-- |
-- Module       : Data.Text.Short.Encoding.Base16
-- Copyright 	: (c) 2019 Emily Pillmore
-- License	: BSD-style
--
-- Maintainer	: Emily Pillmore <emilypi@cohomolo.gy>
-- Stability	: Experimental
-- Portability	: portable
--
-- This module contains the combinators implementing the
-- RFC 4648 specification for the Base16 encoding including
-- unpadded and lenient variants for text values
--
module Data.Text.Short.Encoding.Base16
( encodeBase16
, decodeBase16
, decodeBase16With
, decodeBase16Lenient
, isBase16
, isValidBase16
) where


import Data.Bifunctor (first)
import qualified Data.ByteString.Base16 as B16
import Data.ByteString.Short (ShortByteString)
import qualified Data.ByteString.Short.Base16 as BS16
import Data.Text (Text)
import qualified Data.Text.Encoding.Base16 as B16T
import Data.Text.Encoding.Base16.Error
import Data.Text.Short
import Data.Text.Short.Unsafe


-- | Encode a 'ShortText' value in Base16 with padding.
--
-- See: <https://tools.ietf.org/html/rfc4648#section-8 RFC-4648 section 8>
--
encodeBase16 :: ShortText -> ShortText
encodeBase16 = fromByteStringUnsafe . B16.encodeBase16' . toByteString
{-# INLINE encodeBase16 #-}

-- | Decode a Base16-encoded lazy 'ShortText' value.
--
-- See: <https://tools.ietf.org/html/rfc4648#section-8 RFC-4648 section 8>
--
decodeBase16 :: ShortText -> Either Text ShortText
decodeBase16 = fmap fromText . B16T.decodeBase16 . toText
{-# INLINE decodeBase16 #-}

-- | Attempt to decode a lazy 'ShortText' value as Base16, converting from
-- 'ByteString' to 'ShortText' according to some encoding function. In practice,
-- This is something like 'decodeUtf8'', which may produce an error.
--
-- See: <https://tools.ietf.org/html/rfc4648#section-8 RFC-4648 section 8>
--
-- Example:
--
-- @
-- 'decodeBase16With' 'T.decodeUtf8''
--   :: 'ShortText' -> 'Either' ('Base16Error' 'UnicodeException') 'ShortText'
-- @
--
decodeBase16With
    :: (ShortByteString -> Either err ShortText)
      -- ^ convert a bytestring to text (e.g. 'T.decodeUtf8'')
    -> ShortText
      -- ^ Input text to decode
    -> Either (Base16Error err) ShortText
decodeBase16With f t = case BS16.decodeBase16 (toShortByteString t) of
  Left de -> Left $ DecodeError de
  Right a -> first ConversionError (f a)
{-# INLINE decodeBase16With #-}

-- | Decode a Base16-encoded lazy 'ShortText' value leniently, using a
-- strategy that never fails, catching unicode exceptions raised in the
-- process of converting to text values.
--
-- N.B.: this is not RFC 4648-compliant.
--
decodeBase16Lenient :: ShortText -> ShortText
decodeBase16Lenient = fromText . B16T.decodeBase16Lenient . toText
{-# INLINE decodeBase16Lenient #-}

-- | Tell whether a 'ShortText' value is Base16-encoded.
--
-- Examples:
--
-- This example will fail. It conforms to the alphabet, but
-- is not valid because it has an incorrect (odd) length.
--
-- >>> isBase16 "666f6"
-- False
--
-- This example will succeed because it satisfies the alphabet
-- and is considered "valid" (i.e. of the correct size and shape).
--
-- >>> isBase16 "666f"
-- True
--
isBase16 :: ShortText -> Bool
isBase16 = B16.isBase16 . toByteString
{-# INLINE isBase16 #-}

-- | Tell whether a 'ShortText' value is a valid Base16 format.
--
-- This will not tell you whether or not this is a correct Base16 representation,
-- only that it conforms to the correct shape. To check whether it is a true
-- Base16 encoded 'ShortText' value, use 'isBase16'.
--
-- Examples:
--
-- This example will fail because it does not conform to the Hex
-- alphabet.
--
-- >>> isValidBase16 "666f+/6"
-- False
--
-- This example will succeed because it satisfies the alphabet
-- and is considered "valid" (i.e. of the correct size and shape), but
-- is not correct base16 because it is the wrong shape.
--
-- >>> isValidBase16 "666f6"
-- True
--
isValidBase16 :: ShortText -> Bool
isValidBase16 = B16.isValidBase16 . toByteString
{-# INLINE isValidBase16 #-}