module TextViewport.Render.Segmentation where

import Data.DList qualified as DL
import Data.HashMap.Strict qualified as HM
import Data.List (minimumBy)
import Data.Ord (comparing)
import Data.Text (Text)
import Data.Text qualified as T
import Data.Vector (Vector)
import Data.Vector qualified as V
import Text.Hyphenation qualified as H
import TextViewport.Buffer.Item
import TextViewport.Render.RenderedLine (RenderedLine(..)) -- TODO qualified

applyStrategy :: SegmentStrategy -> Int -> Int -> Text -> Vector RenderedLine

applyStrategy NoSegments width itemIx txt =
  let rawLines = T.splitOn "\n" txt
      chunks  = map (T.take width) rawLines -- crop
      offsets = scanOffsetsWithNewlines chunks
  in V.fromList
       [ RenderedLine { rlText = chunk, rlItemIx = itemIx, rlLineIx = lineIx, rlCharStart = off }
       | (lineIx, (off, chunk)) <- zip [0..] (zip offsets chunks)
       ]

applyStrategy FixedWidthSegments width itemIx txt =
  let rawLines = T.splitOn "\n" txt
      (dl, _) = foldl step (DL.empty, 0) rawLines
      step (acc, off0) line =
        let chunks   = chunkFixed width line
            offsets  = scanOffsetsFrom off0 chunks
            offNext  = off0 + T.length line + 1
            acc'     = acc `DL.append` DL.fromList (zip offsets chunks)
        in (acc', offNext)
      allChunks = DL.toList dl
  in V.fromList
       [ RenderedLine { rlText = chunk, rlItemIx = itemIx, rlLineIx = lineIx, rlCharStart = off }
       | (lineIx, (off, chunk)) <- zip [0..] allChunks
       ]

applyStrategy (HyphenateSegments dict cache0) width itemIx txt =
  let rawLines = T.splitOn "\n" txt

      -- fold over each physical line, accumulating:
      --   * all rendered (offset, chunk) pairs
      --   * updated hyphenation cache (unused for now)
      --   * running character offset across lines
      (dl, _cache1, _) =
        foldl segmentOneLine (DL.empty, cache0, 0) rawLines
      allChunks = DL.toList dl
  in V.fromList
       [ RenderedLine { rlText = chunk, rlItemIx = itemIx, rlLineIx = lineIx, rlCharStart = off }
       | (lineIx, (off, chunk)) <- zip [0..] allChunks
       ]
  where
    -- Segment a single physical line using TeX‑lite hyphenation
    --segmentOneLine
    --  :: ([(Int, Text)], HM.HashMap Text [(Text, Text)], Int)
    --  -> Text
    --  -> ([(Int, Text)], HM.HashMap Text [(Text, Text)], Int)
    segmentOneLine (acc, cache, off0) line =
      let (chunks, cache1) = segmentWithHyphenationTeXLite dict width line cache
          offsets          = scanOffsetsFrom off0 chunks
          offNext          = off0 + T.length line + 1
          acc'             = acc `DL.append` DL.fromList (zip offsets chunks)
      in (acc', cache1, offNext)
    --segmentOneLine (acc, cache, off0) line =
    --  let chunks  = segmentWithHyphenationTeXLite dict width line
    --      offsets = scanOffsetsFrom off0 chunks
    --      offNext = off0 + T.length line + 1   -- +1 for newline
    --      acc'    = acc ++ zip offsets chunks
    --  in (acc', cache, offNext)

-- | Compute running character offsets for a list of chunks.
scanOffsetsWithNewlines :: [Text] -> [Int]
scanOffsetsWithNewlines = go 0
  where
    go !_ []     = []
    go !o (l:ls) =
      let off = o
          o'  = o + T.length l + 1   -- +1 for newline
      in off : go o' ls

-- | Chunk a single line into fixed-width pieces.
chunkFixed :: Int -> Text -> [Text]
chunkFixed w t
  | w <= 0    = []
  | T.null t  = [""]
  | otherwise =
      let (h, rest) = T.splitAt w t
      in h : if T.null rest then [] else chunkFixed w rest

--------------------------------------------------------------------------------
-- Hyphenation-aware segmenting (TeX-lite)
--------------------------------------------------------------------------------

-- Compute offsets starting from a base offset
scanOffsetsFrom :: Int -> [Text] -> [Int]
scanOffsetsFrom start = go start
  where
    go !_ []     = []
    go !o (t:ts) = o : go (o + T.length t) ts

segmentWithHyphenationTeXLite
  :: H.Hyphenator
  -> Int
  -> Text
  -> HM.HashMap Text [(Text, Text)]
  -> ([Text], HM.HashMap Text [(Text, Text)])
segmentWithHyphenationTeXLite dict width txt cache0 =
    go cache0 (T.words txt)
  where
    go cache [] = ([], cache)
    go cache ws =
      case lineCandidates dict width cache ws of
        ([], cache1) ->
          let chunks = breakWordSafe width ws
          in (chunks, cache1)
        (cs, cache1) ->
          let (line, rest, _) =
                minimumBy (comparing (scoreCandidate width)) cs
              (more, cache2) = go cache1 rest
          in (line : more, cache2)

-- | Lossless fallback: treat remaining words as one long text and
--   chunk it into width-sized pieces. Never truncates, never drops text.
breakWordSafe :: Int -> [Text] -> [Text]
breakWordSafe width ws =
  chunk (T.unwords ws)
  where
    chunk t
      | T.null t            = []
      | T.length t <= width = [t]
      | otherwise =
          let (c, r) = T.splitAt width t
          in c : chunk r

type Candidate = (Text, [Text], Bool)

lineCandidates
  :: H.Hyphenator
  -> Int
  -> HM.HashMap Text [(Text, Text)]
  -> [Text]
  -> ([(Text, [Text], Bool)], HM.HashMap Text [(Text, Text)])
lineCandidates dict width cache0 ws0 =
  go [] [] cache0 ws0
  where
    go _    acc cache [] = (acc, cache)
    go line acc cache (w:ws) =
      let space   = if null line then "" else " "
          baseTxt = T.unwords line
          wholeTxt = baseTxt <> space <> w
          wholeLen = T.length wholeTxt

          acc1 =
            if wholeLen <= width && not (T.null wholeTxt)
              then (wholeTxt, ws, False) : acc
              else acc

          (hyphs, cache1) =
            case HM.lookup w cache of
              Just hs -> (hs, cache)
              Nothing ->
                let hs = hyphenateWord dict w
                in (hs, HM.insert w hs cache)

          hyphCands =
            [ (preTxt, suf : ws, True)
            | (pre, suf) <- hyphs
            , not (T.null pre)
            , let preTxt = baseTxt <> space <> pre <> "-"
            , T.length preTxt <= width
            ]

          acc2 = hyphCands ++ acc1
      in if wholeLen <= width
           then go (line ++ [w]) acc2 cache1 ws
           else (acc2, cache1)

hyphenateWord :: H.Hyphenator -> Text -> [(Text, Text)]
hyphenateWord dict word =
    let parts = H.hyphenate dict (T.unpack word)
    in [ ( T.pack (concat (take i parts))
         , T.pack (concat (drop i parts))
         )
       | i <- [1 .. length parts - 1]
       ]

scoreCandidate :: Int -> Candidate -> Int
scoreCandidate width (line, _, endsWithHyphen) =
    let len      = T.length line
        remSpace = max 0 (width - len)
        badness  = remSpace * remSpace * remSpace
        hyphenPenalty =
          if endsWithHyphen then 50 else 0
        shortPenalty =
          if len < width `div` 2 then 200 else 0
    in badness + hyphenPenalty + shortPenalty