-----------------------------------------------------------------------------
-- |
-- Module      :  Haddock.Backends.Html
-- Copyright   :  (c) Simon Marlow      2003-2006,
--                    David Waern       2006-2009,
--                    Mark Lentczner    2010,
--                    Mateusz Kowalczyk 2013
-- License     :  BSD-like
--
-- Maintainer  :  haddock@projects.haskell.org
-- Stability   :  experimental
-- Portability :  portable
-----------------------------------------------------------------------------
{-# LANGUAGE CPP              #-}
{-# LANGUAGE NamedFieldPuns   #-}
{-# LANGUAGE TupleSections    #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies     #-}
{-# LANGUAGE BangPatterns     #-}

module Haddock.Backends.Xhtml (
  ppHtml, copyHtmlBits,
  ppHtmlIndex, ppHtmlContents,
  ppJsonIndex
) where


import Prelude hiding (div)

import Haddock.Backends.Xhtml.Decl
import Haddock.Backends.Xhtml.DocMarkup
import Haddock.Backends.Xhtml.Layout
import Haddock.Backends.Xhtml.Names
import Haddock.Backends.Xhtml.Themes
import Haddock.Backends.Xhtml.Types
import Haddock.Backends.Xhtml.Utils
import Haddock.InterfaceFile (PackageInfo (..), PackageInterfaces (..), ppPackageInfo)
import Haddock.ModuleTree
import Haddock.Options (Visibility (..))
import Haddock.Types
import Haddock.Version
import Haddock.Utils
import Haddock.Utils.Json
import Text.XHtml hiding ( name, title, p, quote )
import qualified Text.XHtml as XHtml
import Haddock.GhcUtils

import Control.Monad         ( when, unless )
import qualified Data.ByteString.Builder as Builder
import Control.DeepSeq       (force)
import Data.Bifunctor        ( bimap )
import Data.Char             ( toUpper, isSpace )
import Data.Either           ( partitionEithers )
import Data.Foldable         ( traverse_, foldl')
import Data.List             ( sortBy, isPrefixOf, intersperse )
import Data.Maybe
import System.Directory
import System.FilePath hiding ( (</>) )
import qualified System.IO as IO
import qualified System.FilePath as FilePath
import Data.Map.Strict       (Map)
import qualified Data.Map.Strict as Map
import qualified Data.Set as Set hiding ( Set )
import Data.Ord              ( comparing )

import GHC hiding ( NoLink, moduleInfo,LexicalFixity(..), anchor )
import GHC.Types.Name
import GHC.Unit.State

--------------------------------------------------------------------------------
-- * Generating HTML documentation
--------------------------------------------------------------------------------

ppHtml :: UnitState
       -> String                       -- ^ Title
       -> Maybe String                 -- ^ Package
       -> [Interface]
       -> [InstalledInterface]         -- ^ Reexported interfaces
       -> FilePath                     -- ^ Destination directory
       -> Maybe (MDoc GHC.RdrName)     -- ^ Prologue text, maybe
       -> Themes                       -- ^ Themes
       -> Maybe String                 -- ^ The mathjax URL (--mathjax)
       -> SourceURLs                   -- ^ The source URL (--source)
       -> WikiURLs                     -- ^ The wiki URL (--wiki)
       -> BaseURL                      -- ^ The base URL (--base-url)
       -> Maybe String                 -- ^ The contents URL (--use-contents)
       -> Maybe String                 -- ^ The index URL (--use-index)
       -> Bool                         -- ^ Whether to use unicode in output (--use-unicode)
       -> Maybe String                 -- ^ Package name
       -> PackageInfo                  -- ^ Package info
       -> QualOption                   -- ^ How to qualify names
       -> Bool                         -- ^ Output pretty html (newlines and indenting)
       -> Bool                         -- ^ Also write Quickjump index
       -> IO ()

ppHtml state doctitle maybe_package ifaces reexported_ifaces odir prologue
        themes maybe_mathjax_url maybe_source_url maybe_wiki_url
        maybe_base_url maybe_contents_url maybe_index_url unicode
        pkg packageInfo qual debug withQuickjump = do
  let
    visible_ifaces = filter visible ifaces
    visible i = OptHide `notElem` ifaceOptions i

  when (isNothing maybe_contents_url) $
    ppHtmlContents state odir doctitle maybe_package
        themes maybe_mathjax_url maybe_index_url maybe_source_url maybe_wiki_url
        [PackageInterfaces
          { piPackageInfo = packageInfo
          , piVisibility  = Visible
          , piInstalledInterfaces = map toInstalledIface visible_ifaces
                                 ++ reexported_ifaces
          }]
        False -- we don't want to display the packages in a single-package contents
        prologue debug pkg (makeContentsQual qual)

  when (isNothing maybe_index_url) $ do
    ppHtmlIndex odir doctitle maybe_package
      themes maybe_mathjax_url maybe_contents_url maybe_source_url maybe_wiki_url
      (map toInstalledIface visible_ifaces ++ reexported_ifaces) debug

  when withQuickjump $
    ppJsonIndex odir maybe_source_url maybe_wiki_url unicode pkg qual
      visible_ifaces []

  mapM_ (ppHtmlModule odir doctitle themes
           maybe_mathjax_url maybe_source_url maybe_wiki_url maybe_base_url
           maybe_contents_url maybe_index_url unicode pkg qual debug) visible_ifaces


copyHtmlBits :: FilePath -> FilePath -> Themes -> Bool -> IO ()
copyHtmlBits odir libdir themes withQuickjump = do
  let
    libhtmldir = joinPath [libdir, "html"]
    copyCssFile f = copyFile f (combine odir (takeFileName f))
    copyLibFile f = copyFile (joinPath [libhtmldir, f]) (joinPath [odir, f])
  mapM_ copyCssFile (cssFiles themes)
  copyLibFile haddockJsFile
  copyCssFile (joinPath [libhtmldir, quickJumpCssFile])
  when withQuickjump (copyLibFile jsQuickJumpFile)
  return ()


headHtml :: String -> Themes -> Maybe String -> Maybe String -> Html
headHtml docTitle themes mathjax_url base_url =
      header ! (maybe [] (\url -> [identifier "head", strAttr "data-base-url" url ]) base_url)
    <<
    [ meta ! [ httpequiv "Content-Type", content "text/html; charset=UTF-8"]
    , meta ! [ XHtml.name "viewport", content "width=device-width, initial-scale=1"]
    , thetitle << docTitle
    , styleSheet base_url themes
    , thelink ! [ rel "stylesheet"
                , thetype "text/css"
                , href (withBaseURL base_url quickJumpCssFile) ]
             << noHtml
    , thelink ! [ rel "stylesheet", thetype "text/css", href fontUrl] << noHtml
    , script ! [ src (withBaseURL base_url haddockJsFile)
               , emptyAttr "async"
               , thetype "text/javascript" ]
            << noHtml
    , script ! [thetype "text/x-mathjax-config"] << primHtml mjConf
    , script ! [src mjUrl, thetype "text/javascript"] << noHtml
    ]
  where
    fontUrl = "https://fonts.googleapis.com/css?family=PT+Sans:400,400i,700"
    mjUrl = fromMaybe "https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/MathJax.js?config=TeX-AMS-MML_HTMLorMML" mathjax_url
    mjConf = unwords [ "MathJax.Hub.Config({"
                     ,   "tex2jax: {"
                     ,     "processClass: \"mathjax\","
                     ,     "ignoreClass: \".*\""
                     ,   "}"
                     , "});" ]

srcButton :: SourceURLs -> Maybe Interface -> Maybe Html
srcButton (Just src_base_url, _, _, _) Nothing =
  Just (anchor ! [href src_base_url] << "Source")
srcButton (_, Just src_module_url, _, _) (Just iface) =
  let url = spliceURL (Just $ ifaceMod iface) Nothing Nothing src_module_url
   in Just (anchor ! [href url] << "Source")
srcButton _ _ =
  Nothing


wikiButton :: WikiURLs -> Maybe Module -> Maybe Html
wikiButton (Just wiki_base_url, _, _) Nothing =
  Just (anchor ! [href wiki_base_url] << "User Comments")

wikiButton (_, Just wiki_module_url, _) (Just mdl) =
  let url = spliceURL (Just mdl) Nothing Nothing wiki_module_url
   in Just (anchor ! [href url] << "User Comments")

wikiButton _ _ =
  Nothing


contentsButton :: Maybe String -> Maybe Html
contentsButton maybe_contents_url
  = Just (anchor ! [href url] << "Contents")
  where url = fromMaybe contentsHtmlFile maybe_contents_url


indexButton :: Maybe String -> Maybe Html
indexButton maybe_index_url
  = Just (anchor ! [href url] << "Index")
  where url = fromMaybe indexHtmlFile maybe_index_url


bodyHtml :: String -> Maybe Interface
    -> SourceURLs -> WikiURLs
    -> Maybe String -> Maybe String
    -> Html -> Html
bodyHtml doctitle iface
           maybe_source_url maybe_wiki_url
           maybe_contents_url maybe_index_url
           pageContent =
  body << [
    divPackageHeader << [
      nonEmptySectionName << doctitle,
      unordList (catMaybes [
        srcButton maybe_source_url iface,
        wikiButton maybe_wiki_url (ifaceMod <$> iface),
        contentsButton maybe_contents_url,
        indexButton maybe_index_url])
            ! [theclass "links", identifier "page-menu"]
      ],
    divContent << pageContent,
    divFooter << paragraph << (
      "Produced by " +++
      (anchor ! [href projectUrl] << toHtml projectName) +++
      (" version " ++ projectVersion)
      )
    ]

moduleInfo :: Interface -> Html
moduleInfo iface =
   let
      info = ifaceInfo iface

      doOneEntry :: (String, HaddockModInfo GHC.Name -> Maybe String) -> Maybe HtmlTable
      doOneEntry (fldNm, fld) =
        fld info >>= \a -> return (th << fldNm <-> td << a)

      entries :: [HtmlTable]
      entries = maybeToList copyrightsTable ++ mapMaybe doOneEntry [
          ("License",hmi_license),
          ("Maintainer",hmi_maintainer),
          ("Stability",hmi_stability),
          ("Portability",hmi_portability),
          ("Safe Haskell",hmi_safety),
          ("Language", lg)
          ] ++ extsForm
        where
          lg inf = fmap show (hmi_language inf)

          multilineRow :: String -> [String] -> HtmlTable
          multilineRow title xs = (th ! [valign "top"]) << title <-> td << (toLines xs)
            where toLines = mconcat . intersperse br . map toHtml

          copyrightsTable :: Maybe HtmlTable
          copyrightsTable = fmap (multilineRow "Copyright" . split) (hmi_copyright info)
            where split = map (trim . filter (/= ',')) . lines

          extsForm
            | OptShowExtensions `elem` ifaceOptions iface =
              let fs = map (dropOpt . show) (hmi_extensions info)
              in case map stringToHtml fs of
                [] -> []
                [x] -> extField x -- don't use a list for a single extension
                xs -> extField $ unordList xs ! [theclass "extension-list"]
            | otherwise = []
            where
              extField x = return $ th << "Extensions" <-> td << x
              dropOpt x = if "Opt_" `isPrefixOf` x then drop 4 x else x
   in
      case entries of
         [] -> noHtml
         _ -> table ! [theclass "info"] << aboves entries


--------------------------------------------------------------------------------
-- * Generate the module contents
--------------------------------------------------------------------------------


ppHtmlContents
   :: UnitState
   -> FilePath
   -> String
   -> Maybe String
   -> Themes
   -> Maybe String
   -> Maybe String
   -> SourceURLs
   -> WikiURLs
   -> [PackageInterfaces] -> Bool -> Maybe (MDoc GHC.RdrName)
   -> Bool
   -> Maybe Package  -- ^ Current package
   -> Qualification  -- ^ How to qualify names
   -> IO ()
ppHtmlContents state odir doctitle _maybe_package
  themes mathjax_url maybe_index_url
  maybe_source_url maybe_wiki_url packages showPkgs prologue debug pkg qual = do
  let trees =
        [ ( piPackageInfo pinfo
          , mkModuleTree state showPkgs
            [(instMod iface, toInstalledDescription iface)
            | iface <- piInstalledInterfaces pinfo
            , not (instIsSig iface)
            ]
          )
        | pinfo <- packages
        ]
      sig_trees =
        [ ( piPackageInfo pinfo
          , mkModuleTree state showPkgs
            [(instMod iface, toInstalledDescription iface)
            | iface <- piInstalledInterfaces pinfo
            , instIsSig iface
            ]
          )
        | pinfo <- packages
        ]
      html =
        headHtml doctitle themes mathjax_url Nothing +++
        bodyHtml doctitle Nothing
          maybe_source_url maybe_wiki_url
          Nothing maybe_index_url << [
            ppPrologue pkg qual doctitle prologue,
            ppSignatureTrees pkg qual sig_trees,
            ppModuleTrees pkg qual trees
          ]
  createDirectoryIfMissing True odir
  writeUtf8File (joinPath [odir, contentsHtmlFile]) (renderToString debug html)
  where
    -- Extract a module's short description.
    toInstalledDescription :: InstalledInterface -> Maybe (MDoc Name)
    toInstalledDescription = fmap mkMeta . hmi_description . instInfo


ppPrologue :: Maybe Package -> Qualification -> String -> Maybe (MDoc GHC.RdrName) -> Html
ppPrologue _ _ _ Nothing = noHtml
ppPrologue pkg qual title (Just doc) =
  divDescription << (h1 << title +++ docElement thediv (rdrDocToHtml pkg qual doc))

ppSignatureTrees :: Maybe Package -> Qualification -> [(PackageInfo, [ModuleTree])] -> Html
ppSignatureTrees _ _ tss | all (null . snd) tss = mempty
ppSignatureTrees pkg qual [(info, ts)] =
  divPackageList << (sectionName << "Signatures" +++ ppSignatureTree pkg qual "n" info ts)
ppSignatureTrees pkg qual tss =
  divModuleList <<
    (sectionName << "Signatures"
     +++ concatHtml [ ppSignatureTree pkg qual("n."++show i++".") info ts
                    | (i, (info, ts)) <- zip [(1::Int)..] tss
                    ])

ppSignatureTree :: Maybe Package -> Qualification -> String -> PackageInfo -> [ModuleTree] -> Html
ppSignatureTree _ _ _ _ [] = mempty
ppSignatureTree pkg qual p info ts =
  divModuleList << (sectionName << ppPackageInfo info +++ mkNodeList pkg qual [] p ts)

ppModuleTrees :: Maybe Package -> Qualification -> [(PackageInfo, [ModuleTree])] -> Html
ppModuleTrees _ _ tss | all (null . snd) tss = mempty
ppModuleTrees pkg qual [(info, ts)] =
  divModuleList << (sectionName << "Modules" +++ ppModuleTree pkg qual "n" info ts)
ppModuleTrees pkg qual tss =
  divPackageList <<
    (sectionName << "Packages"
     +++ concatHtml [ppModuleTree pkg qual ("n."++show i++".") info ts
                    | (i, (info, ts)) <- zip [(1::Int)..] tss
                    ])

ppModuleTree :: Maybe Package -> Qualification -> String -> PackageInfo -> [ModuleTree] -> Html
ppModuleTree _ _ _ _ [] = mempty
ppModuleTree pkg qual p info ts =
  divModuleList << (sectionName << ppPackageInfo info +++ mkNodeList pkg qual [] p ts)


mkNodeList :: Maybe Package -> Qualification -> [String] -> String -> [ModuleTree] -> Html
mkNodeList pkg qual ss p ts = case ts of
  [] -> noHtml
  _ -> unordList (zipWith (mkNode pkg qual ss) ps ts)
  where
    ps = [ p ++ '.' : show i | i <- [(1::Int)..]]


mkNode :: Maybe Package -> Qualification -> [String] -> String -> ModuleTree -> Html
mkNode pkg qual ss p (Node s leaf _pkg srcPkg short ts) =
  htmlModule <+> shortDescr +++ htmlPkg +++ subtree
  where
    modAttrs = case (ts, leaf) of
      (_:_, Nothing) -> collapseControl p "module"
      (_,   _    ) -> [theclass "module"]

    cBtn = case (ts, leaf) of
      (_:_, Just _) -> thespan ! collapseControl p "" << spaceHtml
      ([] , Just _) -> thespan ! [theclass "noexpander"] << spaceHtml
      (_,   _   ) -> noHtml
      -- We only need an explicit collapser button when the module name
      -- is also a leaf, and so is a link to a module page. Indeed, the
      -- spaceHtml is a minor hack and does upset the layout a fraction.

    htmlModule = thespan ! modAttrs << (cBtn +++
      case leaf of
        Just m -> ppModule m
        Nothing -> toHtml s
      )

    shortDescr = maybe noHtml (origDocToHtml pkg qual) short
    htmlPkg = maybe noHtml (thespan ! [theclass "package"] <<) srcPkg

    subtree =
      if null ts then noHtml else
      collapseDetails p DetailsOpen (
        thesummary ! [ theclass "hide-when-js-enabled" ] << "Submodules" +++
        mkNodeList pkg qual (s:ss) p ts
      )

--------------------------------------------------------------------------------
-- * Generate the index
--------------------------------------------------------------------------------

data JsonIndexEntry = JsonIndexEntry {
      jieHtmlFragment :: String,
      jieName         :: String,
      jieModule       :: String,
      jieLink         :: String
    }
  deriving Show

instance ToJSON JsonIndexEntry where
    toJSON JsonIndexEntry
        { jieHtmlFragment
        , jieName
        , jieModule
        , jieLink } =
      Object
        [ "display_html" .= String jieHtmlFragment
        , "name"         .= String jieName
        , "module"       .= String jieModule
        , "link"         .= String jieLink
        ]

instance FromJSON JsonIndexEntry where
    parseJSON = withObject "JsonIndexEntry" $ \v ->
      JsonIndexEntry
        <$> v .: "display_html"
        <*> v .: "name"
        <*> v .: "module"
        <*> v .: "link"

ppJsonIndex :: FilePath
           -> SourceURLs                   -- ^ The source URL (--source)
           -> WikiURLs                     -- ^ The wiki URL (--wiki)
           -> Bool
           -> Maybe Package
           -> QualOption
           -> [Interface]
           -> [FilePath]                   -- ^ file paths to interface files
                                           -- (--read-interface)
           -> IO ()
ppJsonIndex odir maybe_source_url maybe_wiki_url unicode pkg qual_opt ifaces installedIfacesPaths = do
  createDirectoryIfMissing True odir
  (errors, installedIndexes) <-
    partitionEithers
      <$> traverse
            (\ifaceFile -> do
              let indexFile = takeDirectory ifaceFile
                    FilePath.</> "doc-index.json"
              a <- doesFileExist indexFile
              if a then
                    bimap (indexFile,) (map (fixLink ifaceFile))
                <$> eitherDecodeFile @[JsonIndexEntry] indexFile
                   else
                    return (Right [])
            )
            installedIfacesPaths
  traverse_ (\(indexFile, err) -> putStrLn $ "haddock: Coudn't parse " ++ indexFile ++ ": " ++ err)
            errors
  IO.withBinaryFile (joinPath [odir, indexJsonFile]) IO.WriteMode $ \h ->
      Builder.hPutBuilder
        h (encodeToBuilder (encodeIndexes (concat installedIndexes)))
  where
    encodeIndexes :: [JsonIndexEntry] -> Value
    encodeIndexes installedIndexes =
      toJSON
        (concatMap fromInterface ifaces
         ++ installedIndexes)

    fromInterface :: Interface -> [JsonIndexEntry]
    fromInterface iface =
        mkIndex mdl qual `mapMaybe` ifaceRnExportItems iface
      where
        qual    = makeModuleQual qual_opt mdl
        mdl     = ifaceMod iface

    mkIndex :: Module -> Qualification -> ExportItem DocNameI -> Maybe JsonIndexEntry
    mkIndex mdl qual item
      | Just item_html <- processExport True links_info unicode pkg qual item
      = Just JsonIndexEntry
          { jieHtmlFragment = showHtmlFragment item_html
          , jieName         = unwords (map getOccString names)
          , jieModule       = moduleString mdl
          , jieLink         = fromMaybe "" (listToMaybe (map (nameLink mdl) names))
          }
      | otherwise = Nothing
      where
        names = exportName item ++ exportSubs item

    exportSubs :: ExportItem DocNameI -> [IdP DocNameI]
    exportSubs (ExportDecl (RnExportD { rnExpDExpD = ExportD { expDSubDocs } })) = map fst expDSubDocs
    exportSubs _ = []

    exportName :: ExportItem DocNameI -> [IdP DocNameI]
    exportName (ExportDecl (RnExportD { rnExpDExpD = ExportD { expDDecl } })) = getMainDeclBinderI (unLoc expDDecl)
    exportName ExportNoDecl { expItemName } = [expItemName]
    exportName _ = []

    nameLink :: NamedThing name => Module -> name -> String
    nameLink mdl = moduleNameUrl' (moduleName mdl) . nameOccName . getName

    links_info = (maybe_source_url, maybe_wiki_url)

    -- update link using relative path to output directory
    fixLink :: FilePath
            -> JsonIndexEntry -> JsonIndexEntry
    fixLink ifaceFile jie =
      jie { jieLink = makeRelative odir (takeDirectory ifaceFile)
                        FilePath.</> jieLink jie }

ppHtmlIndex :: FilePath
            -> String
            -> Maybe String
            -> Themes
            -> Maybe String
            -> Maybe String
            -> SourceURLs
            -> WikiURLs
            -> [InstalledInterface]
            -> Bool
            -> IO ()
ppHtmlIndex odir doctitle _maybe_package themes
  maybe_mathjax_url maybe_contents_url maybe_source_url maybe_wiki_url ifaces debug = do
  let html = indexPage split_indices Nothing
              (if split_indices then [] else index)

  createDirectoryIfMissing True odir

  when split_indices $ do
    mapM_ (do_sub_index index) initialChars
    -- Let's add a single large index as well for those who don't know exactly what they're looking for:
    let mergedhtml = indexPage False Nothing index
    writeUtf8File (joinPath [odir, subIndexHtmlFile merged_name]) (renderToString debug mergedhtml)

  writeUtf8File (joinPath [odir, indexHtmlFile]) (renderToString debug html)

  where
    indexPage showLetters ch items =
      headHtml (doctitle ++ " (" ++ indexName ch ++ ")") themes maybe_mathjax_url Nothing +++
      bodyHtml doctitle Nothing
        maybe_source_url maybe_wiki_url
        maybe_contents_url Nothing << [
          if showLetters then indexInitialLetterLinks else noHtml,
          if null items then noHtml else
            divIndex << [sectionName << indexName ch, buildIndex items]
          ]

    indexName ch = "Index" ++ maybe "" (\c -> " - " ++ [c]) ch
    merged_name = "All"

    buildIndex items = table << aboves (map indexElt items)

    -- an arbitrary heuristic:
    -- too large, and a single-page will be slow to load
    -- too small, and we'll have lots of letter-indexes with only one
    --   or two members in them, which seems inefficient or
    --   unnecessarily hard to use.
    split_indices = length index > 150

    indexInitialLetterLinks =
      divAlphabet <<
         unordList (map (\str -> anchor ! [href (subIndexHtmlFile str)] << str) $
                        [ [c] | c <- initialChars
                              , any ((==c) . toUpper . head . fst) index ] ++
                        [merged_name])

    -- todo: what about names/operators that start with Unicode
    -- characters?
    -- Exports beginning with '_' can be listed near the end,
    -- presumably they're not as important... but would be listed
    -- with non-split index!
    initialChars = [ 'A'..'Z' ] ++ ":!#$%&*+./<=>?@\\^|-~" ++ "_"

    do_sub_index this_ix c
      = unless (null index_part) $
          writeUtf8File (joinPath [odir, subIndexHtmlFile [c]]) (renderToString debug html)
      where
        html = indexPage True (Just c) index_part
        index_part = [(n,stuff) | (n,stuff) <- this_ix, toUpper (head n) == c]


    index :: [(String, Map GHC.Name [(Module,Bool)])]
    index = sortBy cmp (Map.toAscList full_index)
      where cmp (n1,_) (n2,_) = comparing (map toUpper) n1 n2

    -- for each name (a plain string), we have a number of original HsNames that
    -- it can refer to, and for each of those we have a list of modules
    -- that export that entity.  Each of the modules exports the entity
    -- in a visible or invisible way (hence the Bool).
    full_index :: Map String (Map GHC.Name [(Module,Bool)])
    full_index = foldl' f Map.empty ifaces
      where
        f :: Map String (Map Name [(Module, Bool)])
          -> InstalledInterface
          -> Map String (Map Name [(Module, Bool)])
        f !idx iface =
          Map.unionWith
            (Map.unionWith (\a b -> let !x = force $ a ++ b in x))
            idx
            (getIfaceIndex iface)


    getIfaceIndex :: InstalledInterface -> Map String (Map Name [(Module, Bool)])
    getIfaceIndex iface =
        foldl' f Map.empty (instExports iface)
      where
        f :: Map String (Map Name [(Module, Bool)])
          -> Name
          -> Map String (Map Name [(Module, Bool)])
        f !idx name =
          let !vis =  name `Set.member` visible
          in
            Map.insertWith
              (Map.unionWith (++))
              (getOccString name)
              (Map.singleton name [(mdl, vis)])
              idx

        mdl = instMod iface
        visible = Set.fromList (instVisibleExports iface)

    indexElt :: (String, Map GHC.Name [(Module,Bool)]) -> HtmlTable
    indexElt (str, entities) =
       case Map.toAscList entities of
          [(nm,entries)] ->
              td ! [ theclass "src" ] << toHtml str <->
                          indexLinks nm entries
          many_entities ->
              td ! [ theclass "src" ] << toHtml str <-> td << spaceHtml </>
                  aboves (zipWith (curry doAnnotatedEntity) [1..] many_entities)

    doAnnotatedEntity :: (Integer, (Name, [(Module, Bool)])) -> HtmlTable
    doAnnotatedEntity (j,(nm,entries))
          = td ! [ theclass "alt" ] <<
                  toHtml (show j) <+> parens (ppAnnot (nameOccName nm)) <->
                   indexLinks nm entries

    ppAnnot n | not (isValOcc n) = toHtml "Type/Class"
              | isDataOcc n      = toHtml "Data Constructor"
              | otherwise        = toHtml "Function"

    indexLinks nm entries =
       td ! [ theclass "module" ] <<
          hsep (punctuate comma
          [ if visible then
               linkId mdl (Just nm) << toHtml (moduleString mdl)
            else
               toHtml (moduleString mdl)
          | (mdl, visible) <- entries ])


--------------------------------------------------------------------------------
-- * Generate the HTML page for a module
--------------------------------------------------------------------------------


ppHtmlModule
        :: FilePath -> String -> Themes
        -> Maybe String -> SourceURLs -> WikiURLs -> BaseURL
        -> Maybe String -> Maybe String -> Bool -> Maybe Package -> QualOption
        -> Bool -> Interface -> IO ()
ppHtmlModule odir doctitle themes
  maybe_mathjax_url maybe_source_url maybe_wiki_url maybe_base_url
  maybe_contents_url maybe_index_url unicode pkg qual debug iface = do
  let
      mdl = ifaceMod iface
      mdl_str = moduleString mdl
      mdl_str_annot = mdl_str ++ if ifaceIsSig iface
                                    then " (signature)"
                                    else ""
      mdl_str_linked
        | ifaceIsSig iface
        = mdl_str +++ " (signature" +++
                       sup << ("[" +++ anchor ! [href signatureDocURL] << "?" +++ "]" ) +++
                       ")"
        | otherwise
        = toHtml mdl_str
      real_qual = makeModuleQual qual mdl
      html =
        headHtml mdl_str_annot themes maybe_mathjax_url maybe_base_url +++
        bodyHtml doctitle (Just iface)
          maybe_source_url maybe_wiki_url
          maybe_contents_url maybe_index_url << [
            divModuleHeader << (moduleInfo iface +++ (sectionName << mdl_str_linked)),
            ifaceToHtml maybe_source_url maybe_wiki_url iface unicode pkg real_qual
          ]

  createDirectoryIfMissing True odir
  writeUtf8File (joinPath [odir, moduleHtmlFile mdl]) (renderToString debug html)

signatureDocURL :: String
signatureDocURL = "https://wiki.haskell.org/Module_signature"


ifaceToHtml :: SourceURLs -> WikiURLs -> Interface -> Bool -> Maybe Package -> Qualification -> Html
ifaceToHtml maybe_source_url maybe_wiki_url iface unicode pkg qual
  = ppModuleContents pkg qual exports (not . null $ ifaceRnOrphanInstances iface) +++
    description +++
    synopsis +++
    divInterface (maybe_doc_hdr +++ bdy +++ orphans)
  where
    exports = numberSectionHeadings (ifaceRnExportItems iface)

    -- todo: if something has only sub-docs, or fn-args-docs, should
    -- it be measured here and thus prevent omitting the synopsis?
    has_doc
      ( ExportDecl
        ( RnExportD
          { rnExpDExpD =
            ExportD
            { expDMbDoc =
              ( Documentation mDoc mWarn, _ )
            }
          }
        )
      ) = isJust mDoc || isJust mWarn
    has_doc (ExportNoDecl _ _) = False
    has_doc (ExportModule _) = False
    has_doc _ = True

    no_doc_at_all = not (any has_doc exports)

    description | isNoHtml doc = doc
                | otherwise    = divDescription $ sectionName << "Description" +++ doc
                where doc = docSection Nothing pkg qual (ifaceRnDoc iface)

        -- omit the synopsis if there are no documentation annotations at all
    synopsis
      | no_doc_at_all = noHtml
      | otherwise
      = divSynopsis $
            collapseDetails "syn" DetailsClosed (
              thesummary << "Synopsis" +++
              shortDeclList (
                  mapMaybe (processExport True linksInfo unicode pkg qual) exports
              ) ! collapseToggle "syn" ""
            )

        -- if the documentation doesn't begin with a section header, then
        -- add one ("Documentation").
    maybe_doc_hdr
      = case exports of
          [] -> noHtml
          ExportGroup {} : _ -> noHtml
          _ -> h1 << "Documentation"

    bdy =
      foldr (+++) noHtml $
        mapMaybe (processExport False linksInfo unicode pkg qual) exports

    orphans =
      ppOrphanInstances linksInfo (ifaceRnOrphanInstances iface) False unicode pkg qual

    linksInfo = (maybe_source_url, maybe_wiki_url)


ppModuleContents :: Maybe Package -- ^ This package
                 -> Qualification
                 -> [ExportItem DocNameI]
                 -> Bool          -- ^ Orphans sections
                 -> Html
ppModuleContents pkg qual exports orphan
  | null sections && not orphan  = noHtml
  | otherwise                    = contentsDiv
 where
  contentsDiv = divTableOfContents << (divContentsList << (
    (sectionName << "Contents") ! [ strAttr "onclick" "window.scrollTo(0,0)" ] +++
    unordList (sections ++ orphanSection)))

  (sections, _leftovers{-should be []-}) = process 0 exports
  orphanSection
    | orphan =  [ linkedAnchor "section.orphans" << "Orphan instances" ]
    | otherwise = []

  process :: Int -> [ExportItem DocNameI] -> ([Html],[ExportItem DocNameI])
  process _ [] = ([], [])
  process n items@(ExportGroup lev id0 doc : rest)
    | lev <= n  = ( [], items )
    | otherwise = ( html:secs, rest2 )
    where
      html = linkedAnchor (groupId id0)
             << docToHtmlNoAnchors (Just id0) pkg qual (mkMeta doc) +++ mk_subsections ssecs
      (ssecs, rest1) = process lev rest
      (secs,  rest2) = process n   rest1
  process n (_ : rest) = process n rest

  mk_subsections [] = noHtml
  mk_subsections ss = unordList ss

-- we need to assign a unique id to each section heading so we can hyperlink
-- them from the contents:
numberSectionHeadings :: [ExportItem DocNameI] -> [ExportItem DocNameI]
numberSectionHeadings = go 1
  where go :: Int -> [ExportItem DocNameI] -> [ExportItem DocNameI]
        go _ [] = []
        go n (ExportGroup lev _ doc : es)
          = case collectAnchors doc of
              [] -> ExportGroup lev (show n) doc : go (n+1) es
              (a:_) -> ExportGroup lev a doc : go (n+1) es
        go n (other:es)
          = other : go n es

        collectAnchors :: DocH (Wrap (ModuleName, OccName)) (Wrap DocName) -> [String]
        collectAnchors (DocAppend a b) = collectAnchors a ++ collectAnchors b
        collectAnchors (DocAName a) = [a]
        collectAnchors _ = []

processExport :: Bool -> LinksInfo -> Bool -> Maybe Package -> Qualification
              -> ExportItem DocNameI -> Maybe Html
processExport _ _ _ _ _
    ( ExportDecl
      ( RnExportD
        { rnExpDExpD =
            ExportD
            { expDDecl = L _ (InstD {})
            }
        }
      )
    )
  = Nothing -- Hide empty instances
processExport summary links unicode pkg qual
    ( ExportDecl
      ( RnExportD
        { rnExpDExpD =
            ExportD decl pats doc subdocs insts fixities splice
        }
      )
    )
  = processDecl summary $ ppDecl summary links decl pats doc insts fixities subdocs splice unicode pkg qual
processExport summary _ _ pkg qual (ExportGroup lev id0 doc)
  = nothingIf summary $ groupHeading lev id0 << docToHtmlNoAnchors (Just id0) pkg qual (mkMeta doc)
processExport summary _ _ _ qual (ExportNoDecl y [])
  = processDeclOneLiner summary $ ppDocName qual Prefix True y
processExport summary _ _ _ qual (ExportNoDecl y subs)
  = processDeclOneLiner summary $
      ppDocName qual Prefix True y
      +++ parenList (map (ppDocName qual Prefix True) subs)
processExport summary _ _ pkg qual (ExportDoc doc)
  = nothingIf summary $ docSection_ Nothing pkg qual doc
processExport summary _ _ _ _ (ExportModule mdl)
  = processDeclOneLiner summary $ toHtml "module" <+> ppModule mdl


nothingIf :: Bool -> a -> Maybe a
nothingIf True _ = Nothing
nothingIf False a = Just a


processDecl :: Bool -> Html -> Maybe Html
processDecl True = Just
processDecl False = Just . divTopDecl

trim :: String -> String
trim = f . f
  where f = reverse . dropWhile isSpace

processDeclOneLiner :: Bool -> Html -> Maybe Html
processDeclOneLiner True = Just
processDeclOneLiner False = Just . divTopDecl . declElem

groupHeading :: Int -> String -> Html -> Html
groupHeading lev id0 = linkedAnchor grpId . groupTag lev ! [identifier grpId]
  where grpId = groupId id0

groupTag :: Int -> Html -> Html
groupTag lev
  | lev == 1  = h1
  | lev == 2  = h2
  | lev == 3  = h3
  | otherwise = h4
