such as "fr" or "ja". Koyomi.Holidays.to_client/3 shows name to a locale in that language and english to the others. A provider without it always shows name.
• country/0 - the value of Koyomi.Holiday.country for its holidays. The provider module otherwise.

Koyomi.Holidays.Rules has the date rules that the built-in countries use, such as Koyomi.Holidays.Rules.easter/1.