{-# LANGUAGE DefaultSignatures #-}

-- | Parsing attributes
module Thermoprint.Printout.BBCode.Attribute
       ( Attribute(..)
       , lookupAttr
       ) where

import Data.Text (Text)
import qualified Data.Text as T (unpack)

import Data.Map (Map)
import qualified Data.Map as Map (lookup)

import Data.CaseInsensitive (CI)
import qualified Data.CaseInsensitive as CI
  
import Text.Read (readMaybe)
import Data.Maybe (fromMaybe)

-- | We build our own version of 'Read' so we can override the presentation used
--
-- We provide a default implementation for 'Read a => Attribute a'
class Attribute a where
  attrRead :: Text -> Maybe a
  default attrRead :: Read a => Text -> Maybe a
  attrRead = readMaybe . T.unpack

instance Attribute Integer

lookupAttr :: Attribute a => CI Text -> a -> Map (CI Text) Text -> a
-- ^ Extract an attribute by name 
lookupAttr t def attrs = fromMaybe def $ Map.lookup t attrs >>= attrRead