// Command teleportfling-icon regenerates the application icon assets in
// assets/ from scratch. It draws a rounded green square with two lighter
// "fling" dots suggesting motion.
//
// Usage:
//
//	teleportfling-icon
//
// The generated PNGs are committed to the repo and embedded into the binary
// via the assets package; this tool exists so the icon can be tweaked and
// regenerated without a design tool.
package main

import (
	"bytes"
	"image"
	"image/color"
	"image/png"
	"os"
)

// sizes are the icon sizes to emit. Hosts scale from these; 512 is used for
// the app icon, 256 and 64 for smaller contexts.
var sizes = []int{512, 256, 64}

// outputDir is where the PNGs are written (the repo assets directory).
const outputDir = "assets"

// inRoundedRect reports whether (x,y) lies inside a square with rounded
// corners of the given radius.
func inRoundedRect(x, y, radius, size int) bool {
	m := size - 1
	switch {
	case x >= radius && x <= m-radius:
		return true
	case y >= radius && y <= m-radius:
		return true
	}
	var cx, cy int
	if x < radius {
		cx = radius
	} else {
		cx = m - radius
	}
	if y < radius {
		cy = radius
	} else {
		cy = m - radius
	}
	dx, dy := x-cx, y-cy
	return dx*dx+dy*dy <= radius*radius
}

// render draws the icon at the given size into a PNG.
func render(size int, bg, dot color.NRGBA) []byte {
	img := image.NewNRGBA(image.Rect(0, 0, size, size))
	radius := size / 5
	for y := 0; y < size; y++ {
		for x := 0; x < size; x++ {
			if inRoundedRect(x, y, radius, size) {
				img.SetNRGBA(x, y, bg)
			}
		}
	}
	// Two dots suggesting a flung stream, offset diagonally.
	for i, off := range []int{3, 9} {
		cx, cy, r := size/2, size/2+off*size/32, size/8-i
		for y := cy - r; y <= cy+r; y++ {
			for x := cx - r; x <= cx+r; x++ {
				if (x-cx)*(x-cx)+(y-cy)*(y-cy) <= r*r {
					img.SetNRGBA(x, y, dot)
				}
			}
		}
	}
	var buf bytes.Buffer
	_ = png.Encode(&buf, img)
	return buf.Bytes()
}

func main() {
	bg := color.NRGBA{R: 46, G: 125, B: 50, A: 255} // teleport green
	dot := color.NRGBA{R: 150, G: 220, B: 140, A: 255}

	//nolint:gosec // writing generated PNG assets into the repo, not secrets
	if err := os.MkdirAll(outputDir, 0o755); err != nil {
		panic(err)
	}

	for _, size := range sizes {
		name := "teleportfling"
		if size != 512 {
			name += "-" + itoa(size)
		}
		path := outputDir + "/" + name + ".png"
		//nolint:gosec // generated PNG assets, world-readable for installers
		if err := os.WriteFile(path, render(size, bg, dot), 0o644); err != nil {
			panic(err)
		}
	}
}

func itoa(v int) string {
	if v == 0 {
		return "0"
	}
	var buf [10]byte
	i := len(buf)
	for v > 0 {
		i--
		buf[i] = byte('0' + v%10)
		v /= 10
	}
	return string(buf[i:])
}