-- The following warning is disabled due to a necessary instance of SatResult
-- defined in this module.
{-# OPTIONS_GHC -fno-warn-orphans #-}
-- | Test copilot-theorem:Copilot.Theorem.What4.
module Test.Copilot.Theorem.What4 where

-- External imports
import Data.Int                             (Int8)
import Test.Framework                       (Test, testGroup)
import Test.Framework.Providers.QuickCheck2 (testProperty)
import Test.QuickCheck                      (Property, arbitrary, forAll)
import Test.QuickCheck.Monadic              (monadicIO, run)

-- External imports: Copilot
import           Copilot.Core.Expr      (Expr (Const, Op2))
import           Copilot.Core.Operators (Op2 (..))
import           Copilot.Core.Spec      (Spec (..))
import qualified Copilot.Core.Spec      as Copilot
import           Copilot.Core.Type      (Typed (typeOf))

-- Internal imports: Modules being tested
import Copilot.Theorem.What4 (SatResult (..), Solver (..), prove)

-- * Constants

-- | Unit tests for copilot-theorem:Copilot.Theorem.What4.
tests :: Test.Framework.Test
tests =
  testGroup "Copilot.Theorem.What4"
    [ testProperty "Prove via Z3 that true is valid"    testProveZ3True
    , testProperty "Prove via Z3 that false is invalid" testProveZ3False
    , testProperty "Prove via Z3 that x == x is valid"  testProveZ3EqConst
    ]

-- * Individual tests

-- | Test that Z3 is able to prove the following expression valid:
-- @
--   constant True
-- @
testProveZ3True :: Property
testProveZ3True =
    monadicIO $ run $ checkResult Z3 propName spec Valid
  where
    propName :: String
    propName = "prop"

    spec :: Spec
    spec = propSpec propName $ Const typeOf True

-- | Test that Z3 is able to prove the following expression invalid:
-- @
--   constant False
-- @
testProveZ3False :: Property
testProveZ3False =
    monadicIO $ run $ checkResult Z3 propName spec Invalid
  where
    propName :: String
    propName = "prop"

    spec :: Spec
    spec = propSpec propName $ Const typeOf False

-- | Test that Z3 is able to prove the following expresion valid:
-- @
--   for all (x :: Int8), constant x == constant x
-- @
testProveZ3EqConst :: Property
testProveZ3EqConst = forAll arbitrary $ \x ->
    monadicIO $ run $ checkResult Z3 propName (spec x) Valid
  where
    propName :: String
    propName = "prop"

    spec :: Int8 -> Spec
    spec x = propSpec propName $
      Op2 (Eq typeOf) (Const typeOf x) (Const typeOf x)

-- | Check that the solver's satisfiability result for the given property in
-- the given spec matches the expectation.
checkResult :: Solver -> String -> Spec -> SatResult -> IO Bool
checkResult solver propName spec expectation = do
  results <- prove solver spec

  -- Find the satisfiability result for propName.
  let propResult = lookup propName results

  -- The following check also works for the case in which the property name
  -- does not exist in the results, in which case the lookup returns 'Nothing'.
  return $ propResult == Just expectation

-- * Auxiliary

-- | Build a 'Spec' that contains one property with the given name and defined
-- by the given boolean expression.
propSpec :: String -> Expr Bool -> Spec
propSpec propName propExpr = Spec [] [] [] [Copilot.Property propName propExpr]

-- | Equality for 'SatResult'.
--
-- This is an orphan instance, so we suppress the warning that GHC would
-- normally produce with a GHC option at the top.
instance Eq SatResult where
  Valid   == Valid   = True
  Invalid == Invalid = True
  Unknown == Unknown = True
  _       == _       = False