{-# LANGUAGE MultiWayIf #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE RecordWildCards #-}
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module Xanthous.Game
  ( GameState(..)
  , entities
  , messageHistory
  , randomGen

  , getInitialState

  , positionedCharacter
  , character
  , characterPosition

  , MessageHistory(..)
  , pushMessage
  , popMessage
  , hideMessage

    -- * collisions
  , Collision(..)
  , collisionAt
  ) where
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import           Xanthous.Prelude
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import           Data.List.NonEmpty ( NonEmpty((:|)))
import qualified Data.List.NonEmpty as NonEmpty
import           System.Random
import           Test.QuickCheck
import           Test.QuickCheck.Arbitrary.Generic
import           Control.Monad.State.Class
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import           Xanthous.Data.EntityMap (EntityMap, EntityID)
import qualified Xanthous.Data.EntityMap as EntityMap
import           Xanthous.Data (Positioned, Position(..), positioned, position)
import           Xanthous.Entities (SomeEntity(..), downcastEntity, entityIs)
import           Xanthous.Entities.Character
import           Xanthous.Entities.Creature
import           Xanthous.Entities.Arbitrary ()
import           Xanthous.Orphans ()
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data MessageHistory
  = NoMessageHistory
  | MessageHistory (NonEmpty Text) Bool
  deriving stock (Show, Eq, Generic)
  deriving anyclass (NFData, CoArbitrary, Function)

instance Arbitrary MessageHistory where
  arbitrary = genericArbitrary

pushMessage :: Text -> MessageHistory -> MessageHistory
pushMessage msg NoMessageHistory = MessageHistory (msg :| []) True
pushMessage msg (MessageHistory msgs _) = MessageHistory (NonEmpty.cons msg msgs) True

popMessage :: MessageHistory -> MessageHistory
popMessage NoMessageHistory = NoMessageHistory
popMessage (MessageHistory msgs False) = MessageHistory msgs True
popMessage (MessageHistory msgs@(_ :| []) _) = MessageHistory msgs True
popMessage (MessageHistory (_ :| (msg : msgs)) True) = MessageHistory (msg :| msgs) True

hideMessage :: MessageHistory -> MessageHistory
hideMessage NoMessageHistory = NoMessageHistory
hideMessage (MessageHistory msgs _) = MessageHistory msgs False

data GameState = GameState
  { _entities          :: EntityMap SomeEntity
  , _characterEntityID :: EntityID
  , _messageHistory    :: MessageHistory
  , _randomGen         :: StdGen
  }
  deriving stock (Show)
makeLenses ''GameState

instance Eq GameState where
  (GameState es₁ ceid₁ mh₁ _) == (GameState es₂ ceid₂ mh₂ _)
    = es₁ == es₂
    && ceid₁ == ceid₂
    && mh₁ == mh₂

instance Arbitrary GameState where
  arbitrary = do
    char <- arbitrary @Character
    charPos <- arbitrary
    _messageHistory <- arbitrary
    (_characterEntityID, _entities) <- arbitrary <&>
      EntityMap.insertAtReturningID charPos (SomeEntity char)
    _randomGen <- mkStdGen <$> arbitrary
    pure $ GameState {..}

getInitialState :: IO GameState
getInitialState = do
  _randomGen <- getStdGen
  let char = mkCharacter
      (_characterEntityID, _entities)
        = EntityMap.insertAtReturningID
          (Position 0 0)
          (SomeEntity char)
          mempty
      _messageHistory = NoMessageHistory
  pure GameState {..}

positionedCharacter :: Lens' GameState (Positioned Character)
positionedCharacter = lens getPositionedCharacter setPositionedCharacter
  where
    setPositionedCharacter :: GameState -> Positioned Character -> GameState
    setPositionedCharacter game char
      = game
      &  entities . at (game ^. characterEntityID)
      ?~ fmap SomeEntity char

    getPositionedCharacter :: GameState -> Positioned Character
    getPositionedCharacter game
      = over positioned
        ( fromMaybe (error "Invariant error: Character was not a character!")
        . downcastEntity
        )
      . fromMaybe (error "Invariant error: Character not found!")
      $ EntityMap.lookupWithPosition
        (game ^. characterEntityID)
        (game ^. entities)


character :: Lens' GameState Character
character = positionedCharacter . positioned

characterPosition :: Lens' GameState Position
characterPosition = positionedCharacter . position

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data Collision
  = Stop
  | Combat
  deriving stock (Show, Eq, Ord, Generic)
  deriving anyclass (NFData)

collisionAt :: MonadState GameState m => Position -> m (Maybe Collision)
collisionAt pos = do
  ents <- use $ entities . EntityMap.atPosition pos
  pure $
    if | null ents -> Nothing
       | any (entityIs @Creature) ents -> pure Combat
       | otherwise -> pure Stop