package main

import (
	"image"
	"image/color"
	"image/gif"
	"io"
	"math"
	"math/rand/v2"
	"os"
)

var palette = []color.Color{
	color.Black,
	color.RGBA{0x00, 0xff, 0x00, 0xff},
}

const (
	backgroundIndex = iota
	foregroundIndex
)

func main() {
	lissajous(os.Stdout)
}

func lissajous(out io.Writer) {
	const (
		cycles  = 5
		res     = 0.001
		size    = 100
		nframes = 64
		delay   = 8
	)

	// Note that this generates the exact same random number per
	// run of the program.
	freq := rand.Float64() * 3.0
	anim := gif.GIF{LoopCount: nframes}

	for i := range nframes {
		img := newImage(size, cycles, float64(i)/10, res, freq)

		anim.Delay = append(anim.Delay, delay)
		anim.Image = append(anim.Image, img)
	}

	gif.EncodeAll(out, &anim)
}

func newImage(size, cycles int, phase, res, freq float64) *image.Paletted {
	rect := image.Rect(0, 0, 2*size+1, 2*size+1)
	img := image.NewPaletted(rect, palette)

	for t := 0.0; t < float64(cycles)*2*math.Pi; t += res {
		x := math.Sin(t)
		y := math.Sin(t*freq + phase)
		img.SetColorIndex(size+int(x*float64(size)+0.5), size+int(y*float64(size)+0.5), foregroundIndex)
	}

	return img
}