    {-# LANGUAGE ScopedTypeVariables #-}
    {-
    Copyright (C) 2008-9 John MacFarlane <jgm@berkeley.edu>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    -}

    {- Handlers for wiki functions.
    -}

    module Network.Gitit.Handlers (
                            handleAny
                          , debugHandler
                          , randomPage
                          , discussPage
                          , createPage
                          , showActivity
                          , goToPage
                          , searchResults
                          , uploadForm
                          , uploadFile
                          , indexPage
                          , categoryPage
                          , categoryListPage
                          , preview
                          , showRawPage
                          , showFileAsText
                          , showPageHistory
                          , showFileHistory
                          , showPage
                          , showPageDiff
                          , showFileDiff
                          , exportPage
                          , updatePage
                          , editPage
                          , deletePage
                          , confirmDelete
                          , showHighlightedSource
                          , expireCache
                          , feedHandler
                          )
    where
    import Safe
    import Network.Gitit.Server
    import Network.Gitit.Framework
    import Network.Gitit.Layout
    import Network.Gitit.Types
    import Network.Gitit.Feed (filestoreToXmlFeed, FeedConfig(..))
    import Network.Gitit.Util (orIfNull)
    import Network.Gitit.Cache (expireCachedFile, lookupCache, cacheContents)
    import Network.Gitit.ContentTransformer (showRawPage, showFileAsText, showPage,
            exportPage, showHighlightedSource, preview, applyPreCommitPlugins)
    import Network.Gitit.Page (readCategories)
    import qualified Control.Exception as E
    import System.FilePath
    import Network.Gitit.State
    import Text.XHtml hiding ( (</>), dir, method, password, rev )
    import qualified Text.XHtml as X ( method )
    import Data.List (intercalate, intersperse, delete, nub, sortBy, find, isPrefixOf, inits, sort, (\\))
    import Data.List.Split (wordsBy)
    import Data.Maybe (fromMaybe, mapMaybe, isJust, catMaybes)
    import Data.Ord (comparing)
    import Data.Char (toLower, isSpace)
    import Control.Monad.Reader
    import qualified Data.ByteString.Lazy as B
    import qualified Data.ByteString as S
    import Network.HTTP (urlEncodeVars)
    import Data.Time (getCurrentTime, addUTCTime)
    import Data.Time.Clock (diffUTCTime, UTCTime(..))
    import Data.FileStore
    import System.Log.Logger (logM, Priority(..))

    handleAny :: Handler
    handleAny = withData $ \(params :: Params) -> uriRest $ \uri ->
      let path' = uriPath uri
      in  do fs <- getFileStore
             let rev = pRevision params
             mimetype <- getMimeTypeForExtension
                          (takeExtension path')
             res <- liftIO $ E.try
                    (retrieve fs path' rev :: IO B.ByteString)
             case res of
                    Right contents -> ignoreFilters >>  -- don't compress
                                      (ok $ setContentType mimetype $
                                        (toResponse noHtml) {rsBody = contents})
                                        -- ugly hack
                    Left NotFound  -> mzero
                    Left e         -> error (show e)

    debugHandler :: Handler
    debugHandler = withData $ \(params :: Params) -> do
      req <- askRq
      liftIO $ logM "gitit" DEBUG (show req)
      page <- getPage
      liftIO $ logM "gitit" DEBUG $ "Page = '" ++ page ++ "'\n" ++
                  show params
      mzero

    randomPage :: Handler
    randomPage = do
      fs <- getFileStore
      base' <- getWikiBase
      prunedFiles <- liftIO (index fs) >>= filterM isPageFile >>= filterM isNotDiscussPageFile
      let pages = map dropExtension prunedFiles
      if null pages
         then error "No pages found!"
         else do
           secs <- liftIO (fmap utctDayTime getCurrentTime)
           let newPage = pages !!
                         (truncate (secs * 1000000) `mod` length pages)
           seeOther (base' ++ urlForPage newPage) $ toResponse $
             p << "Redirecting to a random page"

    discussPage :: Handler
    discussPage = do
      page <- getPage
      base' <- getWikiBase
      seeOther (base' ++ urlForPage (if isDiscussPage page then page else ('@':page))) $
                         toResponse "Redirecting to discussion page"

    createPage :: Handler
    createPage = do
      page <- getPage
      base' <- getWikiBase
      case page of
           ('_':_) -> mzero   -- don't allow creation of _index, etc.
           _       -> formattedPage defaultPageLayout{
                                          pgPageName = page
                                        , pgTabs = []
                                        , pgTitle = "Create " ++ page ++ "?"
                                        } $
                        (p << stringToHtml
                            ("There is no page named '" ++ page ++ "'. You can:"))
                            +++
                        (unordList $
                          [ anchor !
                                [href $ base' ++ "/_edit" ++ urlForPage page] <<
                                  ("Create the page '" ++ page ++ "'")
                          , anchor !
                                [href $ base' ++ "/_search?" ++
                                    (urlEncodeVars [("patterns", page)])] <<
                                  ("Search for pages containing the text '" ++
                                    page ++ "'")])

    uploadForm :: Handler
    uploadForm = withData $ \(params :: Params) -> do
      let origPath = pFilename params
      let wikiname = pWikiname params `orIfNull` takeFileName origPath
      let logMsg = pLogMsg params
      let upForm = form ! [X.method "post", enctype "multipart/form-data"] <<
           fieldset <<
           [ p << [label ! [thefor "file"] << "File to upload:"
                  , br
                  , afile "file" ! [value origPath] ]
           , p << [ label ! [thefor "wikiname"] << "Name on wiki, including extension"
                  , noscript << " (leave blank to use the same filename)"
                  , stringToHtml ":"
                  , br
                  , textfield "wikiname" ! [value wikiname]
                  , primHtmlChar "nbsp"
                  , checkbox "overwrite" "yes"
                  , label ! [thefor "overwrite"] << "Overwrite existing file" ]
           , p << [ label ! [thefor "logMsg"] << "Description of content or changes:"
                  , br
                  , textfield "logMsg" ! [size "60", value logMsg]
                  , submit "upload" "Upload" ]
           ]
      formattedPage defaultPageLayout{
                       pgMessages = pMessages params,
                       pgScripts = ["uploadForm.js"],
                       pgShowPageTools = False,
                       pgTabs = [],
                       pgTitle = "Upload a file"} upForm

    uploadFile :: Handler
    uploadFile = withData $ \(params :: Params) -> do
      let origPath = pFilename params
      let filePath = pFilePath params
      let wikiname = normalise
                     $ dropWhile (=='/')
                     $ pWikiname params `orIfNull` takeFileName origPath
      let logMsg = pLogMsg params
      cfg <- getConfig
      wPF <- isPageFile wikiname
      mbUser <- getLoggedInUser
      (user, email) <- case mbUser of
                            Nothing -> return ("Anonymous", "")
                            Just u  -> return (uUsername u, uEmail u)
      let overwrite = pOverwrite params
      fs <- getFileStore
      exists <- liftIO $ E.catch (latest fs wikiname >> return True) $ \e ->
                          if e == NotFound
                             then return False
                             else E.throwIO e >> return True
      let inStaticDir = staticDir cfg `isPrefixOf` (repositoryPath cfg </> wikiname)
      let inTemplatesDir = templatesDir cfg `isPrefixOf` (repositoryPath cfg </> wikiname)
      let dirs' = splitDirectories $ takeDirectory wikiname
      let imageExtensions = [".png", ".jpg", ".gif"]
      let errors = validate
                     [ (null . filter (not . isSpace) $ logMsg,
                        "Description cannot be empty.")
                     , (".." `elem` dirs', "Wikiname cannot contain '..'")
                     , (null origPath, "File not found.")
                     , (inStaticDir,  "Destination is inside static directory.")
                     , (inTemplatesDir,  "Destination is inside templates directory.")
                     , (not overwrite && exists, "A file named '" ++ wikiname ++
                        "' already exists in the repository: choose a new name " ++
                        "or check the box to overwrite the existing file.")
                     , (wPF,
                        "This file extension is reserved for wiki pages.")
                     ]
      if null errors
         then do
           expireCachedFile wikiname `mplus` return ()
           fileContents <- liftIO $ B.readFile filePath
           let len = B.length fileContents
           liftIO $ save fs wikiname (Author user email) logMsg fileContents
           let contents = thediv <<
                 [ h2 << ("Uploaded " ++ show len ++ " bytes")
                 , if takeExtension wikiname `elem` imageExtensions
                      then p << "To add this image to a page, use:" +++
                           pre << ("![alt text](/" ++ wikiname ++ ")")
                      else p << "To link to this resource from a page, use:" +++
                           pre << ("[link label](/" ++ wikiname ++ ")") ]
           formattedPage defaultPageLayout{
                           pgMessages = pMessages params,
                           pgShowPageTools = False,
                           pgTabs = [],
                           pgTitle = "Upload successful"}
                         contents
         else withMessages errors uploadForm

    goToPage :: Handler
    goToPage = withData $ \(params :: Params) -> do
      let gotopage = pGotoPage params
      fs <- getFileStore
      pruned_files <- liftIO (index fs) >>= filterM isPageFile
      let allPageNames = map dropExtension pruned_files
      let findPage f = find f allPageNames
      let exactMatch f = gotopage == f
      let insensitiveMatch f = (map toLower gotopage) == (map toLower f)
      let prefixMatch f = (map toLower gotopage) `isPrefixOf` (map toLower f)
      base' <- getWikiBase
      case findPage exactMatch of
           Just m  -> seeOther (base' ++ urlForPage m) $ toResponse
                         "Redirecting to exact match"
           Nothing -> case findPage insensitiveMatch of
                           Just m  -> seeOther (base' ++ urlForPage m) $ toResponse
                                        "Redirecting to case-insensitive match"
                           Nothing -> case findPage prefixMatch of
                                           Just m  -> seeOther (base' ++ urlForPage m) $
                                                      toResponse $ "Redirecting" ++
                                                        " to partial match"
                                           Nothing -> searchResults

    searchResults :: Handler
    searchResults = withData $ \(params :: Params) -> do
      let patterns = pPatterns params `orIfNull` [pGotoPage params]
      fs <- getFileStore
      matchLines <- if null patterns
                       then return []
                       else liftIO $ E.catch (search fs SearchQuery{
                                                      queryPatterns = patterns
                                                    , queryWholeWords = True
                                                    , queryMatchAll = True
                                                    , queryIgnoreCase = True })
                                           -- catch error, because newer versions of git
                                           -- return 1 on no match, and filestore <=0.3.3
                                           -- doesn't handle this properly:
                                           (\(_ :: FileStoreError)  -> return [])
      let contentMatches = map matchResourceName matchLines
      allPages <- liftIO (index fs) >>= filterM isPageFile
      let slashToSpace = map (\c -> if c == '/' then ' ' else c)
      let inPageName pageName' x = x `elem` (words $ slashToSpace $ dropExtension pageName')
      let matchesPatterns pageName' = not (null patterns) &&
           all (inPageName (map toLower pageName')) (map (map toLower) patterns)
      let pageNameMatches = filter matchesPatterns allPages
      prunedFiles <- filterM isPageFile (contentMatches ++ pageNameMatches)
      let allMatchedFiles = nub $ prunedFiles
      let matchesInFile f =  mapMaybe (\x -> if matchResourceName x == f
                                                then Just (matchLine x)
                                                else Nothing) matchLines
      let matches = map (\f -> (f, matchesInFile f)) allMatchedFiles
      let relevance (f, ms) = length ms + if f `elem` pageNameMatches
                                             then 100
                                             else 0
      let preamble = if null patterns
                        then h3 << ["Please enter a search term."]
                        else h3 << [ stringToHtml (show (length matches) ++ " matches found for ")
                                   , thespan ! [identifier "pattern"] << unwords patterns]
      base' <- getWikiBase
      let toMatchListItem (file, contents) = li <<
            [ anchor ! [href $ base' ++ urlForPage (dropExtension file)] << dropExtension file
            , stringToHtml (" (" ++ show (length contents) ++ " matching lines)")
            , stringToHtml " "
            , anchor ! [href "#", theclass "showmatch",
                        thestyle "display: none;"] << if length contents > 0
                                                         then "[show matches]"
                                                         else ""
            , pre ! [theclass "matches"] << unlines contents]
      let htmlMatches = preamble +++
                        olist << map toMatchListItem
                                 (reverse $ sortBy (comparing relevance) matches)
      formattedPage defaultPageLayout{
                      pgMessages = pMessages params,
                      pgShowPageTools = False,
                      pgTabs = [],
                      pgScripts = ["search.js"],
                      pgTitle = "Search results"}
                    htmlMatches

    showPageHistory :: Handler
    showPageHistory = withData $ \(params :: Params) -> do
      page <- getPage
      cfg <- getConfig
      showHistory (pathForPage page $ defaultExtension cfg) page params

    showFileHistory :: Handler
    showFileHistory = withData $ \(params :: Params) -> do
      file <- getPage
      showHistory file file params

    showHistory :: String -> String -> Params -> Handler
    showHistory file page params =  do
      fs <- getFileStore
      hist <- liftIO $ history fs [file] (TimeRange Nothing Nothing)
                (Just $ pLimit params)
      base' <- getWikiBase
      let versionToHtml rev pos = li ! [theclass "difflink", intAttr "order" pos,
                                        strAttr "revision" (revId rev),
                                        strAttr "diffurl" (base' ++ "/_diff/" ++ page)] <<
            [ thespan ! [theclass "date"] << (show $ revDateTime rev)
            , stringToHtml " ("
            , thespan ! [theclass "author"] << anchor ! [href $ base' ++ "/_activity?" ++
                urlEncodeVars [("forUser", authorName $ revAuthor rev)]] <<
                  (authorName $ revAuthor rev)
            , stringToHtml "): "
            , anchor ! [href (base' ++ urlForPage page ++ "?revision=" ++ revId rev)] <<
               thespan ! [theclass "subject"] <<  revDescription rev
            , noscript <<
                ([ stringToHtml " [compare with "
                 , anchor ! [href $ base' ++ "/_diff" ++ urlForPage page ++ "?to=" ++ revId rev] <<
                      "previous" ] ++
                 (if pos /= 1
                      then [ primHtmlChar "nbsp"
                           , primHtmlChar "bull"
                           , primHtmlChar "nbsp"
                           , anchor ! [href $ base' ++ "/_diff" ++ urlForPage page ++ "?from=" ++
                                      revId rev] << "current"
                           ]
                      else []) ++
                 [stringToHtml "]"])
            ]
      let contents = if null hist
                        then noHtml
                        else ulist ! [theclass "history"] <<
                               zipWith versionToHtml hist
                               [length hist, (length hist - 1)..1]
      let more = if length hist == pLimit params
                    then anchor ! [href $ base' ++ "/_history" ++ urlForPage page
                                     ++ "?limit=" ++ show (pLimit params + 100)] <<
                                     "Show more..."
                    else noHtml
      let tabs = if file == page  -- source file, not wiki page
                    then [ViewTab,HistoryTab]
                    else pgTabs defaultPageLayout
      formattedPage defaultPageLayout{
                       pgPageName = page,
                       pgMessages = pMessages params,
                       pgScripts = ["dragdiff.js"],
                       pgTabs = tabs,
                       pgSelectedTab = HistoryTab,
                       pgTitle = ("Changes to " ++ page)
                       } $ contents +++ more

    showActivity :: Handler
    showActivity = withData $ \(params :: Params) -> do
      cfg <- getConfig
      currTime <- liftIO getCurrentTime
      let defaultDaysAgo = fromIntegral (recentActivityDays cfg)
      let daysAgo = addUTCTime (defaultDaysAgo * (-60) * 60 * 24) currTime
      let since = case pSince params of
                       Nothing -> Just daysAgo
                       Just t  -> Just t
      let forUser = pForUser params
      fs <- getFileStore
      hist <- liftIO $ history fs [] (TimeRange since Nothing)
                         (Just $ pLimit params)
      let hist' = case forUser of
                       Nothing -> hist
                       Just u  -> filter (\r -> authorName (revAuthor r) == u) hist
      let fileFromChange (Added f)    = f
          fileFromChange (Modified f) = f
          fileFromChange (Deleted f)  = f
      base' <- getWikiBase
      let fileAnchor revis file = if takeExtension file == "." ++ (defaultExtension cfg)
            then anchor ! [href $ base' ++ "/_diff" ++ urlForPage (dropExtension file) ++ "?to=" ++ revis] << dropExtension file
            else anchor ! [href $ base' ++ urlForPage file ++ "?revision=" ++ revis] << file
      let filesFor changes revis = intersperse (stringToHtml " ") $
            map (fileAnchor revis . fileFromChange) changes
      let heading = h1 << ("Recent changes by " ++ fromMaybe "all users" forUser)
      let revToListItem rev = li <<
            [ thespan ! [theclass "date"] << (show $ revDateTime rev)
            , stringToHtml " ("
            , thespan ! [theclass "author"] <<
                anchor ! [href $ base' ++ "/_activity?" ++
                  urlEncodeVars [("forUser", authorName $ revAuthor rev)]] <<
                    (authorName $ revAuthor rev)
            , stringToHtml "): "
            , thespan ! [theclass "subject"] << revDescription rev
            , stringToHtml " ("
            , thespan ! [theclass "files"] << filesFor (revChanges rev) (revId rev)
            , stringToHtml ")"
            ]
      let contents = ulist ! [theclass "history"] << map revToListItem hist'
      formattedPage defaultPageLayout{
                      pgMessages = pMessages params,
                      pgShowPageTools = False,
                      pgTabs = [],
                      pgTitle = "Recent changes"
                      } (heading +++ contents)

    showPageDiff :: Handler
    showPageDiff = withData $ \(params :: Params) -> do
      page <- getPage
      cfg <- getConfig
      showDiff (pathForPage page $ defaultExtension cfg) page params

    showFileDiff :: Handler
    showFileDiff = withData $ \(params :: Params) -> do
      page <- getPage
      showDiff page page params

    showDiff :: String -> String -> Params -> Handler
    showDiff file page params = do
      let from = pFrom params
      let to = pTo params
      -- 'to' or 'from' must be given
      when (from == Nothing && to == Nothing) mzero
      fs <- getFileStore
      -- if 'to' is not specified, defaults to current revision
      -- if 'from' is not specified, defaults to revision immediately before 'to'
      from' <- case (from, to) of
                  (Just _, _)        -> return from
                  (Nothing, Nothing) -> return from
                  (Nothing, Just t)  -> do
                    pageHist <- liftIO $ history fs [file]
                                         (TimeRange Nothing Nothing)
                                         Nothing
                    let (_, upto) = break (\r -> idsMatch fs (revId r) t)
                                      pageHist
                    return $ if length upto >= 2
                                -- immediately preceding revision
                                then Just $ revId $ upto !! 1
                                else Nothing
      result' <- liftIO $ E.try $ getDiff fs file from' to
      case result' of
           Left NotFound  -> mzero
           Left e         -> liftIO $ E.throwIO e
           Right htmlDiff -> formattedPage defaultPageLayout{
                                              pgPageName = page,
                                              pgRevision = from' `mplus` to,
                                              pgMessages = pMessages params,
                                              pgTabs = DiffTab :
                                                       pgTabs defaultPageLayout,
                                              pgSelectedTab = DiffTab,
                                              pgTitle = page
                                              }
                                           htmlDiff

    getDiff :: FileStore -> FilePath -> Maybe RevisionId -> Maybe RevisionId
            -> IO Html
    getDiff fs file from to = do
      rawDiff <- diff fs file from to
      let diffLineToHtml (Both xs _) = thespan << unlines xs
          diffLineToHtml (First xs) = thespan ! [theclass "deleted"] << unlines xs
          diffLineToHtml (Second xs) = thespan ! [theclass "added"]  << unlines xs
      return $ h2 ! [theclass "revision"] <<
                 ("Changes from " ++ fromMaybe "beginning" from ++
                  " to " ++ fromMaybe "current" to) +++
               pre ! [theclass "diff"] << map diffLineToHtml rawDiff

    editPage :: Handler
    editPage = withData editPage'

    editPage' :: Params -> Handler
    editPage' params = do
      let rev = pRevision params  -- if this is set, we're doing a revert
      fs <- getFileStore
      page <- getPage
      cfg <- getConfig
      let getRevisionAndText = E.catch
            (do c <- liftIO $ retrieve fs (pathForPage page $ defaultExtension cfg) rev
                -- even if pRevision is set, we return revId of latest
                -- saved version (because we're doing a revert and
                -- we don't want gitit to merge the changes with the
                -- latest version)
                r <- liftIO $ latest fs (pathForPage page $ defaultExtension cfg) >>= revision fs
                return (Just $ revId r, c))
            (\e -> if e == NotFound
                      then return (Nothing, "")
                      else E.throwIO e)
      (mbRev, raw) <- case pEditedText params of
                             Nothing -> liftIO getRevisionAndText
                             Just t  -> let r = if null (pSHA1 params)
                                                   then Nothing
                                                   else Just (pSHA1 params)
                                        in return (r, t)
      let messages = pMessages params
      let logMsg = pLogMsg params
      let sha1Box = case mbRev of
                     Just r  -> textfield "sha1" ! [thestyle "display: none",
                                                    value r]
                     Nothing -> noHtml
      let readonly = if isJust (pRevision params)
                        -- disable editing of text box if it's a revert
                        then [strAttr "readonly" "yes",
                              strAttr "style" "color: gray"]
                        else []
      base' <- getWikiBase
      let editForm = gui (base' ++ urlForPage page) ! [identifier "editform"] <<
                       [ sha1Box
                       , textarea ! (readonly ++ [cols "80", name "editedText",
                                      identifier "editedText"]) << raw
                       , br
                       , label ! [thefor "logMsg"] << "Description of changes:"
                       , br
                       , textfield "logMsg" ! (readonly ++ [value (logMsg `orIfNull` defaultSummary cfg) ])
                       , submit "update" "Save"
                       , primHtmlChar "nbsp"
                       , submit "cancel" "Discard"
                       , primHtmlChar "nbsp"
                       , input ! [thetype "button", theclass "editButton",
                                  identifier "previewButton",
                                  strAttr "onClick" "updatePreviewPane();",
                                  strAttr "style" "display: none;",
                                  value "Preview" ]
                       , thediv ! [ identifier "previewpane" ] << noHtml
                       ]
      let pgScripts' = ["preview.js"]
      let pgScripts'' = case mathMethod cfg of
           JsMathScript -> "jsMath/easy/load.js" : pgScripts'
           MathML       -> "MathMLinHTML.js" : pgScripts'
           MathJax url  -> url : pgScripts'
           _            -> pgScripts'
      formattedPage defaultPageLayout{
                      pgPageName = page,
                      pgMessages = messages,
                      pgRevision = rev,
                      pgShowPageTools = False,
                      pgShowSiteNav = False,
                      pgMarkupHelp = Just $ markupHelp cfg,
                      pgSelectedTab = EditTab,
                      pgScripts = pgScripts'',
                      pgTitle = ("Editing " ++ page)
                      } editForm

    confirmDelete :: Handler
    confirmDelete = do
      page <- getPage
      fs <- getFileStore
      cfg <- getConfig
      -- determine whether there is a corresponding page, and if not whether there
      -- is a corresponding file
      pageTest <- liftIO $ E.try $ latest fs (pathForPage page $ defaultExtension cfg)
      fileToDelete <- case pageTest of
                           Right _        -> return $ pathForPage page $ defaultExtension cfg -- a page
                           Left  NotFound -> do
                             fileTest <- liftIO $ E.try $ latest fs page
                             case fileTest of
                                  Right _       -> return page  -- a source file
                                  Left NotFound -> return ""
                                  Left e        -> fail (show e)
                           Left e        -> fail (show e)
      let confirmForm = gui "" <<
            [ p << "Are you sure you want to delete this page?"
            , input ! [thetype "text", name "filetodelete",
                       strAttr "style" "display: none;", value fileToDelete]
            , submit "confirm" "Yes, delete it!"
            , stringToHtml " "
            , submit "cancel" "No, keep it!"
            , br ]
      formattedPage defaultPageLayout{ pgTitle = "Delete " ++ page ++ "?" } $
        if null fileToDelete
           then ulist ! [theclass "messages"] << li <<
                "There is no file or page by that name."
           else confirmForm

    deletePage :: Handler
    deletePage = withData $ \(params :: Params) -> do
      page <- getPage
      cfg <- getConfig
      let file = pFileToDelete params
      mbUser <- getLoggedInUser
      (user, email) <- case mbUser of
                            Nothing -> return ("Anonymous", "")
                            Just u  -> return (uUsername u, uEmail u)
      let author = Author user email
      let descrip = deleteSummary cfg
      base' <- getWikiBase
      if pConfirm params && (file == page || file == page <.> (defaultExtension cfg))
         then do
           fs <- getFileStore
           liftIO $ Data.FileStore.delete fs file author descrip
           seeOther (base' ++ "/") $ toResponse $ p << "File deleted"
         else seeOther (base' ++ urlForPage page) $ toResponse $ p << "Not deleted"

    updatePage :: Handler
    updatePage = withData $ \(params :: Params) -> do
      page <- getPage
      cfg <- getConfig
      mbUser <- getLoggedInUser
      (user, email) <- case mbUser of
                            Nothing -> return ("Anonymous", "")
                            Just u  -> return (uUsername u, uEmail u)
      editedText <- case pEditedText params of
                         Nothing -> error "No body text in POST request"
                         Just b  -> applyPreCommitPlugins b
      let logMsg = pLogMsg params `orIfNull` defaultSummary cfg
      let oldSHA1 = pSHA1 params
      fs <- getFileStore
      base' <- getWikiBase
      if null . filter (not . isSpace) $ logMsg
         then withMessages ["Description cannot be empty."] editPage
         else do
           when (length editedText > fromIntegral (maxPageSize cfg)) $
              error "Page exceeds maximum size."
           -- check SHA1 in case page has been modified, merge
           modifyRes <- if null oldSHA1
                           then liftIO $ create fs (pathForPage page $ defaultExtension cfg)
                                           (Author user email) logMsg editedText >>
                                         return (Right ())
                           else do
                             expireCachedFile (pathForPage page $ defaultExtension cfg) `mplus` return ()
                             liftIO $ E.catch (modify fs (pathForPage page $ defaultExtension cfg)
                                                oldSHA1 (Author user email) logMsg
                                                editedText)
                                         (\e -> if e == Unchanged
                                                   then return (Right ())
                                                   else E.throwIO e)
           case modifyRes of
                Right () -> seeOther (base' ++ urlForPage page) $ toResponse $ p << "Page updated"
                Left (MergeInfo mergedWithRev conflicts mergedText) -> do
                   let mergeMsg = "The page has been edited since you checked it out. " ++
                          "Changes from revision " ++ revId mergedWithRev ++
                          " have been merged into your edits below. " ++
                          if conflicts
                             then "Please resolve conflicts and Save."
                             else "Please review and Save."
                   editPage' $
                     params{ pEditedText = Just mergedText,
                             pSHA1       = revId mergedWithRev,
                             pMessages   = [mergeMsg] }

    indexPage :: Handler
    indexPage = do
      path' <- getPath
      base' <- getWikiBase
      cfg <- getConfig
      let ext = defaultExtension cfg
      let prefix' = if null path' then "" else path' ++ "/"
      fs <- getFileStore
      listing <- liftIO $ directory fs prefix'
      let isNotDiscussionPage (FSFile f) = isNotDiscussPageFile f
          isNotDiscussionPage (FSDirectory _) = return True
      prunedListing <- filterM isNotDiscussionPage listing
      let htmlIndex = fileListToHtml base' prefix' ext prunedListing
      formattedPage defaultPageLayout{
                      pgPageName = prefix',
                      pgShowPageTools = False,
                      pgTabs = [],
                      pgScripts = [],
                      pgTitle = "Contents"} htmlIndex

    fileListToHtml :: String -> String -> String -> [Resource] -> Html
    fileListToHtml base' prefix ext files =
      let fileLink (FSFile f) | takeExtension f == "." ++ ext =
            li ! [theclass "page"  ] <<
              anchor ! [href $ base' ++ urlForPage (prefix ++ dropExtension f)] <<
                dropExtension f
          fileLink (FSFile f) = li ! [theclass "upload"] << concatHtml
            [ anchor ! [href $ base' ++ urlForPage (prefix ++ f)] << f
            , anchor ! [href $ base' ++ "_delete" ++ urlForPage (prefix ++ f)] << "(delete)"
            ]
          fileLink (FSDirectory f) =
            li ! [theclass "folder"] <<
              anchor ! [href $ base' ++ urlForPage (prefix ++ f) ++ "/"] << f
          updirs = drop 1 $ inits $ splitPath $ '/' : prefix
          uplink = foldr (\d accum ->
                      concatHtml [ anchor ! [theclass "updir",
                                             href $ if length d <= 1
                                                       then base' ++ "/_index"
                                                       else base' ++
                                                            urlForPage (joinPath $ drop 1 d)] <<
                      lastNote "fileListToHtml" d, accum]) noHtml updirs
      in uplink +++ ulist ! [theclass "index"] << map fileLink files

    -- NOTE:  The current implementation of categoryPage does not go via the
    -- filestore abstraction.  That is bad, but can only be fixed if we add
    -- more sophisticated searching options to filestore.
    categoryPage :: Handler
    categoryPage = do
      path' <- getPath
      cfg <- getConfig
      let pcategories = wordsBy (==',') path'
      let repoPath = repositoryPath cfg
      let categoryDescription = "Category: " ++ (intercalate " + " pcategories)
      fs <- getFileStore
      pages <- liftIO (index fs) >>= filterM isPageFile >>= filterM isNotDiscussPageFile
      matches <- liftM catMaybes $
                 forM pages $ \f -> do
                   categories <- liftIO $ readCategories $ repoPath </> f
                   return $ if all ( `elem` categories) pcategories
                               then Just (f, categories \\ pcategories)
                               else Nothing
      base' <- getWikiBase
      let toMatchListItem file = li <<
            [ anchor ! [href $ base' ++ urlForPage (dropExtension file)] << dropExtension file ]
      let toRemoveListItem cat = li <<
            [ anchor ! [href $ base' ++
            (if null (tail pcategories)
             then "/_categories"
             else "/_category" ++ urlForPage (intercalate "," $ Data.List.delete cat pcategories)) ]
            << ("-" ++ cat) ]
      let toAddListItem cat = li <<
            [ anchor ! [href $ base' ++
              "/_category" ++ urlForPage (path' ++ "," ++ cat) ]
            << ("+" ++ cat) ]
      let matchList = ulist << map toMatchListItem (fst $ unzip matches) +++
                      thediv ! [ identifier "categoryList" ] <<
                      ulist << (++) (map toAddListItem (nub $ concat $ snd $ unzip matches))
                                    (map toRemoveListItem pcategories)
      formattedPage defaultPageLayout{
                      pgPageName = categoryDescription,
                      pgShowPageTools = False,
                      pgTabs = [],
                      pgScripts = ["search.js"],
                      pgTitle = categoryDescription }
                    matchList

    categoryListPage :: Handler
    categoryListPage = do
      cfg <- getConfig
      let repoPath = repositoryPath cfg
      fs <- getFileStore
      pages <- liftIO (index fs) >>= filterM isPageFile >>= filterM isNotDiscussPageFile
      categories <- liftIO $ liftM (nub . sort . concat) $ forM pages $ \f ->
                      readCategories (repoPath </> f)
      base' <- getWikiBase
      let toCatLink ctg = li <<
            [ anchor ! [href $ base' ++ "/_category" ++ urlForPage ctg] << ctg ]
      let htmlMatches = ulist << map toCatLink categories
      formattedPage defaultPageLayout{
                      pgPageName = "Categories",
                      pgShowPageTools = False,
                      pgTabs = [],
                      pgScripts = ["search.js"],
                      pgTitle = "Categories" } htmlMatches

    expireCache :: Handler
    expireCache = do
      page <- getPage
      cfg <- getConfig
      -- try it as a page first, then as an uploaded file
      expireCachedFile (pathForPage page $ defaultExtension cfg)
      expireCachedFile page
      ok $ toResponse ()

    feedHandler :: Handler
    feedHandler = do
      cfg <- getConfig
      when (not $ useFeed cfg) mzero
      base' <- getWikiBase
      feedBase <- if null (baseUrl cfg)  -- if baseUrl blank, try to get it from Host header
                     then do
                       mbHost <- getHost
                       case mbHost of
                            Nothing    -> error "Could not determine base URL"
                            Just hn    -> return $ "http://" ++ hn ++ base'
                     else case baseUrl cfg ++ base' of
                               w@('h':'t':'t':'p':'s':':':'/':'/':_) -> return w
                               x@('h':'t':'t':'p':':':'/':'/':_) -> return x
                               y                                 -> return $ "http://" ++ y
      let fc = FeedConfig{
                  fcTitle = wikiTitle cfg
                , fcBaseUrl = feedBase
                , fcFeedDays = feedDays cfg }
      path' <- getPath     -- e.g. "foo/bar" if they hit /_feed/foo/bar
      let file = (path' `orIfNull` "_site") <.> "feed"
      let mbPath = if null path' then Nothing else Just path'
      -- first, check for a cached version that is recent enough
      now <- liftIO getCurrentTime
      let isRecentEnough t = truncate (diffUTCTime now t) < 60 * feedRefreshTime cfg
      mbCached <- lookupCache file
      case mbCached of
           Just (modtime, contents) | isRecentEnough modtime -> do
                let emptyResponse = setContentType "application/atom+xml; charset=utf-8" . toResponse $ ()
                ok $ emptyResponse{rsBody = B.fromChunks [contents]}
           _ -> do
                fs <- getFileStore
                resp' <- liftM toResponse $ liftIO (filestoreToXmlFeed fc fs mbPath)
                cacheContents file $ S.concat $ B.toChunks $ rsBody resp'
                ok . setContentType "application/atom+xml; charset=UTF-8" $ resp'