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-- | Module containing various functions to manipulate contexts.
module Text.Hakyll.Context
( Context
, ContextManipulation
, renderValue
, changeValue
, renderDate
, changeExtension
) where
import qualified Data.Map as M
import Data.Map (Map)
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 Text.Hakyll.Regex (substituteRegex)
-- | Type for a context.
type Context = Map String String
-- | 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.
-> ContextManipulation
renderValue src dst f context = case M.lookup src context of
Nothing -> context
(Just value) -> M.insert dst (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 of which the value should be changed.
-> (String -> String) -- ^ Function to apply on the value.
-> ContextManipulation
changeValue key = renderValue key key
-- | 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 value when the date cannot be parsed.
-> ContextManipulation
renderDate key format defaultValue context = M.insert key value context
where
value = fromMaybe defaultValue pretty
pretty = do filePath <- M.lookup "path" context
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.
-> ContextManipulation
changeExtension extension = changeValue "url" changeExtension'
where
changeExtension' = flip addExtension extension . dropExtension
|
