servant/servant-examples/tutorial/T3.hs

{-# LANGUAGE DataKinds     #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE TypeFamilies  #-}
{-# LANGUAGE TypeOperators #-}
module T3 where

import           Control.Monad.Trans.Except
import           Data.Aeson
import           Data.List
import           GHC.Generics
import           Network.Wai
import           Servant

data Position = Position
  { x :: Int
  , y :: Int
  } deriving (Show, Generic)

instance FromJSON Position
instance ToJSON Position

newtype HelloMessage = HelloMessage { msg :: String }
  deriving (Show, Generic)

instance FromJSON HelloMessage
instance ToJSON HelloMessage

data ClientInfo = ClientInfo
  { name          :: String
  , email         :: String
  , age           :: Int
  , interested_in :: [String]
  } deriving (Show, Generic)

instance FromJSON ClientInfo
instance ToJSON ClientInfo

data Email = Email
  { from    :: String
  , to      :: String
  , subject :: String
  , body    :: String
  } deriving (Show, Generic)

instance FromJSON Email
instance ToJSON Email

emailForClient :: ClientInfo -> Email
emailForClient c = Email from' to' subject' body'

  where from'    = "great@company.com"
        to'      = email c
        subject' = "Hey " ++ name c ++ ", we miss you!"
        body'    = "Hi " ++ name c ++ ",\n\n"
                ++ "Since you've recently turned " ++ show (age c)
                ++ ", have you checked out our latest "
                ++ intercalate ", " (interested_in c)
                ++ " products? Give us a visit!"

type API = "position" :> Capture "x" Int :> Capture "y" Int :> Get '[JSON] Position
      :<|> "hello" :> QueryParam "name" String :> Get '[JSON] HelloMessage
      :<|> "marketing" :> ReqBody '[JSON] ClientInfo :> Post '[JSON] Email

api :: Proxy API
api = Proxy

server :: Server API
server = position
    :<|> hello
    :<|> marketing

  where position :: Int -> Int -> ExceptT ServantErr IO Position
        position x y = return (Position x y)

        hello :: Maybe String -> ExceptT ServantErr IO HelloMessage
        hello mname = return . HelloMessage $ case mname of
          Nothing -> "Hello, anonymous coward"
          Just n  -> "Hello, " ++ n

        marketing :: ClientInfo -> ExceptT ServantErr IO Email
        marketing clientinfo = return (emailForClient clientinfo)

app :: Application
app = serve api server