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{-# LANGUAGE DeriveDataTypeable #-}
module Hakyll.Web.Tags
( Tags (..)
, readTagsWith
, readTags
, readCategories
) where
import Control.Applicative ((<$>))
import Data.Map (Map)
import qualified Data.Map as M
import Data.Typeable (Typeable)
import Data.Binary (Binary, get, put)
import Hakyll.Web.Page
import Hakyll.Web.Util.String
import Hakyll.Core.Writable
-- | Data about tags
--
data Tags a = Tags
{ tagsMap :: Map String [Page a]
} deriving (Show, Typeable)
instance Binary a => Binary (Tags a) where
get = Tags <$> get
put (Tags m) = put m
instance Writable (Tags a) where
write _ _ = return ()
-- | Higher-level function to read tags
--
readTagsWith :: (Page a -> [String]) -- ^ Function extracting tags from a page
-> [Page a] -- ^ Pages
-> Tags a -- ^ Resulting tags
readTagsWith f pages = Tags
{ tagsMap = foldl (M.unionWith (++)) M.empty (map readTagsWith' pages)
}
where
-- Create a tag map for one page
readTagsWith' page =
let tags = f page
in M.fromList $ zip tags $ repeat [page]
-- | Read a tagmap using the @tags@ metadata field
--
readTags :: [Page a] -> Tags a
readTags = readTagsWith $ map trim . splitAll "," . getField "tags"
-- | Read a tagmap using the @category@ metadata field
--
readCategories :: [Page a] -> Tags a
readCategories = readTagsWith $ return . getField "category"
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