{-# LANGUAGE BlockArguments    #-}
{-# LANGUAGE FlexibleContexts  #-}
{-# LANGUAGE OverloadedStrings #-}

{-# OPTIONS_GHC -fno-warn-name-shadowing #-}

module Blagda.Markdown where

import           Blagda.Agda
import           Blagda.Equations (hideSteps)
import           Blagda.Latex
import           Blagda.References (linkDocument)
import           Blagda.Types
import           Control.Monad.IO.Class
import qualified Data.ByteString.Lazy as LazyBS
import           Data.Digest.Pure.SHA
import           Data.Map.Lazy (Map)
import qualified Data.Map.Lazy as Map
import           Data.Maybe
import           Data.Text (Text)
import qualified Data.Text as Text
import qualified Data.Text.Encoding as Text
import qualified Data.Text.IO as Text
import           Development.Shake
import           Development.Shake.FilePath
import           Network.URI.Encode (decodeText)
import qualified System.Directory as Dir
import           Text.HTML.TagSoup
import           Text.Pandoc
import           Text.Pandoc.Walk


data Reference = Reference
  { refHref :: Text
  , refClasses :: [Text]
  } deriving (Eq, Show)

------------------------------------------------------------------------------
-- | The return type here is whether or not this markdown file is a BLOG POST.
-- Even if it isn't, the file still gets generated.
loadMarkdown :: (Meta -> a) -> String -> FilePath -> Action (Post Pandoc a)
loadMarkdown f commit input = do
  let url = dropExtension (dropDirectory1 input) <.> "html"
      modname = moduleName (dropDirectory1 (dropDirectory1 (dropExtension input)))
      permalink = commit </> input

      title
        | length modname > 24 = '…':reverse (take 24 (reverse modname))
        | otherwise = modname

  Pandoc meta markdown <- liftIO do
    contents <- Text.readFile input
    either (fail . show) pure =<< runIO do
      md <- readMarkdown def { readerExtensions = getDefaultExtensions "markdown" } [(input, contents)]
      pure md
      -- applyFilters def [JSONFilter "agda-reference-filter"] ["html"] md

  let
  liftIO $ Dir.createDirectoryIfMissing False "_build/diagrams"

  markdown <- pure . walk patchInlines . Pandoc (patchMeta title permalink meta) $ markdown
  markdown <- walkM patchInline markdown
  markdown <- walkM patchBlock markdown
  markdown <- pure $ linkDocument markdown

  pure $ Post
    { p_path = url
    , p_contents = markdown
    , p_meta = f meta
    }



htmlInl :: Text -> Inline
htmlInl = RawInline (Format "html")


-- | Replace any expression $foo$-bar with <span ...>$foo$-bar</span>, so that
-- the equation is not split when word wrapping.
patchInlines :: [Inline] -> [Inline]
patchInlines (m@Math{}:s@(Str txt):xs)
  | not (Text.isPrefixOf " " txt)
  = htmlInl "<span style=\"white-space: nowrap;\">" : m : s : htmlInl "</span>"
  : patchInlines xs
patchInlines (x:xs) = x:patchInlines xs
patchInlines [] = []


-- Make all headers links, and add an anchor emoji.
patchBlock :: MonadIO f => Block -> f Block
patchBlock (Header i a@(ident, _, _) inl) = pure $ Header i a
  $ htmlInl (Text.concat ["<a href=\"#", ident, "\" class=\"header-link\">"])
  : inl
  ++ [htmlInl "<span class=\"header-link-emoji\">🔗</span></a>"]
-- Replace quiver code blocks with a link to an SVG file, and depend on the SVG file.
patchBlock (CodeBlock (id, classes, attrs) contents) | "quiver" `elem` classes = do
  let
    digest = showDigest . sha1 . LazyBS.fromStrict $ Text.encodeUtf8 contents
    title = fromMaybe "commutative diagram" (lookup "title" attrs)
  writeFile' ("_build/diagrams" </> digest <.> "tex") $ Text.unpack contents

  pure $ Div ("", ["diagram-container"], [])
    [ Plain [ Image (id, "diagram":classes, attrs) [] (Text.pack (digest <.> "svg"), title) ]
    ]
patchBlock h = pure h


patchInline :: Inline -> Action Inline
patchInline (Math DisplayMath contents) = htmlInl <$> buildLatexEqn True contents
patchInline (Math InlineMath contents) = htmlInl <$> buildLatexEqn False contents
patchInline h = pure h


mStr :: String -> MetaValue
mStr = MetaString . Text.pack


patchMeta :: String -> String -> Meta -> Meta
patchMeta title permalink (Meta m) =
  Meta $ m <> Map.fromList [ ("title", mStr title)
                           , ("source", mStr permalink)
                           ]

-- | Parse an Agda module (in the final build directory) to find a list
-- of its definitions.
parseFileIdents :: Text -> Action (Map Text Reference, Map Text Text)
parseFileIdents mdl =
  do
    let path = "_build/html1" </> Text.unpack mdl <.> "html"
    need [ path ]
    traced ("parsing " ++ Text.unpack mdl) do
      go mempty mempty . parseTags <$> Text.readFile path
  where
    go fwd rev (TagOpen "a" attrs:TagText name:TagClose "a":xs)
      | Just id <- lookup "id" attrs, Just href <- lookup "href" attrs
      , Just classes <- lookup "class" attrs
      , mdl `Text.isPrefixOf` href, id `Text.isSuffixOf` href
      = go (Map.insert name (Reference href (Text.words classes)) fwd)
           (Map.insert href name rev) xs
      | Just classes <- lookup "class" attrs, Just href <- lookup "href" attrs
      , "Module" `elem` Text.words classes, mdl `Text.isPrefixOf` href
      = go (Map.insert name (Reference href (Text.words classes)) fwd)
           (Map.insert href name rev) xs
    go fwd rev (_:xs) = go fwd rev xs
    go fwd rev [] = (fwd, rev)


defaultWriterOptions :: WriterOptions
defaultWriterOptions = def
  { writerExtensions = getDefaultExtensions "html"
  }

renderPost
    :: (Text -> Action (Map Text Reference, Map Text Text))
    -> WriterOptions
    -> Post Pandoc a
    -> Action (Post Text a)
renderPost fileIdents options po = do
  text <- liftIO $ either (fail . show) pure =<< runIO do
    writeHtml5String options $ p_contents po
  tags <- traverse (parseAgdaLink fileIdents) $ parseTags text
  pure $ po
    { p_path = dropExtension (p_path po) <.> "html"
    , p_contents = renderHTML5 $ hideSteps False tags
    }


-- writeTemplate :: FilePath -> Context Text -> (Text -> Action (Map Text Reference, Map Text Text)) -> Pandoc -> FilePath -> Action ()
-- writeTemplate templateName context fileIdents markdown output = do
--   text <- liftIO $ either (fail . show) pure =<< runIO do
--     template <- getTemplate templateName >>= runWithPartials . compileTemplate templateName
--                 >>= either (throwError . PandocTemplateError . Text.pack) pure
--     let
--       options = def { writerTemplate = Just template
--                     , writerTableOfContents = True
--                     , writerVariables = context
--                     , writerExtensions = getDefaultExtensions "html" }
--     writeHtml5String options markdown

--   tags <- traverse (parseAgdaLink fileIdents) $ parseTags text
--   writeFile' output $ Text.unpack $ renderHTML5 $ hideSteps False tags


renderHTML5 :: [Tag Text] -> Text
renderHTML5 = renderTagsOptions renderOptions
  { optMinimize = flip elem ["br", "meta", "link", "img", "hr"]
  }

  -- command_ [] "agda-fold-equations" [output]


-- | Possibly interpret an <a href="agda://"> link to be a honest-to-god
-- link to the definition.
parseAgdaLink :: (Text -> Action (Map Text Reference, Map Text Text))
                 -> Tag Text -> Action (Tag Text)
parseAgdaLink fileIds (TagOpen "a" attrs)
  | Just href <- lookup "href" attrs, Text.pack "agda://" `Text.isPrefixOf` href =
    let
      href' = Text.splitOn "#" $ Text.drop (Text.length "agda://") href
      cont mdl ident = do
        (idMap, _) <- fileIds mdl
        case Map.lookup ident idMap of
          Just (Reference href'' _) -> do
            pure (TagOpen "a" (emplace [("href", href'')] attrs))
          _ -> error $ "Could not compile Agda link: " ++ show href'
     in case href' of
          [mdl] -> cont mdl mdl
          [mdl, ident] -> cont mdl (decodeText ident)
          _ -> error $ "Could not parse Agda link: " ++ show href
parseAgdaLink _ x = pure x


emplace :: Eq a => [(a, b)] -> [(a, b)] -> [(a, b)]
emplace ((p, x) : xs) ys = (p, x) : emplace xs (filter ((/= p) . fst) ys)
emplace [] ys = ys


-- | Lookup an identifier given a module name and ID within that module,
-- returning its type.
addLinkType :: (Text -> Action (Map Text Reference, Map Text Text)) -- ^ Lookup an ident from a module name and location
             -> (() -> Action (Map Text Text)) -- ^ Lookup a type from a module name and ident
             -> Tag Text -> Action (Tag Text)
addLinkType fileIds fileTys tag@(TagOpen "a" attrs)
  | Just href <- lookup "href" attrs
  , [mdl, _] <- Text.splitOn ".html#" href = do
    case Text.isInfixOf "/" mdl of
      True -> pure tag
      False -> do
        ty <- resolveId mdl href <$> fileIds mdl <*> fileTys ()
        pure $ case ty of
          Nothing -> tag
          Just ty -> TagOpen "a" (emplace [("data-type", ty)] attrs)

    where
      resolveId _ href (_, _) types = Map.lookup href types
addLinkType _ _ x = pure x