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

      -- * Functions working on pages/compilers
    , pageReadPandoc
    , pageReadPandocWith
    , pageRenderPandoc
    , pageRenderPandocWith

      -- * Default options
    , defaultParserState
    , defaultWriterOptions
    ) where

import Prelude hiding (id)
import Control.Applicative ((<$>))
import Control.Arrow ((>>^), (&&&))
import Control.Category (id)

import Text.Pandoc (Pandoc)
import qualified Text.Pandoc as P

import Hakyll.Core.Compiler
import Hakyll.Web.FileType
import Hakyll.Web.Page

-- | Read a string using pandoc, with the default options
--
readPandoc :: FileType  -- ^ File type, determines how parsing happens
           -> String    -- ^ String to read
           -> Pandoc    -- ^ Resulting document
readPandoc = readPandocWith defaultParserState

-- | Read a string using pandoc, with the supplied options
--
readPandocWith :: P.ParserState  -- ^ Parser options
               -> FileType       -- ^ File type, determines how parsing happens
               -> String         -- ^ String to read
               -> Pandoc         -- ^ Resulting document
readPandocWith state fileType' = case fileType' of
    Html              -> P.readHtml state
    LaTeX             -> P.readLaTeX state
    LiterateHaskell t -> readPandocWith state {P.stateLiterateHaskell = True} t
    Markdown          -> P.readMarkdown state
    Rst               -> P.readRST state
    t                 -> error $
        "readPandoc: I don't know how to read " ++ show t

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

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

-- | Read the resource using pandoc
--
pageReadPandoc :: Compiler (Page String) (Page Pandoc)
pageReadPandoc = pageReadPandocWith defaultParserState

-- | Read the resource using pandoc
--
pageReadPandocWith :: P.ParserState -> Compiler (Page String) (Page Pandoc)
pageReadPandocWith state =
    id &&& getFileType >>^ pageReadPandocWith'
  where
    pageReadPandocWith' (p, t) = readPandocWith state t <$> p

-- | Render the resource using pandoc
--
pageRenderPandoc :: Compiler (Page String) (Page String)
pageRenderPandoc = pageRenderPandocWith defaultParserState defaultWriterOptions

-- | Render the resource using pandoc
--
pageRenderPandocWith :: P.ParserState
                     -> P.WriterOptions
                     -> Compiler (Page String) (Page String)
pageRenderPandocWith state options =
    pageReadPandocWith state >>^ (fmap $ writePandocWith options)

-- | The default reader options for pandoc parsing in hakyll
--
defaultParserState :: P.ParserState
defaultParserState = P.defaultParserState
    { -- The following option causes pandoc to read smart typography, a nice
      -- and free bonus.
      P.stateSmart = True
    }

-- | The default writer options for pandoc rendering in hakyll
--
defaultWriterOptions :: P.WriterOptions
defaultWriterOptions = P.defaultWriterOptions
    { -- This option causes literate haskell to be written using '>' marks in
      -- html, which I think is a good default.
      P.writerLiterateHaskell = True
    }