-- |
-- Module      :  Text.Mustache.Compile.TH
-- Copyright   :  © 2016 Stack Builders
-- License     :  BSD 3 clause
--
-- Maintainer  :  Mark Karpov <markkarpov@openmailbox.org>
-- Stability   :  experimental
-- Portability :  portable
--
-- Template Haskell helpers to compile Mustache templates at compile time.
-- This module is not imported as part of "Text.Mustache", so you need to
-- import it yourself. Qualified import is recommended, but not necessary.
--
-- At the moment, functions in this module only work with GHC 8 (they
-- require at least @template-haskell-2.11@).

{-# LANGUAGE CPP               #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RankNTypes        #-}
{-# LANGUAGE TemplateHaskell   #-}

module Text.Mustache.Compile.TH
  ( compileMustacheDir
  , compileMustacheFile
  , compileMustacheText
  , mustache )
where

import Control.Monad.Catch (try)
import Data.Text.Lazy (Text)
import Data.Typeable (cast)
import Language.Haskell.TH hiding (Dec)
import Language.Haskell.TH.Quote (QuasiQuoter (..))
import Language.Haskell.TH.Syntax (lift)
import Text.Megaparsec hiding (try)
import Text.Mustache.Type
import qualified Data.Text             as T
import qualified Data.Text.Lazy        as TL
import qualified Text.Mustache.Compile as C

#if !MIN_VERSION_base(4,8,0)
import Control.Applicative
#endif

#if MIN_VERSION_template_haskell(2,11,0)
import Language.Haskell.TH.Syntax (dataToExpQ)
#else
import Data.Data (Data)
dataToExpQ :: Data a => (forall b. Data b => b -> Maybe (Q Exp)) -> a -> Q Exp
dataToExpQ _ _ = fail "The feature requires at least GHC 8 to work"
#endif

-- | Compile all templates in specified directory and select one. Template
-- files should have extension @mustache@, (e.g. @foo.mustache@) to be
-- recognized. This function /does not/ scan the directory recursively.
--
-- This version compiles the templates at compile time.

compileMustacheDir
  :: PName             -- ^ Which template to select after compiling
  -> FilePath          -- ^ Directory with templates
  -> Q Exp             -- ^ The resulting template
compileMustacheDir pname path =
  (runIO . try) (C.compileMustacheDir pname path) >>= handleEither

-- | Compile single Mustache template and select it.
--
-- This version compiles the template at compile time.

compileMustacheFile
  :: FilePath          -- ^ Location of the file
  -> Q Exp
compileMustacheFile path =
  (runIO . try) (C.compileMustacheFile path) >>= handleEither

-- | Compile Mustache template from 'Text' value. The cache will contain
-- only this template named according to given 'Key'.
--
-- This version compiles the template at compile time.

compileMustacheText
  :: PName             -- ^ How to name the template?
  -> Text              -- ^ The template to compile
  -> Q Exp
compileMustacheText pname text =
  handleEither (C.compileMustacheText pname text)

-- | Compile Mustache using QuasiQuoter. Usage:
--
-- > {-# LANGUAGE QuasiQuotes #-}
-- > import Text.Mustache.Compile.TH (mustache)
-- >
-- > foo :: Template
-- > foo = [mustache|This is my inline {{ template }}.|]
--
-- Name of created partial is set to @"quasi-quoted"@. You can extend cache
-- of 'Template' created this way using 'mappend' and so work with partials
-- as usual.
--
-- @since 0.1.7

mustache :: QuasiQuoter
mustache = QuasiQuoter
  { quoteExp  = compileMustacheText "quasi-quoted" . TL.pack
  , quotePat  = undefined
  , quoteType = undefined
  , quoteDec  = undefined }

-- | Given an 'Either' result return 'Right' and signal pretty-printed error
-- if we have a 'Left'.

handleEither :: Either (ParseError Char Dec) Template -> Q Exp
handleEither val =
  case val of
    Left err -> fail (parseErrorPretty err)
    Right template -> dataToExpQ (fmap liftText . cast) template

-- | Lift strict 'T.Text' to 'Q' 'Exp'.

liftText :: T.Text -> Q Exp
liftText txt = AppE (VarE 'T.pack) <$> lift (T.unpack txt)