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

  , getInitialState

  , positionedCharacter
  , character
  , characterPosition
  , updateCharacterVision

  , 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.Util (appendVia)
import           Xanthous.Data.EntityMap (EntityMap, EntityID)
import qualified Xanthous.Data.EntityMap as EntityMap
import           Xanthous.Data.EntityMap.Graphics
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
    -- | A subset of the overall set of entities
  , _revealedEntities  :: EntityMap SomeEntity
  , _characterEntityID :: EntityID
  , _messageHistory    :: MessageHistory
  , _randomGen         :: StdGen
  }
  deriving stock (Show)
makeLenses ''GameState

instance Eq GameState where
  (==) = (==) `on` \gs ->
    ( gs ^. entities
    , gs ^. revealedEntities
    , gs ^. characterEntityID
    , gs ^. messageHistory
    )

instance Arbitrary GameState where
  arbitrary = do
    char <- arbitrary @Character
    charPos <- arbitrary
    _messageHistory <- arbitrary
    (_characterEntityID, _entities) <- arbitrary <&>
      EntityMap.insertAtReturningID charPos (SomeEntity char)
    revealedPositions <- sublistOf $ EntityMap.positions _entities
    let _revealedEntities = mempty &~ do
          for_ revealedPositions $ \pos -> do
            let ents = _entities ^. EntityMap.atPosition pos
            EntityMap.atPosition pos <>= ents
    _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
      _revealedEntities = _entities
  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

visionRadius :: Word
visionRadius = 12 -- TODO make this dynamic

-- | Update the revealed entities at the character's position based on their vision
updateCharacterVision :: GameState -> GameState
updateCharacterVision game =
  let charPos = game ^. characterPosition
      visible = visibleEntities charPos visionRadius $ game ^. entities
  in game & revealedEntities %~ appendVia EntityMap.Deduplicate visible


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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