module Data.Derive.Arbitrary(makeArbitrary) where
import "QuickCheck" Test.QuickCheck

example :: Custom

instance Arbitrary (Sample a) where
    arbitrary = do
        x <- choose (0::Int,length [First{},Second{},Third{}] - 1)
        case x of
            0 -> do return (First)
            1 -> do x1 <- arbitrary
                    x2 <- arbitrary
                    return (Second x1 x2)
            2 -> do x1 <- arbitrary
                    return (Third x1)
            _ -> error "FATAL ERROR: Arbitrary instance, logic bug"

test :: State
instance (CoArbitrary s, Arbitrary s, Arbitrary a) => Arbitrary (State s a) where
    arbitrary = do x1 <- arbitrary
                   return (StateT x1)

import Data.Derive.DSL.HSE
import qualified Language.Haskell as H
import Data.List
import Data.Generics.PlateData


import Data.Derive.DSL.DSL
import Data.Derive.Internal.Derivation

makeArbitrary :: Derivation
makeArbitrary = derivationCustomDSL "Arbitrary" custom $
    List [Instance [] "Arbitrary" (List [App "InsDecl" (List [App
    "PatBind" (List [App "PVar" (List [App "Ident" (List [String
    "arbitrary"])]),App "Nothing" (List []),App "UnGuardedRhs" (List [
    App "Do" (List [List [App "Generator" (List [App "PVar" (List [App
    "Ident" (List [String "x"])]),App "App" (List [App "Var" (List [
    App "UnQual" (List [App "Ident" (List [String "choose"])])]),App
    "Tuple" (List [List [App "ExpTypeSig" (List [App "Lit" (List [App
    "Int" (List [Int 0])]),App "TyCon" (List [App "UnQual" (List [App
    "Ident" (List [String "Int"])])])]),App "InfixApp" (List [App
    "App" (List [App "Var" (List [App "UnQual" (List [App "Ident" (
    List [String "length"])])]),App "List" (List [MapCtor (App
    "RecConstr" (List [App "UnQual" (List [App "Ident" (List [CtorName
    ])]),List []]))])]),App "QVarOp" (List [App "UnQual" (List [App
    "Symbol" (List [String "-"])])]),App "Lit" (List [App "Int" (List
    [Int 1])])])]])])]),App "Qualifier" (List [App "Case" (List [App
    "Var" (List [App "UnQual" (List [App "Ident" (List [String "x"])])
    ]),Concat (List [MapCtor (App "Alt" (List [App "PLit" (List [App
    "Int" (List [CtorIndex])]),App "UnGuardedAlt" (List [App "Do" (
    List [Concat (List [MapField (App "Generator" (List [App "PVar" (
    List [App "Ident" (List [Concat (List [String "x",ShowInt
    FieldIndex])])]),App "Var" (List [App "UnQual" (List [App "Ident"
    (List [String "arbitrary"])])])])),List [App "Qualifier" (List [
    App "App" (List [App "Var" (List [App "UnQual" (List [App "Ident"
    (List [String "return"])])]),App "Paren" (List [Application (
    Concat (List [List [App "Con" (List [App "UnQual" (List [App
    "Ident" (List [CtorName])])])],MapField (App "Var" (List [App
    "UnQual" (List [App "Ident" (List [Concat (List [String "x",
    ShowInt FieldIndex])])])]))]))])])])]])])]),App "BDecls" (List [
    List []])])),List [App "Alt" (List [App "PWildCard" (List []),App
    "UnGuardedAlt" (List [App "App" (List [App "Var" (List [App
    "UnQual" (List [App "Ident" (List [String "error"])])]),App "Lit"
    (List [App "String" (List [String
    "FATAL ERROR: Arbitrary instance, logic bug"])])])]),App "BDecls"
    (List [List []])])]])])])]])]),App "BDecls" (List [List []])])])])

custom = customContext context

-- Fix the context
-- C a b => Arbitrary a, Arbitrary b
-- a -> b => CoArbitrary a, Arbitrary b
context :: FullDataDecl -> Context
context (_,d) = nub $ concatMap (f True . fromBangType . snd) $ concatMap ctorDeclFields $ dataDeclCtors d
        f b (TyVar x) = [ClassA (qname $ b ? "Arbitrary" $ "CoArbitrary") [TyVar x]]
        f b (TyFun x y) = f (not b) x ++ f b y
        f b x = concatMap (f b) (children x)