package check

import (
	"fmt"
	"math"
	"regexp"
	"strconv"
)

// canonColours and what it reaches, from rastrillo's ui/derived_test.go:
// untagged, so the CSS gates that read text and the browser drives that
// read computed styles both use it. The derived-colour evaluator it sat
// beside (evalColour, rgba, accentSupportsBlock) is ported with the
// gate that uses it.

// oklchClip renders OKLCh as eight-bit sRGB the way Chromium paints an
// out-of-gamut colour: each linear channel clipped to 0..1. Lightness
// and chroma are both kept, so a clipped colour is brighter than the
// one asked for; that is what the dark fill's lightness drop exists to
// absorb (day.css, the @supports comment).
func oklchClip(l, c, hue float64) [3]uint8 {
	rad := hue * math.Pi / 180
	lin := oklabToLinear(l, c*math.Cos(rad), c*math.Sin(rad))
	var v [3]uint8
	for i, ch := range lin {
		n := math.Round(linearToSRGB(math.Min(1, math.Max(0, ch))) * 255)
		v[i] = uint8(math.Min(255, math.Max(0, n)))
	}
	return v
}

var (
	srgbSer  = regexp.MustCompile(`color\(srgb ([0-9.e-]+) ([0-9.e-]+) ([0-9.e-]+)(?: / ([0-9.e-]+))?\)`)
	oklchSer = regexp.MustCompile(`oklch\(([0-9.e-]+) ([0-9.e-]+) ([0-9.e-]+)(?: / ([0-9.e-]+))?\)`)
)

// canonColours rewrites the colour functions Chromium serialises a
// derived colour as, color(srgb …) for a color-mix() and oklch(…) for a
// relative colour, into the rgb()/rgba() the drives compare against.
// A computed value that is a legacy colour is already in that form.
// Without this every literal in the depth drives would have to be the
// six-decimal serialisation of a float, which changes with the engine's
// printing rather than with the colour.
func canonColours(s string) string {
	s = srgbSer.ReplaceAllStringFunc(s, func(m string) string {
		p := srgbSer.FindStringSubmatch(m)
		var ch [3]int
		for i := range ch {
			f, _ := strconv.ParseFloat(p[i+1], 64)
			ch[i] = int(math.Round(f * 255))
		}
		if p[4] == "" {
			return fmt.Sprintf("rgb(%d, %d, %d)", ch[0], ch[1], ch[2])
		}
		return fmt.Sprintf("rgba(%d, %d, %d, %s)", ch[0], ch[1], ch[2], p[4])
	})
	return oklchSer.ReplaceAllStringFunc(s, func(m string) string {
		p := oklchSer.FindStringSubmatch(m)
		l, _ := strconv.ParseFloat(p[1], 64)
		c, _ := strconv.ParseFloat(p[2], 64)
		h, _ := strconv.ParseFloat(p[3], 64)
		rgb := oklchClip(l, c, h)
		if p[4] == "" {
			return fmt.Sprintf("rgb(%d, %d, %d)", rgb[0], rgb[1], rgb[2])
		}
		return fmt.Sprintf("rgba(%d, %d, %d, %s)", rgb[0], rgb[1], rgb[2], p[4])
	})
}