//go:build ignore

package main

import (
	"image"
	"image/color"
	"image/gif"
	"log"
	"math"
	"os"
)

const (
	width   = 16
	height  = 32
	radius  = 2.6
	levels  = 16
	samples = 4
	delay   = 8
)

var frames = []rune("⠋⠙⠹⠸⠼⠴⠦⠧⠇⠏")

var dots = [6][2]float64{{4.5, 8}, {4.5, 16}, {4.5, 24}, {11.5, 8}, {11.5, 16}, {11.5, 24}}

func main() {
	render("img/spinner-light.gif", color.RGBA{0x1a, 0x45, 0xbd, 0xff}, color.RGBA{0xfb, 0xfb, 0xfa, 0xff})
	render("img/spinner-dark.gif", color.RGBA{0x8a, 0xb4, 0xff, 0xff}, color.RGBA{0x15, 0x17, 0x1a, 0xff})
}

func render(path string, fg, bg color.RGBA) {
	palette := color.Palette{color.RGBA{}}
	for i := 1; i <= levels; i++ {
		palette = append(palette, blend(bg, fg, float64(i)/levels))
	}

	anim := &gif.GIF{}
	for _, r := range frames {
		bits := int(r - 0x2800)
		img := image.NewPaletted(image.Rect(0, 0, width, height), palette)
		for y := 0; y < height; y++ {
			for x := 0; x < width; x++ {
				level := int(math.Round(coverage(bits, x, y) * levels))
				img.SetColorIndex(x, y, uint8(level))
			}
		}
		anim.Image = append(anim.Image, img)
		anim.Delay = append(anim.Delay, delay)
		anim.Disposal = append(anim.Disposal, gif.DisposalBackground)
	}

	f, err := os.Create(path)
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()
	err = gif.EncodeAll(f, anim)
	if err != nil {
		log.Fatal(err)
	}
}

func coverage(bits, x, y int) float64 {
	hit := 0
	for sy := 0; sy < samples; sy++ {
		for sx := 0; sx < samples; sx++ {
			px := float64(x) + (float64(sx)+0.5)/samples
			py := float64(y) + (float64(sy)+0.5)/samples
			for i, d := range dots {
				if bits&(1<<i) == 0 {
					continue
				}
				if math.Hypot(px-d[0], py-d[1]) <= radius {
					hit++
					break
				}
			}
		}
	}
	return float64(hit) / (samples * samples)
}

func blend(a, b color.RGBA, t float64) color.RGBA {
	mix := func(p, q uint8) uint8 {
		return uint8(math.Round(float64(p) + (float64(q)-float64(p))*t))
	}
	return color.RGBA{mix(a.R, b.R), mix(a.G, b.G), mix(a.B, b.B), 0xff}
}