module Main where

import Data.Aeson (FromJSON, parseJSON, withObject, withText, (.:), decode)

data Program = Program { programFns :: [Function] }
    deriving (Show)

data Function = Function {
        functionName :: String,
        returnType :: Maybe Type,
        functionArgs :: [FunctionArg]
    } deriving (Show)

data Type = Int | Bool
    deriving (Show)

data FunctionArg = FunctionArg {
        argName :: String,
        argType :: Type
    } deriving (Show)

instance FromJSON Program  where
    parseJSON = withObject "Program" $ \v -> Program
        <$> v .: "functions"

instance FromJSON Function where
    parseJSON = withObject "Function" $ \v -> Function
        <$> v .: "name"
        <*> v .: "type"
        <*> v .: "args"

instance FromJSON FunctionArg where
    parseJSON = withObject "FunctionArg" $ \v -> FunctionArg
        <$> v .: "name"
        <*> v .: "type"

instance FromJSON Type where
    parseJSON = withText "Type" $ \v ->
        case v of
             "int" -> return Int
             "bool" -> return Bool
             _ -> fail "wrong type"

main :: IO ()
main = do
    putStrLn $ show (decode "int" :: Maybe Type)