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-- | This module exports a number of functions to manipulate metadata of
-- resources
--
module Text.Hakyll.ContextManipulations
( renderValue
, changeValue
, changeUrl
, copyValue
, renderDate
, renderDateWithLocale
, changeExtension
) where
import System.Locale (TimeLocale, defaultTimeLocale)
import System.FilePath (takeFileName, addExtension, dropExtension)
import Data.Time.Format (parseTime, formatTime)
import Data.Time.Clock (UTCTime)
import Data.Maybe (fromMaybe)
import qualified Data.Map as M
import Text.Hakyll.Regex (substituteRegex)
import Text.Hakyll.Transformer (Transformer (..), transformMetadata)
import Text.Hakyll.Resource
-- | Do something with a value in a @Context@, but keep the old value as well.
-- If the key given is not present in the @Context@, nothing will happen.
--
renderValue :: 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.
-> Transformer a a -- ^ Resulting transformer
renderValue source destination f = transformMetadata $ \(Metadata m) ->
Metadata $ case M.lookup source m of
Nothing -> m
(Just value) -> M.insert destination (f value) m
-- | Change a value in the metadata
--
-- > import Data.Char (toUpper)
-- > changeValue "title" (map toUpper)
--
-- Will put the title in UPPERCASE.
changeValue :: String -- ^ Key to change.
-> (String -> String) -- ^ Function to apply on the value.
-> Transformer a a
changeValue key = renderValue key key
-- | Change the URL of a page. You should always use this function instead of
-- 'changeValue' for this, because using 'changeValue' might break dependency
-- handling when changing the @url@ field.
--
changeUrl :: (String -> String) -- ^ Function to change URL with.
-> Transformer a a -- ^ Resulting action.
changeUrl f = let t = changeValue "url" f
in t {transformerUrl = return . f}
-- | Copy a metadata value from one key to another
--
copyValue :: String -- ^ Source key.
-> String -- ^ Destination key.
-> Transformer a a -- ^ Resulting transformer
copyValue source destination = renderValue source destination id
-- | When the context has a key called @path@ in a
-- @folder/yyyy-mm-dd-title.extension@ format (the convention for pages),
-- this function can render the date.
--
-- > renderDate "date" "%B %e, %Y" "Date unknown"
--
-- Will render something like @January 32, 2010@.
--
renderDate :: String -- ^ Key in which the rendered date should be placed.
-> String -- ^ Format to use on the date.
-> String -- ^ Default key, in case the date cannot be parsed.
-> Transformer a a
renderDate = renderDateWithLocale defaultTimeLocale
-- | This is an extended version of 'renderDate' that allows you to specify a
-- time locale that is used for outputting the date. For more details, see
-- 'renderDate'.
--
renderDateWithLocale :: TimeLocale -- ^ Output time locale.
-> String -- ^ Destination key.
-> String -- ^ Format to use on the date.
-> String -- ^ Default key.
-> Transformer a a
renderDateWithLocale locale key format defaultValue =
renderValue "path" key renderDate'
where
renderDate' filePath = fromMaybe defaultValue $ do
let dateString = substituteRegex "^([0-9]*-[0-9]*-[0-9]*).*" "\\1"
(takeFileName filePath)
time <- parseTime defaultTimeLocale
"%Y-%m-%d"
dateString :: Maybe UTCTime
return $ formatTime locale format time
-- | Change the extension of a file. This is only needed when you want to
-- render, for example, mardown to @.php@ files instead of @.html@ files.
--
-- > changeExtension "php"
--
-- Will render @test.markdown@ to @test.php@ instead of @test.html@.
changeExtension :: String -- ^ Extension to change to.
-> Transformer a a -- ^ Resulting transformer
changeExtension extension = changeValue "url" changeExtension'
where
changeExtension' = flip addExtension extension . dropExtension
|
