localize

defmodule Localize.Collation.Tailoring.LocaleDefaults do
  @moduledoc """
  Preset collation option defaults for common locales.

  Maps BCP47 language tags to their standard collation option overrides
  as defined by CLDR. These defaults are applied before any explicit
  BCP47 `-u-` extension keys.

  """

  @locale_defaults %{
    "cu" => [case_first: :upper],
    "da" => [case_first: :upper],
    "mt" => [case_first: :upper],
    "nb" => [case_first: :upper],
    "nn" => [case_first: :upper],
    "no" => [case_first: :upper]
  }

  @locale_type_defaults %{
    "de" => :standard,
    "es" => :standard
  }

  @doc """
  Get option overrides for a locale.

  ### Arguments

  * `locale` - a BCP47 locale string (e.g., `"da"`, `"de-AT"`, `"sv-SE"`).

  ### Returns

  A keyword list of option overrides, or an empty list if no defaults exist.

  ### Examples

      iex> Localize.Collation.Tailoring.LocaleDefaults.options_for("da")
      [case_first: :upper]

      iex> Localize.Collation.Tailoring.LocaleDefaults.options_for("en")
      []

  """
  @spec options_for(String.t()) :: keyword()
  def options_for(locale) when is_binary(locale) do
    language = extract_language(locale)

    case Map.get(@locale_defaults, language) do
      nil -> options_from_parent(language)
      defaults -> defaults
    end
  end

  defp options_from_parent(language) do
    case Localize.validate_locale(language) do
      {:ok, tag} ->
        case Localize.Locale.parent(tag) do
          {:ok, parent_tag} ->
            parent_lang = parent_tag.language |> to_string()

            if parent_lang != language and parent_lang != "und" do
              options_for(parent_lang)
            else
              []
            end

          {:error, _} ->
            []
        end

      {:error, _} ->
        []
    end
  end

  @doc """
  Get the default collation type for a locale.

  ### Arguments

  * `locale` - a BCP47 locale string.

  ### Returns

  The default collation type atom for the locale, or `:standard`.

  ### Examples

      iex> Localize.Collation.Tailoring.LocaleDefaults.default_type("de")
      :standard

      iex> Localize.Collation.Tailoring.LocaleDefaults.default_type("es")
      :standard

  """
  @spec default_type(String.t()) :: atom()
  def default_type(locale) when is_binary(locale) do
    language = extract_language(locale)
    Map.get(@locale_type_defaults, language, :standard)
  end

  @doc """
  Extract the language subtag from a BCP47 locale string.

  ### Arguments

  * `locale` - a BCP47 locale string.

  ### Returns

  The lowercase language subtag string.

  ### Examples

      iex> Localize.Collation.Tailoring.LocaleDefaults.extract_language("de-AT-u-co-phonebk")
      "de"

      iex> Localize.Collation.Tailoring.LocaleDefaults.extract_language("sv")
      "sv"

  """
  @spec extract_language(String.t()) :: String.t()
  def extract_language(locale) do
    locale
    |> String.split("-", parts: 2)
    |> hd()
    |> String.downcase()
  end
end