module Data.Text.ParagraphLayout.Internal.Plain
    (Paragraph(..)
    ,ParagraphLayout(..)
    ,ParagraphOptions(..)
    ,SpanLayout(..)
    ,layoutPlain
    )
where

import Control.Applicative (ZipList(ZipList), getZipList)
import Data.Int (Int32)
import Data.List (mapAccumL)
import Data.List.NonEmpty (NonEmpty((:|)))
import qualified Data.List.NonEmpty as NonEmpty
import Data.Maybe (catMaybes, fromMaybe, listToMaybe)
import Data.Text.Foreign (lengthWord8)
import Data.Text.Glyphize
    (Buffer(..)
    ,ContentType(ContentTypeUnicode)
    ,FontExtents(..)
    ,GlyphInfo
    ,GlyphPos(x_advance)
    ,defaultBuffer
    ,fontExtentsForDir
    ,shape
    )
import Data.Text.ICU (LocaleName(Locale), breakLine)
import qualified Data.Text.ICU as BreakStatus (Line)
import Data.Text.Internal (Text(Text))
import qualified Data.Text.Lazy as Lazy

import Data.Text.ParagraphLayout.Internal.Break
import Data.Text.ParagraphLayout.Internal.Fragment
import Data.Text.ParagraphLayout.Internal.LineHeight
import Data.Text.ParagraphLayout.Internal.Paragraph
import qualified Data.Text.ParagraphLayout.Internal.ProtoFragment as PF
import Data.Text.ParagraphLayout.Internal.Rect
import Data.Text.ParagraphLayout.Internal.ResolvedSpan (WithSpan(WithSpan))
import qualified Data.Text.ParagraphLayout.Internal.ResolvedSpan as RS
import Data.Text.ParagraphLayout.Internal.Run
import Data.Text.ParagraphLayout.Internal.Span
import Data.Text.ParagraphLayout.Internal.TextContainer

-- | Lay out a paragraph of plain, unidirectional text using a single font.
layoutPlain :: Paragraph -> ParagraphLayout
layoutPlain p@(Paragraph _ _ _ opts) = paragraphLayout sls
    where
        sls = map SpanLayout fragsBySpan
        fragsBySpan = take (length spans) $ RS.splitBySpanIndex frags
        frags = layoutAndAlignLines maxWidth $ spansToRunsWrapped spans
        maxWidth = paragraphMaxWidth opts
        spans = resolveSpans p

-- | Split a number of spans into a flat array of runs and add a wrapper
-- so that each run can be traced back to its originating span.
spansToRunsWrapped :: [RS.ResolvedSpan] -> [WithSpan Run]
spansToRunsWrapped ss = concat $ map spanToRunsWrapped ss

-- | Split a span into runs and add a wrapper
-- so that each run can be traced back to its originating span.
spanToRunsWrapped :: RS.ResolvedSpan -> [WithSpan Run]
spanToRunsWrapped s = map (WithSpan s) (spanToRuns s)

-- | Create a multi-line layout from the given runs, splitting them as
-- necessary to fit within the requested line width.
--
-- The output is a flat list of fragments positioned in both dimensions.
layoutAndAlignLines :: Int32 -> [WithSpan Run] -> [WithSpan Fragment]
layoutAndAlignLines maxWidth runs = frags
    where
        frags = concat fragsInLines
        (_, fragsInLines) = mapAccumL alignLineH originY protoFragsInLines
        protoFragsInLines = layoutLines maxWidth runs
        originY = paragraphOriginY

-- | Create a multi-line layout from the given runs, splitting them as
-- necessary to fit within the requested line width.
--
-- The output is a two-dimensional list of fragments positioned along the
-- horizontal axis.
layoutLines :: Int32 -> [WithSpan Run] -> [[WithSpan PF.ProtoFragment]]
layoutLines maxWidth runs
    | null rest
        -- Everything fits. We are done.
        = fitting : []
    | null fitting
        -- Nothing fits. We must resolve this by overflowing.
        = overflowing : []
    | otherwise
        -- Something fits, the rest goes on the next line.
        = fitting : layoutLines maxWidth rest
    where
        (fitting, rest) = tryAddRunsH maxWidth originX runs
        overflowing = addRunsH originX runs
        originX = paragraphOriginX

-- TODO: Allow a run across multiple spans (e.g. if they only differ by colour).

-- | Align all the given horizontal fragments vertically on the same line,
-- using `originY` as its top edge, and return the bottom edge for continuation.
--
-- Glyphs will be aligned by their ascent line, similar to the behaviour of
-- @vertical-align: top@ in CSS.
--
-- TODO: For rich text, allow other types of vertical alignment.
alignLineH :: Int32 -> [WithSpan PF.ProtoFragment] ->
    (Int32, [WithSpan Fragment])
alignLineH originY pfs = (nextY, frags)
    where
        nextY = maximum $ map y_min rects
        rects = map (\(WithSpan _ r) -> fragmentRect r) frags
        frags = map (alignFragmentH originY) pfs

-- | Align the given horizontal fragment vertically on a line,
-- using `originY` as its top edge.
alignFragmentH :: Int32 -> WithSpan PF.ProtoFragment -> WithSpan Fragment
alignFragmentH originY (WithSpan rs pf) =
    WithSpan rs (Fragment rect (penX, penY) (PF.glyphs pf))
    where
        rect = Rect (PF.offset pf) originY (PF.advance pf) (-lineHeight)
        penX = 0
        penY = descent + leading `div` 2 - lineHeight
        lineHeight = case RS.spanLineHeight rs of
            Normal -> normalLineHeight
            Absolute h -> h
        leading = lineHeight - normalLineHeight
        normalLineHeight = ascent + descent
        ascent = ascender extents
        descent = - descender extents
        extents = fontExtentsForDir font (PF.direction pf)
        font = RS.spanFont rs

-- | Like `addRunsH`, but break the input runs as necessary to prevent
-- overflowing the maximum line width,
-- and return the remaining runs to be placed on other lines.
tryAddRunsH :: Int32 -> Int32 -> [WithSpan Run] ->
    ([WithSpan PF.ProtoFragment], [WithSpan Run])
tryAddRunsH maxWidth currentX runs =
    fromMaybe lastResortSplit $ listToMaybe validSplits
    where
        lastResortSplit = do
            let (runs1, runs2) = splitTextsAt8 1 runs
            let (_, pfs) = mapAccumL addRunH currentX runs1
            (pfs, runs2)
        applySplit (runs1, runs2) = do
            let (nextX, pfs) = mapAccumL addRunH currentX runs1
            if abs nextX <= maxWidth
                then Just (pfs, runs2)
                else Nothing
        validSplits = catMaybes $ map applySplit splits
        splits = noSplit : (filter hasContent $ breakSplits [] (reverse runs))
        noSplit = (runs, [])
        hasContent = not . null . fst

-- | Recursive function for finding all possible ways to split a list of runs
-- into two on a valid line-breaking boundary, including the start of the first
-- run and excluding the end of the last run.
--
-- The first input list is the suffix consisting of runs that have already been
-- considered for breaking. These will be appended to the output suffix as they
-- are.
--
-- The second input list is the prefix consisting of runs to be considered for
-- breaking, in reverse order.
--
-- The results in the form (prefix, suffix) will be ordered from the longest
-- prefix to shortest.
breakSplits :: [WithSpan Run] -> [WithSpan Run] ->
    [([WithSpan Run], [WithSpan Run])]
breakSplits _ [] = []
breakSplits closed (x:xs) = splits ++ breakSplits (x:closed) xs
    where
        splits = map mapFunc $ runLineSplits x
        mapFunc ((x1, x2), _) =
            (reverse $ collapse $ x1 :| xs, collapse $ x2 :| closed)

-- | Calculate layout for multiple runs on the same line and
-- arrange them in one horizontal direction starting from the given x_offset.
addRunsH :: Int32 -> [WithSpan Run] -> [WithSpan PF.ProtoFragment]
addRunsH currentX runs = snd $ mapAccumL addRunH currentX runs

-- | Calculate layout for the given run,
-- place the generated fragment horizontally at the given x_offset in a line,
-- and return the final x_offset for continuation.
addRunH :: Int32 -> WithSpan Run -> (Int32, WithSpan PF.ProtoFragment)
addRunH currentX run = (nextX, WithSpan rs pf)
    where
        WithSpan rs pf = layoutRun currentX run
        nextX = currentX + PF.advance pf

-- | Calculate layout for the given run and position it in a line.
layoutRun :: Int32 -> WithSpan Run -> WithSpan PF.ProtoFragment
layoutRun originX (WithSpan rs run) = WithSpan rs pf
    where
        pf = PF.ProtoFragment dir originX totalX glyphs
        glyphs = shapeRun (WithSpan rs run)
        positions = map snd glyphs
        totalX = sum $ map x_advance positions
        dir = runDirection run

-- | Calculate layout for the given run independently of its position.
shapeRun :: WithSpan Run -> [(GlyphInfo, GlyphPos)]
shapeRun (WithSpan rs run) = shape font buffer features
    where
        font = RS.spanFont rs
        -- TODO: Set beginsText / endsText.
        buffer = defaultBuffer
            { text = Lazy.fromStrict $ runText run
            , contentType = Just ContentTypeUnicode
            , direction = runDirection run
            , script = runScript run
            , language = Just $ RS.spanLanguage rs
            }
        features = []

resolveSpans :: Paragraph -> [RS.ResolvedSpan]
resolveSpans p@(Paragraph arr pStart spans pOpts) = do
    let sBounds = paragraphSpanBounds p
    let pEnd = NonEmpty.last sBounds
    let sStarts = NonEmpty.init sBounds
    let sLengths = map spanLength spans

    (i, s, sStart, sLen) <- getZipList $ (,,,)
        <$> ZipList [0..]
        <*> ZipList spans
        <*> ZipList sStarts
        <*> ZipList sLengths
    let lang = spanLanguage $ spanOptions s
    let breaks = paragraphLineBreaks p pEnd lang
    return RS.ResolvedSpan
        { RS.spanIndex = i
        , RS.spanOffsetInParagraph = sStart - pStart
        -- TODO: Consider adding checks for array bounds.
        , RS.spanText = Text arr sStart sLen
        , RS.spanFont = paragraphFont pOpts
        , RS.spanLineHeight = paragraphLineHeight pOpts
        , RS.spanLanguage = lang
        , RS.spanLineBreaks = subOffsetsDesc (sStart - pStart) breaks
        }

paragraphLineBreaks :: Paragraph -> Int -> String -> [(Int, BreakStatus.Line)]
paragraphLineBreaks (Paragraph arr off _ _) end lang =
    breaksDesc (breakLine (localeFromLanguage lang)) paragraphText
    where
        paragraphText = Text arr off (end - off)

-- | Split the given run at every valid line break position.
runLineSplits :: WithSpan Run ->
    [((WithSpan Run, WithSpan Run), BreakStatus.Line)]
runLineSplits r = map split $ runLineBreaks r
    where
        split (i, status) = (splitTextAt8 i r, status)

runLineBreaks :: WithSpan Run -> [(Int, BreakStatus.Line)]
runLineBreaks (WithSpan rs run) = dropWhile (not . valid) $
    subOffsetsDesc (runOffsetInSpan run) $ RS.spanLineBreaks rs
    where
        valid (off, _) = off < runLength
        runLength = lengthWord8 $ getText run

-- TODO: Identify and correct for differences between the two.
localeFromLanguage :: String -> LocaleName
localeFromLanguage x = Locale x