{-# LANGUAGE OverloadedStrings #-}
-- | Infrastructure for parsing & desugaring length units & keywords,
-- in reference to the selected font.
module Graphics.Layout.CSS.Length(Unitted, auto, parseLength, parseLength',
        n2f, finalizeLength, px2pt, Font'(..)) where

import Data.CSS.Syntax.Tokens (Token(..), NumericValue(..))
import qualified Data.Text as Txt
import Data.Scientific (toRealFloat)
import Debug.Trace (trace) -- For warnings.
import Data.Text.Glyphize (Font)
import Graphics.Text.Font.Choose (Pattern(..))

import Graphics.Layout.Box

-- | A number+unit, prior to resolving side units.
-- The unit may alternately represent a keyword, in which case the number is
-- ignored & typically set to 0.
type Unitted = (Double, Txt.Text)
-- | The CSS `auto` keyword.
auto :: Unitted
auto = (0,"auto")

-- | Parse a pre-tokenized CSS length value.
parseLength :: [Token] -> Maybe Unitted
parseLength [Percentage _ x] = Just (n2f x,"%")
parseLength [Dimension _ x unit]
    | n2f x == 0 && unit == "" = Just (0,"px")
    | unit `elem` units = Just (n2f x,unit)
parseLength [Ident "auto"] = Just (0,"auto")
parseLength [Ident "initial"] = Just (0,"auto")
parseLength _ = Nothing
-- | Variant of `parseLength` which supports min-content & max-content keywords.
parseLength' [Ident "min-content"] = Just (0,"min-content")
parseLength' [Ident "max-content"] = Just (0,"max-content")
parseLength' toks = parseLength toks

-- | Supported length units.
units = Txt.words "cap ch em ex ic lh rem rlh vh vw vmax vmin px cm mm Q in pc pt %"

-- | Convert a lexed number to a Double.
n2f :: (Fractional x, RealFloat x) => NumericValue -> x
n2f (NVInteger x) = realToFrac x
n2f (NVNumber x) = toRealFloat x

-- | Resolve a parsed length according to the sizing parameters in a given `Font'`.
finalizeLength :: Unitted -> Font' -> Length
finalizeLength (x,"cap") f = Pixels $ x*fontHeight f 'A'
finalizeLength (x,"ch") f = Pixels $ x*fontAdvance f '0'
finalizeLength (x,"em") f = Pixels $ x*fontSize f
finalizeLength (x,"") f = Pixels $ x*fontSize f -- For line-height.
finalizeLength (x,"ex") f = Pixels $ x*fontHeight f 'x'
finalizeLength (x,"ic") f = Pixels $ x*fontHeight f '水' -- CJK water ideograph
finalizeLength (x,"lh") f = Pixels $ x*lineheight f
finalizeLength (x,"rem") f = Pixels $ x*rootEm f
finalizeLength (x,"rlh") f = Pixels $ x*rlh f
finalizeLength (x,"vh") f = Pixels $ x*vh f
finalizeLength (x,"vb") f = Pixels $ x*vh f -- TODO: Support vertical text
finalizeLength (x,"vw") f = Pixels $ x*vw f
finalizeLength (x,"vi") f = Pixels $ x*vw f -- TODO: Support vertical text
finalizeLength (x,"vmax") f = Percent $ x*vmax f
finalizeLength (x,"vmin") f = Percent $ x*vmin f
finalizeLength (x,"px") f = Pixels $ x*scale f
finalizeLength (x,"cm") f = Pixels $ x*scale f*96/2.54
finalizeLength (x,"in") f = Pixels $ x*96*scale f
finalizeLength (x,"mm") f | Pixels x' <- finalizeLength (x,"cm") f = Pixels $ x'/10
finalizeLength (x,"Q") f | Pixels x' <- finalizeLength (x,"cm") f = Pixels $ x'/40
finalizeLength (x,"pc") f | Pixels x' <- finalizeLength (x,"in") f = Pixels $ x'/6
finalizeLength (x,"pt") f | Pixels x' <- finalizeLength (x,"in") f = Pixels $ x'/72
finalizeLength (x,"%") _ = Percent $ x/100
finalizeLength (_,"auto") _ = Auto
finalizeLength (_,"min-content") _ = Min
finalizeLength (_,"max-content") _ = Preferred
finalizeLength (x, " ") _ = Pixels x -- Internal constant value...
finalizeLength (_,unit) _ = trace ("Invalid unit " ++ Txt.unpack unit) $ Pixels 0
-- | Convert from a computed length to the "pt" unit.
px2pt f x = x / scale f / 96 * 72

-- | A Harfbuzz font with sizing parameters.
data Font' = Font' {
    -- | The Harfbuzz font used to shape text & query character-size information.
    hbFont :: Font,
    -- | The FontConfig query result. Useful to incorporate into output rendering.
    pattern :: Pattern,
    -- | Query the height of a character.
    -- Used for cap, ex, or ic units.
    fontHeight :: Char -> Double,
    -- | Query the width of a character, used for ch unit.
    fontAdvance :: Char -> Double,
    -- | The desired font-size, used for em unit.
    fontSize :: Double,
    -- | The root font's size, used for rem unit.
    rootEm :: Double,
    -- | The desired line-height, used for lh unit.
    lineheight :: Double,
    -- | The root font's line-height, used for rlh unit.
    rlh :: Double,
    -- | Scale-factor for vh unit.
    vh :: Double,
    -- | Scale-factor for vw unit.
    vw :: Double,
    -- | Scale-factor for vmax unit.
    vmax :: Double,
    -- | Scale-factor for vmin unit.
    vmin :: Double,
    -- | How many device pixels in a CSS px?
    scale :: Double
}

instance Eq Font' where
    a == b = pattern a == pattern b