Types.hs

{-# LANGUAGE CPP, DeriveDataTypeable, GADTs, StandaloneDeriving #-}
module Facebook.Types
    ( Credentials(..)
    , appIdBS
    , appSecretBS
    , AccessToken(..)
    , UserAccessToken
    , AppAccessToken
    , AccessTokenData
    , Id(..)
    , UserId
    , accessTokenData
    , accessTokenExpires
    , accessTokenUserId
    , UserKind
    , AppKind
    , Argument
    , (<>)
    , FbUTCTime(..)
    ) where

import Control.Applicative ((<$>), (<*>), pure)
import Control.Monad (mzero)
import Data.ByteString (ByteString)
import Data.Int (Int64)
import Data.Monoid (Monoid, mappend)
import Data.String (IsString)
import Data.Text (Text)
import Data.Time (UTCTime, parseTime)
import Data.Time.Clock.POSIX (posixSecondsToUTCTime)
import Data.Typeable (Typeable, Typeable1)
#if MIN_VERSION_time(1,5,0)
import Data.Time (defaultTimeLocale)
#else
import System.Locale (defaultTimeLocale)
#endif

import qualified Data.Aeson as A
import qualified Data.Aeson.Types as A
import qualified Data.Text as T
import qualified Data.Text.Encoding as TE
import qualified Data.Text.Lazy as TL
import qualified Data.Text.Lazy.Builder as TLB
import qualified Data.Text.Lazy.Builder.Int as TLBI


-- | Credentials that you get for your app when you register on
-- Facebook.
data Credentials =
    Credentials { appName   :: Text -- ^ Your application name (e.g. for Open Graph calls).
                , appId     :: Text -- ^ Your application ID.
                , appSecret :: Text -- ^ Your application secret key.
                }
    deriving (Eq, Ord, Show, Read, Typeable)

-- | 'appId' for 'ByteString'.
appIdBS :: Credentials -> ByteString
appIdBS = TE.encodeUtf8 . appId

-- | 'appSecret' for 'ByteString'.
appSecretBS :: Credentials -> ByteString
appSecretBS = TE.encodeUtf8 . appSecret


-- | An access token.  While you can make some API calls without
-- an access token, many require an access token and some will
-- give you more information with an appropriate access token.
--
-- There are two kinds of access tokens:
--
-- [User access token] An access token obtained after an user
-- accepts your application.  Let's you access more information
-- about that user and act on their behalf (depending on which
-- permissions you've asked for).
--
-- [App access token] An access token that allows you to take
-- administrative actions for your application.
--
-- These two kinds of access tokens are distinguished by the
-- phantom type on 'AccessToken', which can be 'UserKind' or
-- 'AppKind'.
data AccessToken kind where
    UserAccessToken :: UserId -> AccessTokenData -> UTCTime -> AccessToken UserKind
    AppAccessToken  :: AccessTokenData -> AccessToken AppKind

-- | Type synonym for @'AccessToken' 'UserKind'@.
type UserAccessToken = AccessToken UserKind

-- | Type synonym for @'AccessToken' 'AppKind'@.
type AppAccessToken = AccessToken AppKind


deriving instance Eq   (AccessToken kind)
deriving instance Ord  (AccessToken kind)
deriving instance Show (AccessToken kind)
deriving instance Typeable1 AccessToken


-- | The access token data that is passed to Facebook's API
-- calls.
type AccessTokenData = Text

-- | The identification code of an object.
newtype Id = Id { idCode :: Text }
    deriving (Eq, Ord, Show, Read, Typeable, IsString)

instance A.FromJSON Id where
    parseJSON (A.Object v) = v A..: "id"
    parseJSON (A.String s) = pure $ Id s
    parseJSON (A.Number d) = pure $ Id $ from $ floor d
      where from i = TL.toStrict $ TLB.toLazyText $ TLBI.decimal (i :: Int64)
    parseJSON o = fail $ "Can't parse Facebook.Id from " ++ show o

instance A.ToJSON Id where
    toJSON (Id t) = A.String t


-- | A Facebook user ID such as @1008905713901@.
type UserId = Id


-- | Get the access token data.
accessTokenData :: AccessToken anyKind -> AccessTokenData
accessTokenData (UserAccessToken _ d _) = d
accessTokenData (AppAccessToken d)      = d

-- | Expire time of an access token.  It may never expire, in
-- which case it will be @Nothing@.
accessTokenExpires :: AccessToken anyKind -> Maybe UTCTime
accessTokenExpires (UserAccessToken _ _ expt) = Just expt
accessTokenExpires (AppAccessToken _)         = Nothing

-- | Get the user ID of an user access token.
accessTokenUserId :: UserAccessToken -> UserId
accessTokenUserId (UserAccessToken uid _ _) = uid

-- | Phantom type used mark an 'AccessToken' as an user access
-- token.
data UserKind deriving (Typeable)

-- | Phantom type used mark an 'AccessToken' as an app access
-- token.
data AppKind deriving (Typeable)


-- | An argument given to an API call.
type Argument = (ByteString, ByteString)


-- | Synonym for 'mappend'.
(<>) :: Monoid a => a -> a -> a
(<>) = mappend


----------------------------------------------------------------------


-- | /Since 0.14.9./ Not a Facebook JSON format, but a custom @fb@
-- format for convenience if you need to serialize access tokens.
instance A.ToJSON (AccessToken kind) where
  toJSON (UserAccessToken uid data_ expires) =
    A.object
      [ "kind"    A..= ("user" :: Text)
      , "id"      A..= uid
      , "token"   A..= data_
      , "expires" A..= expires ]
  toJSON (AppAccessToken data_) =
    A.object
      [ "kind"    A..= ("app" :: Text)
      , "token"   A..= data_ ]


-- | (Internal) Since the user of 'parseJSON' is going to choose
-- via its @kind@ whether a 'UserAccessToken' or an
-- 'AppAccessToken' is wanted, we need this type class to
-- implement 'FromJSON'.
class ParseAccessToken kind where
  parseTokenJSON :: A.Object -> A.Parser (AccessToken kind)

instance ParseAccessToken UserKind where
  parseTokenJSON v =
    checkKind v "user" $
      UserAccessToken <$> v A..: "id"
                      <*> v A..: "token"
                      <*> v A..: "expires"

instance ParseAccessToken AppKind where
  parseTokenJSON v =
    checkKind v "app" $
      AppAccessToken <$> v A..: "token"

-- | (Internal) Used to implement 'parseTokenJSON'.
checkKind :: A.Object -> Text -> A.Parser a -> A.Parser a
checkKind v kind ok = do
  kind' <- v A..: "kind"
  if kind == kind'
    then ok
    else fail $ "Expected access token kind " <> show kind <>
                " but found " <> show kind' <> "."

-- | /Since 0.14.9./ Parses the format that 'ToJSON' produces.
-- Note that you need to statically decide whether you want to
-- parse a user access token or an app access token.
instance ParseAccessToken kind => A.FromJSON (AccessToken kind) where
  parseJSON (A.Object v) = parseTokenJSON v
  parseJSON _            = mzero


----------------------------------------------------------------------


-- | @newtype@ for 'UTCTime' that follows Facebook's
-- conventions of JSON parsing.
--
--  * As a string, while @aeson@ expects a format of @%FT%T%Q@,
--    Facebook gives time values formatted as @%FT%T%z@.
--
--  * As a number, 'FbUTCTime' accepts a number of seconds since
--    the Unix epoch.
newtype FbUTCTime = FbUTCTime { unFbUTCTime :: UTCTime }
  deriving (Eq, Ord, Show, Read, Typeable)

instance A.FromJSON FbUTCTime where
  parseJSON (A.String t) =
    case parseTime defaultTimeLocale "%FT%T%z" (T.unpack t) of
      Just d -> return (FbUTCTime d)
      _      -> fail $ "could not parse FbUTCTime string " ++ show t
  parseJSON (A.Number n) =
    return $ FbUTCTime $ posixSecondsToUTCTime $ fromInteger $ floor n
  parseJSON _ = fail "could not parse FbUTCTime from something which is not a string or number"