Parsing JSON players file with Aeson

hs-pathfinder.cabal

@@ -28,7 +28,8 @@ library
   -- other-modules:
   -- other-extensions:
   build-depends:
-    base
+    base,
+    aeson >= 0.6.1.0
 
   hs-source-dirs:
     src

src/Main.hs

@@ -1,46 +1,49 @@
 module Main where
 
+import Paizo.Core.Types (Player)
+import Paizo.Plugin.FileLoader (getPlayers)
+
 import Control.Monad (when)
 import Control.Monad.State
 import System.IO (stdin, stdout, hSetEcho, hSetBuffering, BufferMode(..))
 
-data AppConfig = AppConfig
-    { crRound :: Int
-    } deriving (Show)
+data AppConfig =
+    AppConfig { players :: [Player]
+              , crRound :: Int
+              } deriving (Show)
 
 type App = StateT AppConfig IO
 
-loadEngine :: App ()
-loadEngine = liftIO $ do
-  hSetEcho stdin False
-  hSetBuffering stdin NoBuffering
-  hSetBuffering stdout NoBuffering
+initGUI :: App ()
+initGUI = liftIO $ do
+    hSetEcho stdin False
+    hSetBuffering stdin NoBuffering
+    hSetBuffering stdout NoBuffering
 
 printT :: (MonadIO m) => String -> m ()
 printT s = liftIO . putStrLn $ s
 
 loadGame :: App ()
-loadGame = printT "Loading game"
+loadGame = do
+    printT "Loading game"
+    players <- liftIO getPlayers
+    put AppConfig { players = players, crRound = 0 }
 
 gameLoop :: App ()
 gameLoop = do
     printT "Play round"
     config <- get
-    put $ AppConfig { crRound = crRound config + 1 }
+    put $ AppConfig { players = players config, crRound = crRound config + 1 }
     char <- liftIO getChar
     when (char == 'c') gameLoop
 
 main2 :: App ()
-main2 = do
-    loadEngine
-    loadGame
-    gameLoop
+main2 = initGUI >> loadGame >> gameLoop
 
-main :: IO ()
-main = do
-  putStrLn "hello world"
+--main :: IO ()
+main = runApp main2
 
 runApp :: App a -> IO (a, AppConfig)
 runApp k =
-  let config = AppConfig 0
+  let config = AppConfig [] 0
   in runStateT k config

src/Paizo/Core/Types.hs

@@ -1,9 +1,19 @@
+{-# LANGUAGE DeriveGeneric #-}
+
 module Paizo.Core.Types (
   -- * Player
   Player(..)
   ) where
 
+import Data.Aeson
+import GHC.Generics
+
 data Player = Player {
       hitPoints :: Int
     , consScore :: Int
-    } deriving (Show)
+    } deriving (Show, Generic)
+
+-- Instances to convert our type to/from JSON.
+
+instance FromJSON Player
+instance ToJSON Player

src/Paizo/Plugin/FileLoader.hs

@@ -0,0 +1,26 @@
+module Paizo.Plugin.FileLoader (
+  -- * Functions
+  getPlayers
+  ) where
+
+import Paizo.Core.Types (Player)
+
+import Control.Monad.IO.Class (liftIO)
+import Data.Aeson (eitherDecode)
+import qualified Data.ByteString.Lazy as B
+
+-- | Location of the players file
+jsonFile :: FilePath
+jsonFile = "players.json"
+
+-- | Read the local copy of the JSON file.
+getJSON :: IO B.ByteString
+getJSON = B.readFile jsonFile
+
+-- | Returns the list of players from JSON file
+getPlayers :: IO [Player]
+getPlayers = do
+    d <- (eitherDecode <$> getJSON) :: IO (Either String [Player])
+    case d of
+        Left err -> return []
+        Right players -> return players

src/players.json

@@ -0,0 +1,4 @@
+[
+  { "hitPoints": 20, "consScore": 5 },
+  { "hitPoints": 15, "consScore": 7 }
+]