module Hakyll.Web.Template.Util
    ( functionField1
    , slug
    , cat
    , identifierLink
    ) where

import Prolog
import Hakyll
import Hakyll.Web.Template.Context
import Data.String.Slugger
import System.FilePath
import Witherable

functionField1 :: String -> (String -> Compiler String) -> Context a
functionField1 n f = functionField n $ \case
    [x] -> \_ -> f x
    xs -> \_ -> fail $ "Expecting exactly one argument to " <> n <> ". Instead got " <> show (length xs)

slug :: Context a
slug = functionField "slug" $ \strs _ -> pure $ toSlug $ unwords strs

cat :: Context a
cat = functionField "cat" $ \strs _ -> pure $ concat strs


identifierLink :: Context a
identifierLink = functionField1 "identifier" $ \str -> do
    getPaths (fromString str) >>= \case
        [] -> noResult $ "No filepaths match the pattern " <> str
        x@(_:_:_) -> noResult $ "Multiple filepaths match the pattern " <> str <> ": " <> show x
        [x] -> pure x


getPaths :: Pattern -> Compiler [FilePath]
getPaths = getMatches >=> witherM getRoute