Generates encode and decode methods for base 2->62

base_n.exs

for {base, name} <- (2..62 |> Enum.map(&({&1, "Base#{&1}" |> String.to_atom}))) do
  # NOTE: Modules will be named :Base2, :Base3, ..., :Base62
  defmodule name do
    @moduledoc """
    Automatically generated #{name} encode/decode functions
    """
    @base base
    @alphabet [?0..?9, ?a..?z, ?A..?Z]
    |> Enum.flat_map(fn x -> x end)
    |> to_string
    |> String.split("", trim: true)
    |> Enum.take(@base)

    @validator Regex.compile!("^[#{ @alphabet |> Enum.join }]+$")

    def alphabet, do: @alphabet |> Enum.join

    for {char, ix} <- (@alphabet |> Enum.with_index) do
      defp index_of(unquote(char)), do: unquote(ix)
      defp char_at(unquote(ix)), do: unquote(char)
    end

    @doc """
    Encodes an integer to a #{name} string

    ## Examples

    \tiex> :#{name}.encode(123)
    """
    def encode(int) when is_integer(int) do
      encode(div(int, @base), rem(int, @base), "")
    end

    defp encode(0, mod, str), do: char_at(mod) <> str
    defp encode(int, mod, str) when is_integer(int) do
      encode(div(int, @base), rem(int, @base), char_at(mod) <> str)
    end

    @doc """
    Decodes a #{name} string to an integer

    ## Examples

    \tiex> :#{name}.decode("foo")
    """
    def decode(str) when is_binary(str) do
      case Regex.match?(@validator, str) do
        false ->
          {:error, "Not a valid #{unquote(name)} string"}
        true ->
          {:ok, str
            |> String.reverse
            |> String.split("", trim: true)
            |> Enum.with_index
            |> Enum.reduce(0, fn({char, index}, acc) -> acc + index_of(char) * (:math.pow(@base, index) |> round) end)
          }
      end
    end
  end
end