{-# LANGUAGE PatternGuards #-}
module Text.XML.HaXml.Schema.TypeConversion
  ( module Text.XML.HaXml.Schema.TypeConversion
  ) where

import Text.XML.HaXml.Types (QName(..),Name(..),Namespace(..))
import Text.XML.HaXml.Namespaces (printableName,localName)
import Text.XML.HaXml.Schema.Environment
import Text.XML.HaXml.Schema.XSDTypeModel     as XSD
import Text.XML.HaXml.Schema.HaskellTypeModel as Haskell
import Text.XML.HaXml.Schema.NameConversion
import Text.XML.HaXml.Schema.Parse (xsd)

import qualified Data.Map as Map
import Data.Map (Map)
import Data.List (foldl')
import Data.Maybe (fromMaybe,fromJust,isNothing,isJust)
import Data.Monoid

-- | Transform a Schema by lifting all locally-defined anonymous types to
--   the top-level, naming them, and planting a referend at their original
--   location.
typeLift :: Schema -> Schema
typeLift s = s{ schema_items =
                    concat [ hoist e | SchemaElement e <- schema_items s ]
                    ++ map renameLocals (schema_items s) }
  where
    hoist :: ElementDecl -> [SchemaItem]
    hoist e = flip concatMap (findE e) $
              \e@ElementDecl{elem_nameOrRef=Left (NT{ theName=n
                                                  {-, theType=Nothing-}})}->
                  localType n (elem_content e)

    findE :: ElementDecl -> [ElementDecl]
    findE e = ( case elem_nameOrRef e of
                  Left (NT{theType=Nothing}) -> (e:)
                  Left (NT{theType=Just t})  -> case elem_content e of
                                                  Just (Right
                                                    (ComplexType
                                                       {complex_name=Just t'}))
                                                 {--| t==t'-}
                                                    -> (e:)
                                                  _ -> id
                  _                          -> id
              ) $
              ( case elem_content e of
                  Nothing        -> []
                  Just (Left  _) -> []
                  Just (Right c) ->
                    case complex_content c of
                      v@SimpleContent{ci_stuff=Left (Restriction1 p)} -> particle p
                      v@SimpleContent{ci_stuff=Right (Extension{extension_newstuff=PA p _ _})} -> particle p
                      v@ComplexContent{ci_stuff=Left (Restriction1 p)} -> particle p
                      v@ComplexContent{ci_stuff=Right (Extension{extension_newstuff=PA p _ _})} -> particle p
                      v@ThisType{ci_thistype=PA p _ _} -> particle p
              )
    particle Nothing = []
    particle (Just (Left cos)) = choiceOrSeq cos
    particle (Just (Right g))  = maybe [] choiceOrSeq $ group_stuff g
    choiceOrSeq (XSD.All _ es)        = concatMap findE es
    choiceOrSeq (XSD.Choice   _ _ es) = concatMap etc es
    choiceOrSeq (XSD.Sequence _ _ es) = concatMap etc es
    etc (HasElement e) = findE e
    etc (HasGroup g)   = maybe [] choiceOrSeq $ group_stuff g
    etc (HasCS cos)    = choiceOrSeq cos
    etc (HasAny _)     = []

    localType n Nothing          = []
    localType n (Just (Left s))  = [Simple  (renameSimple n s)]
    localType n (Just (Right c)) = [Complex c{ complex_name = Just n }]

    renameSimple n s@Primitive{}  = s
    renameSimple n s@Restricted{} = s{ simple_name  = Just n }
    renameSimple n s@ListOf{}     = s{ simple_name  = Just n }
    renameSimple n s@UnionOf{}    = s{ simple_name  = Just n }


    -- * For now, rather than walk the tree, giving typenames to nodes that were
    --   previously locally-typed, we will instead assume in the pretty-printer
    --   that it can always replace a missing typename with the element name, and
    --   have it resolve to something sensible.
    renameLocals :: SchemaItem -> SchemaItem
    renameLocals s = s
--  renameLocals (SchemaElement e)
--                 | Left (NT{theName=n,theType=Nothing}) <- elem_nameOrRef e
--                 = SchemaElement e{ elem_nameOrRef = Left (NT{theName=n
--                                                             ,theType=Just n})
--                                  }
--            -- still gotta do the recursive search + rename


-- | Given an environment of schema type mappings, and a schema module,
--   create a bunch of Decls that describe the types in a more
--   Haskell-friendly way.
convert :: Environment -> Schema -> [Haskell.Decl]
convert env s = concatMap item (schema_items s)
  where
    item (Include loc ann)    = [XSDInclude (xname loc) (comment ann)]
    item (Import uri loc ann) = [XSDImport  (xname loc)
                                            (fmap xname $
                                             Map.lookup uri (env_namespace env))
                                            (comment ann)]
    item (Redefine _ _)       = [] -- ignoring redefinitions for now
    item (Annotation ann)     = [XSDComment (comment ann)]
    item (Simple st)          = simple st
    item (Complex ct)         = complex ct
    item (SchemaElement ed)   = topElementDecl ed
    item (SchemaAttribute ad) = [] -- attributeDecl ad
    item (AttributeGroup ag)  = [] -- attrgroup ag
    item (SchemaGroup g)      = group g

    simple (Primitive prim)     = []
    simple s@(Restricted a n f r)
        | (Just enums) <- isEnumeration s
                                = [EnumSimpleType
                                       (maybe (error "missing Name") xname n)
                                       enums (comment a) ]
        | otherwise             = [RestrictSimpleType
                                       (maybe (error "missing Name") xname n)
                                       (maybe (xname "unknownSimple") XName
                                                             (restrict_base r))
                                       (mkRestrict r)
                                       (comment a)]
    simple (ListOf a n f t)     = error "Not yet implemented: ListOf simpleType"
                              --  [NamedSimpleType    (xname n) (nameOfSimple s)
                              --                      (comment a)]
    simple s@(UnionOf a n f u m)
        | (Just enums) <- isEnumeration s
                                = [EnumSimpleType
                                       (maybe (error "missing Name") xname n)
                                       enums (comment a) ]
        | otherwise             = [UnionSimpleTypes
                                       (maybe (error "missing Name") xname n)
                                       (map (xname . printableName) m) -- XXX ignores content 'u'
                                       (comment a)]

    isEnumeration :: SimpleType -> Maybe [(XName,Comment)]
    isEnumeration (Primitive _)        = Nothing
    isEnumeration (ListOf _ _ _ _)     = Nothing
    isEnumeration (Restricted _ _ _ r) =
        case r of
            RestrictSim1 ann base r1  -> Nothing
            RestrictType _ _ _ facets ->
                let enum = [ (xname v, comment ann)
                           | (Facet UnorderedEnumeration ann v _) <- facets ]
                in if null enum then Nothing else Just enum
    isEnumeration (UnionOf _ _ _ u ms) =
        squeeze [] ( flip map ms (\m-> case Map.lookup m (env_type env) of
                                         Just (Left s)-> isEnumeration s
                                         _            -> Nothing)
                     ++ map isEnumeration u )
        where squeeze _  (Nothing:_)    = Nothing
              squeeze xs (Just ys:rest) = squeeze (xs++ys) rest
              squeeze xs []             = Just xs

    complex ct =
      let nx  = N $ fromMaybe ("errorMissingName") (complex_name ct)
          n   = XName nx
      in singleton $
      case complex_content ct of
        c@SimpleContent{}  ->
            case ci_stuff c of
                Left r  ->
                    RestrictSimpleType n ({-simple-}xname $ "Unimplemented") []
                                     (comment (complex_annotation ct
                                              `mappend` ci_annotation c))
                Right e ->
                    ExtendSimpleType n
                                     ({-supertype-}XName $ extension_base e)
                                     ({-attrs-}snd $
                                      particleAttrs $ extension_newstuff e)
                                     (comment (complex_annotation ct
                                              `mappend` ci_annotation c
                                              `mappend` extension_annotation e))
        c@ComplexContent{} ->
            case ci_stuff c of
                Left r  ->
                    RestrictComplexType n ({-complex-}xname $ "Can'tBeRight")
                                     (comment (complex_annotation ct
                                              `mappend` ci_annotation c))
                Right e ->
                    let myLoc  = fromMaybe "NUL" (Map.lookup nx
                                                             (env_typeloc env))
                        supLoc = fromMaybe "NUL" (Map.lookup (extension_base e)
                                                             (env_typeloc env))
                    in
                    if complex_abstract ct then
                        ExtendComplexTypeAbstract n
                             ({-supertype-}XName $ extension_base e)
                             ({-subtypes-}
                              maybe (error ("ExtendComplexTypeAbstract "++show nx))
                                    (map (\(t,l)->(XName t,if l/=myLoc
                                                           then Just (xname l)
                                                           else Nothing)))
                                    (Map.lookup nx (env_extendty env)))
                             ({-fwddecl-}if myLoc/=supLoc
                                         then Just (xname supLoc) else Nothing)
                             ({-grandsupers-}
                              map XName $ repeatedly (supertypeOf env) nx)
                             (comment (complex_annotation ct
                                      `mappend` ci_annotation c
                                      `mappend` extension_annotation e))
                    else
                    let (es,as) = particleAttrs (extension_newstuff e)
                        es'     | ci_mixed c = mkMixedContent es
                                | otherwise  = es
                        (oldEs,oldAs) = contentInfo $
                                            Map.lookup (extension_base e)
                                                       (env_type env)
                    in
                    ExtendComplexType n
                        ({-supertype-}XName $ extension_base e)
                        ({-supertype elems-}oldEs)
                        ({-supertype attrs-}oldAs)
                        ({-elems-}es)
                        ({-attrs-}as)
                        ({-fwddecl-}if myLoc/=supLoc then Just (xname supLoc)
                                                     else Nothing)
                        ({-abstract supertype-}
                         maybe False (either (const False) complex_abstract)
                                     (Map.lookup (extension_base e)
                                                 (env_type env)))
                        ({-grandsupers-}
                         map XName $ repeatedly (supertypeOf env)
                                   $ extension_base e)
                        (comment (complex_annotation ct
                                 `mappend` ci_annotation c
                                 `mappend` extension_annotation e))
        c@ThisType{} | complex_abstract ct ->
            let myLoc  = fromMaybe "NUL"
                                   (Map.lookup nx (env_typeloc env)) in
            ElementsAttrsAbstract n
                          {-all instance types: -}
                          (map (\ (x,loc)->(XName x,if loc/=myLoc
                                                    then Just (xname loc)
                                                    else Nothing))
                               $ fromMaybe []
                               $ Map.lookup nx (env_extendty env))
                          (comment (complex_annotation ct))
        c@ThisType{} | otherwise ->
            let (es,as) = particleAttrs (ci_thistype c)
                es'     | complex_mixed ct = mkMixedContent es
                        | otherwise        = es
            in
            ElementsAttrs n es' as (comment (complex_annotation ct))

    mkMixedContent [e@OneOf{}] = [e{ elem_oneOf = [Text]: elem_oneOf e }]
    mkMixedContent es          = Text: concatMap (\e->[e,Text]) es

    topElementDecl :: XSD.ElementDecl -> [Haskell.Decl]
    topElementDecl ed = case elem_nameOrRef ed of
        Left  n   -> case theType n of
                       Nothing ->
                       --error "Not implemented: contentInfo on topElementDecl"
                       --I'm pretty sure a topElementDecl can't be abstract...
                         let (es,as) = contentInfo (elem_content ed) in
                         [ ElementsAttrs ({-name-}xname $ theName n)
                                         ({-elems-}es)
                                         ({-attrs-}as)
                                         (comment (elem_annotation ed))
                         , ElementOfType $ elementDecl ed
                           --  Element{ elem_name = xname (theName n)
                           --         , elem_type = checkXName s (N $ theName n)
                           --         , elem_modifier =
                           --                 occursToModifier (elem_occurs ed)
                           --         , elem_byRef   = False
                           --         , elem_locals  = []
                           --         , elem_substs  = Nothing
                           --         , elem_comment =
                           --                     (comment (elem_annotation ed))
                           --         }
                         ]
                       Just t | elem_abstract ed ->
                         let nm     = N $ theName n
                             myLoc  = fromMaybe "NUL"
                                          (Map.lookup nm (env_typeloc env)) in
                         singleton $
                         ElementAbstractOfType
                                 (XName nm)
                                 (checkXName s t)
                                 (map (\ (x,loc)->(XName x,if loc/=myLoc
                                                           then Just (xname loc)
                                                           else Nothing))
                                     $ fromMaybe []
                                     $ Map.lookup nm (env_substGrp env))
                                 (comment (elem_annotation ed))
                       Just t | otherwise ->
                         singleton $ ElementOfType $ elementDecl ed
                     --  Element{ elem_name    = xname $ theName n
                     --         , elem_type    = checkXName s t
                     --         , elem_modifier=
                     --                       occursToModifier (elem_occurs ed)
                     --         , elem_byRef   = False
                     --         , elem_locals  = []
                     --         , elem_substs  = Nothing
                     --         , elem_comment = comment (elem_annotation ed)
                     --         }
        Right ref -> case Map.lookup ref (env_element env) of
           Nothing -> error $ "<topElementDecl> unknown element reference "
                            ++printableName ref
           Just e' -> topElementDecl e'

    elementDecl :: XSD.ElementDecl -> Haskell.Element
    elementDecl ed = case elem_nameOrRef ed of
        Left  n   -> Element { elem_name     = xname $ theName n
                             , elem_type     = maybe (localTypeExp ed)
                                                     (checkXName s)
                                                     (theType n)
                             , elem_modifier = occursToModifier $ elem_occurs ed
                             , elem_byRef    = False   -- by reference
                             , elem_locals   = []      -- internal Decl
                             , elem_substs   = Nothing -- substitution group
                         --  , elem_substs   = if elem_abstract ed
                         --                    then fmap (map XName) $
                         --                         Map.lookup (N $ theName n)
                         --                                (env_substGrp env)
                         --                    else Nothing
                             , elem_comment  = comment $ elem_annotation ed
                             }
        Right ref -> case Map.lookup ref (env_element env) of
                       Just e' -> (elementDecl e')
                                      { elem_modifier =
                                              occursToModifier (elem_occurs ed)
                                      , elem_byRef = True }
                       Nothing -> -- possible ref is imported qualified?
                           case Map.lookup (N $ localName ref)
                                           (env_element env) of
                               Just e' -> (elementDecl e')
                                            { elem_modifier =
                                               occursToModifier (elem_occurs ed)
                                            , elem_byRef = True }
                               Nothing -> Element ({-name-}XName ref)
                                              -- best guess at type
                                              ({-type-}XName ref)
                                              (occursToModifier (elem_occurs ed))
                                              True [] Nothing Nothing

    localTypeExp :: XSD.ElementDecl -> XName
    localTypeExp ed | isJust (elem_content ed) =
                          case fromJust (elem_content ed) of
                            Left st@Primitive{}   -> xname "SomethingPrimitive"
                            Left st@Restricted{}  -> (\x-> maybe x xname
                                                          (simple_name st)) $
                                                     (maybe (xname "GiveUp")
                                                            XName $
                                                      restrict_base $
                                                      simple_restriction st)
                            Left st@ListOf{}      -> xname "SomethingListy"
                            Left st@UnionOf{}     -> xname "SomethingUnionLike"
                            Right c@ComplexType{} -> maybe (localTypeExp ed{elem_content=Nothing})
                                                           xname
                                                     $ complex_name c
                    | otherwise =
                          case elem_nameOrRef ed of
                            Left n  -> xname $ theName n
                            Right _ -> xname $ "unknownElement"

    attributeDecl :: XSD.AttributeDecl -> [Haskell.Attribute]
    attributeDecl ad = case attr_nameOrRef ad of
        Left  n   -> singleton $
                     Attribute (xname $ theName n)
                               (maybe (maybe (xname $ "String")
                                           -- guess at an attribute typename?
                                           --(error "XSD.attributeDecl->")
                                             nameOfSimple
                                             (attr_simpleType ad))
                                      XName
                                      (theType n))
                               (attr_use ad == Required)
                               (comment  (attr_annotation ad))
        Right ref -> case Map.lookup ref (env_attribute env) of
                       Nothing -> error $ "<attributeDecl> unknown attribute reference "
                                          ++printableName ref
                       Just a' -> attributeDecl a'

    attrgroup :: XSD.AttrGroup -> [Haskell.Attribute]
    attrgroup g = case attrgroup_nameOrRef g of
        Left  n   -> concatMap (either attributeDecl attrgroup)
                               (attrgroup_stuff g)
        Right ref -> case Map.lookup ref (env_attrgroup env) of
                       Nothing -> error $ "unknown attribute group reference "
                                          ++printableName ref
                       Just g' -> attrgroup g'

    group :: XSD.Group -> [Haskell.Decl]
    group g = case group_nameOrRef g of
        Left  n   -> let ({-highs,-}es) = choiceOrSeq (fromMaybe (error "XSD.group")
                                                             (group_stuff g))
                     in {-highs ++-} singleton $
                           Haskell.Group (xname n)
                                         (map (\e->e{elem_modifier=
                                                         combineOccursModifier
                                                             (group_occurs g)
                                                             (elem_modifier e)})
                                              es)
                                         (comment (group_annotation g))
        Right ref -> case Map.lookup ref (env_group env) of
                  --   Nothing -> error $ "bad group reference "
                  --                      ++printableName ref
                       Nothing -> singleton $
                                  Haskell.Group (xname ("unknown-group-"++printableName ref)) []
                                                (comment (group_annotation g))
                       Just g' -> group g'{ group_occurs=group_occurs g }

    particleAttrs :: ParticleAttrs -> ([Haskell.Element],[Haskell.Attribute])
    particleAttrs (PA part attrs _) = -- ignoring AnyAttr for now
        (particle part, concatMap (either attributeDecl attrgroup) attrs)

    particle :: Particle -> [Haskell.Element] -- XXX fix to ret Decls
    particle Nothing          = []
    particle (Just (Left cs)) = {-snd $-} choiceOrSeq cs
    particle (Just (Right g)) = let [Haskell.Group _ es _] = group g in es

--  choiceOrSeq :: ChoiceOrSeq -> ([Haskell.Decl],[Haskell.Element])
    choiceOrSeq :: ChoiceOrSeq -> [Haskell.Element]
    choiceOrSeq (XSD.All      ann eds)   = error "not yet implemented: XSD.All"
    choiceOrSeq (XSD.Choice   ann o ees) = [ OneOf (anyToEnd
                                                     (map elementEtc ees))
                                                   (occursToModifier o)
                                                   (comment ann) ]
    choiceOrSeq (XSD.Sequence ann _ ees) = concatMap elementEtc ees

    elementEtc :: ElementEtc -> [Haskell.Element]
    elementEtc (HasElement ed) = [elementDecl ed]
    elementEtc (HasGroup g)    = let [Haskell.Group _ es _] = group g in es
    elementEtc (HasCS cs)      = choiceOrSeq cs
    elementEtc (HasAny a)      = any a

    any :: XSD.Any -> [Haskell.Element]
    any a@XSD.Any{}  = [Haskell.AnyElem
                           { elem_modifier = occursToModifier (any_occurs a)
                           , elem_comment  = comment (any_annotation a) }]

    -- If an ANY element is part of a choice, ensure it is the last part.
    anyToEnd :: [[Haskell.Element]] -> [[Haskell.Element]]
    anyToEnd = go Nothing
      where go _ (e@[AnyElem{}]:[]) = e:[]
            go _ (e@[AnyElem{}]:es) = go (Just e) es
            go Nothing  []        = []
            go (Just e) []        = e:[]
            go m (e:es)           = e:go m es

    contentInfo :: Maybe (Either SimpleType ComplexType)
                   -> ([Haskell.Element],[Haskell.Attribute])
    contentInfo Nothing  = ([],[])
    contentInfo (Just e) = either simple complex e
      where
        simple  :: SimpleType  -> ([Element],[Attribute])
        complex :: ComplexType -> ([Element],[Attribute])
        simple _         = ([], [])  -- XXX clearly wrong
     -- simple (Primitive p)        = ([], [])  -- XXX clearly wrong
     -- simple (Restricted n _ _ _) =
        complex ct = case complex_content ct of
                       SimpleContent{}     -> ([],[]) -- XXX clearly wrong
                       ci@ComplexContent{} -> either restr exten (ci_stuff ci)
                       ThisType pa         -> particleAttrs pa
        restr :: Restriction1 -> ([Element],[Attribute])
        exten :: Extension    -> ([Element],[Attribute])
        restr (Restriction1 p)  = (particle p,[])
        exten e = let (oes,oas) = contentInfo (Map.lookup (extension_base e)
                                                          (env_type env))
                      (nes,nas) = particleAttrs (extension_newstuff e)
                  in (oes++nes, oas++nas)


comment :: Annotation -> Comment
comment (Documentation s) = Just s
comment (AppInfo s)       = Just s
comment (NoAnnotation _)  = Nothing

xname :: String -> XName
xname = XName . N

checkXName :: Schema -> QName -> XName
checkXName s n@(N _)     = XName n
checkXName s n@(QN ns m) | (Just uri) <- schema_targetNamespace s
                         , nsURI ns == uri = XName $ N m
                         | otherwise       = XName n

nameOfSimple :: SimpleType -> XName
nameOfSimple (Primitive prim)            = XName . xsd . show $ prim
nameOfSimple (Restricted _ (Just n) _ _) = xname n
nameOfSimple (ListOf _ (Just n) _ _)     = xname n -- ("["++n++"]")
nameOfSimple (UnionOf _ (Just n) _ _ _)  = xname n -- return to this
nameOfSimple s                           = xname "String" -- anonymous simple

mkRestrict :: XSD.Restriction -> [Haskell.Restrict]
mkRestrict (RestrictSim1 ann base r1) = []
--      = error "Not yet implemented: Restriction1 on simpletype"
--      ^ This branch is not strictly correct.  There ought to be some
--        restrictions.
mkRestrict (RestrictType _ _ _ facets) =
    (let occurs = [ (f,ann,v)  | (Facet f ann v _) <- facets
                               , f `elem` [OrderedBoundsMinIncl
                                          ,OrderedBoundsMinExcl
                                          ,OrderedBoundsMaxIncl
                                          ,OrderedBoundsMaxExcl] ]
     in if null occurs then []
        else [Haskell.RangeR (foldl consolidate (Occurs Nothing Nothing) occurs)
                             (comment $ foldr mappend mempty
                                              [ ann | (_,ann,_) <- occurs])]
    ) ++
    [ Haskell.Pattern v (comment ann)
              | (Facet UnorderedPattern ann v _) <- facets ]
    ++
    (let enum = [ (v,comment ann)
                | (Facet UnorderedEnumeration ann v _) <- facets ]
     in if null enum then []
                     else [Haskell.Enumeration enum]
    ) ++
    (let occurs = [ (f,ann,v)  | (Facet f ann v _) <- facets
                               , f `elem` [UnorderedLength
                                          ,UnorderedMaxLength
                                          ,UnorderedMinLength] ]
     in if null occurs then []
        else [Haskell.StrLength
                 (foldl consolidate (Occurs Nothing Nothing) occurs)
                 (comment $ foldr mappend mempty [ ann | (_,ann,_) <- occurs])]
    )

singleton :: a -> [a]
singleton = (:[])

-- | Consolidate a Facet occurrence into a single Occurs value.
consolidate :: Occurs -> (FacetType,Annotation,String) -> Occurs
consolidate (Occurs min max) (OrderedBoundsMinIncl,_,n) =
             Occurs (Just (read n)) max
consolidate (Occurs min max) (OrderedBoundsMinExcl,_,n) =
             Occurs (Just ((read n)+1)) max
consolidate (Occurs min max) (OrderedBoundsMaxIncl,_,n) =
             Occurs min (Just (read n))
consolidate (Occurs min max) (OrderedBoundsMaxExcl,_,n) =
             Occurs min (Just ((read n)-1))
consolidate (Occurs min max) (UnorderedLength,_,n) =
             Occurs (Just (read n)) (Just (read n))
consolidate (Occurs min max) (UnorderedMinLength,_,n) =
             Occurs (Just (read n)) max
consolidate (Occurs min max) (UnorderedMaxLength,_,n) =
             Occurs min (Just (read n))

instance Monoid Occurs where
    mempty = Occurs Nothing Nothing
    (Occurs Nothing  Nothing)  `mappend` o  = o
    (Occurs (Just z) Nothing)  `mappend` (Occurs min max)
                                        = Occurs (Just $ maybe z (*z) min) max
    (Occurs Nothing  (Just x)) `mappend` (Occurs min max)
                                        = Occurs min (Just $ maybe x (*x) max)
    (Occurs (Just z) (Just x)) `mappend` (Occurs min max)
                                        = Occurs (Just $ maybe z (*z) min)
                                                 (Just $ maybe x (*x) max)

-- | Push another Occurs value inside an existing Modifier.
combineOccursModifier :: Occurs -> Modifier -> Modifier
combineOccursModifier o Haskell.Single     = occursToModifier $ mappend o
                                                    $ Occurs (Just 1) (Just 1)
combineOccursModifier o Haskell.Optional   = occursToModifier $ mappend o
                                                    $ Occurs (Just 0) (Just 1)
combineOccursModifier o (Haskell.Range o') = occursToModifier $ mappend o o'

-- | Convert an occurs range to a Haskell-style type modifier (Maybe, List, Id)
occursToModifier :: Occurs -> Modifier
occursToModifier (Occurs Nothing  Nothing)  = Haskell.Single
occursToModifier (Occurs (Just 0) Nothing)  = Haskell.Optional
occursToModifier (Occurs (Just 0) (Just 1)) = Haskell.Optional
occursToModifier (Occurs (Just 1) (Just 1)) = Haskell.Single
occursToModifier o                          = Haskell.Range o


-- | Find the supertype (if it exists) of a given type name.
supertypeOf :: Environment -> QName -> Maybe QName
supertypeOf env t =
    do typ <- Map.lookup t (env_type env)
       a <- either (const Nothing) (Just . complex_content) typ
       b <- case a of ComplexContent{} -> Just (ci_stuff a)
                      _ -> Nothing
       either (const Nothing) (Just . extension_base) b

-- | Keep applying the function to transform the value, until it yields
--   Nothing.  Returns the sequence of transformed values.
repeatedly :: (a->Maybe a) -> a -> [a]
repeatedly f x = case f x of Nothing -> []
                             Just y  -> y : repeatedly f y