defmodule HL7.FieldGrammar do
  require Logger

  @moduledoc false

  @spec to_indices(String.t()) :: list()
  def to_indices(schema) when is_binary(schema) do
    use_repeat = String.contains?(schema, "[")
    use_segment = String.contains?(schema, "-")
    chunks = chunk_schema(schema)
    [head | tail] = chunks

    case use_segment do
      true ->
        case use_repeat do
          true ->
            [head | tail |> Enum.map(&String.to_integer/1)]

          false ->
            [head | tail |> Enum.map(&String.to_integer/1) |> List.insert_at(1, 1)]
        end
        |> Enum.take(5)
        |> Enum.with_index()
        |> Enum.map(fn {v, i} -> if i > 1, do: v - 1, else: v end)

      false ->
        case use_repeat do
          true ->
            chunks |> Enum.map(&String.to_integer/1)

          false ->
            chunks |> Enum.map(&String.to_integer/1) |> List.insert_at(1, 1)
        end
        |> Enum.take(4)
        |> Enum.with_index()
        |> Enum.map(fn {v, i} -> if i > 0, do: v - 1, else: v end)
    end
  end

  @spec chunk_schema(String.t()) :: list()
  defp chunk_schema(schema) do
    Regex.split(~r{(\.|\-|\[|\]|\s)}, schema, include_captures: false, trim: true)
  end
end