{-# LANGUAGE GHC2021 #-}
{-# LANGUAGE OverloadedStrings #-}
module Compilers
    ( essayCompiler
    , postCompiler
    , pageCompiler
    , poetryCompiler
    , fictionCompiler
    , compositionCompiler
    , readerOpts
    , writerOpts
    ) where

import           Hakyll
import           Hakyll.Core.Metadata       (lookupStringList)
import           Text.Pandoc.Definition     (Pandoc (..), Block (..),
                                             Inline (..))
import           Text.Pandoc.Options        (ReaderOptions (..), WriterOptions (..),
                                             HTMLMathMethod (..))
import           Text.Pandoc.Extensions     (enableExtension, Extension (..))
import qualified Data.Text                  as T
import           Data.Maybe                 (fromMaybe)
import           System.FilePath            (takeDirectory)
import           Utils                      (wordCount, readingTime, escapeHtml)
import           Filters                    (applyAll, preprocessSource)
import qualified Citations
import qualified Filters.Score              as Score
import qualified Filters.Viz               as Viz

-- ---------------------------------------------------------------------------
-- Reader / writer options
-- ---------------------------------------------------------------------------

readerOpts :: ReaderOptions
readerOpts = defaultHakyllReaderOptions

-- | Reader options with hard_line_breaks enabled — every source newline within
--   a paragraph becomes a <br>. Used for poetry so stanza lines render as-is.
poetryReaderOpts :: ReaderOptions
poetryReaderOpts = readerOpts
    { readerExtensions = enableExtension Ext_hard_line_breaks
                            (readerExtensions readerOpts) }

writerOpts :: WriterOptions
writerOpts = defaultHakyllWriterOptions
    { writerHTMLMathMethod  = KaTeX ""
    , writerHighlightStyle  = Nothing
    , writerNumberSections  = False
    , writerTableOfContents = False
    }

-- ---------------------------------------------------------------------------
-- Inline stringification (local, avoids depending on Text.Pandoc.Shared)
-- ---------------------------------------------------------------------------

stringify :: [Inline] -> T.Text
stringify = T.concat . map inlineToText
  where
    inlineToText (Str t)           = t
    inlineToText Space             = " "
    inlineToText SoftBreak         = " "
    inlineToText LineBreak         = " "
    inlineToText (Emph ils)        = stringify ils
    inlineToText (Strong ils)      = stringify ils
    inlineToText (Strikeout ils)   = stringify ils
    inlineToText (Superscript ils) = stringify ils
    inlineToText (Subscript ils)   = stringify ils
    inlineToText (SmallCaps ils)   = stringify ils
    inlineToText (Quoted _ ils)    = stringify ils
    inlineToText (Cite _ ils)      = stringify ils
    inlineToText (Code _ t)        = t
    inlineToText (RawInline _ t)   = t
    inlineToText (Link _ ils _)    = stringify ils
    inlineToText (Image _ ils _)   = stringify ils
    inlineToText (Note _)          = ""
    inlineToText (Span _ ils)      = stringify ils
    inlineToText _                 = ""

-- ---------------------------------------------------------------------------
-- TOC extraction
-- ---------------------------------------------------------------------------

-- | Collect (level, identifier, title-text) for h2/h3 headings.
collectHeadings :: Pandoc -> [(Int, T.Text, String)]
collectHeadings (Pandoc _ blocks) = concatMap go blocks
  where
    go (Header lvl (ident, _, _) inlines)
        | lvl == 2 || lvl == 3
        = [(lvl, ident, T.unpack (stringify inlines))]
    go _ = []

-- ---------------------------------------------------------------------------
-- TOC tree
-- ---------------------------------------------------------------------------

data TOCNode = TOCNode T.Text String [TOCNode]

buildTree :: [(Int, T.Text, String)] -> [TOCNode]
buildTree = go 2
  where
    go _ [] = []
    go lvl ((l, i, t) : rest)
        | l == lvl  =
            let (childItems, remaining) = span (\(l', _, _) -> l' > lvl) rest
                children                = go (lvl + 1) childItems
            in  TOCNode i t children : go lvl remaining
        | l < lvl   = []
        | otherwise = go lvl rest   -- skip unexpected deeper items at this level

renderTOC :: [TOCNode] -> String
renderTOC [] = ""
renderTOC nodes = "<ol>\n" ++ concatMap renderNode nodes ++ "</ol>\n"
  where
    renderNode (TOCNode i t children) =
        "<li><a href=\"#" ++ T.unpack i ++ "\" data-target=\"" ++ T.unpack i ++ "\">"
        ++ Utils.escapeHtml t ++ "</a>" ++ renderTOC children ++ "</li>\n"

-- | Build a TOC HTML string from a Pandoc document.
buildTOC :: Pandoc -> String
buildTOC doc = renderTOC (buildTree (collectHeadings doc))

-- ---------------------------------------------------------------------------
-- Compilers
-- ---------------------------------------------------------------------------

-- | Shared compiler pipeline parameterised on reader options.
--   Saves toc/word-count/reading-time/bibliography snapshots.
essayCompilerWith :: ReaderOptions -> Compiler (Item String)
essayCompilerWith rOpts = do
    -- Raw Markdown source (used for word count / reading time).
    body <- getResourceBody
    let src = itemBody body

    -- Apply source-level preprocessors (wikilinks, etc.) before parsing.
    let body' = itemSetBody (preprocessSource src) body

    -- Parse to Pandoc AST.
    pandocItem <- readPandocWith rOpts body'

    -- Get further-reading keys from Hakyll metadata (YAML frontmatter is stripped
    -- before being passed to readPandocWith, so we read it from Hakyll instead).
    ident <- getUnderlying
    meta  <- getMetadata ident
    let frKeys = map T.pack $ fromMaybe [] (lookupStringList "further-reading" meta)

    -- Run citeproc, transform citation spans → superscripts, extract bibliography.
    (pandocWithCites, bibHtml, furtherHtml) <- unsafeCompiler $
        Citations.applyCitations frKeys (itemBody pandocItem)

    -- Inline SVG score fragments and data visualizations (both read files
    -- relative to the source file's directory).
    filePath <- getResourceFilePath
    let srcDir = takeDirectory filePath
    pandocWithScores <- unsafeCompiler $
        Score.inlineScores srcDir pandocWithCites
    pandocWithViz <- unsafeCompiler $
        Viz.inlineViz srcDir pandocWithScores

    -- Apply remaining AST-level filters (sidenotes, smallcaps, links, etc.).
    let pandocFiltered = applyAll pandocWithViz
    let pandocItem'    = itemSetBody pandocFiltered pandocItem

    -- Build TOC from the filtered AST.
    let toc = buildTOC pandocFiltered

    -- Write HTML.
    let htmlItem = writePandocWith writerOpts pandocItem'

    -- Save snapshots keyed to this item's identifier.
    _ <- saveSnapshot "toc"                  (itemSetBody toc                            htmlItem)
    _ <- saveSnapshot "word-count"           (itemSetBody (show (wordCount src))         htmlItem)
    _ <- saveSnapshot "reading-time"         (itemSetBody (show (readingTime src))       htmlItem)
    _ <- saveSnapshot "bibliography"         (itemSetBody (T.unpack bibHtml)             htmlItem)
    _ <- saveSnapshot "further-reading-refs" (itemSetBody (T.unpack furtherHtml)         htmlItem)

    return htmlItem

-- | Compiler for essays.
essayCompiler :: Compiler (Item String)
essayCompiler = essayCompilerWith readerOpts

-- | Compiler for blog posts: same pipeline as essays.
postCompiler :: Compiler (Item String)
postCompiler = essayCompiler

-- | Compiler for poetry: enables hard_line_breaks so each source line becomes
--   a <br>, preserving verse line endings without manual trailing-space markup.
poetryCompiler :: Compiler (Item String)
poetryCompiler = essayCompilerWith poetryReaderOpts

-- | Compiler for fiction: same pipeline as essays; visual differences are
--   handled entirely by the reading template and reading.css.
fictionCompiler :: Compiler (Item String)
fictionCompiler = essayCompiler

-- | Compiler for music composition landing pages: full essay pipeline
--   (TOC, sidenotes, score fragments, citations, smallcaps, etc.).
compositionCompiler :: Compiler (Item String)
compositionCompiler = essayCompiler

-- | Compiler for simple pages: filters applied, no TOC snapshot.
pageCompiler :: Compiler (Item String)
pageCompiler = do
    body <- getResourceBody
    let src   = itemBody body
        body' = itemSetBody (preprocessSource src) body
    pandocItem <- fmap (fmap applyAll) (readPandocWith readerOpts body')
    let htmlItem = writePandocWith writerOpts pandocItem
    _ <- saveSnapshot "word-count"   (itemSetBody (show (wordCount src))   htmlItem)
    _ <- saveSnapshot "reading-time" (itemSetBody (show (readingTime src)) htmlItem)
    return htmlItem