module Build where

import           Data.Aeson
import qualified Data.Text                     as T
import           Data.Time
import           GHC.Exts                       ( fromList )
import           System.FilePath
import           Text.Pandoc

import           Post                           ( renderPost
                                                , RawPost
                                                , RichPost
                                                )
import           Utils                          ( escapeHTML
                                                , lookupMeta'
                                                , sortByDate
                                                )

parseDay :: String -> Day
parseDay = parseTimeOrError True defaultTimeLocale "%Y-%m-%d"

buildRawPost :: FilePath -> IO RawPost
buildRawPost path = do
  contents <- readFile path
  return (path, T.pack contents)

buildIndexPage :: String -> [RichPost] -> Either String T.Text
buildIndexPage layout rawPosts = case compileTemplate (T.pack layout) of
  Left  err      -> Left err
  Right template -> Right $ renderTemplate template (buildPostListing rawPosts)

buildPostListing :: [RichPost] -> Value
buildPostListing posts =
  let postListing = map buildPostListingItem (sortByDate posts)
  in  object [(T.pack "posts", Array $ fromList postListing)]

buildPostListingItem :: RichPost -> Value
buildPostListingItem (path, Pandoc m b) =
  let keys = ["title", "date", "slug"]
      bindings = map (\key -> T.pack key .= lookupMeta' key m) keys
      body = case renderPost "<article>$body$</article>" (path, Pandoc m b) of
        Left  _error   -> ""
        Right contents -> T.unpack contents
  in  object
        $  bindings
        ++ [ ( T.pack "link"
             , toJSON
               $ T.concat [T.pack "/posts/", lookupMeta' "slug" m, T.pack "/"]
             )
           , (T.pack "body", toJSON $ escapeHTML body)
           , ( T.pack "iso_date"
             , toJSON $ formatTime defaultTimeLocale
                                   "%a, %d %b %Y 00:00:00 +0000"
                                   (parseDay (T.unpack $ lookupMeta' "date" m))
             )
           ]

buildRSSFeed :: String -> [RichPost] -> Either String T.Text
buildRSSFeed layout posts = case compileTemplate (T.pack layout) of
  Left  err      -> Left err
  Right template -> Right $ renderTemplate template (buildPostListing posts)