Put link into Meta, add prev and next (fix #5)

-- | Reads in a single document to a Pandoc value using an extra Meta.

read :: (PandocMonad m, MonadIO m) => Meta -> (Path Rel File, Text) -> m (Path Rel File, Pandoc)

read extraMeta (path, content) = do

read (Meta extraMetaMap) (path, content) = do

    contentR <- read' content

    -- TODO: This should really be done without IO...

    newPath <- liftIO $ setFileExtension ".html" path

    return (newPath, addMeta extraMeta contentR)

    return (newPath, addMeta (Meta $ Map.insert "link" (MetaString $ unpack $ toFilePath newPath) extraMetaMap) contentR)

    where read' = readMarkdown $ def {readerExtensions = pandocExtensions}

-- | Writes a single Pandoc document to HTML5 output using a template.

    templateArticle <- readFileUtf8 "template/article.html"

    templateIndex <- readFileUtf8 "template/index.html"

    articlesInput <- read extraMeta `mapM` inputs

    let indexInput = generateIndex extraMeta articlesInput

    articlesInput' <- read extraMeta `mapM` inputs

    let neighbors = getNeighbors $ snd <$> articlesInput'

    -- TODO Refactor!

    let articlesInput = map (\((prevM, nextM), (path, art)) -> (path, addMeta (Meta $ Map.fromList [("prev", fromMaybe (MetaString "") prevM), ("next", fromMaybe (MetaString "") nextM)]) art)) (zip neighbors articlesInput')

    let indexInput = generateIndex extraMeta (snd <$> articlesInput)

    articlesOutput <- write templateArticle `mapMT` articlesInput

    indexOutput <- write templateIndex indexInput

    where extraMeta = Meta $ Map.fromList [("navbar", navbar)]

getNeighbors :: [Pandoc] -> [(Maybe MetaValue, Maybe MetaValue)]

getNeighbors articles = f <$> [0..(length articles - 1)] where

    f n = (getLink =<< articles `safeIndex` (n-1), getLink =<< articles `safeIndex` (n+1))

getLink :: Pandoc -> Maybe MetaValue

getLink (Pandoc meta _) = lookupMeta "link" meta

safeIndex :: [a] -> Int -> Maybe a

safeIndex [] _ = Nothing

safeIndex _ n | n < 0 = Nothing

safeIndex (x:_) 0 = Just x

safeIndex (_:xs) n = safeIndex xs (n-1)

-- | Generate an index page from a list of Articles.

generateIndex :: Meta -> [(Path Rel File, Pandoc)] -> Pandoc

-- Expects each article to contain a meta value "link" with its link path.

generateIndex :: Meta -> [Pandoc] -> Pandoc

generateIndex extraMeta = generateIndex' . sort where

    sort = sortOn (Down . (\(_, Pandoc meta _) -> lookupMeta "date" meta))

    sort = sortOn (Down . (\(Pandoc meta _) -> lookupMeta "date" meta))

    generateIndex' articles = Pandoc metaOutput [] where

        metaOutput = extraMeta <> Meta (Map.fromList

            [("pagetitle", MetaString "Home"), ("articles", MetaList articlesOutput)])

        articlesOutput = uncurry generateIndexMeta <$> articles

        articlesOutput = generateIndexMeta <$> articles

-- | Generates the Pandoc MetaMap for a document for the index page.

-- It contains the meta of the source, the link and the body.

generateIndexMeta :: Path Rel File -> Pandoc -> MetaValue

generateIndexMeta path (Pandoc (Meta metaMap) body) = MetaMap $ metaMap

    <> Map.fromList [("link", MetaString $ toFilePath path), ("body", MetaBlocks body)]

generateIndexMeta :: Pandoc -> MetaValue

generateIndexMeta (Pandoc (Meta metaMap) body) = MetaMap $ metaMap

    <> Map.fromList [("body", MetaBlocks body)]

-- | Adds a Meta block to a pandocument. Already known keys are overwritten.

addMeta :: Meta -> Pandoc -> Pandoc