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module Hakyll.Web.Template.Context
    ( Context
    , field

    , defaultContext
    , bodyField
    , urlField
    , pathField
    , categoryField
    , titleField
    ) where


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import           Control.Applicative      (empty, (<|>))
import           Control.Arrow
import           System.FilePath          (takeBaseName, takeDirectory)


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import           Hakyll.Core.Compiler
import           Hakyll.Core.Identifier
import           Hakyll.Web.Page.Internal
import           Hakyll.Web.Urls


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type Context a = Compiler (String, (Identifier a, a)) String


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field :: String -> Compiler (Identifier a, a) String -> Context a
field key value = arr checkKey >>> (empty ||| value)
  where
    checkKey (k, x)
        | k /= key  = Left ()
        | otherwise = Right x


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defaultContext :: Context Page
defaultContext =
    bodyField     "body"     <|>
    urlField      "url"      <|>
    pathField     "path"     <|>
    categoryField "category" <|>
    titleField    "title"    <|>
    missingField


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bodyField :: String -> Context Page
bodyField key = field key $ arr snd


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urlField :: String -> Context a
urlField key = field key $ fst ^>> getRouteFor >>^ maybe empty toUrl


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pathField :: String -> Context a
pathField key = field key $ arr $ toFilePath . fst


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categoryField :: String -> Context a
categoryField key = pathField key >>^ (takeBaseName . takeDirectory)


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titleField :: String -> Context a
titleField key = pathField key >>^ takeBaseName


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missingField :: Context a
missingField = arr $ \(k, _) -> "$" ++ k ++ "$"