defmodule Tesourex do
  def header(tesouro_csv) do
    tesouro_csv |> split_fields |> Enum.at(0)
  end

  def summary(tesouro_csv) do
    tesouro_csv
    |> split_fields
    |> Enum.reduce(%{}, &group_by_name_and_most_recent/2)
  end

  defp group_by_name_and_most_recent([""], acc), do: acc

  defp group_by_name_and_most_recent(row, acc) do
    Map.update(acc, name_with_year(row), row, fn current ->
      most_recent(current, row)
    end)
  end

  defp most_recent(a, b) do
    [_,_,date_a|_] = a
    [_,_,date_b|_] = b

    case Date.compare(to_date(date_a), to_date(date_b)) do
      :gt -> a
      _ -> b
    end
  end

  defp to_date(tesouro_date) do
    parts = tesouro_date
            |> String.split("/")
            |> Enum.reverse
            |> Enum.map(&String.to_integer/1)

    {:ok, date} = apply(&Date.new/3, parts)

    date
  end

  defp name_with_year([name,date|_]) do
    year = date
           |> String.split("/")
           |> Enum.at(2)

    "#{name} #{year}"
  end

  defp split_fields(tesouro_csv) do
    tesouro_csv
    |> Stream.map(&(&1 |> String.trim() |> String.split(";")))
  end
end