refactor(users/glittershark): Rename to grfn

Rename my //users directory and all places that refer to glittershark to
grfn, including nix references and documentation.

This may require some extra attention inside of gerrit's database after
it lands to allow me to actually push things.

Change-Id: I4728b7ec2c60024392c1c1fa6e0d4a59b3e266fa
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2933
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: lukegb <lukegb@tvl.fyi>
Reviewed-by: glittershark <grfn@gws.fyi>

users/grfn/xanthous/src/Xanthous/AI/Gormlak.hs

@@ -0,0 +1,124 @@
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+{-# LANGUAGE UndecidableInstances #-}
+--------------------------------------------------------------------------------
+module Xanthous.AI.Gormlak
+  ( HasVisionRadius(..)
+  , GormlakBrain(..)
+  ) where
+--------------------------------------------------------------------------------
+import           Xanthous.Prelude hiding (lines)
+--------------------------------------------------------------------------------
+import           Control.Monad.State
+import           Control.Monad.Random
+import           Data.Aeson (object)
+import qualified Data.Aeson as A
+import           Data.Generics.Product.Fields
+--------------------------------------------------------------------------------
+import           Xanthous.Data
+                 ( Positioned(..), positioned, position
+                 , diffPositions, stepTowards, isUnit
+                 , Ticks, (|*|), invertedRate
+                 )
+import           Xanthous.Data.EntityMap
+import           Xanthous.Entities.Creature.Hippocampus
+import           Xanthous.Entities.Character (Character)
+import qualified Xanthous.Entities.Character as Character
+import qualified Xanthous.Entities.RawTypes as Raw
+import           Xanthous.Entities.RawTypes (CreatureType)
+import           Xanthous.Game.State
+import           Xanthous.Game.Lenses
+                 ( entitiesCollision, collisionAt
+                 , character, characterPosition
+                 )
+import           Xanthous.Data.EntityMap.Graphics (linesOfSight, canSee)
+import           Xanthous.Random
+import           Xanthous.Monad (say)
+--------------------------------------------------------------------------------
+
+--  TODO move the following two classes to a more central location
+
+class HasVisionRadius a where visionRadius :: a -> Word
+
+type IsCreature entity =
+  ( HasVisionRadius entity
+  , HasField "_hippocampus" entity entity Hippocampus Hippocampus
+  , HasField "_creatureType" entity entity CreatureType CreatureType
+  , A.ToJSON entity
+  )
+
+--------------------------------------------------------------------------------
+
+stepGormlak
+  :: forall entity m.
+    ( MonadState GameState m, MonadRandom m
+    , IsCreature entity
+    )
+  => Ticks
+  -> Positioned entity
+  -> m (Positioned entity)
+stepGormlak ticks pe@(Positioned pos creature) = do
+  dest <- maybe (selectDestination pos creature) pure
+         $ creature ^. field @"_hippocampus" . destination
+  let progress' =
+        dest ^. destinationProgress
+        + creature ^. field @"_creatureType" . Raw.speed . invertedRate |*| ticks
+  if progress' < 1
+    then pure
+         $ pe
+         & positioned . field @"_hippocampus" . destination
+         ?~ (dest & destinationProgress .~ progress')
+    else do
+      let newPos = dest ^. destinationPosition
+          remainingSpeed = progress' - 1
+      newDest <- selectDestination newPos creature
+                <&> destinationProgress +~ remainingSpeed
+      let pe' = pe & positioned . field @"_hippocampus" . destination ?~ newDest
+      collisionAt newPos >>= \case
+        Nothing -> pure $ pe' & position .~ newPos
+        Just Stop -> pure pe'
+        Just Combat -> do
+          ents <- use $ entities . atPosition newPos
+          when (any (entityIs @Character) ents) attackCharacter
+          pure pe'
+  where
+    selectDestination pos' creature' = destinationFromPos <$> do
+      canSeeCharacter <- uses entities $ canSee (entityIs @Character) pos' vision
+      if canSeeCharacter
+        then do
+          charPos <- use characterPosition
+          if isUnit (pos' `diffPositions` charPos)
+            then attackCharacter $> pos'
+            else pure $ pos' `stepTowards` charPos
+      else do
+        lines <- map (takeWhile (isNothing . entitiesCollision . map snd . snd)
+                    -- the first item on these lines is always the creature itself
+                    . fromMaybe mempty . tailMay)
+                . linesOfSight pos' (visionRadius creature')
+                <$> use entities
+        line <- choose $ weightedBy length lines
+        pure $ fromMaybe pos' $ fmap fst . headMay =<< line
+
+    vision = visionRadius creature
+    attackCharacter = do
+      say ["combat", "creatureAttack"] $ object [ "creature" A..= creature ]
+      character %= Character.damage 1
+
+newtype GormlakBrain entity = GormlakBrain { _unGormlakBrain :: entity }
+
+instance (IsCreature entity) => Brain (GormlakBrain entity) where
+  step ticks
+    = fmap (fmap GormlakBrain)
+    . stepGormlak ticks
+    . fmap _unGormlakBrain
+  entityCanMove = const True
+
+--------------------------------------------------------------------------------
+
+-- instance Brain Creature where
+--   step = brainVia GormlakBrain
+--   entityCanMove = const True
+
+-- instance Entity Creature where
+--   blocksVision _ = False
+--   description = view $ Creature.creatureType . Raw.description
+--   entityChar = view $ Creature.creatureType . char