{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE Safe                  #-}
{-# LANGUAGE TypeSynonymInstances  #-}

-- | Type classes for convertion between different string representations.

module Conv
       ( ConvertUtf8 (..)
       , ToString (..)
       , ToLText (..)
       , ToText (..)
       ) where

import qualified Data.ByteString           as B
import qualified Data.ByteString.Lazy      as LB
import qualified Data.ByteString.Lazy.UTF8 as LBU
import qualified Data.ByteString.UTF8      as BU
import qualified Data.Text                 as T
import qualified Data.Text.Encoding        as T
import qualified Data.Text.Encoding.Error  as T
import qualified Data.Text.Lazy            as LT
import qualified Data.Text.Lazy.Encoding   as LT

import           Data.Either               (Either)
import           Data.Function             (id, (.))
import           Data.String               (String)
import           Functor                   ((<$>))

-- | Type class for conversion to utf8 representation of text.
class ConvertUtf8 a b where
    -- | Encode as utf8 string (usually 'B.ByteString').
    --
    -- >>> encodeUtf8 @Text @ByteString "патак"
    -- "\208\191\208\176\209\130\208\176\208\186"
    encodeUtf8 :: a -> b

    -- | Decode from utf8 string.
    --
    -- >>> decodeUtf8 @Text @ByteString "\208\191\208\176\209\130\208\176\208\186"
    -- "\1087\1072\1090\1072\1082"
    -- >>> putStrLn $ decodeUtf8 @Text @ByteString "\208\191\208\176\209\130\208\176\208\186"
    -- патак
    decodeUtf8 :: b -> a

    -- | Decode as utf8 string but returning execption if byte sequence is malformed.
    --
    -- >>> decodeUtf8 @Text @ByteString "\208\208\176\209\130\208\176\208\186"
    -- "\65533\65533\1090\1072\1082"
    -- >>> decodeUtf8Strict @Text @ByteString "\208\208\176\209\130\208\176\208\186"
    -- Left Cannot decode byte '\xd0': Data.Text.Internal.Encoding.decodeUtf8: Invalid UTF-8 stream
    decodeUtf8Strict :: b -> Either T.UnicodeException a

instance ConvertUtf8 String B.ByteString where
    encodeUtf8 = BU.fromString
    decodeUtf8 = BU.toString
    decodeUtf8Strict = (T.unpack <$>) . decodeUtf8Strict

instance ConvertUtf8 T.Text B.ByteString where
    encodeUtf8 = T.encodeUtf8
    decodeUtf8 = T.decodeUtf8With T.lenientDecode
    decodeUtf8Strict = T.decodeUtf8'

instance ConvertUtf8 LT.Text B.ByteString where
    encodeUtf8 = LB.toStrict . encodeUtf8
    decodeUtf8 = LT.decodeUtf8With T.lenientDecode . LB.fromStrict
    decodeUtf8Strict = decodeUtf8Strict . LB.fromStrict

instance ConvertUtf8 String LB.ByteString where
    encodeUtf8 = LBU.fromString
    decodeUtf8 = LBU.toString
    decodeUtf8Strict = (T.unpack <$>) . decodeUtf8Strict

instance ConvertUtf8 T.Text LB.ByteString where
    encodeUtf8 = LB.fromStrict . T.encodeUtf8
    decodeUtf8 = T.decodeUtf8With T.lenientDecode . LB.toStrict
    decodeUtf8Strict = T.decodeUtf8' . LB.toStrict

instance ConvertUtf8 LT.Text LB.ByteString where
    encodeUtf8 = LT.encodeUtf8
    decodeUtf8 = LT.decodeUtf8With T.lenientDecode
    decodeUtf8Strict = LT.decodeUtf8'

-- | Type class for converting other strings to 'T.Text'.
class ToText a where
    toText :: a -> T.Text

instance ToText String where
    toText = T.pack

instance ToText T.Text where
    toText = id

instance ToText LT.Text where
    toText = LT.toStrict

-- | Type class for converting other strings to 'LT.Text'.
class ToLText a where
    toLText :: a -> LT.Text

instance ToLText String where
    toLText = LT.pack

instance ToLText T.Text where
    toLText = LT.fromStrict

instance ToLText LT.Text where
    toLText = id

-- | Type class for converting other strings to 'String'.
class ToString a where
    toString :: a -> String

instance ToString String where
    toString = id

instance ToString T.Text where
    toString = T.unpack

instance ToString LT.Text where
    toString = LT.unpack