defmodule Vasov do
  @external_resource "README.md"

  @moduledoc @external_resource
             |> File.read!()
             |> String.split("<!-- MDOC !-->")
             |> Enum.fetch!(1)

  @transliteration_table %{
    "Р" => "R",
    "з" => "z",
    "Т" => "T",
    "Ш" => "Sh",
    "т" => "t",
    "А" => "A",
    "ч" => "ch",
    "р" => "r",
    "И" => "I",
    "Ь" => "Y",
    "м" => "m",
    "ц" => "ts",
    "Е" => "E",
    "щ" => "sht",
    "У" => "U",
    "Л" => "L",
    "Ч" => "Ch",
    "н" => "n",
    "Й" => "Y",
    "Ж" => "Zh",
    "о" => "o",
    "Ю" => "Yu",
    "ь" => "y",
    "Б" => "B",
    "х" => "h",
    "г" => "g",
    "ш" => "sh",
    "л" => "l",
    "Ц" => "Ts",
    "П" => "P",
    "в" => "v",
    "К" => "K",
    "с" => "s",
    "ъ" => "a",
    "С" => "S",
    "ж" => "zh",
    "ф" => "f",
    "д" => "d",
    "Х" => "H",
    "а" => "a",
    "б" => "b",
    "Я" => "Ya",
    "М" => "M",
    "й" => "y",
    "у" => "u",
    "п" => "p",
    "Г" => "G",
    "О" => "O",
    "ю" => "yu",
    "е" => "e",
    "к" => "k",
    "Н" => "N",
    "я" => "ya",
    "В" => "V",
    "Ъ" => "A",
    "Ф" => "F",
    "и" => "i",
    "З" => "Z",
    "Д" => "D",
    "Щ" => "Sht"
  }

  @doc """
  Transliterates a text from bulgarian cyrillic language to roman latin

  Usage:
  ```
  iex> Vasov.transliterate_to_latin("Бургас")
  "Burgas"
  iex> Vasov.transliterate_to_latin("София")
  "Sofia"
  iex> Vasov.transliterate_to_latin("България")
  "Bulgaria"
  ```
  """
  def transliterate_to_latin(text) do
    text
    |> normalize()
    |> String.graphemes()
    |> Enum.reduce("", fn
      original, acc -> acc <> Map.get(@transliteration_table, original, original)
    end)
  end

  @doc """
  Returns the transliteration table as a map
  """
  def transliteration_table, do: @transliteration_table

  defp normalize(text) do
    text
    |> normalize_state_name()
    |> normalize_final_ya()
  end

  defp normalize_state_name(text) do
    Regex.replace(~r/^(б)(ъ)(лгария)/ui, text, fn _word, token_1, ua_token, token_2 ->
      replacement =
        case ua_token do
          "ъ" -> "у"
          "Ъ" -> "У"
        end

      token_1 <> replacement <> token_2
    end)
  end

  defp normalize_final_ya(text) do
    Regex.replace(~r/^(.+и)(я)\b/ui, text, fn _word, word, ending ->
      replacement =
        case ending do
          "я" -> "а"
          "Я" -> "А"
        end

      word <> replacement
    end)
  end
end