HtmlParser.hs

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

{- |
   Module     : Text.XML.HXT.Parser.HtmlParser
   Copyright  : Copyright (C) 2005 Uwe Schmidt
   License    : MIT

   Maintainer : Uwe Schmidt (uwe@fh-wedel.de)
   Stability  : stable
   Portability: portable

   This parser tries to interprete everything as HTML
   no errors are emitted during parsing. If something looks
   weired, warning messages are inserted in the document tree.
  
   Module contains state filter for easy parsing and error handling
   real work is done in 'Text.XML.HXT.Parser.HtmlParsec'

-}

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

module Text.XML.HXT.Parser.HtmlParser
    ( getHtmlDoc
    , parseHtmlDoc
    , runHtmlParser
    , module Text.XML.HXT.Parser.HtmlParsec
    )

where

import Text.XML.HXT.DOM.XmlTree
import Text.XML.HXT.DOM.XmlState
import Text.XML.HXT.Parser.HtmlParsec

import Text.XML.HXT.Parser.XmlInput
    ( getXmlContents
    )

import Text.XML.HXT.Parser.XmlOutput
    ( traceTree
    , traceSource
    , traceMsg
    )

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

-- |
-- read a document and parse it with 'parseHtmlDoc'. The main entry point of this module
--
-- The input tree must be a root tree like in '	Text.XML.HXT.Parser.MainFunctions.getXmlDoc'. The content is read with 'Text.XML.HXT.Parser.XmlInput.getXmlContents',
-- is parsed with 'parseHtmlDoc' and canonicalized (char refs are substituted in content and attributes,
-- but comment is preserved)
--
-- see also : 'Text.XML.HXT.Parser.DTDProcessing.getWellformedDoc'

getHtmlDoc	:: XmlStateFilter state
getHtmlDoc
    = setSystemParams
      .>>
      getXmlContents
      .>>
      parseHtmlDoc

-- | The HTML parsing filter
--
-- The input is parsed with 'runHtmlParser', everything is interpreted as HTML,
-- if errors ocuur, the parser will try to do some meaningfull action and continues
-- parsing. Afterwards the entitiy references for defined for XHTML are resovled,
-- any unresolved reference is transformed into plain text.
--
-- Error messages
-- during parsing and entity resolving are added as warning nodes into the resulting tree.
--
-- The warnings are issued, if the 1. parameter noWarnings is set to True,
-- afterwards all are removed from the resulting tree.

parseHtmlDoc	:: XmlStateFilter a
parseHtmlDoc
    = parseDoc
      `whenM` ( isRoot .> getChildren .> isXText )
      where
      parseDoc t'
	  = ( traceMsg 2 ("parseHtmlDoc: parse HTML document " ++ show loc)
	      .>>
	      runHtmlParser
	      .>>
	      liftMf (processTopDown substHtmlEntities)
	      .>>
	      removeWarnings
	      .>>
	      traceTree
	      .>>
	      traceSource
              ) $ t'
	  where
	  loc    = valueOf a_source t'			-- get document source uri

      removeWarnings	:: XmlStateFilter a
      removeWarnings t'
	  = let
	    noWarnings  = not (satisfies (hasOption a_issue_warnings) t')
	    selWarnings = deep
			  ( choice [ isWarning :-> this
				   , isXTag    :-> (getAttrl .> selWarnings)
				   ]
			  )
	    remWarnings = processTopDown
			  ( choice [ isWarning :-> none
				   , isXTag    :-> (processAttrl (remWarnings $$))
				   , this      :-> this
				   ]
			  )
	    warnings = selWarnings t'
	    in do 
	       if null warnings
		  then thisM t'
		  else do
		       if noWarnings
			  then return []
			  else do
			       issueError $$< warnings
		       return (remWarnings t')

-- | The pure HTML parser, usually called via 'parseHtmlDoc'.
--

runHtmlParser	:: XmlStateFilter a
runHtmlParser t
    = if null errs
      then do
	   return (replaceChildren res t)
      else do
	   issueError $$< errs
	   return (setStatus c_err "parsing HTML" t)
      where
      res  = getChildren .> parseHtmlText loc $ t
      errs = isXError .> neg isWarning $$ res
      loc  = valueOf a_source t


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