module Data.Text.ParagraphLayout.Internal.ParagraphLayout
    (ParagraphLayout(..)
    ,appendFragments
    ,emptyParagraphLayout
    ,filterFragments
    ,mapFragments
    ,paragraphFragments
    ,paragraphLayout
    ,paragraphOriginX
    ,paragraphOriginY
    ,paragraphSpanBounds
    ,shapedRuns
    )
where

import Data.Int (Int32)
import Data.List.NonEmpty (NonEmpty)
import qualified Data.List.NonEmpty as NonEmpty

import Data.Text.ParagraphLayout.Internal.Fragment
import Data.Text.ParagraphLayout.Internal.Paragraph
import Data.Text.ParagraphLayout.Internal.Rect
import Data.Text.ParagraphLayout.Internal.Span

-- | The resulting layout of the whole paragraph.
data ParagraphLayout = ParagraphLayout
    { paragraphRect :: Rect Int32
    -- ^ The containing block (CSS3).
    , spanLayouts :: [SpanLayout]
    }
    deriving (Eq, Read, Show)

-- | Calculate the offsets into the `Paragraph`'s underlying `Data.Text.Array`
-- where each span starts and ends, in ascending order. The resulting list
-- will be one larger than the list of input spans.
paragraphSpanBounds :: Paragraph -> NonEmpty Int
paragraphSpanBounds (Paragraph _ initialOffset spans _) =
    NonEmpty.scanl (+) initialOffset (map spanLength spans)

paragraphOriginX :: (Num a) => a
paragraphOriginX = 0

paragraphOriginY :: (Num a) => a
paragraphOriginY = 0

empty :: (Num a) => Rect a
empty = Rect
    { x_origin = paragraphOriginX
    , y_origin = paragraphOriginY
    , x_size = 0
    , y_size = 0
    }

containRects :: (Ord a, Num a) => [Rect a] -> Rect a
containRects = foldr union empty

-- | Wrap the given `SpanLayout`s and compute their containing rectangle.
paragraphLayout :: [SpanLayout] -> ParagraphLayout
paragraphLayout sls = ParagraphLayout pRect sls
    where pRect = containRects $ concat $ map spanRects sls

-- | A `ParagraphLayout` with an infinite number of empty spans.
-- Useful as an identity element for `appendFragments`.
emptyParagraphLayout :: ParagraphLayout
emptyParagraphLayout = ParagraphLayout empty $ repeat (SpanLayout [])

-- | Remove fragments that do not match the given predicate.
--
-- The containing rectangle will be recalculated.
filterFragments :: (Fragment -> Bool) -> ParagraphLayout -> ParagraphLayout
filterFragments fragPred (ParagraphLayout _ sls) = paragraphLayout sls'
    where
        sls' = map slMapFunc sls
        slMapFunc (SpanLayout frags) = SpanLayout (filter fragPred frags)

-- | Run a mapping function over each fragment inside a `ParagraphLayout`.
--
-- The containing rectangle will be recalculated.
mapFragments :: (Fragment -> Fragment) -> ParagraphLayout -> ParagraphLayout
mapFragments fragMapFunc (ParagraphLayout _ sls) = paragraphLayout sls'
    where
        sls' = map slMapFunc sls
        slMapFunc (SpanLayout frags) = SpanLayout (map fragMapFunc frags)

-- | Combine fragments from two `ParagraphLayout`s.
--
-- The containing rectangle will be recalculated.
appendFragments :: ParagraphLayout -> ParagraphLayout -> ParagraphLayout
appendFragments pla plb = paragraphLayout sls'
    where
        sls' = zipWith zipFunc slsa slsb
        slsa = spanLayouts pla
        slsb = spanLayouts plb
        zipFunc (SpanLayout fa) (SpanLayout fb) = SpanLayout (fa ++ fb)

-- | Return all fragments of shaped text in one flat list,
-- discarding information about their associated spans.
paragraphFragments :: ParagraphLayout -> [Fragment]
paragraphFragments pl = concat $ map spanFragments $ spanLayouts pl

-- | Return all shaped runs in the paragraph.
shapedRuns :: ParagraphLayout -> [ShapedRun]
shapedRuns pl = map shapedRun $ paragraphFragments pl