/
Internal.hs
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/
Internal.hs
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{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE ScopedTypeVariables #-}
module Hakyll.Web.Template.Internal
( Template (..)
, template
, templateBodyCompiler
, templateCompiler
, applyTemplate
, applyTemplate'
, loadAndApplyTemplate
, applyAsTemplate
, readTemplate
, unsafeReadTemplateFile
, module Hakyll.Web.Template.Internal.Element
, module Hakyll.Web.Template.Internal.Trim
) where
--------------------------------------------------------------------------------
import Control.Monad.Except (MonadError (..))
import Data.Binary (Binary)
import Data.List (intercalate)
import Data.Typeable (Typeable)
import GHC.Exts (IsString (..))
import Prelude hiding (id)
--------------------------------------------------------------------------------
import Hakyll.Core.Compiler
import Hakyll.Core.Identifier
import Hakyll.Core.Item
import Hakyll.Core.Writable
import Hakyll.Web.Template.Context
import Hakyll.Web.Template.Internal.Element
import Hakyll.Web.Template.Internal.Trim
--------------------------------------------------------------------------------
-- | Datatype used for template substitutions.
newtype Template = Template
{ unTemplate :: [TemplateElement]
} deriving (Show, Eq, Binary, Typeable)
--------------------------------------------------------------------------------
instance Writable Template where
-- Writing a template is impossible
write _ _ = return ()
--------------------------------------------------------------------------------
instance IsString Template where
fromString = readTemplate
--------------------------------------------------------------------------------
-- | Wrap the constructor to ensure trim is called.
template :: [TemplateElement] -> Template
template = Template . trim
--------------------------------------------------------------------------------
readTemplate :: String -> Template
readTemplate = Template . trim . readTemplateElems
--------------------------------------------------------------------------------
-- | Read a template, without metadata header
templateBodyCompiler :: Compiler (Item Template)
templateBodyCompiler = cached "Hakyll.Web.Template.templateBodyCompiler" $ do
item <- getResourceBody
file <- getResourceFilePath
return $ fmap (template . readTemplateElemsFile file) item
--------------------------------------------------------------------------------
-- | Read complete file contents as a template
templateCompiler :: Compiler (Item Template)
templateCompiler = cached "Hakyll.Web.Template.templateCompiler" $ do
item <- getResourceString
file <- getResourceFilePath
return $ fmap (template . readTemplateElemsFile file) item
--------------------------------------------------------------------------------
applyTemplate :: Template -- ^ Template
-> Context a -- ^ Context
-> Item a -- ^ Page
-> Compiler (Item String) -- ^ Resulting item
applyTemplate tpl context item = do
body <- applyTemplate' (unTemplate tpl) context item
return $ itemSetBody body item
--------------------------------------------------------------------------------
applyTemplate'
:: forall a.
[TemplateElement] -- ^ Unwrapped Template
-> Context a -- ^ Context
-> Item a -- ^ Page
-> Compiler String -- ^ Resulting item
applyTemplate' tes context x = go tes
where
context' :: String -> [String] -> Item a -> Compiler ContextField
context' = unContext (context `mappend` missingField)
go = fmap concat . mapM applyElem
trimError = error $ "Hakyll.Web.Template.applyTemplate: template not " ++
"fully trimmed."
---------------------------------------------------------------------------
applyElem :: TemplateElement -> Compiler String
applyElem TrimL = trimError
applyElem TrimR = trimError
applyElem (Chunk c) = return c
applyElem (Expr e) = applyExpr e >>= getString e
applyElem Escaped = return "$"
applyElem (If e t mf) = (applyExpr e >> go t) `catchError` handler
where
handler _ = case mf of
Nothing -> return ""
Just f -> go f
applyElem (For e b s) = applyExpr e >>= \cf -> case cf of
StringField _ -> fail $
"Hakyll.Web.Template.applyTemplateWith: expected ListField but " ++
"got StringField for expr " ++ show e
ListField c xs -> do
sep <- maybe (return "") go s
bs <- mapM (applyTemplate' b c) xs
return $ intercalate sep bs
applyElem (Partial e) = do
p <- applyExpr e >>= getString e
Template tpl' <- loadBody (fromFilePath p)
applyTemplate' tpl' context x
---------------------------------------------------------------------------
applyExpr :: TemplateExpr -> Compiler ContextField
applyExpr (Ident (TemplateKey k)) = context' k [] x
applyExpr (Call (TemplateKey k) args) = do
args' <- mapM (\e -> applyExpr e >>= getString e) args
context' k args' x
applyExpr (StringLiteral s) = return (StringField s)
----------------------------------------------------------------------------
getString _ (StringField s) = return s
getString e (ListField _ _) = fail $
"Hakyll.Web.Template.applyTemplateWith: expected StringField but " ++
"got ListField for expr " ++ show e
--------------------------------------------------------------------------------
-- | The following pattern is so common:
--
-- > tpl <- loadBody "templates/foo.html"
-- > someCompiler
-- > >>= applyTemplate tpl context
--
-- That we have a single function which does this:
--
-- > someCompiler
-- > >>= loadAndApplyTemplate "templates/foo.html" context
loadAndApplyTemplate :: Identifier -- ^ Template identifier
-> Context a -- ^ Context
-> Item a -- ^ Page
-> Compiler (Item String) -- ^ Resulting item
loadAndApplyTemplate identifier context item = do
tpl <- loadBody identifier
applyTemplate tpl context item
--------------------------------------------------------------------------------
-- | It is also possible that you want to substitute @$key$@s within the body of
-- an item. This function does that by interpreting the item body as a template,
-- and then applying it to itself.
applyAsTemplate :: Context String -- ^ Context
-> Item String -- ^ Item and template
-> Compiler (Item String) -- ^ Resulting item
applyAsTemplate context item =
let tpl = template $ readTemplateElemsFile file (itemBody item)
file = toFilePath $ itemIdentifier item
in applyTemplate tpl context item
--------------------------------------------------------------------------------
unsafeReadTemplateFile :: FilePath -> Compiler Template
unsafeReadTemplateFile file = do
tpl <- unsafeCompiler $ readFile file
pure $ template $ readTemplateElemsFile file tpl