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-- | Module exporting convenient pandoc bindings
module Hakyll.Web.Pandoc
    ( -- * The basic building blocks
      readPandoc
    , readPandocWith
    , writePandoc
    , writePandocWith
    , renderPandoc
    , renderPandocWith

      -- * Derived compilers
    , pandocCompiler
    , pandocCompilerWith
    , pandocCompilerWithTransform

      -- * Default options
    , defaultHakyllReaderOptions
    , defaultHakyllWriterOptions
    ) where


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import           Control.Applicative        ((<$>))
import qualified Data.Set                   as S
import           Text.Pandoc


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import           Hakyll.Core.Compiler
import           Hakyll.Core.Item
import           Hakyll.Web.Pandoc.FileType


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-- | Read a string using pandoc, with the default options
readPandoc :: Item String  -- ^ String to read
           -> Item Pandoc  -- ^ Resulting document
readPandoc = readPandocWith defaultHakyllReaderOptions


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-- | Read a string using pandoc, with the supplied options
readPandocWith :: ReaderOptions  -- ^ Parser options
               -> Item String    -- ^ String to read
               -> Item Pandoc    -- ^ Resulting document
readPandocWith ropt item = fmap (reader ropt (itemFileType item)) item
  where
    reader ro t = case t of
        Html               -> readHtml ro
        LaTeX              -> readLaTeX ro
        LiterateHaskell t' -> reader (addExt ro Ext_literate_haskell) t'
        Markdown           -> readMarkdown ro
        Rst                -> readRST ro
        Textile            -> readTextile ro
        _                  -> error $
            "Hakyll.Web.readPandocWith: I don't know how to read a file of " ++
            "the type " ++ show t ++ " for: " ++ show (itemIdentifier item)

    addExt ro e = ro {readerExtensions = S.insert e $ readerExtensions ro}


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-- | Write a document (as HTML) using pandoc, with the default options
writePandoc :: Item Pandoc  -- ^ Document to write
            -> Item String  -- ^ Resulting HTML
writePandoc = writePandocWith defaultHakyllWriterOptions


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-- | Write a document (as HTML) using pandoc, with the supplied options
writePandocWith :: WriterOptions  -- ^ Writer options for pandoc
                -> Item Pandoc    -- ^ Document to write
                -> Item String    -- ^ Resulting HTML
writePandocWith wopt = fmap $ writeHtmlString wopt


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-- | Render the resource using pandoc
renderPandoc :: Item String -> Item String
renderPandoc =
    renderPandocWith defaultHakyllReaderOptions defaultHakyllWriterOptions


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-- | Render the resource using pandoc
renderPandocWith :: ReaderOptions -> WriterOptions -> Item String -> Item String
renderPandocWith ropt wopt = writePandocWith wopt . readPandocWith ropt


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-- | Read a page render using pandoc
pandocCompiler :: Compiler (Item String)
pandocCompiler =
    pandocCompilerWith defaultHakyllReaderOptions defaultHakyllWriterOptions


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-- | A version of 'pandocCompiler' which allows you to specify your own pandoc
-- options
pandocCompilerWith :: ReaderOptions -> WriterOptions -> Compiler (Item String)
pandocCompilerWith ropt wopt = pandocCompilerWithTransform ropt wopt id


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-- | An extension of 'pandocCompilerWith' which allows you to specify a custom
-- pandoc transformation for the content
pandocCompilerWithTransform :: ReaderOptions -> WriterOptions
                            -> (Pandoc -> Pandoc)
                            -> Compiler (Item String)
pandocCompilerWithTransform ropt wopt f = cached cacheName $
    writePandocWith wopt . fmap f . readPandocWith ropt <$> getResourceBody
  where
    cacheName = "Hakyll.Web.Page.pageCompilerWithPandoc"


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-- | The default reader options for pandoc parsing in hakyll
defaultHakyllReaderOptions :: ReaderOptions
defaultHakyllReaderOptions = def
    { -- The following option causes pandoc to read smart typography, a nice
      -- and free bonus.
      readerSmart = True
    }


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-- | The default writer options for pandoc rendering in hakyll
defaultHakyllWriterOptions :: WriterOptions
defaultHakyllWriterOptions = def
    { -- This option causes literate haskell to be written using '>' marks in
      -- html, which I think is a good default.
      writerExtensions = S.insert Ext_literate_haskell (writerExtensions def)
    }