{-# LANGUAGE OverloadedStrings #-}

import Hakyll hiding (pandocCompiler)
import Text.Pandoc.Options
import Text.Pandoc.Highlighting

-- Pass custom options to the Pandoc compiler
pandocCompiler :: Compiler (Item String)
pandocCompiler = pandocCompilerWith readerOptions writerOptions where
  writerOptions = defaultHakyllWriterOptions {
    writerExtensions = writerExtensions defaultHakyllWriterOptions
      <> pandocExtensions,
    writerHTMLMathMethod = MathML
  }
  readerOptions = defaultHakyllReaderOptions {
    readerExtensions = readerExtensions defaultHakyllReaderOptions
      <> pandocExtensions
      <> extensionsFromList [Ext_lists_without_preceding_blankline]
  }

-- Loads the template specified in a post's metadata, if it exists
loadLayoutTemplate :: Context String -> Item String -> Compiler (Item String)
loadLayoutTemplate context item = do
  field <- getMetadataField (itemIdentifier item) "layout"
  case field of
    Just path ->
      let templatePath = "_templates/" ++ path ++ ".html" in
      loadAndApplyTemplate (fromFilePath templatePath) context item
    _ -> return item

main :: IO ()
main = hakyll $ do
  -- Compile templates for future use
  match "_templates/*" $ compile templateBodyCompiler

  -- Detect whether HTML files are standalone or in need of a template
  match ("**.html" .||. "**.htm") $ do
    route idRoute
    compile $ do
      identifier <- getUnderlying
      field <- getMetadataField identifier "layout"
      case field of
        Just _ -> pandocCompiler
        Nothing -> getResourceBody
      >>= loadLayoutTemplate defaultContext
      >>= relativizeUrls

  -- Match all other renderable files and apply their template, if it exists
  match ("**.md" .||. "**.rst" .||. "**.org" .||. "**.adoc") $ do
    route $ setExtension "html"
    compile $ pandocCompiler
      >>= loadLayoutTemplate defaultContext
      >>= relativizeUrls

  -- Additionally copy non-HTML files raw, without front matter
  match ("**.md" .||. "**.rst" .||. "**.org" .||. "**.adoc") $ version "raw" $ do
    route idRoute
    compile getResourceBody

  -- Copy all additional files verbatium
  match "**" $ do
    route idRoute
    compile copyFileCompiler