module Data.Text.ParagraphLayout.Internal.ProtoFragment
    ( ProtoFragment (direction, advance, glyphs)
    , protoFragmentH
    )
where

import Data.Int (Int32)
import Data.Text.Glyphize (Direction (..), GlyphInfo, GlyphPos (x_advance))

import Data.Text.ParagraphLayout.Internal.BiDiLevels

-- | A box fragment which has not been positioned yet.
data ProtoFragment = ProtoFragment
    { direction :: Maybe Direction
    -- ^ Text direction, which is constant within a fragment.
    , advance :: Int32
    -- ^ Total advance of glyphs in this fragment,
    -- depending on the text direction.
    , glyphs :: [(GlyphInfo, GlyphPos)]
    }

-- | Construct a `ProtoFragment`, automatically calculating the total advance
-- for a horizontal text direction.
protoFragmentH :: Maybe Direction -> [(GlyphInfo, GlyphPos)] -> ProtoFragment
protoFragmentH dir gs = ProtoFragment dir adv gs
    where
        adv = sum $ map (x_advance . snd) gs

instance WithLevel ProtoFragment where
    level pf = case direction pf of
        -- TODO: Allow externally set paragraph embedding level.
        -- TODO: Properly calculate BiDi levels.
        Just DirLTR -> 0
        Just DirRTL -> 1
        Just DirTTB -> 0
        Just DirBTT -> 1
        Nothing -> 0