# `Koyomi.Holidays.Provider`
[🔗](https://github.com/hattoriai/koyomi/blob/v0.2.1/lib/koyomi/holidays/provider.ex#L1)

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`.

# `entry`

```elixir
@type entry() :: {Date.t(), String.t(), String.t()}
```

A holiday: `{date, name, english}`.

# `country`
*optional* 

```elixir
@callback country() :: String.t()
```

Returns the country of the holidays, such as "FR".

# `holidays`

```elixir
@callback holidays(year :: integer()) :: [entry()]
```

Returns the holidays of `year`.

# `language`
*optional* 

```elixir
@callback language() :: String.t()
```

Returns the language of the names, such as "fr".

---

*Consult [api-reference.md](api-reference.md) for complete listing*