-- |
-- Module    :  Data.XCB.FromXML
-- Copyright :  (c) Antoine Latter 2008
-- License   :  BSD3
--
-- Maintainer:  Antoine Latter <aslatter@gmail.com>
-- Stability :  provisional
-- Portability: portable
--
-- Handls parsing the data structures from XML files.
--
-- In order to support copying events and errors across module
-- boundaries, all modules which may have cross-module event copies and
-- error copies must be parsed at once.
--
-- There is no provision for preserving the event copy and error copy
-- declarations - the copies are handled during parsing.
module Data.XCB.FromXML(fromFiles
                       ,fromStrings
                       ) where

import Data.XCB.Types
import Data.XCB.Utils

import Text.XML.Light

import Data.List as List
import qualified Data.Map as Map
import Data.Maybe (catMaybes, mapMaybe, maybeToList)

import Control.Monad (MonadPlus (mzero, mplus), guard, liftM, liftM2)
import Control.Monad.Reader (ReaderT, runReaderT, ask, lift, withReaderT)

import System.IO (openFile, IOMode (ReadMode), hSetEncoding, utf8, hGetContents)

-- |Process the listed XML files.
-- Any files which fail to parse are silently dropped.
-- Any declaration in an XML file which fail to parse are
-- silently dropped.
fromFiles :: [FilePath] -> IO [XHeader]
fromFiles xs = do
  strings <- sequence $ map readFileUTF8 xs
  return $ fromStrings strings

-- | Like 'readFile', but forces the encoding
-- of the file to UTF8.
readFileUTF8 :: FilePath -> IO String
readFileUTF8 fp = do
  h <- openFile fp ReadMode
  hSetEncoding h utf8
  hGetContents h

-- |Process the strings as if they were XML files.
-- Any files which fail to parse are silently dropped.
-- Any declaration in an XML file which fail to parse are
-- silently dropped.
fromStrings :: [String] -> [XHeader]
fromStrings xs =
   let rs = mapAlt fromString xs
       headers = concat $ maybeToList $ runReaderT rs headers
   in headers

-- The 'Parse' monad.  Provides the name of the
-- current module, and a list of all of the modules.
type Parse = ReaderT ([XHeader],Name) Maybe

-- operations in the 'Parse' monad

localName :: Parse Name
localName = snd `liftM` ask

allModules :: Parse [XHeader]
allModules = fst `liftM` ask

-- Extract an Alignment from a list of Elements. This assumes that the
-- required_start_align is the first element if it exists at all.
extractAlignment :: (MonadPlus m, Functor m) => [Element] -> m (Maybe Alignment, [Element])
extractAlignment (el : xs) | el `named` "required_start_align" = do
                               align <- el `attr` "align" >>= readM
                               offset <- el `attr` "offset" >>= readM
                               return (Just (Alignment align offset), xs)
                           | otherwise = return (Nothing, el : xs)
extractAlignment xs = return (Nothing, xs)

-- a generic function for looking up something from
-- a named XHeader.
--
-- this implements searching both the current module and
-- the xproto module if the name is not specified.
lookupThingy :: ([XDecl] -> Maybe a)
             -> (Maybe Name)
             -> Parse (Maybe a)
lookupThingy f Nothing = do
  lname <- localName
  liftM2 mplus (lookupThingy f $ Just lname)
               (lookupThingy f $ Just "xproto") -- implicit xproto import
lookupThingy f (Just mname) = do
  xs <- allModules
  return $ do
    x <- findXHeader mname xs
    f $ xheader_decls x

-- lookup an event declaration by name.
lookupEvent :: Maybe Name -> Name -> Parse (Maybe EventDetails)
lookupEvent mname evname = flip lookupThingy mname $ \decls ->
                 findEvent evname decls

-- lookup an error declaration by name.
lookupError :: Maybe Name -> Name -> Parse (Maybe ErrorDetails)
lookupError mname ername = flip lookupThingy mname $ \decls ->
                 findError ername decls

findXHeader :: Name -> [XHeader] -> Maybe XHeader
findXHeader name = List.find $ \ x -> xheader_header x == name

findError :: Name -> [XDecl] -> Maybe ErrorDetails
findError pname xs =
      case List.find f xs of
        Nothing -> Nothing
        Just (XError name code alignment elems) -> Just $ ErrorDetails name code alignment elems
        _ -> error "impossible: fatal error in Data.XCB.FromXML.findError"
    where  f (XError name _ _ _) | name == pname = True
           f _ = False

findEvent :: Name -> [XDecl] -> Maybe EventDetails
findEvent pname xs =
      case List.find f xs of
        Nothing -> Nothing
        Just (XEvent name code alignment xge elems noseq) ->
            Just $ EventDetails name code alignment xge elems noseq
        _ -> error "impossible: fatal error in Data.XCB.FromXML.findEvent"
   where f (XEvent name _ _ _ _ _) | name == pname = True
         f _ = False 

data EventDetails = EventDetails Name Int (Maybe Alignment) (Maybe Bool) [StructElem] (Maybe Bool)
data ErrorDetails = ErrorDetails Name Int (Maybe Alignment) [StructElem]

---

-- extract a single XHeader from a single XML document
fromString :: String -> ReaderT [XHeader] Maybe XHeader
fromString str = do
  el@(Element _qname _ats cnt _) <- lift $ parseXMLDoc str
  guard $ el `named` "xcb"
  header <- el `attr` "header"
  let name = el `attr` "extension-name"
      xname = el `attr` "extension-xname"
      maj_ver = el `attr` "major-version" >>= readM
      min_ver = el `attr` "minor-version" >>= readM
      multiword = el `attr` "extension-multiword" >>= readM . ensureUpper
  decls <- withReaderT (\r -> (r,header)) $ extractDecls cnt
  return $ XHeader {xheader_header = header
                   ,xheader_xname = xname
                   ,xheader_name = name
                   ,xheader_multiword = multiword
                   ,xheader_major_version = maj_ver
                   ,xheader_minor_version = min_ver
                   ,xheader_decls = decls
                   }

-- attempts to extract declarations from XML content, discarding failures.
extractDecls :: [Content] -> Parse [XDecl]
extractDecls = mapAlt declFromElem . onlyElems

-- attempt to extract a module declaration from an XML element
declFromElem :: Element -> Parse XDecl
declFromElem el
    | el `named` "request" = xrequest el
    | el `named` "event"   = xevent el
    | el `named` "eventcopy" = xevcopy el
    | el `named` "error" = xerror el
    | el `named` "errorcopy" = xercopy el
    | el `named` "struct" = xstruct el
    | el `named` "union" = xunion el
    | el `named` "xidtype" = xidtype el
    | el `named` "xidunion" = xidunion el
    | el `named` "typedef" = xtypedef el
    | el `named` "enum" = xenum el
    | el `named` "import" = ximport el
    | el `named` "eventstruct" = xeventstruct el
    | otherwise = mzero


ximport :: Element -> Parse XDecl
ximport = return . XImport . strContent

xenum :: Element -> Parse XDecl
xenum el = do
  nm <- el `attr` "name"
  fields <- mapAlt enumField $ elChildren el
  guard $ not $ null fields
  return $ XEnum nm fields

enumField :: Element -> Parse (EnumElem Type)
enumField el = do
  guard $ el `named` "item"
  name <- el `attr` "name"
  let expr = firstChild el >>= expression
  return $ EnumElem name expr

xrequest :: Element -> Parse XDecl
xrequest el = do
  nm <- el `attr` "name"
  code <- el `attr` "opcode" >>= readM
  -- TODO - I don't think I like 'mapAlt' here.
  -- I don't want to be silently dropping fields
  (alignment, xs) <- extractAlignment $ elChildren el
  fields <- mapAlt structField $ xs
  let reply = getReply el
  return $ XRequest nm code alignment fields reply

getReply :: Element -> Maybe XReply
getReply el = do
  childElem <- unqual "reply" `findChild` el
  (alignment, xs) <- extractAlignment $ elChildren childElem
  fields <- mapM structField xs
  guard $ not $ null fields
  return $ GenXReply alignment fields

xevent :: Element -> Parse XDecl
xevent el = do
  name <- el `attr` "name"
  number <- el `attr` "number" >>= readM
  let xge = ensureUpper `liftM` (el `attr` "xge") >>= readM
  let noseq = ensureUpper `liftM` (el `attr` "no-sequence-number") >>= readM
  (alignment, xs) <- extractAlignment (elChildren el)
  fields <- mapM structField $ xs
  guard $ not $ null fields
  return $ XEvent name number alignment xge fields noseq

xevcopy :: Element -> Parse XDecl
xevcopy el = do
  name <- el `attr` "name"
  number <- el `attr` "number" >>= readM
  ref <- el `attr` "ref"
  -- do we have a qualified ref?
  let (mname,evname) = splitRef ref
  details <- lookupEvent mname evname
  return $ let EventDetails _ _ alignment xge fields noseq =
                 case details of
                   Nothing ->
                       error $ "Unresolved event: " ++ show mname ++ " " ++ ref
                   Just x -> x  
           in XEvent name number alignment xge fields noseq

-- we need to do string processing to distinguish qualified from
-- unqualified types.
mkType :: String -> Type
mkType str =
    let (mname, name) = splitRef str
    in case mname of
         Just modifier -> QualType modifier name
         Nothing  -> UnQualType name

splitRef :: Name -> (Maybe Name, Name)
splitRef ref = case split ':' ref of
                 (x,"") -> (Nothing, x)
                 (a, b) -> (Just a, b)

-- |Neither returned string contains the first occurance of the
-- supplied Char.
split :: Char -> String -> (String, String)
split c = go
    where go [] = ([],[])
          go (x:xs) | x == c = ([],xs)
                    | otherwise =
                        let (lefts, rights) = go xs
                        in (x:lefts,rights)


xerror :: Element -> Parse XDecl
xerror el = do
  name <- el `attr` "name"
  number <- el `attr` "number" >>= readM
  (alignment, xs) <- extractAlignment $ elChildren el
  fields <- mapM structField $ xs
  return $ XError name number alignment fields


xercopy :: Element -> Parse XDecl
xercopy el = do
  name <- el `attr` "name"
  number <- el `attr` "number" >>= readM
  ref <- el `attr` "ref"
  let (mname, ername) = splitRef ref
  details <- lookupError mname ername
  return $ uncurry (XError name number) $ case details of
               Nothing -> error $ "Unresolved error: " ++ show mname ++ " " ++ ref
               Just (ErrorDetails _ _ alignment elems) -> (alignment, elems)

xstruct :: Element -> Parse XDecl
xstruct el = do
  name <- el `attr` "name"
  (alignment, xs) <- extractAlignment $ elChildren el
  fields <- mapAlt structField $ xs
  guard $ not $ null fields
  return $ XStruct name alignment fields

xunion :: Element -> Parse XDecl
xunion el = do
  name <- el `attr` "name"
  (alignment, xs) <- extractAlignment $ elChildren el
  fields <- mapAlt structField $ xs
  guard $ not $ null fields
  return $ XUnion name alignment fields

xidtype :: Element -> Parse XDecl
xidtype el = liftM XidType $ el `attr` "name"

xidunion :: Element -> Parse XDecl
xidunion el = do
  name <- el `attr` "name"
  let types = mapMaybe xidUnionElem $ elChildren el
  guard $ not $ null types
  return $ XidUnion name types

xidUnionElem :: Element -> Maybe XidUnionElem
xidUnionElem el = do
  guard $ el `named` "type"
  return $ XidUnionElem $ mkType $ strContent el

xtypedef :: Element -> Parse XDecl
xtypedef el = do
  oldtyp <- liftM mkType $ el `attr` "oldname"
  newname <- el `attr` "newname"
  return $ XTypeDef newname oldtyp

xeventstruct :: Element -> Parse XDecl
xeventstruct el = do
  name <- el `attr` "name"
  allowed <- mapAlt allowedEvent $ elChildren el
  return $ XEventStruct name allowed

allowedEvent :: (MonadPlus m, Functor m) => Element -> m AllowedEvent
allowedEvent el = do
  extension <- el `attr` "name"
  xge <- el `attr` "xge" >>= readM
  opMin <- el `attr` "opcode-min" >>= readM
  opMax <- el `attr` "opcode-max" >>= readM
  return $ AllowedEvent extension xge opMin opMax

structField :: (MonadFail m, MonadPlus m, Functor m) => Element -> m StructElem
structField el
    | el `named` "field" = do
        typ <- liftM mkType $ el `attr` "type"
        let enum = liftM mkType $ el `attr` "enum"
        let mask = liftM mkType $ el `attr` "mask"
        name <- el `attr` "name"
        return $ SField name typ enum mask

    | el `named` "pad" = do
        let bytes = liftM (Pad PadBytes) $ el `attr` "bytes" >>= readM
        let align = liftM (Pad PadAlignment) $ el `attr` "align" >>= readM

        return $ head $ catMaybes $ [bytes, align]

    | el `named` "list" = do
        typ <- liftM mkType $ el `attr` "type"
        name <- el `attr` "name"
        let enum = liftM mkType $ el `attr` "enum"
        let expr = firstChild el >>= expression
        return $ List name typ expr enum

    | el `named` "valueparam" = do
        mask_typ <- liftM mkType $ el `attr` "value-mask-type"
        mask_name <- el `attr` "value-mask-name"
        let mask_pad = el `attr` "value-mask-pad" >>= readM
        list_name <- el `attr` "value-list-name"
        return $ ValueParam mask_typ mask_name mask_pad list_name

    | el `named` "switch" = do
        nm <- el `attr` "name"
        (exprEl,caseEls) <- unconsChildren el
        expr <- expression exprEl
        (alignment, xs) <- extractAlignment $ caseEls
        cases <- mapM bitCase xs
        return $ Switch nm expr alignment cases

    | el `named` "exprfield" = do
        typ <- liftM mkType $ el `attr` "type"
        name <- el `attr` "name"
        expr <- firstChild el >>= expression
        return $ ExprField name typ expr

    | el `named` "reply" = fail "" -- handled separate

    | el `named` "doc" = do
        fields <- el `children` "field"
        let mkField = \x -> fmap (\y -> (y, strContent x)) $ x `attr` "name"
            fields' = Map.fromList $ catMaybes $ map mkField fields
            sees = findChildren (unqual "see") el
            sees' = catMaybes $ flip map sees $ \s -> do typ <- s `attr` "type"
                                                         name <- s `attr` "name"
                                                         return (typ, name)
            brief = fmap strContent $ findChild (unqual "brief") el
        return $ Doc brief fields' sees'

    | el `named` "fd" = do
        name <- el `attr` "name"
        return $ Fd name

    | el `named` "length" = do
        expr <- firstChild el >>= expression
        let typ = mkType "CARD32"
        return $ Length typ expr

    | otherwise = let name = elName el
                  in error $ "I don't know what to do with structelem "
 ++ show name

bitCase :: (MonadFail m, MonadPlus m, Functor m) => Element -> m BitCase
bitCase el | el `named` "bitcase" || el `named` "case" = do
              let mName = el `attr` "name"
              (exprEl, fieldEls) <- unconsChildren el
              expr <- expression exprEl
              (alignment, xs) <- extractAlignment $ fieldEls
              fields <- mapM structField xs
              return $ BitCase mName expr alignment fields
           | otherwise =
              let name = elName el
              in error $ "Invalid bitCase: " ++ show name

expression :: (MonadFail m, MonadPlus m, Functor m) => Element -> m XExpression
expression el | el `named` "fieldref"
                    = return $ FieldRef $ strContent el
              | el `named` "enumref" = do
                   enumTy <- mkType <$> el `attr` "ref"
                   let enumVal = strContent el
                   guard $ enumVal /= ""
                   return $ EnumRef enumTy enumVal
              | el `named` "value"
                    = Value `liftM` readM (strContent el)
              | el `named` "bit"
                    = Bit `liftM` do
                        n <- readM (strContent el)
                        guard $ n >= 0
                        return n
              | el `named` "op" = do
                    binop <- el `attr` "op" >>= toBinop
                    [exprLhs,exprRhs] <- mapM expression $ elChildren el
                    return $ Op binop exprLhs exprRhs
              | el `named` "unop" = do
                    op <- el `attr` "op" >>= toUnop
                    expr <- firstChild el >>= expression
                    return $ Unop op expr
              | el `named` "popcount" = do
                    expr <- firstChild el >>= expression
                    return $ PopCount expr
              | el `named` "sumof" = do
                    ref <- el `attr` "ref"
                    return $ SumOf ref
              | el `named` "paramref"
                    =  return $ ParamRef $ strContent el
              | otherwise =
                  let nm = elName el
                  in error $ "Unknown epression " ++ show nm ++ " in Data.XCB.FromXML.expression"


toBinop :: MonadPlus m => String -> m Binop
toBinop "+"  = return Add
toBinop "-"  = return Sub
toBinop "*"  = return Mult
toBinop "/"  = return Div
toBinop "&"  = return And
toBinop "&amp;" = return And
toBinop ">>" = return RShift
toBinop _ = mzero

toUnop :: MonadPlus m => String -> m Unop
toUnop "~" = return Complement
toUnop _ = mzero


----
----
-- Utility functions
----
----

firstChild :: MonadPlus m => Element -> m Element
firstChild = listToM . elChildren

unconsChildren :: MonadPlus m => Element -> m (Element, [Element])
unconsChildren el
    = case elChildren el of
        (x:xs) -> return (x,xs)
        _ -> mzero

listToM :: MonadPlus m => [a] -> m a
listToM [] = mzero
listToM (x:_) = return x

named :: Element -> String -> Bool
named (Element qname _ _ _) name | qname == unqual name = True
named _ _ = False

attr :: MonadPlus m => Element -> String -> m String
(Element _ xs _ _) `attr` name = case List.find p xs of
      Just (Attr _ res) -> return res
      _ -> mzero
    where p (Attr qname _) | qname == unqual name = True
          p _ = False

children :: MonadPlus m => Element -> String -> m [Element]
(Element _ _ xs _) `children` name = case List.filter p xs of
      [] -> mzero
      some -> return $ onlyElems some
    where p (Elem (Element n _ _ _)) | n == unqual name = True
          p _ = False

-- adapted from Network.CGI.Protocol
readM :: (MonadPlus m, Read a) => String -> m a
readM = liftM fst . listToM . reads
