package color

import (
	"math"
)

// LCH represents a color using lightness, chroma and hue.
func LCH(lightness Value, chroma Value, hue Value) Color {
	lightness = min(max(lightness, 0), 1)
	hue *= math.Pi / 180
	a := math.Cos(hue)
	b := math.Sin(hue)

	if !inSRGB(lightness, a, b, chroma) {
		chroma = findChromaInSRGB(chroma, lightness, a, b, 0.01)
	}

	a *= chroma
	b *= chroma

	r, g, b := oklabToLinearRGB(lightness, a, b)

	r = sRGB(r)
	g = sRGB(g)
	b = sRGB(b)

	return Color{r, g, b}
}

// findChromaInSRGB tries to find the closest chroma that can be represented in sRGB color space.
func findChromaInSRGB(chroma Value, lightness Value, a Value, b Value, precision Value) Value {
	high := chroma
	low := 0.0
	chroma *= 0.5

	for high-low > precision {
		if inSRGB(lightness, a, b, chroma) {
			low = chroma
		} else {
			high = chroma
		}

		chroma = (high + low) * 0.5
	}

	return chroma
}

// OKLAB to linear RGB.
// Source: https://bottosson.github.io/posts/oklab/
func oklabToLinearRGB(lightness Value, a Value, b Value) (Value, Value, Value) {
	l := lightness + 0.3963377773761749*a + 0.21580375730991364*b
	m := lightness - 0.10556134581565857*a - 0.0638541728258133*b
	s := lightness - 0.08948418498039246*a - 1.2914855480194092*b

	l = l * l * l
	m = m * m * m
	s = s * s * s

	red := 4.0767416621*l - 3.3077115913*m + 0.2309699292*s
	green := -1.2684380046*l + 2.6097574011*m - 0.3413193965*s
	blue := -0.0041960863*l - 0.7034186147*m + 1.7076147010*s

	return red, green, blue
}