    {- |
       Maintainer  :  simons@cryp.to
       Stability   :  experimental
       Portability :  portable

       The preferred method for rendering a 'Document' or single 'Content'
       is by using the pretty printing facility defined in "Pretty".
       Pretty-printing does not work well for cases, however, where the
       formatting in the XML document is significant. Examples of this
       case are XHTML's @\<pre\>@ tag, Docbook's @\<literallayout\>@ tag,
       and many more.

       Theoretically, the document author could avoid this problem by
       wrapping the contents of these tags in a \<![CDATA[...]]\> section,
       but often this is not practical, for instance when the
       literal-layout section contains other elements. Finally, program
       writers could manually format these elements by transforming them
       into a 'literal' string in their 'CFliter', etc., but this is
       annoying to do and prone to omissions and formatting errors.

       As an alternative, this module provides the function 'verbatim',
       which will format XML 'Content' as a 'String' while retaining the
       formatting of the input document unchanged.

       /Know problems/:

        * HaXml's parser eats line feeds between two tags.

        * 'Attribute's should be formatted by making them an instance of
          'Verbatim' as well, but since an 'Attribute' is just a tuple,
          not a full data type, the helper function 'verbAttr' must be
          used instead.

        * 'CMisc' is not yet supported.

        * 'Element's, which contain no content, are formatted as
           @\<element-name\/\>@, even if they were not defined as being of
           type @EMPTY@. In XML this perfectly alright, but in SGML it is
           not. Those, who wish to use 'verbatim' to format parts of say
           an HTML page will have to (a) replace problematic elements by
           'literal's /before/ running 'verbatim' or (b) use a second
           search-and-replace stage to fix this.
     -}

    module Text.XML.HaXml.Verbatim where

    import Text.XML.HaXml.Types

    -- |This class promises that the function 'verbatim' knows how to
    -- format this data type into a string without changing the
    -- formatting.

    class Verbatim a where
        verbatim :: a -> String

    instance (Verbatim a) => Verbatim [a] where
        verbatim  = concat . (map verbatim)

    instance Verbatim Char where
        verbatim c = [c]

    instance (Verbatim a, Verbatim b) => Verbatim (Either a b) where
        verbatim (Left v)  = verbatim v
        verbatim (Right v) = verbatim v

    instance Verbatim (Content i) where
        verbatim (CElem c _)     = verbatim c
        verbatim (CString _ c _) = c
        verbatim (CRef c _)      = verbatim c
        verbatim (CMisc _ _)     = error "NYI: verbatim not defined for CMisc"

    instance Verbatim (Element i) where
        verbatim (Elem nam att [])   = "<" ++ nam ++ (concat . (map verbAttr)) att
                                       ++ "/>"
        verbatim (Elem nam att cont) = "<" ++ nam ++ (concat . (map verbAttr)) att
                                       ++ ">" ++ verbatim cont ++ "</" ++ nam ++ ">"

    instance Verbatim Reference where
        verbatim (RefEntity r) = "&" ++ verbatim r ++ ";"
        verbatim (RefChar c)   = "&#" ++ show c ++ ";"

    -- |This is a helper function is required because Haskell does not
    -- allow to make an ordinary tuple (like 'Attribute') an instance of a
    -- class. The resulting output will preface the actual attribute with
    -- a single blank so that lists of 'Attribute's can be handled
    -- implicitly by the definition for lists of 'Verbatim' data types.

    verbAttr :: Attribute -> String
    verbAttr (n, AttValue v) = " " ++ n ++ "=\"" ++ verbatim v ++ "\""