# thanks to https://github.com/probably-not/redix-cluster/blob/master/lib/redix_cluster/hash.ex
defmodule RedixClustered.CRC16 do
  use Bitwise

  @crcdef <<0x00, 0x00, 0x10, 0x21, 0x20, 0x42, 0x30, 0x63, 0x40, 0x84, 0x50, 0xA5, 0x60, 0xC6,
            0x70, 0xE7, 0x81, 0x08, 0x91, 0x29, 0xA1, 0x4A, 0xB1, 0x6B, 0xC1, 0x8C, 0xD1, 0xAD,
            0xE1, 0xCE, 0xF1, 0xEF, 0x12, 0x31, 0x02, 0x10, 0x32, 0x73, 0x22, 0x52, 0x52, 0xB5,
            0x42, 0x94, 0x72, 0xF7, 0x62, 0xD6, 0x93, 0x39, 0x83, 0x18, 0xB3, 0x7B, 0xA3, 0x5A,
            0xD3, 0xBD, 0xC3, 0x9C, 0xF3, 0xFF, 0xE3, 0xDE, 0x24, 0x62, 0x34, 0x43, 0x04, 0x20,
            0x14, 0x01, 0x64, 0xE6, 0x74, 0xC7, 0x44, 0xA4, 0x54, 0x85, 0xA5, 0x6A, 0xB5, 0x4B,
            0x85, 0x28, 0x95, 0x09, 0xE5, 0xEE, 0xF5, 0xCF, 0xC5, 0xAC, 0xD5, 0x8D, 0x36, 0x53,
            0x26, 0x72, 0x16, 0x11, 0x06, 0x30, 0x76, 0xD7, 0x66, 0xF6, 0x56, 0x95, 0x46, 0xB4,
            0xB7, 0x5B, 0xA7, 0x7A, 0x97, 0x19, 0x87, 0x38, 0xF7, 0xDF, 0xE7, 0xFE, 0xD7, 0x9D,
            0xC7, 0xBC, 0x48, 0xC4, 0x58, 0xE5, 0x68, 0x86, 0x78, 0xA7, 0x08, 0x40, 0x18, 0x61,
            0x28, 0x02, 0x38, 0x23, 0xC9, 0xCC, 0xD9, 0xED, 0xE9, 0x8E, 0xF9, 0xAF, 0x89, 0x48,
            0x99, 0x69, 0xA9, 0x0A, 0xB9, 0x2B, 0x5A, 0xF5, 0x4A, 0xD4, 0x7A, 0xB7, 0x6A, 0x96,
            0x1A, 0x71, 0x0A, 0x50, 0x3A, 0x33, 0x2A, 0x12, 0xDB, 0xFD, 0xCB, 0xDC, 0xFB, 0xBF,
            0xEB, 0x9E, 0x9B, 0x79, 0x8B, 0x58, 0xBB, 0x3B, 0xAB, 0x1A, 0x6C, 0xA6, 0x7C, 0x87,
            0x4C, 0xE4, 0x5C, 0xC5, 0x2C, 0x22, 0x3C, 0x03, 0x0C, 0x60, 0x1C, 0x41, 0xED, 0xAE,
            0xFD, 0x8F, 0xCD, 0xEC, 0xDD, 0xCD, 0xAD, 0x2A, 0xBD, 0x0B, 0x8D, 0x68, 0x9D, 0x49,
            0x7E, 0x97, 0x6E, 0xB6, 0x5E, 0xD5, 0x4E, 0xF4, 0x3E, 0x13, 0x2E, 0x32, 0x1E, 0x51,
            0x0E, 0x70, 0xFF, 0x9F, 0xEF, 0xBE, 0xDF, 0xDD, 0xCF, 0xFC, 0xBF, 0x1B, 0xAF, 0x3A,
            0x9F, 0x59, 0x8F, 0x78, 0x91, 0x88, 0x81, 0xA9, 0xB1, 0xCA, 0xA1, 0xEB, 0xD1, 0x0C,
            0xC1, 0x2D, 0xF1, 0x4E, 0xE1, 0x6F, 0x10, 0x80, 0x00, 0xA1, 0x30, 0xC2, 0x20, 0xE3,
            0x50, 0x04, 0x40, 0x25, 0x70, 0x46, 0x60, 0x67, 0x83, 0xB9, 0x93, 0x98, 0xA3, 0xFB,
            0xB3, 0xDA, 0xC3, 0x3D, 0xD3, 0x1C, 0xE3, 0x7F, 0xF3, 0x5E, 0x02, 0xB1, 0x12, 0x90,
            0x22, 0xF3, 0x32, 0xD2, 0x42, 0x35, 0x52, 0x14, 0x62, 0x77, 0x72, 0x56, 0xB5, 0xEA,
            0xA5, 0xCB, 0x95, 0xA8, 0x85, 0x89, 0xF5, 0x6E, 0xE5, 0x4F, 0xD5, 0x2C, 0xC5, 0x0D,
            0x34, 0xE2, 0x24, 0xC3, 0x14, 0xA0, 0x04, 0x81, 0x74, 0x66, 0x64, 0x47, 0x54, 0x24,
            0x44, 0x05, 0xA7, 0xDB, 0xB7, 0xFA, 0x87, 0x99, 0x97, 0xB8, 0xE7, 0x5F, 0xF7, 0x7E,
            0xC7, 0x1D, 0xD7, 0x3C, 0x26, 0xD3, 0x36, 0xF2, 0x06, 0x91, 0x16, 0xB0, 0x66, 0x57,
            0x76, 0x76, 0x46, 0x15, 0x56, 0x34, 0xD9, 0x4C, 0xC9, 0x6D, 0xF9, 0x0E, 0xE9, 0x2F,
            0x99, 0xC8, 0x89, 0xE9, 0xB9, 0x8A, 0xA9, 0xAB, 0x58, 0x44, 0x48, 0x65, 0x78, 0x06,
            0x68, 0x27, 0x18, 0xC0, 0x08, 0xE1, 0x38, 0x82, 0x28, 0xA3, 0xCB, 0x7D, 0xDB, 0x5C,
            0xEB, 0x3F, 0xFB, 0x1E, 0x8B, 0xF9, 0x9B, 0xD8, 0xAB, 0xBB, 0xBB, 0x9A, 0x4A, 0x75,
            0x5A, 0x54, 0x6A, 0x37, 0x7A, 0x16, 0x0A, 0xF1, 0x1A, 0xD0, 0x2A, 0xB3, 0x3A, 0x92,
            0xFD, 0x2E, 0xED, 0x0F, 0xDD, 0x6C, 0xCD, 0x4D, 0xBD, 0xAA, 0xAD, 0x8B, 0x9D, 0xE8,
            0x8D, 0xC9, 0x7C, 0x26, 0x6C, 0x07, 0x5C, 0x64, 0x4C, 0x45, 0x3C, 0xA2, 0x2C, 0x83,
            0x1C, 0xE0, 0x0C, 0xC1, 0xEF, 0x1F, 0xFF, 0x3E, 0xCF, 0x5D, 0xDF, 0x7C, 0xAF, 0x9B,
            0xBF, 0xBA, 0x8F, 0xD9, 0x9F, 0xF8, 0x6E, 0x17, 0x7E, 0x36, 0x4E, 0x55, 0x5E, 0x74,
            0x2E, 0x93, 0x3E, 0xB2, 0x0E, 0xD1, 0x1E, 0xF0>>

  def hash(key) when is_binary(key), do: key |> to_charlist() |> hash()
  def hash(key), do: 0 |> crc16(key)

  defp crc16(crc, []), do: crc

  defp crc16(crc, [b | rest]) do
    index = crc |> bsr(8) |> bxor(b) |> band(0xFF)
    crc |> bsl(8) |> band(0xFFFF) |> bxor(crc_index(index)) |> crc16(rest)
  end

  defp crc_index(n) do
    <<crc::16>> = :binary.part(@crcdef, n * 2, 2)
    crc
  end
end