module Data.GenValidity.Tree where

import           Data.GenValidity

import           Test.QuickCheck

import           Data.Tree

instance GenValidity a => GenValidity (Tree a) where
    genUnchecked = genTreeOf genUnchecked

    genValid     = genTreeOf genValid

    -- | There should be at least one invalid element, either it's here or it's
    -- further down the tree.
    genInvalid   = sized $ \n -> do
        size   <- upTo n
        (a, b) <- genSplit size
        oneof
            [ Node <$> resize a genInvalid   <*> resize b genUnchecked
            , Node <$> resize a genUnchecked <*> resize b genInvalid
            ]

-- | Generate a tree of values that are generated as specified.
--
-- This takes the size parameter much better into account
genTreeOf :: Gen a -> Gen (Tree a)
genTreeOf func = sized $ \n -> do
    size   <- upTo n
    (a, b) <- genSplit size
    value  <- resize a func
    forest <- resize b $ genListOf $ genTreeOf func
    return $ Node value forest