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

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

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

       Compound arrows for reading an XML\/HTML document or an XML\/HTML string

    -}

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

    module Text.XML.HXT.Arrow.ReadDocument
        ( readDocument
        , readFromDocument
        , readString
        , readFromString
        , hread
        , xread
        )
    where

    import Control.Arrow.ListArrows

    import Data.Maybe                               ( fromMaybe )
    import qualified Data.Map                       as M

    import Text.XML.HXT.DOM.Interface

    import Text.XML.HXT.Arrow.XmlArrow
    import Text.XML.HXT.Arrow.Edit                  ( canonicalizeAllNodes
                                                    , canonicalizeForXPath
                                                    , rememberDTDAttrl
                                                    , removeDocWhiteSpace
                                                    )
    import Text.XML.HXT.Arrow.ParserInterface
    import Text.XML.HXT.Arrow.ProcessDocument       ( getDocumentContents
                                                    , parseXmlDocument
                                                    , parseXmlDocumentWithExpat
                                                    , parseHtmlDocument
                                                    , propagateAndValidateNamespaces
                                                    , andValidateNamespaces
                                                    )
    import Text.XML.HXT.Arrow.XmlState
    import Text.XML.HXT.Arrow.XmlState.TypeDefs

    -- ------------------------------------------------------------
    --
    {- |
    the main document input filter

    this filter can be configured by a list of configuration options,
    a value of type 'Text.XML.HXT.XmlState.TypeDefs.SysConfig'

    for all available options see module 'Text.XML.HXT.Arrow.XmlState.SystemConfig'

    - @withValidate yes\/no@ :
      switch on\/off DTD validation. Only for XML parsed documents, not for HTML parsing.

    - @withSubstDTDEntities yes\/no@ :
      switch on\/off entity substitution for general entities defined in DTD validation.
      Default is @yes@.
      Switching this option and the validation off can lead to faster parsing, in that case
      reading the DTD documents is not longer necessary.
      Only used with XML parsed documents, not with HTML parsing.

    - @withSubstHTMLEntities yes\/no@ :
      switch on\/off entity substitution for general entities defined in HTML validation.
      Default is @no@.
      Switching this option on and the validation and substDTDEntities off can lead to faster parsing,
      in that case
      reading the DTD documents is not longer necessary, HTML general entities are still substituted.
      Only used with XML parsed documents, not with HTML parsing.

    - @withParseHTML yes\/no@ :
      switch on HTML parsing.

    - @withParseByMimeType yes\/no@ :
      select XML\/HTML parser by document mime type.
      text\/xml and text\/xhtml are parsed as XML, text\/html as HTML.

    - @withCheckNamespaces yes\/no@ :
      Switch on\/off namespace propagation and checking

    - @withInputEncoding \<encoding-spec\>@ :
      Set default encoding.

    - @withTagSoup@ :
      use light weight and lazy parser based on tagsoup lib.
      This is only available when package hxt-tagsoup is installed and
      the source contains an @import Text.XML.HXT.TagSoup@.

    - @withRelaxNG \<schema.rng\>@ :
      validate document with Relax NG, the parameter is for the schema URI.
      This implies using XML parser, no validation against DTD, and canonicalisation.

    - @withCurl [\<curl-option\>...]@ :
      Use the libCurl binding for HTTP access.
      This is only available when package hxt-curl is installed and
      the source contains an @import Text.XML.HXT.Curl@.

    - @withHTTP [\<http-option\>...]@ :
      Use the Haskell HTTP package for HTTP access.
      This is only available when package hxt-http is installed and
      the source contains an @import Text.XML.HXT.HTTP@.

    examples:

    > readDocument [] "test.xml"

    reads and validates a document \"test.xml\", no namespace propagation, only canonicalization is performed

    > ...
    > import Text.XML.HXT.Curl
    > ...
    >
    > readDocument [ withValidate        no
    >              , withInputEncoding   isoLatin1
    >              , withParseByMimeType yes
    >              , withCurl []
    >              ] "http://localhost/test.php"

    reads document \"test.php\", parses it as HTML or XML depending on the mimetype given from the server, but without validation, default encoding 'isoLatin1'.
    HTTP access is done via libCurl.

    > readDocument [ withParseHTML       yes
    >              , withInputEncoding   isoLatin1
    >              ] ""

    reads a HTML document from standard input, no validation is done when parsing HTML, default encoding is 'isoLatin1',

    > readDocument [ withInputEncoding  isoLatin1
    >              , withValidate       no
    >              , withMimeTypeFile   "/etc/mime.types"
    >              , withStrictInput    yes
    >              ] "test.svg"

    reads an SVG document from \"test.svg\", sets the mime type by looking in the system mimetype config file,
    default encoding is 'isoLatin1',

    > ...
    > import Text.XML.HXT.Curl
    > import Text.XML.HXT.TagSoup
    > ...
    >
    > readDocument [ withParseHTML      yes
    >              , withTagSoup
    >              , withProxy          "www-cache:3128"
    >              , withCurl           []
    >              , withWarnings       no
    >              ] "http://www.haskell.org/"

    reads Haskell homepage with HTML parser, ignoring any warnings
    (at the time of writing, there were some HTML errors),
    with http access via libCurl interface
    and proxy \"www-cache\" at port 3128,
    parsing is done with tagsoup HTML parser.
    This requires packages \"hxt-curl\" and \"hxt-tagsoup\" to be installed

    > readDocument [ withValidate          yes
    >              , withCheckNamespaces   yes
    >              , withRemoveWS          yes
    >              , withTrace             2
    >              , withHTTP              []
    >              ] "http://www.w3c.org/"

    read w3c home page (xhtml), validate and check namespaces, remove whitespace between tags,
    trace activities with level 2.
    HTTP access is done with Haskell HTTP package

    > readDocument [ withValidate          no
    >              , withSubstDTDEntities  no
    >              ...
    >              ] "http://www.w3c.org/"

    read w3c home page (xhtml), but without accessing the DTD given in that document.
    Only the predefined XML general entity refs are substituted.

    > readDocument [ withValidate          no
    >              , withSubstDTDEntities  no
    >              , withSubstHTMLEntities yes
    >              ...
    >              ] "http://www.w3c.org/"

    same as above, but with substituion of all general entity refs defined in XHTML.

    for minimal complete examples see 'Text.XML.HXT.Arrow.WriteDocument.writeDocument'
    and 'runX', the main starting point for running an XML arrow.
    -}

    readDocument    :: SysConfigList -> String -> IOStateArrow s b XmlTree
    readDocument config src
        = localSysEnv
          $
          readDocument' config src

    readDocument'   :: SysConfigList -> String -> IOStateArrow s b XmlTree
    readDocument' config src
        = configSysVars config
          >>>
          readD $< getSysVar theWithCache
        where
        readD True
            = constA undefined              -- just for generalizing the signature to: IOStateArrow s b       XmlTree
              >>>                           -- instead of                              IOStateArrow s XmlTree XmlTree
              (withoutUserState $< (getSysVar theCacheRead >>^ ($ src)))
        readD False
            = readDocument'' src

    readDocument''   :: String -> IOStateArrow s b XmlTree
    readDocument'' src
        = getDocumentContents src
          >>>
          ( processDoc
            $<<
            ( getMimeType
              &&&
              getSysVar (theParseByMimeType   .&&&.
                         theParseHTML         .&&&.
                         theAcceptedMimeTypes .&&&.
                         theRelaxValidate     .&&&.
                         theXmlSchemaValidate
                        )
            )
          )
          >>>
          traceMsg 1 ("readDocument: " ++ show src ++ " processed")
          >>>
          traceSource
          >>>
          traceTree
        where
        processNoneEmptyDoc p
            = ifA (fromLA hasEmptyBody)
                  (replaceChildren none)
                  p
            where
              hasEmptyBody
                  = hasAttrValue transferStatus (/= "200")        -- test on empty response body for not o.k. responses
                    `guards`                                      -- e.g. 3xx status values
                    ( neg getChildren
                      <+>
                      ( getChildren >>> isWhiteSpace )
                    )

        getMimeType
            = getAttrValue transferMimeType >>^ stringToLower

        applyMimeTypeHandler mt
            = withoutUserState (applyMTH $< getSysVar theMimeTypeHandlers)
            where
              applyMTH mtTable
                  = fromMaybe none $
                    fmap (\ f -> processNoneEmptyDoc
                                 (traceMimeStart >>> f >>> traceMimeEnd)
                         ) $
                    M.lookup mt mtTable
              traceMimeStart
                  = traceMsg 2 $
                    "readDocument: calling user defined document parser"
              traceMimeEnd
                  = traceMsg 2 $
                    "readDocument: user defined document parser finished"

        processDoc mimeType options
            = traceMsg 1 (unwords [ "readDocument:", show src
                                  , "(mime type:", show mimeType, ") will be processed"
                                  ]
                         )
              >>>
              ( applyMimeTypeHandler mimeType       -- try user defined document handlers
                `orElse`
                processDoc' mimeType options
              )

        processDoc' mimeType ( parseByMimeType
                             , ( parseHtml
                               , ( acceptedMimeTypes
                                 , ( validateWithRelax
                                   , validateWithXmlSchema
                                   ))))
            = ( if isAcceptedMimeType acceptedMimeTypes mimeType
                then ( processNoneEmptyDoc
                       ( ( parse $< getSysVar (theValidate              .&&&.
                                               theSubstDTDEntities      .&&&.
                                               theSubstHTMLEntities     .&&&.
                                               theIgnoreNoneXmlContents .&&&.
                                               theTagSoup               .&&&.
                                               theExpat
                                              )
                         )
                         >>>
                         ( if isXmlOrHtml
                           then ( ( checknamespaces $< getSysVar (theCheckNamespaces .&&&.
                                                                  theTagSoup
                                                                 )
                                  )
                                  >>>
                                  rememberDTDAttrl
                                  >>>
                                  ( canonicalize $< getSysVar (thePreserveComment .&&&.
                                                               theCanonicalize    .&&&.
                                                               theTagSoup
                                                              )
                                  )
                                  >>>
                                  ( whitespace $< getSysVar (theRemoveWS .&&&.
                                                             theTagSoup
                                                            )
                                  )
                                  >>>
                                  relaxOrXmlSchema
                                )
                           else this
                         )
                       )
                     )
                else ( traceMsg 1 (unwords [ "readDocument:", show src
                                           , "mime type:", show mimeType, "not accepted"])
                       >>>
                       replaceChildren none         -- remove contents of not accepted mimetype
                     )
              )
            where
            isAcceptedMimeType              :: [String] -> String -> Bool
            isAcceptedMimeType mts mt
                | null mts
                  ||
                  null mt                   = True
                | otherwise                 = foldr (matchMt mt') False $ mts'
                where
                mt'                         = parseMt mt
                mts'                        = map parseMt
                                              $
                                              mts
                parseMt                     = break (== '/')
                                              >>>
                                              second (drop 1)
                matchMt (ma,mi) (mas,mis) r = ( (ma == mas || mas == "*")
                                                &&
                                                (mi == mis || mis == "*")
                                              )
                                              || r
            parse ( validate
                  , ( substDTD
                    , ( substHTML
                      , ( removeNoneXml
                        , ( withTagSoup'
                          , withExpat'
                          )))))
                | not isXmlOrHtml           = if removeNoneXml
                                              then replaceChildren none             -- don't parse, if mime type is not XML nor HTML
                                              else this                             -- but remove contents when option is set

                | isHtml
                  ||
                  withTagSoup'              = configSysVar (setS theLowerCaseNames isHtml)
                                              >>>
                                              parseHtmlDocument                     -- parse as HTML or with tagsoup XML

                | isXml                     = if withExpat'
                                              then parseXmlDocumentWithExpat
                                              else parseXmlDocument
                                                   validate
                                                   substDTD
                                                   substHTML
                                                   validateWithRelax
                                                                                    -- parse as XML
                | otherwise                 = this                                  -- suppress warning

            checknamespaces (withNamespaces, withTagSoup')
                | withNamespaces
                  &&
                  withTagSoup'              = andValidateNamespaces                 -- propagation is done in tagsoup

                | withNamespaces
                  ||
                  validateWithRelax
                  ||
                  validateWithXmlSchema
                                            = propagateAndValidateNamespaces        -- RelaxNG and XML Schema require correct namespaces

                | otherwise                 = this

            canonicalize (preserveCmt, (canonicalize', withTagSoup'))
                | withTagSoup'              = this                                  -- tagsoup already removes redundant stuff
                | validateWithRelax
                  ||
                  validateWithXmlSchema     = canonicalizeAllNodes                  -- no comments in schema validation

                | canonicalize'
                  &&
                  preserveCmt               = canonicalizeForXPath
                | canonicalize'             = canonicalizeAllNodes
                | otherwise                 = this

            relaxOrXmlSchema
                | validateWithXmlSchema     = withoutUserState $< getSysVar theXmlSchemaValidator
                | validateWithRelax         = withoutUserState $< getSysVar theRelaxValidator
                | otherwise                 = this

            whitespace (removeWS, withTagSoup')
                | ( removeWS
                    ||
                    validateWithXmlSchema                                           -- XML Schema does not like WS
                  )
                  &&
                  not withTagSoup'          = removeDocWhiteSpace                   -- tagsoup already removes whitespace
                | otherwise                 = this

            isHtml                          = ( not parseByMimeType && parseHtml )  -- force HTML
                                              ||
                                              ( parseByMimeType && isHtmlMimeType mimeType )

            isXml                           = ( not parseByMimeType && not parseHtml )
                                              ||
                                              ( parseByMimeType
                                                &&
                                                ( isXmlMimeType mimeType
                                                  ||
                                                  null mimeType
                                                )                                   -- mime type is XML or not known
                                              )

            isXmlOrHtml     = isHtml || isXml

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

    -- |
    -- the arrow version of 'readDocument', the arrow input is the source URI

    readFromDocument :: SysConfigList -> IOStateArrow s String XmlTree
    readFromDocument config
        = applyA ( arr $ readDocument config )

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

    -- |
    -- read a document that is stored in a normal Haskell String
    --
    -- the same function as readDocument, but the parameter forms the input.
    -- All options available for 'readDocument' are applicable for readString,
    -- except input encoding options.
    --
    -- Encoding: No decoding is done, the String argument is taken as Unicode string
    -- All decoding must be done before calling readString, even if the
    -- XML document contains an encoding spec.

    readString :: SysConfigList -> String -> IOStateArrow s b XmlTree
    readString config content
        = readDocument config (stringProtocol ++ content)

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

    -- |
    -- the arrow version of 'readString', the arrow input is the source URI

    readFromString :: SysConfigList -> IOStateArrow s String XmlTree
    readFromString config
        = applyA ( arr $ readString config )

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

    -- |
    -- parse a string as HTML content, substitute all HTML entity refs and canonicalize tree.
    -- (substitute char refs, ...). Errors are ignored.
    --
    -- This arrow delegates all work to the parseHtmlContent parser in module HtmlParser.
    --
    -- This is a simpler version of 'readFromString' without any options,
    -- but it does not run in the IO monad.

    hread :: ArrowXml a => a String XmlTree
    hread
        = fromLA $
          parseHtmlContent                      -- substHtmlEntityRefs is done in parser
          >>>                                   -- as well as subst HTML char refs
          editNTreeA [isError :-> none]         -- ignores all errors

    {- no longer neccesary, text nodes are merged in parser
          >>>
          canonicalizeContents
    -- -}

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

    -- |
    -- parse a string as XML content, substitute all predefined XML entity refs and canonicalize tree
    -- This xread arrow delegates all work to the xread parser function in module XmlParsec

    xread :: ArrowXml a => a String XmlTree
    xread
        = parseXmlContent

    {- -- the old version, where the parser does not subst char refs and cdata
    xread                   = root [] [parseXmlContent]       -- substXmlEntityRefs is done in parser
                              >>>
                              canonicalizeContents
                              >>>
                              getChildren
    -- -}

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