SerialNumber.hs

-- from
-- https://www.youtube.com/watch?v=lxjIUWGMUqE
-- Haskell at Work - Validation with Smart Constructors

module SerialNumber 
    ( SerialNumber
    , ValidataionError(..)
    , makeSerialNumber   
    , renderSerialNumber 
    ) where

import           Data.Text (Text)
import qualified Data.Text as Text
import qualified Data.HashSet as HashSet
import           Data.HashSet (HashSet)

newtype SerialNumber = 
    SerialNumber [Text]
    deriving (Eq, Show)

data ValidataionError
    = WrongNumerOfGroups Int
    | InvalidGroupLength Int
                         Text
    | InvalidCharacters (HashSet Char)
    deriving (Eq, Show)

validChars = HashSet.fromList (['A' .. 'Z'] ++ ['0' .. '9'])

separator :: Text
separator = Text.singleton '-'

makeSerialNumber :: Text -> Either ValidataionError SerialNumber
makeSerialNumber t =  do
    gs <- mapM validateGroup (Text.splitOn (Text.singleton '-') t)
    if length gs == 4
        then Right (SerialNumber gs)
        else Left (WrongNumerOfGroups (length gs))
    where
        validateGroup group
            | len /= 4 = Left(InvalidGroupLength len group)
            | not (HashSet.null invalidChars) = Left (InvalidCharacters invalidChars)
            | otherwise = Right group
                where
                    len = Text.length group
                    invalidChars = HashSet.difference (HashSet.fromList (Text.unpack group)) validChars

renderSerialNumber :: SerialNumber -> Text
renderSerialNumber (SerialNumber groups) =
    Text.intercalate separator groups