defmodule PokeLib.Utils do
  require Bitwise

  @doc "Gets a part at offset of size."
  def get_part(data, offset, size, parser \\ nil) do
    <<_ :: binary-size(offset), fetched :: binary-size(size), _rest :: binary>> = data
    if parser, do: parser.(fetched), else: fetched
  end

  @doc "Decodes two bytes into an integer."
  def two_bytes_to_integer(<<a, b>>) do
    a = a |> :binary.encode_unsigned |> Base.encode16
    b = b |> :binary.encode_unsigned |> Base.encode16
    {res, _} = Integer.parse(a <> b, 16)
    res
  end

  def three_bytes_to_integer(<<a, b, c>>) do
    a = a |> :binary.encode_unsigned |> Base.encode16
    b = b |> :binary.encode_unsigned |> Base.encode16
    c = c |> :binary.encode_unsigned |> Base.encode16
    {res, _} = (a <> b <> c) |> Integer.parse(16)
    res
  end

  @doc "Encodes an integer into two bytes."
  def integer_to_two_bytes(int) do
    b = Bitwise.&&&(int, 0xFF)
    a = Bitwise.>>>(int, 8) |> Bitwise.&&&(0xFF)
    <<a, b>>
  end

  @doc "Decodes an integer into three bytes."
  def integer_to_three_bytes(int) do
    a = Bitwise.>>>(int, 16) |> Bitwise.&&&(0xFF)
    b = Bitwise.>>>(int, 8) |> Bitwise.&&&(0xFF)
    c = Bitwise.&&&(int, 0xFF)
    <<a, b, c>>
  end

  @doc "Pads up to three digits."
  def get_four_bits(data) do
    case Integer.digits(data, 2) do
      [_, _, _, _] = res -> res
      [a, b, c]          -> [0, a, b, c]
      [a, b]             -> [0, 0, a, b]
      [a]                -> [0, 0, 0, a]
    end
  end

end