#3 Restrict player going places

lib/RPGEngine/Input/Player.hs

@@ -1,19 +1,44 @@
-module RPGEngine.Input.Player 
-( movePlayer
+module RPGEngine.Input.Player
+( spawnPlayer
+, movePlayer
 ) where
 
-import RPGEngine.Data (Game(..), Direction(..), Player(..), X, Y)
+import RPGEngine.Data (Game(..), Direction(..), Player(..), X, Y, Physical (..), Level(..))
+import RPGEngine.Input.Level (whatIsAt, findFirst)
+import Data.Maybe (fromJust, isNothing)
+
+----------------------------- Constants ------------------------------
 
-movePlayer :: Direction -> Game -> Game
-movePlayer dir g@Game{ player = p@Player{ coord = (x, y) }} = newGame
-    where newGame   = g{ player = newPlayer }
-          newPlayer = p{ coord  = newCoord  }
-          newCoord  = (x + xD, y + yD)
-          (xD, yD)  = diffs dir
 
 diffs :: Direction -> (X, Y)
-diffs North  = (0, 1)
-diffs East   = (1, 0)
-diffs South  = (0, -1)
-diffs West   = (-1, 0)
-diffs Center = (0, 0)
+diffs North  = ( 0,  1)
+diffs East   = ( 1,  0)
+diffs South  = ( 0, -1)
+diffs West   = (-1,  0)
+diffs Center = ( 0,  0)
+
+----------------------------------------------------------------------
+
+-- Set the initial position of the player in a given level.
+spawnPlayer :: Level -> Player -> Player
+spawnPlayer l@Level{ layout = lay } p@Player{ position = prevPos } = p{ position = newPos }
+    where try    = findFirst l Entrance
+          newPos | isNothing try = prevPos
+                 | otherwise     = fromJust try
+
+-- Move a player in a direction if possible.
+movePlayer :: Direction -> Game -> Game
+movePlayer dir g@Game{ player = p@Player{ position = (x, y) }} = newGame
+    where newGame   = g{ player   = newPlayer }
+          newPlayer = p{ position = newCoord  }
+          newCoord  | isLegalMove dir g = (x + xD, y + yD)
+                    | otherwise         = (x, y)
+          (xD, yD)  = diffs dir
+
+-- Check if a move is legal by checking what is located at the new position.
+isLegalMove :: Direction -> Game -> Bool
+isLegalMove dir g@Game{ playing = lvl, player = p@Player{ position = (x, y) }} = legality
+    where legality = physical `elem` [Walkable, Entrance, Exit]
+          physical = whatIsAt newPos lvl
+          newPos   = (x + xD, y + yD)
+          (xD, yD) = diffs dir