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module Hakyll.Web.Template
( Template
, readTemplate
, applyTemplate
, applySelf
) where
import Data.List (isPrefixOf)
import Data.Char (isAlphaNum)
import Data.Maybe (fromMaybe)
import qualified Data.Map as M
import Hakyll.Web.Template.Internal
import Hakyll.Web.Page
-- | Construct a @Template@ from a string.
--
readTemplate :: String -> Template
readTemplate = Template . readTemplate'
where
readTemplate' [] = []
readTemplate' string
| "$$" `isPrefixOf` string =
let (key, rest) = readIdentifier $ drop 2 string
in Escaped key : readTemplate' rest
| "$" `isPrefixOf` string =
let (key, rest) = readIdentifier $ drop 1 string
in Identifier key : readTemplate' rest
| otherwise =
let (chunk, rest) = break (== '$') string
in Chunk chunk : readTemplate' rest
-- Parse an identifier into (identifier, rest)
readIdentifier = span isAlphaNum
-- | Substitutes @$identifiers@ in the given @Template@ by values from the given
-- "Page". When a key is not found, it is left as it is. You can specify
-- the characters used to replace escaped dollars (@$$@) here.
--
applyTemplate :: Template -> Page String -> Page String
applyTemplate template page =
fmap (const $ substitute =<< unTemplate template) page
where
substitute (Chunk chunk) = chunk
substitute (Identifier key) =
fromMaybe ('$' : key) $ M.lookup key $ toMap page
substitute (Escaped key) = '$' : key
-- | Apply a page as it's own template. This is often very useful to fill in
-- certain keys like @$root@ and @$url@.
--
applySelf :: Page String -> Page String
applySelf page = applyTemplate (readTemplate $ pageBody page) page
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