package utils

import (
	"fmt"
	"math"
)

const (
	Pred   float64 = 0.299
	Pgreen float64 = 0.587
	Pblue  float64 = 0.114
)

var (
	DarkAltFallback  = []uint8{0x1c, 0x10, 0x10}
	LightAltFallback = []uint8{0xf2, 0xef, 0xef}
)

func IntToRgb(color uint32) (uint8, uint8, uint8) {
	b := color % 256
	g := color / 256 % 256
	r := color / (256 * 256) % 256

	return uint8(r), uint8(g), uint8(b)
}

func RgbToString(r, g, b uint8) string {
	return fmt.Sprintf("#%02x%02x%02x", r, g, b)
}

func AltColor(r, g, b uint8) (uint8, uint8, uint8) {
	l1 := Luminance(r, g, b)
	isDark := l1 <= 0.5098

	brightnessAmount := -0.6
	if isDark { // color is dark
		brightnessAmount = 0.85
	}

	r2, g2, b2 := Brighten(r, g, b, brightnessAmount)

	l2 := Luminance(r2, g2, b2)
	ratio := WCAGRatio(l1, l2)

	// log.Printf("isDark=%v, ratio: %f, l1(%f)=%s, l2(%f)=%s", isDark, ratio, l1, RgbToString(r, g, b), l2, RgbToString(r2, g2, b2))

	if ratio >= 3 {
		return r2, g2, b2
	}

	if isDark {
		return LightAltFallback[0], LightAltFallback[1], LightAltFallback[2]
	} else {
		return DarkAltFallback[0], DarkAltFallback[1], DarkAltFallback[3]
	}
}

func Brighten(r, g, b uint8, amount float64) (uint8, uint8, uint8) {
	return multiply(r, amount), multiply(g, amount), multiply(b, amount)
}

func multiply(i uint8, amount float64) uint8 {
	iF := float64(i)
	return uint8(
		math.Max(
			0,
			math.Min(
				255, iF+255*amount,
			),
		),
	)
}

func sRGB(c uint8) float64 {
	cf := float64(c) / 255
	if cf <= 0.03928 {
		return cf / 12.92
	} else {
		return math.Pow((cf+0.055)/1.055, 2.4)
	}
}

func Luminance(r, g, b uint8) float64 {
	rC := Pred * math.Pow(sRGB(r), 2)
	gC := Pgreen * math.Pow(sRGB(g), 2)
	bC := Pblue * math.Pow(sRGB(b), 2)

	return math.Sqrt(rC + gC + bC)
}

func WCAGRatio(l1, l2 float64) float64 {
	return (math.Max(l1, l2) + 0.05) / (math.Min(l1, l2) + 0.05)
}