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+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE RecordWildCards #-}
+--------------------------------------------------------------------------------
+module Xanthous.Data.Entities
+  ( -- * Collisions
+    Collision(..)
+  , _Stop
+  , _Combat
+    -- * Entity Attributes
+  , EntityAttributes(..)
+  , blocksVision
+  , blocksObject
+  , collision
+  , defaultEntityAttributes
+  ) where
+--------------------------------------------------------------------------------
+import           Xanthous.Prelude
+--------------------------------------------------------------------------------
+import           Data.Aeson (ToJSON(..), FromJSON(..), (.:?), (.!=), withObject)
+import           Data.Aeson.Generic.DerivingVia
+import           Xanthous.Util.QuickCheck (GenericArbitrary(..))
+import           Test.QuickCheck
+--------------------------------------------------------------------------------
+
+data Collision
+  = Stop   -- ^ Can't move through this
+  | Combat -- ^ Moving into this equates to hitting it with a stick
+  deriving stock (Show, Eq, Ord, Generic)
+  deriving anyclass (NFData, CoArbitrary, Function)
+  deriving Arbitrary via GenericArbitrary Collision
+  deriving (ToJSON, FromJSON)
+       via WithOptions '[ AllNullaryToStringTag 'True ]
+           Collision
+makePrisms ''Collision
+
+-- | Attributes of an entity
+data EntityAttributes = EntityAttributes
+  { _blocksVision :: Bool
+    -- | Does this entity block a large object from being put in the same tile as
+    -- it - eg a a door being closed on it
+  , _blocksObject :: Bool
+    -- | What type of collision happens when moving into this entity?
+  , _collision :: Collision
+  }
+  deriving stock (Show, Eq, Ord, Generic)
+  deriving anyclass (NFData, CoArbitrary, Function)
+  deriving Arbitrary via GenericArbitrary EntityAttributes
+  deriving (ToJSON)
+       via WithOptions '[ FieldLabelModifier '[Drop 1] ]
+           EntityAttributes
+makeLenses ''EntityAttributes
+
+instance FromJSON EntityAttributes where
+  parseJSON = withObject "EntityAttributes" $ \o -> do
+    _blocksVision <- o .:? "blocksVision"
+                      .!= _blocksVision defaultEntityAttributes
+    _blocksObject <- o .:? "blocksObject"
+                      .!= _blocksObject defaultEntityAttributes
+    _collision    <- o .:? "collision"
+                      .!= _collision defaultEntityAttributes
+    pure EntityAttributes {..}
+
+defaultEntityAttributes :: EntityAttributes
+defaultEntityAttributes = EntityAttributes
+  { _blocksVision = False
+  , _blocksObject = False
+  , _collision    = Stop
+  }