    -- |
    -- Support for source code annotation feature of GHC. That is the ANN pragma.
    --
    -- (c) The University of Glasgow 2006
    -- (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
    --
    module Annotations (
            -- * Main Annotation data types
            Annotation(..), AnnPayload,
            AnnTarget(..), CoreAnnTarget,
            getAnnTargetName_maybe,

            -- * AnnEnv for collecting and querying Annotations
            AnnEnv,
            mkAnnEnv, extendAnnEnvList, plusAnnEnv, emptyAnnEnv, findAnns,
            deserializeAnns
        ) where

    import Binary
    import Module           ( Module )
    import Name
    import Outputable
    import Serialized
    import UniqFM
    import Unique

    import Control.Monad
    import Data.Maybe
    import Data.Typeable
    import Data.Word        ( Word8 )

    -- | Represents an annotation after it has been sufficiently desugared from
    -- it's initial form of 'HsDecls.AnnDecl'
    data Annotation = Annotation {
            ann_target :: CoreAnnTarget,    -- ^ The target of the annotation
            ann_value  :: AnnPayload
        }

    type AnnPayload = Serialized    -- ^ The "payload" of an annotation
                                    --   allows recovery of its value at a given type,
                                    --   and can be persisted to an interface file

    -- | An annotation target
    data AnnTarget name
      = NamedTarget name          -- ^ We are annotating something with a name:
                                  --      a type or identifier
      | ModuleTarget Module       -- ^ We are annotating a particular module

    -- | The kind of annotation target found in the middle end of the compiler
    type CoreAnnTarget = AnnTarget Name

    instance Functor AnnTarget where
        fmap f (NamedTarget nm) = NamedTarget (f nm)
        fmap _ (ModuleTarget mod) = ModuleTarget mod

    -- | Get the 'name' of an annotation target if it exists.
    getAnnTargetName_maybe :: AnnTarget name -> Maybe name
    getAnnTargetName_maybe (NamedTarget nm) = Just nm
    getAnnTargetName_maybe _                = Nothing

    instance Uniquable name => Uniquable (AnnTarget name) where
        getUnique (NamedTarget nm) = getUnique nm
        getUnique (ModuleTarget mod) = deriveUnique (getUnique mod) 0
        -- deriveUnique prevents OccName uniques clashing with NamedTarget

    instance Outputable name => Outputable (AnnTarget name) where
        ppr (NamedTarget nm) = text "Named target" <+> ppr nm
        ppr (ModuleTarget mod) = text "Module target" <+> ppr mod

    instance Binary name => Binary (AnnTarget name) where
        put_ bh (NamedTarget a) = do
            putByte bh 0
            put_ bh a
        put_ bh (ModuleTarget a) = do
            putByte bh 1
            put_ bh a
        get bh = do
            h <- getByte bh
            case h of
                0 -> liftM NamedTarget  $ get bh
                _ -> liftM ModuleTarget $ get bh

    instance Outputable Annotation where
        ppr ann = ppr (ann_target ann)

    -- | A collection of annotations
    -- Can't use a type synonym or we hit bug #2412 due to source import
    newtype AnnEnv = MkAnnEnv (UniqFM [AnnPayload])

    -- | An empty annotation environment.
    emptyAnnEnv :: AnnEnv
    emptyAnnEnv = MkAnnEnv emptyUFM

    -- | Construct a new annotation environment that contains the list of
    -- annotations provided.
    mkAnnEnv :: [Annotation] -> AnnEnv
    mkAnnEnv = extendAnnEnvList emptyAnnEnv

    -- | Add the given annotation to the environment.
    extendAnnEnvList :: AnnEnv -> [Annotation] -> AnnEnv
    extendAnnEnvList (MkAnnEnv env) anns
      = MkAnnEnv $ addListToUFM_C (++) env $
        map (\ann -> (getUnique (ann_target ann), [ann_value ann])) anns

    -- | Union two annotation environments.
    plusAnnEnv :: AnnEnv -> AnnEnv -> AnnEnv
    plusAnnEnv (MkAnnEnv env1) (MkAnnEnv env2) = MkAnnEnv $ plusUFM_C (++) env1 env2

    -- | Find the annotations attached to the given target as 'Typeable'
    --   values of your choice. If no deserializer is specified,
    --   only transient annotations will be returned.
    findAnns :: Typeable a => ([Word8] -> a) -> AnnEnv -> CoreAnnTarget -> [a]
    findAnns deserialize (MkAnnEnv ann_env)
      = (mapMaybe (fromSerialized deserialize))
        . (lookupWithDefaultUFM ann_env [])

    -- | Deserialize all annotations of a given type. This happens lazily, that is
    --   no deserialization will take place until the [a] is actually demanded and
    --   the [a] can also be empty (the UniqFM is not filtered).
    deserializeAnns :: Typeable a => ([Word8] -> a) -> AnnEnv -> UniqFM [a]
    deserializeAnns deserialize (MkAnnEnv ann_env)
      = mapUFM (mapMaybe (fromSerialized deserialize)) ann_env