defmodule StarkBank.Utils.Case do
  @moduledoc false

  def camel_to_kebab(string) do
    string
     |> camel_to_snake
     |> String.replace("_", "-")
  end

  def camel_to_snake(string) do
    string
      |> String.graphemes
      |> camel_to_snake_graphemes
      |> strip_underscore
      |> Enum.join
  end

  defp camel_to_snake_graphemes([letter | rest]) do
    cond do
      letter == letter |> String.upcase -> ["_" | [String.downcase(letter) | camel_to_snake_graphemes(rest)]]
      :error != Integer.parse(letter) -> ["_" | [letter | camel_to_snake_graphemes(rest)]]
      true -> [letter | camel_to_snake_graphemes(rest)]
    end
  end

  defp camel_to_snake_graphemes([]) do
    []
  end

  defp strip_underscore([letter | rest]) when letter == "_" do
    rest
  end

  defp strip_underscore(string) do
    string
  end

  def snake_to_camel(string) do
    string
     |> String.graphemes
     |> snake_to_camel_graphemes
     |> Enum.join
  end

  defp snake_to_camel_graphemes([letter | rest]) when letter == "_" do
    snake_to_camel_graphemes([String.upcase(hd(rest)) | tl(rest)])
  end

  defp snake_to_camel_graphemes([letter | rest]) do
    [letter | snake_to_camel_graphemes(rest)]
  end

  defp snake_to_camel_graphemes([]) do
    []
  end
end