{-# LANGUAGE InstanceSigs #-}

module Ema.Route.Url (
  -- * Create URL from route
  routeUrl,
  routeUrlWith,
  UrlStrategy (..),
  urlToFilePath,
) where

import Data.Aeson (FromJSON (parseJSON), Value)
import Data.Aeson.Types (Parser)
import Data.Text qualified as T
import Network.URI.Slug qualified as Slug
import Optics.Core (Prism', review)

{- | Return the relative URL of the given route

 Note: when using relative URLs it is imperative to set the `<base>` URL to your
 site's base URL or path (typically just `/`). Otherwise you must accordingly
 make these URLs absolute yourself.
-}
routeUrlWith :: HasCallStack => UrlStrategy -> Prism' FilePath r -> r -> Text
routeUrlWith urlStrategy rp =
  relUrlFromPath . review rp
  where
    relUrlFromPath :: FilePath -> Text
    relUrlFromPath fp =
      case toString <$> T.stripSuffix (urlStrategySuffix urlStrategy) (toText fp) of
        Just htmlFp ->
          case nonEmpty (filepathToUrl htmlFp) of
            Nothing ->
              ""
            Just (removeLastIfOneOf ["index", "index.html"] -> partsSansIndex) ->
              T.intercalate "/" partsSansIndex
        Nothing ->
          T.intercalate "/" $ filepathToUrl fp
      where
        removeLastIfOneOf :: Eq a => [a] -> NonEmpty a -> [a]
        removeLastIfOneOf x xs =
          if last xs `elem` x
            then init xs
            else toList xs
        urlStrategySuffix = \case
          UrlPretty -> ".html"
          UrlDirect -> ""

filepathToUrl :: FilePath -> [Text]
filepathToUrl =
  fmap (Slug.encodeSlug . fromString @Slug.Slug . toString) . T.splitOn "/" . toText

urlToFilePath :: Text -> FilePath
urlToFilePath =
  toString . T.intercalate "/" . fmap (Slug.unSlug . Slug.decodeSlug) . T.splitOn "/"

-- | Like `routeUrlWith` but uses @UrlDirect@ strategy
routeUrl :: HasCallStack => Prism' FilePath r -> r -> Text
routeUrl =
  routeUrlWith UrlDirect

-- | How to produce URL paths from routes
data UrlStrategy
  = -- | Use pretty URLs. The route encoding "foo/bar.html" produces "foo/bar" as URL.
    UrlPretty
  | -- | Use filepaths as URLs. The route encoding "foo/bar.html" produces "foo/bar.html" as URL.
    UrlDirect
  deriving stock (Eq, Show, Ord, Generic)

instance FromJSON UrlStrategy where
  parseJSON val =
    f UrlPretty "pretty" val <|> f UrlDirect "direct" val
    where
      f :: UrlStrategy -> Text -> Value -> Parser UrlStrategy
      f c s v = do
        x <- parseJSON v
        guard $ x == s
        pure c