defmodule Base58Check do

	b58_alphabet = Enum.with_index('123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz')

	for {encoding, value} <- b58_alphabet do
		defp do_encode58(unquote(value)), do: unquote(encoding)
		defp do_decode58(unquote(encoding)), do: unquote(value)
	end

	def encode58(data) do
		encoded_zeroes = convert_leading_zeroes(data, [])
		integer = if is_binary(data), do: :binary.decode_unsigned(data), else: data
		encode58(integer, [], encoded_zeroes)
	end
	defp encode58(0, acc, encoded_zeroes), do: to_string([encoded_zeroes|acc])
	defp encode58(integer, acc, encoded_zeroes) do
		encode58(div(integer, 58), [do_encode58(rem(integer, 58)) | acc], encoded_zeroes)
	end
	defp convert_leading_zeroes(<<0>> <> data, encoded_zeroes) do
		encoded_zeroes = ['1'|encoded_zeroes]
		convert_leading_zeroes(data, encoded_zeroes)
	end
	defp convert_leading_zeroes(_data, encoded_zeroes), do: encoded_zeroes

	def decode58(code) when is_binary(code) do
		decode58(to_char_list(code), 0)
	end
	def decode58(code), do: raise(ArgumentError, "expects base58-encoded binary")
	defp decode58([], acc), do: acc
	defp decode58([c|code], acc) do
		decode58(code, (acc * 58) + do_decode58(c))
	end

	def encode58check(prefix, data) when is_binary(prefix) and is_binary(data) do
		data = case Base.decode16(String.upcase(data)) do
				{:ok, bin} 	->	bin
				:error 			->	data
			end
		versioned_data = prefix <> data
		checksum = generate_checksum(versioned_data)
		encode58(versioned_data <> checksum)
	end
	def encode58check(prefix, data) do
		prefix = if is_integer(prefix), do: :binary.encode_unsigned(prefix), else: prefix
		IO.inspect prefix
		data = if is_integer(data), do: :binary.encode_unsigned(data), else: data
		encode58check(prefix, data)
	end

	def decode58check(code) do
		decoded_bin = decode58(code) |> :binary.encode_unsigned()
		payload_size = byte_size(decoded_bin) - 5

		<<prefix::binary-size(1), payload::binary-size(payload_size), checksum::binary-size(4)>> = decoded_bin
		if generate_checksum(prefix <> payload) == checksum do
			{prefix, payload}
		else
			raise ArgumentError, "checksum doesn't match"
		end
	end

	defp generate_checksum(versioned_data) do
		<<checksum::binary-size(4), _rest::binary-size(28)>> = versioned_data |> :erlsha2.sha256() |> :erlsha2.sha256()
		checksum
	end
end