{-# LANGUAGE OverloadedStrings #-}

module TextViewport
  ( Item(..)
  , Buffer(..)
  , WrapStrategy(..)
  , RenderedLine(..)
  , RenderedItem(..)
  , CachedRender(..)
  , RenderCache(..)
  , RenderedBuffer
  , renderBuffer
  , flatten
  , modifyItem
  , updateRenderedItem
  , Viewport(..)
  , defaultViewport
  , scrollUp
  , scrollDown
  , visibleLines
  , lookupPosition
  ) where

import Data.List (minimumBy)
import Data.Ord  (comparing)
import Data.Text (Text)
import Data.Vector (Vector)
import qualified Data.HashMap.Strict as HM
import qualified Data.Text as T
import qualified Data.Vector as V
import qualified Text.Hyphenation as H

import qualified Data.Sequence as Seq
import           Data.Sequence (Seq)
import qualified Data.Foldable as F

--------------------------------------------------------------------------------
-- Logical model
--------------------------------------------------------------------------------

data WrapStrategy
  = NoWrap
  | FixedWidthWrap
  | HyphenateWrap
      { hwDict  :: H.Hyphenator
      , hwCache :: HM.HashMap Text [(Text, Text)]
      }

data Item = Item
  { itemText :: Text
  , itemWrap :: WrapStrategy
  }

newtype Buffer = Buffer { unBuffer :: Seq Item }

modifyItem :: Int -> (Item -> Item) -> Buffer -> Buffer
modifyItem ix f (Buffer xs) =
    Buffer (Seq.adjust' f ix xs)

--------------------------------------------------------------------------------
-- Rendering with provenance
--------------------------------------------------------------------------------

data RenderedLine = RenderedLine
  { rlText      :: !Text
  , rlItemIx    :: !Int
  , rlLineIx    :: !Int
  , rlCharStart :: !Int
  } deriving (Show)

type RenderedBuffer = Seq RenderedItem

data RenderedItem = RenderedItem
  { riLines :: !(Vector RenderedLine)
  }

flatten :: RenderedBuffer -> [RenderedLine]
flatten = concatMap (F.toList . riLines) . F.toList

renderBuffer :: Int -> Buffer -> RenderCache -> (RenderCache, RenderedBuffer)
renderBuffer width (Buffer items) (RenderCache cache) =
  let n = Seq.length items
      go i (cAcc, rAcc)
        | i >= n    = (RenderCache cAcc, rAcc)
        | otherwise =
            let item     = Seq.index items i
                mOld     = Seq.index cache i
                newEntry = renderItem width i item mOld
                cAcc'    = Seq.update i (Just newEntry) cAcc
                rAcc'    = rAcc Seq.|> crRendered newEntry
            in go (i + 1) (cAcc', rAcc')
  in go 0 (cache, Seq.empty)

renderItem :: Int -> Int -> Item -> Maybe CachedRender -> CachedRender
renderItem width itemIx (Item txt strategy) mOld =
  case mOld of
    Just old
      | crWidth old == width
      , crText old  == txt
      -> old
    _ ->
      let linesV   = applyStrategy strategy width itemIx txt
          rendered = RenderedItem linesV
      in CachedRender
           { crWidth    = width
           , crStrategy = strategy
           , crText     = txt
           , crRendered = rendered
           }

data CachedRender = CachedRender
  { crWidth    :: !Int
  , crStrategy :: !WrapStrategy
  , crText     :: !Text
  , crRendered :: !RenderedItem
  }

newtype RenderCache = RenderCache { unRenderCache :: Seq (Maybe CachedRender) }

--------------------------------------------------------------------------------
-- Wrapping strategies
--------------------------------------------------------------------------------

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

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

applyStrategy (HyphenateWrap 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
      (allChunks, _cache1, _) =
        foldl wrapOneLine ([], cache0, 0) rawLines
  in V.fromList
       [ RenderedLine { rlText = chunk, rlItemIx = itemIx, rlLineIx = lineIx, rlCharStart = off }
       | (lineIx, (off, chunk)) <- zip [0..] allChunks
       ]
  where
    -- Wrap a single physical line using TeX‑lite hyphenation
    wrapOneLine
      :: ([(Int, Text)], HM.HashMap Text [(Text, Text)], Int)
      -> Text
      -> ([(Int, Text)], HM.HashMap Text [(Text, Text)], Int)
    wrapOneLine (acc, cache, off0) line =
      let chunks  = wrapWithHyphenationTeXLite 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 wrapping (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

wrapWithHyphenationTeXLite :: H.Hyphenator -> Int -> Text -> [Text]
wrapWithHyphenationTeXLite dict width txt =
    go (T.words txt)
  where
    go [] = []
    go ws =
      case lineCandidates dict width ws of
        [] ->
          -- Hyphenation failed: fall back to fixed-width chunking
          breakWordSafe width ws

        cs ->
          let (line, rest, _) =
                minimumBy (comparing (scoreCandidate width)) cs
          in line : go rest

-- | 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 -> [Text] -> [Candidate]
lineCandidates dict width = go [] []
  where
    go :: [Text] -> [Candidate] -> [Text] -> [Candidate]
    go _    acc []         = acc
    go line acc (w:ws) =
      let space   = if null line then "" else " "
          baseTxt = T.unwords line

          -- whole word candidate (no hyphen)
          wholeTxt = baseTxt <> space <> w
          wholeLen = T.length wholeTxt

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

          -- hyphenation candidates for this word
          hyphs = hyphenateWord dict w
          hyphCands =
            [ (preTxt, suf : ws, True)
            | (pre, suf) <- hyphs
            , not (T.null pre)
            , let preTxt = baseTxt <> space <> pre <> "-"
            , let preLen = T.length preTxt
            , preLen <= width
            ]

          acc'' = hyphCands ++ acc'

      in if wholeLen <= width
           then go (line ++ [w]) acc'' ws
           else acc''

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

--------------------------------------------------------------------------------
-- Incremental re-rendering
--------------------------------------------------------------------------------

updateRenderedItem :: Int -> Int -> Buffer -> RenderCache -> Seq RenderedItem -> (RenderCache, Seq RenderedItem)
updateRenderedItem width itemIx (Buffer items) (RenderCache cache) rb =
    let item    = Seq.index items itemIx
        mOld     = Seq.index cache itemIx
        newEntry = renderItem width itemIx item mOld
        newCache = Seq.update itemIx (Just newEntry) cache
        newRB    = Seq.update itemIx (crRendered newEntry) rb
    in (RenderCache newCache, newRB)

--------------------------------------------------------------------------------
-- Viewport
--------------------------------------------------------------------------------

data Viewport = Viewport
  { vpWidth  :: !Int
  , vpHeight :: !Int
  , vpOffset :: !Int
  } deriving (Show)

defaultViewport :: Int -> Int -> RenderedBuffer -> Viewport
defaultViewport w h rb =
    let total = length (flatten rb)
        off   = max 0 (total - h)
    in Viewport w h off

scrollUp :: Int -> Viewport -> Viewport
scrollUp k vp =
    vp { vpOffset = max 0 (vpOffset vp - k) }

scrollDown :: Int -> Int -> Viewport -> Viewport
scrollDown totalLines n vp =
    let newTop = min (totalLines - vpHeight vp) (vpOffset vp + n)
    in vp { vpOffset = max 0 newTop }

visibleLines :: RenderedBuffer -> Viewport -> [RenderedLine]
visibleLines rb vp =
  let allLines = flatten rb
      start    = vpOffset vp
      end      = start + vpHeight vp
  in take (vpHeight vp) . drop start $ allLines

--------------------------------------------------------------------------------
-- Coordinate lookup
--------------------------------------------------------------------------------

lookupPosition
  :: Int
  -> Int
  -> Viewport
  -> RenderedBuffer
  -> Maybe (Int, Int)
lookupPosition x y vp rb =
  let allLines = flatten rb
      idx      = vpOffset vp + y
  in case drop idx allLines of
       (rl:_) ->
         let charIx = rlCharStart rl + x
         in Just (rlItemIx rl, charIx)
       [] -> Nothing