{-# LANGUAGE InstanceSigs #-}
{-# LANGUAGE DerivingStrategies #-}
module Arbitrary.InvalidBrainfuckProgram (InvalidBrainfuckProgram(..)) where

import Data.Text (Text)
import Test.QuickCheck.Gen (Gen)
import Test.QuickCheck.Arbitrary (Arbitrary (arbitrary))

import qualified Data.Text as Text
import qualified Test.QuickCheck.Gen as Gen
import qualified Arbitrary.ValidBrainfuckProgram as ValidBrainfuckProgram

newtype InvalidBrainfuckProgram = InvalidBrainfuckProgram { get :: Text }
  deriving stock Show

instance Arbitrary InvalidBrainfuckProgram where
  arbitrary :: Gen InvalidBrainfuckProgram
  arbitrary = do
    validProgram <- ValidBrainfuckProgram.get <$> arbitrary

    index <- Gen.choose (0, Text.length validProgram)
    badBrace <- Gen.oneof $ map pure "[]"
    let (prefix, suffix) = Text.splitAt index validProgram
    
    pure . InvalidBrainfuckProgram $ Text.concat [prefix, Text.singleton badBrace, suffix]