-- | Provides various functions to manipulate the metadata fields of a page -- module Hakyll.Web.Page.Metadata ( getField , getFieldMaybe , setField , trySetField , setFieldA , setFieldPage , renderField , changeField , copyField , renderDateField , renderDateFieldWith , renderModificationTime , renderModificationTimeWith , copyBodyToField , copyBodyFromField , comparePagesByDate ) where import Control.Arrow (Arrow, arr, (>>>), (***), (&&&)) import Control.Category (id) import Control.Monad (msum) import Data.List (intercalate) import Data.Maybe (fromMaybe) import Data.Ord (comparing) import Prelude hiding (id) import System.FilePath (takeFileName) import System.Locale (TimeLocale, defaultTimeLocale) import qualified Data.Map as M import Data.Time.Calendar (Day (..)) import Data.Time.Clock (UTCTime (..)) import Data.Time.Format (parseTime, formatTime) import Hakyll.Web.Page.Internal import Hakyll.Core.Util.String import Hakyll.Core.Identifier import Hakyll.Core.Compiler import Hakyll.Core.Resource.Provider -- | Get a metadata field. If the field does not exist, the empty string is -- returned. -- getField :: String -- ^ Key -> Page a -- ^ Page -> String -- ^ Value getField key = fromMaybe "" . getFieldMaybe key -- | Get a field in a 'Maybe' wrapper -- getFieldMaybe :: String -- ^ Key -> Page a -- ^ Page -> Maybe String -- ^ Value, if found getFieldMaybe key = M.lookup key . pageMetadata -- | Version of 'trySetField' which overrides any previous value -- setField :: String -- ^ Key -> String -- ^ Value -> Page a -- ^ Page to add it to -> Page a -- ^ Resulting page setField k v (Page m b) = Page (M.insert k v m) b -- | Add a metadata field. If the field already exists, it is not overwritten. -- trySetField :: String -- ^ Key -> String -- ^ Value -> Page a -- ^ Page to add it to -> Page a -- ^ Resulting page trySetField k v (Page m b) = Page (M.insertWith (flip const) k v m) b -- | Arrow-based variant of 'setField'. Because of it's type, this function is -- very usable together with the different 'require' functions. -- setFieldA :: Arrow a => String -- ^ Key -> a x String -- ^ Value arrow -> a (Page b, x) (Page b) -- ^ Resulting arrow setFieldA k v = id *** v >>> arr (uncurry $ flip $ setField k) -- | Set a field of a page to the contents of another page -- setFieldPage :: String -- ^ Key to add the page under -> Identifier (Page String) -- ^ Page to add -> Compiler (Page a) (Page a) -- ^ Page compiler setFieldPage key page = id &&& require_ page >>> setFieldA key (arr pageBody) -- | Do something with a metadata value, but keep the old value as well. If the -- key given is not present in the metadata, nothing will happen. If the source -- and destination keys are the same, the value will be changed (but you should -- use 'changeField' for this purpose). -- renderField :: String -- ^ Key of which the value should be copied -> String -- ^ Key the value should be copied to -> (String -> String) -- ^ Function to apply on the value -> Page a -- ^ Page on which this should be applied -> Page a -- ^ Resulting page renderField src dst f page = case M.lookup src (pageMetadata page) of Nothing -> page Just value -> setField dst (f value) page -- | Change a metadata value. -- -- > import Data.Char (toUpper) -- > changeField "title" (map toUpper) -- -- Will put the title in UPPERCASE. -- changeField :: String -- ^ Key to change. -> (String -> String) -- ^ Function to apply on the value. -> Page a -- ^ Page to change -> Page a -- ^ Resulting page changeField key = renderField key key -- | Make a copy of a metadata field (put the value belonging to a certain key -- under some other key as well) -- copyField :: String -- ^ Key to copy -> String -- ^ Destination to copy to -> Page a -- ^ Page on which this should be applied -> Page a -- ^ Resulting page copyField src dst = renderField src dst id -- | When the metadata has a field called @published@ in one of the -- following formats then this function can render the date. -- -- * @Sun, 01 Feb 2000 13:00:00 UT@ (RSS date format) -- -- * @2000-02-01T13:00:00Z@ (Atom date format) -- -- * @February 1, 2000 1:00 PM@ (PM is usually uppercase) -- -- * @February 1, 2000@ (assumes 12:00 AM for the time) -- -- Alternatively, when the metadata has a field called @path@ in a -- @folder/yyyy-mm-dd-title.extension@ format (the convention for pages) -- and no @published@ metadata field set, this function can render -- the date. -- -- > renderDateField "date" "%B %e, %Y" "Date unknown" -- -- Will render something like @January 32, 2010@. -- renderDateField :: String -- ^ Key in which the rendered date should be placed -> String -- ^ Format to use on the date -> String -- ^ Default value, in case the date cannot be parsed -> Page a -- ^ Page on which this should be applied -> Page a -- ^ Resulting page renderDateField = renderDateFieldWith defaultTimeLocale -- | This is an extended version of 'renderDateField' that allows you to -- specify a time locale that is used for outputting the date. For more -- details, see 'renderDateField'. -- renderDateFieldWith :: TimeLocale -- ^ Output time locale -> String -- ^ Destination key -> String -- ^ Format to use on the date -> String -- ^ Default value -> Page a -- ^ Target page -> Page a -- ^ Resulting page renderDateFieldWith locale key format defaultValue page = setField key renderTimeString page where renderTimeString = fromMaybe defaultValue $ do time <- getUTCMaybe locale page return $ formatTime locale format time -- | Parser to try to extract and parse the time from the @published@ -- field or from the filename. See 'renderDateField' for more information. getUTCMaybe :: TimeLocale -- ^ Output time locale -> Page a -- ^ Input page -> Maybe UTCTime -- ^ Parsed UTCTime getUTCMaybe locale page = msum [ fromPublished "%a, %d %b %Y %H:%M:%S UT" , fromPublished "%Y-%m-%dT%H:%M:%SZ" , fromPublished "%B %e, %Y %l:%M %p" , fromPublished "%B %e, %Y" , getFieldMaybe "path" page >>= parseTime' "%Y-%m-%d" . intercalate "-" . take 3 . splitAll "-" . takeFileName ] where fromPublished f = getFieldMaybe "published" page >>= parseTime' f parseTime' f str = parseTime locale f str -- | Set the modification time as a field in the page renderModificationTime :: String -- ^ Destination key -> String -- ^ Format to use on the time -> Compiler (Page String) (Page String) -- ^ Resulting compiler renderModificationTime = renderModificationTimeWith defaultTimeLocale renderModificationTimeWith :: TimeLocale -- ^ Output time locale -> String -- ^ Destination key -> String -- ^ Format to use on the time -> Compiler (Page String) (Page String) -- ^ Resulting compiler renderModificationTimeWith locale key format = id &&& (getResource >>> getResourceWith resourceModificationTime) >>> setFieldA key (arr (formatTime locale format)) -- | Copy the body of a page to a metadata field -- copyBodyToField :: String -- ^ Destination key -> Page String -- ^ Target page -> Page String -- ^ Resulting page copyBodyToField key page = setField key (pageBody page) page -- | Copy a metadata field to the page body -- copyBodyFromField :: String -- ^ Source key -> Page String -- ^ Target page -> Page String -- ^ Resulting page copyBodyFromField key page = fmap (const $ getField key page) page -- | Compare pages by the date and time parsed as in 'renderDateField', -- where 'LT' implies earlier, and 'GT' implies later. For more details, -- see 'renderDateField'. comparePagesByDate :: Page a -> Page a -> Ordering comparePagesByDate = comparing $ fromMaybe zero . getUTCMaybe defaultTimeLocale where zero = UTCTime (ModifiedJulianDay 0) 0