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-- | Module containing various functions to manipulate contexts.
module Text.Hakyll.Context
( Context
, ContextManipulation
, renderValue
, changeValue
, copyValue
, renderDate
, changeExtension
) where
import Control.Arrow (arr)
import System.Locale (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.HakyllAction (HakyllAction)
import Text.Hakyll.Hakyll (Context)
-- | Type for context manipulating functions.
type ContextManipulation = Context -> Context
-- | Do something with a value in a @Context@, but keep the old value as well.
-- This is probably the most common function to construct a
-- @ContextManipulation@.
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.
-> HakyllAction Context Context
renderValue source destination f = arr $ \context ->
case M.lookup source context of
Nothing -> context
(Just value) -> M.insert destination (f value) context
-- | Change a value in a @Context@.
--
-- > 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.
-> HakyllAction Context Context
changeValue key = renderValue key key
-- | Copy a value from one key to another in a @Context@.
copyValue :: String -- ^ Source key.
-> String -- ^ Destination key.
-> HakyllAction Context Context
copyValue source destination = renderValue source destination id
-- | When the context has a key called @path@ in a @yyyy-mm-dd-title.extension@
-- format (default 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.
-> HakyllAction Context Context
renderDate 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 defaultTimeLocale 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.
--
-- > renderChainWith (changeExtension "php")
-- > ["templates/default.html"]
-- > (createPagePath "test.markdown")
--
-- Will render to @test.php@ instead of @test.html@.
changeExtension :: String -- ^ Extension to change to.
-> HakyllAction Context Context
changeExtension extension = changeValue "url" changeExtension'
where
changeExtension' = flip addExtension extension . dropExtension
|
