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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 = String -> Identifier -> a -> Compiler String


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field :: String -> (Identifier -> a -> Compiler String) -> Context a
field key value k' id' x
    | k' == key = value id' x
    | otherwise = empty


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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 $ \_ x -> return x


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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, _) -> "$" ++ k ++ "$"