ExUnit.start()

defmodule LEB128Test do
  use ExUnit.Case
  doctest WaParser
  test "Encode unsigned" do
    assert WaParser.LEB128.encode_unsigned(0) == <<0x00>>
    assert WaParser.LEB128.encode_unsigned(42) == <<0x2A>>
    assert WaParser.LEB128.encode_unsigned(624_485) == <<0xE5, 0x8E, 0x26>>
  end
end

defmodule WaParser.LEB128 do
  def encode_unsigned(0) do
    <<0x00>>
  end
  def encode_unsigned(int) when int < 0x80 do
    <<int>>
  end
  def encode_unsigned(int) do
    encode_unsigned(int, [])
  end
  defp encode_unsigned(0, acc) do
    size = Enum.count(acc)
    acc
    |> Enum.reverse()
    |> Enum.with_index(fn bits, index ->
      if index < size - 1 do
        <<1::1, bits::7>>
      else
        <<bits>>
      end
    end)
    |> Enum.into(<<>>)
  end
  defp encode_unsigned(int, acc) do
    seven_bits = Bitwise.band(int, 0x7F)
    int = Bitwise.bsr(int, 7)
    encode_unsigned(int, [seven_bits | acc])
  end
end